ﺑﺴﻢ اﷲ اﻟﺮﺣﻤﻦ اﻟﺮﺣﻴﻢ University of Khartoum Natural Pozzolana in Sudan “Characterization and Factors Affecting the Compressive Strength of Lime- Pozzolana Mortar”

By: Mamoun El Tayeb Elmamoun Mohmmed B.Sc. (Hon. Geology), University Of Khartoum M.Sc. (Building Technology), University of Khartoum

A Thesis Submitted to the Graduate College in Accordance With the Requirements for the Degree of Doctor of Philosophy in Building Technology Building and Road Research Institute (BRRI) University of Khartoum July 2004

1

To my brother Omer El Tayeb

2

In the words of our prophet Mohammed (APGUH) said: (smile smarts and smart prays for all). Softly I would like expressing my God donation which is endless for me and other since born and till die by putting his merciful on all over around meaning full and genius great creator. By then appreciation must be made to my supervisor Dr. M. A. Elzamzmi for his endless assistance in both hand tears support and soul treatments through valuable advices, discussions for all stages of the work; filed survey, laboratory testing and thesis preparation, he sacrifice a lot of his own time to correct and revise thesis manuscript. Also all great thanks goes to the co-supervisor Dr. A. S. Dawoud for his helping hand guidance and hearted advices especially in the field part of the work. All the most thanks to the Red Sea University and it was previous director Dr. Abdul Gadir Daffalla and the acting director Dr. Omer El Megli for granting me this scholarship and financial support. Utilizing this chance I would like to pay my appreciation to the staff of the Faculty of Earth Sciences- Red Sea University. My thanks also extending to the Building and Road Research Institute (BRRI) of their generous hosting and helping during this work. My appreciation is also due to the head and staff of the Geological Research Authority of the Sudan (GRAS) for their generous aid and unlimited help concerning field and laboratory work. The geology department staff’s members (U of K) and subsistent organization are also thanked and appreciated.

3 Special thanks to my family relatives and friends. And I hereby thank all others who helped by some way or other in the production of this work.

4 Abstract

The objectives of the study are to characterize and evaluate some natural Pozzolanas reported at different localities in Sudan and to study factors affecting the strength of Pozzolanas. The tools used for characterization include; the geological survey, chemical analysis, X-ray diffraction analysis and strength tests. Beside the already known Pozzolanic deposits, new occurrences were reported namely obsidian at Sabaloka, natural burnt clay at southern of Bayouda, and Quaternary lake deposits at Abu Hadied, however, in all cases these Pozzolanic deposits were systematically studied . The investigations revealed that most of natural Pozzolanas in Sudan were associated with Tertiary volcanics and Quaternary lake deposits. According to compressive strength results , the natural Pozzolanas in Sudan can be classified into three grades ; high grade Pozzolanas represented by obsidian (Sabaloka), diatomites (Gezira), and volcanic tuffs (Bayouda), moderate grade Pozzolanas including pumice (Bayouda), Quaternary lake depots (Abu Hadied), and low grade Pozzolanas in the form of natural burnt clay. Quantitatively and qualitatively the most promising deposit is the volcanic tuffs at Bayouda. The strength of Lime-Pozzolana cement can be improved remarkably by very fine grinding, other factors such as Pozzolana/ lime ratio, curing condition and use of additives may also affect the strength properties. However, generally the degree of fineness outweighs the previously mentioned factors.

5 ﺍﻟﺨﻼﺼﺔ

ﺘﻬﺩﻑ ﺍﻟﺩﺭﺍﺴﺔ ﻟﺘﺤﺩﻴﺩ ﻭﺇﺴﺘﻜﺸﺎﻑ ﻭﺘﻘﻴﻴﻡ ﺃﻤﺎﻜﻥ ﺍﻟﺒﻭﺯﻭﻻﻨﺎ ﺍﻟﻁﺒﻴﻌﻴﺔ ﻓﻲ

ﺍﻟﺴﻭﺩﺍﻥ ، ﻭﺩﺭﺍﺴﺔ ﺍﻟﻌﻭﺍﻤل ﺍﻟﻤﺅﺜﺭﺓ ﻓﻲ ﻤﻘﺎﻭﻤﺔ ﺍﻹﻨﻀﻐﺎﻁ ﻟﻠﺒﻭﺯﻭﻻﻨﺎ.

ﺍﻟﻭﺴﺎﺌل ﺍﻟﻤﺴﺘﺨﺩﻤﺔ ﻟﻤﻌﺭﻓﺔ ﺍﻟﺒﻭﺯﻭﻻﻨﺎ ﻭﺩﺭﺠﺘﻬﺎ ﺸﻤﻠﺕ ﺍﻟﻤﺴﺢ ﺍﻟﺠﻴﻭﻟﻭﺠﻲ ، ﺍﻟﺘﺤﻠﻴل

ﺍﻟﻜﻴﻤﻴﺎﺌﻲ ، ﺍﻟﺘﺤﻠﻴل ﺒﺎﻷﺸﻌﺔ ﺍﻟﺴﻴﻨﻴﺔ ﻭﻤﻘﺎﻭﻤﺔ ﺍﻹﻨﻀﻐﺎﻁ.

ﻓﻰ ﻫﺫﻩ ﺍﻟﺩﺭﺍﺴﺔ ﺘﻡ ﺍﻟﺘﻌﺭﻑ ﻋﻠﻰ ﻤﻭﺍﻗﻊ ﺒﻭﺯﻭﻻﻨﻴﺔ ﺠﺩﻴﺩﺓ ﺸﻤﻠﺕ ﺃﺒﻭ ﺤﺩﻴﺩ

( ﻜﺭﺩﻓﺎﻥ) ، ﺍﻟﺴﺒﻠﻭﻗﻪ ، ﺠﻨﻭﺏ ﻭﺸﻤﺎل ﺒﻴﻭﻀﺔ ، ﺍﻀﺎﻓﺔ ﻟﻤﻭﻗﻊ ﺍﻟﺒﻭﺯﻭﻻﻨﺎ

(ﺍﻟﻘﺭﻴﻘﺭﻴﺏ – ﺍﻟﺠﺯﻴﺭﺓ ) .

ﻏﻴﺭ ﺃﻨﻪ ﻭﻓﻲ ﻜل ﺍﻷﺤﻭﺍل ﺘﻤﺕ ﺩﺭﺍﺴﺔ ﻜل ﺍﻟﻤﻭﺍﻗﻊ ﺍﻟﺒﻭﺯﻭﻻﻨﻴﺔ ﺩﺭﺍﺴﺔ

ﺩﻗﻴﻘﺔ ، ﻭﻭﻀﺤﺕ ﺍﻟﺩﺭﺍﺴﺔ ﺘﻤﻭﻀﻊ ﻜل ﺍﻟﺒﻭﺯﻭﻻﻨﺎ ﻓﻲ ﺍﻟﺘﻜﻭﻴﻨﺎﺕ ﺍﻟﺒﺭﻜﺎﻨﻴﺔ ﻓﻲ

ﺍﻟﻌﺼﺭ ﺍﻟﺜﻼﺜﻲ – ﺍﻟﺤﺩﻴﺙ (Tertiaryٌ-Recent) ﻭﺭﻭﺍﺴﺏ ﺍﻟﺒﺤﻴﺭﺍﺕ ﺤﺩﻴﺜﺔ

ﺍﻟﺘﻜﻭﻴﻥ (Quaternary).

ﺒ ﻨ ﺎ ﺀ ﺍﹰ ﻋﻠﻰ ﻨﺘﺎﺌﺞ ﻤﻘﺎﻭﻤﺔ ﺍﻹﻨﻀﻐﺎﻁ ﻴﻤﻜﻥ ﺘﻘﺴﻴﻡ ﺍﻟﺒﻭﺯﻭﻻﻨﺎ ﺍﻟﻁﺒﻴﻌﻴﺔ ﻓﻲ

ﺍﻟﺴﻭﺩﺍﻥ ﺇﻟﻰ ﺜﻼﺙ ﻤﺠﻤﻭﻋﺎﺕ ، ﻤﺠﻤﻭﻋﺔ ﺫﺍﺕ ﺩﺭﺠﺔ ﺒﻭﺯﻭﻻﻨﻴﺔ ﻋﺎﻟﻴﺔ ﺘﺸﻤل

(ﺘﻜﻭﻴﻨﺎﺕ ﺍﻟﺴﺒﻠﻭﻗﺔ ، ﺍﻟﺠﺯﻴﺭﺓ ، ﺍﻟﺭﻤﺎﺩ ﺍﻟﺒﺭﻜﺎﻨﻲ ﺒﺸﻤﺎل ﺒﻴﻭﻀﺔ) ﻤﺠﻤﻭﻋﺔ ﺫﺍﺕ

ﺩﺭﺠﺔ ﺒﻭﺯﻭﻻﻨﻴﺔ ﻤﺘﻭﺴﻁﺔ ﻭﺘﺸﻤل ﺍﻟﺒﻴﻭﻤﺱ ﺸﻤﺎل ﺒﻴﻭﻀﺔ ، ﻭﺘﻜﻭﻴﻨﺎﺕ ﺍﻟﺒﺤﻴﺭﺍﺕ

ﺍﻟﺤﺩﻴﺜﺔ ( ﺃﺒﻭ ﺤﺩﻴﺩ) ﻭﻤﺠﻤﻭﻋﺔ ﻤﻨﺨﻔﻀﺔ ﺩﺭﺠﺔ ﺍﻟﺒﻭﺯﻭﻻﻨﻴﺔ ﻜﻤﺎ ﻓﻲ ﺍﻟﻁﻴﻥ ﻁﺒﻴﻌﻲ

6 ﺍﻟﺤﺭﻕ. ﻴﻤﺜل ﺍﻟﺭﻤﺎﺩ ﺍﻟﺒﺭﻜﺎﻨﻲ ﺃﻓﻀل ﺍﻟﺒﻭﺯﻭﻻﻨﺎ ﺍﻟﻁﺒﻴﻌﻴﺔ ﻓﻲ ﺍﻟﺴﻭﺩﺍﻥ ﻤﻥ ﻨﺎﺤﻴﺔ

ﺍﻟﻨﻭﻋﻴﺔ ﻭﺍﻟﻜﻤﻴﺔ ﺍﻟﻭﺍﻓﺭﺓ.

ﻴﻤﻜﻥ ﺘﺤﺴﻴﻥ ﻭﺯﻴﺎﺩﺓ ﻤﻘﺎﻭﻤﺔ ﺍﻹﻨﻀﻐﺎﻁ ﻟﻸﺴﻤﻨﺕ ﺠﻴﺭ-ﺒﻭﺯﻭﻻﻨﺎ ﺒﺼﻭﺭﺓ ﻤﻠﺤﻭﻅﺔ

ﺒﺎﻟﻁﺤﻥ ﺍﻟﻨﺎﻋﻡ ﻟﻠﺒﻭﺯﻭﻻﻨﺎ ﻭﺒﺯﻴﺎﺩﺓ ﻨﺴﺒﺔ ﺍﻟﺒﻭﺯﻭﻻﻨﺎ / ﺍﻟﺠﻴﺭ ﻭﺒﻤﺭﺍﻋﺎﺓ ﻅﺭﻭﻑ

ﺍﻹﻨﻀﺎﺝ ﻭﻜﺫﻟﻙ ﺒﺈﻀﺎﻓﺔ ﺒﻌﺽ ﺍﻟﻤﻭﺍﺩ ﺍﻟﻜﻴﻤﻴﺎﺌﻴﺔ. ﻏﻴﺭ ﺃﻥ ﺯﻴﺎﺩﺓ ﺩﺭﺠﺔ ﻨﻌﻭﻤﺔ

ﺍﻟﺒﻭﺯﻭﻻﻨﺎ ﺘﺘﺤﻜﻡ ﻓﻲ ﻜل ﻫﺫﻩ ﺍﻟﻌﻭﺍﻤل ﺍﻟﺴﺎﺒﻘﺔ.

7 List of Contents

Dedication i Acknowledgement ii Abstract iv List of Contents vii List of Tables xi List of Figures xiii Chapter one 1-Introduction 1 1-2 Objective of the work 2 Chapter Two 2 Literature review 3 2-1 What are the Pozzolanas 3 2-2 Uses of Pozzolanas 4 2-3 Types of Pozzolanas 5 2-3-1 Natural Pozzolanas 6 2-3-2. Artificial Pozzolanas 13 2-4 Types of Pozzolanic cements 22 2-4-1 Portland-Pozzolanic cement (PPC) 22 2-4-2 Lime-Pozzolanic cement (LPC) 22 2-5 Properties of Pozzolanic cement 23 2-5-1 setting time. 23 2-5-2 permeability 23 2-5-3 Heat of hydration 23 2-5-4 workability 24 2-5-5 Alkali aggregate reaction 24

8 2-5-6 Sulphate resistance 26 2-5-7 Compressive strength 27 2-6 Factors affecting the development of the strength of Pozzolana 28 2-6-1 Type and quality of Pozzolana 28 2-6-2 Pozzolana/lime ratio 31 2-6-3 Fineness 33 2-6-4 Temperature of firing 34 2-6-5 Curing conditions 35 2-6-6 Use of additives 36 2-7 Mechanism of lime-Pozzolana reactions 37 2-7-1 Old theories 37 2-7-2 Recent theories 38 Chapter Three 42 3 Experimental Techniques 42 3-1 Introduction 42 3-2 Geological field work 42 3-3 Chemical analysis 43 3-4 X-ray diffraction 44 3-5 Compressive strength tests 46 Chapter Four Results and discussion ( part 1) 4. Characterization of Natural –Pozzolana in Sudan 48 4-1 Introduction 48 4-2 Gregrieb diatomite deposits 49 4-2-1 Geology 49 4-2-2 Chemical analysis 54 4-2-3 X-ray diffractions 55 4-2-4 Compressive strength 59

9 4-3 Obsidian (pitchstone ) of Sabaloka 61 4-3-1 Geology 61 4-3-2 Chemical analysis 65 4-3-3 X-ray diffraction 65 4-3-4 Compressive strength 69 4-4 Quaternary lake deposit at Abu Hadied 70 4-4-1 Geology 70 4-4-2 Chemical analysis 74 4-4-3 X-ray diffraction 74 4-4-4 Compressive strength 77 4-5 Natural burnt clay (Southern Bayouda) 78 4-5-1 Geology 78 4-5-2 Chemical analysis 80 4-5-3 X-ray diffraction 80 4-5-4 Compressive strength 83 4-6 Pozzolanaic deposits in Northern Bayouda volcanic fields 84 Geology of Northern Bayouda Volcanic field 84 4-6-1 Volcanic tuffs deposits 88 4-6-1-1 Geology 88 4-6-1-2 Chemical analysis 88 4-6-1-3 X-ray diffraction 89 4-6-1-4 Compressive strength 91 4-6-2 Pumice deposits 92 4-6-2-1 Geology 92 4-6-2-2 Chemical analysis 93

4-6-2-3 X-ray diffraction 93 4-6-2-4 Compressive strength 96 Chapter Five

10 Results and discussion (Part II) 5. Factors Affecting the Compressive Strength of Lime-Pozzolana 97 Mortar 5-1 Introduction 97 5-2 Fineness 97 5-3 Lime/Pozzolana ratio 110 5-4 Type and quality of Pozzolana 116 5-5 Curing conditions 121 5-5-1 Humidity 122 5-5-2 Time 127 5-5-3 Temperature 127 5-6 Use of additives 130 Chapter Six 6. Conclusion and Recommendations 133 References 137

11 List of Tables Table (1): Characteristics of Natural Pozzolana 29 Table (2): Improvement of the strength by addition of gypsum to Lime- 36 Pozzolana cement Table (3): Chemical analysis of Gregrieb deposit 54 Table (4): The compressive strength of lime-Pozzolana mortar cubes 60 of diatomite (Gregrieb) Table (5): Chemical analysis of Obsidian deposit 65 Table (6): The compressive strength of lime-Pozzolana mortar cubes of 69 obsidian (Sabaloka) Table (7): Chemical analysis of Abu Hadied deposit 74 Table (8): The compressive strength of lime-Pozzolana mortar cubes of 77 lake deposit (Abu Hadied) Table (9): Chemical analysis of natural burnet clay 80 Table (10): The compressive strength of lime-Pozzolana mortar cubes 83 of natural burnet clay (Southern Bayouda) Table (11): Chemical analysis of Bayouda volcanic tuffs 88 Table (12): The compressive strength of lime-Pozzolana mortar cubes 91 of volcanic tuffs (Northern Bayouda) Table (13): Chemical analysis of pumice 93 Table (14): The compressive strength tests of lime-Pozzolana mortar 96 cubes of pumice (Northern Bayouda) Table (15): The effect of fineness on the compressive strength of lime- 100 Pozzolana mortar at lime:Pozzolana ratio (1:1) Table (16): The effect of fineness on the compressive strength of lime- 101 Pozzolana mortar at lime:Pozzolana ratio (1:2) Table (17): The effect of fineness on the compressive strength of lime- 102 Pozzolana mortar at lime-Pozzolana ratio (1:3)

12 Table (18): Summary of compressive strength results for different 103 fineness grades and lime-Pozzolana ratios Table (19): The effect of fineness on compressive strength at different 107 lime-Pozzolana ratio Table (20): The effect of fineness on compressive strength at different 108 curing time Table (21): The compressive strength of lime-Pozzolana mortar at 111 different lime/Pozzolana ratio Table (22): The compressive strength of lime-Pozzolana mortar at 112 different lime/Pozzolana ratios Table (23): The effect of type and quality of Pozzolana on the 117 compressive strength of lime-Pozzolana mortar Table (24): Relation between degree of fineness and the quality of 119 Pozzolana Table (25): The effect of type of curing on the strength of 123 lime-Pozzolana cement Table (26): The compressive strength of lime-Pozzolana cement at 128 various temperatures Table (27): The effect of torona additive on the strength of lime- 131 Pozzolana cement

13 List of Figures

Fig. 1 : Natural Pozzolanaic Deposits in Sudan 50 Fig. 1A : Map showing the Locations of Diatomites earth deposits 51 Fig. 2 Section showing the over bank lake deposits of Gregrieb area: 52 Fig. 3 : XRD- patterns of diatomiteof Gregrieb (Gezira) 57 Fig. 4 : XRD- patterns of of diatomite Gregrieb (Gezira) 58 Fig. 5 : Location of the Sablaloka inlier 62 Fig. 6 : Geological map of Ban Gadeed area (Sabaloka) 63 Fig. 7 : XRD- patterns of obsidian of Ban Gadeed (Sabaloka) 67 Fig. 8 : XRD- patterns of obsidian of Ban Gadeed (Sabaloka) 68 Fig. 9 : Geological map of Abu Hdied area (North Kordofan) 20 Fig. 10 : Section showing the mechanism of formation of Abu Hadied lake 73 Deposits Fig. 11 : XRD- patterns of Abu Hadied deposits (Kordofan) 76 Fig. 12 : Section of showing the natural burnt clay at Southern Bayouda 79 Fig. 13 : XRD- patterns of natural burnt clay at Southern Bayouda 82 Fig. 14 : Geological map of the main volcanic field of Northern Bayouda 87 Fig. 15 : XRD- patterns of volcanic tuffs (Bayouda) 90 Fig. 16 : XRD- patterns of pumice (Bayouda) 95 Fig. 17 : The effect of fineness on lime-Pozzolana strength (L/p=1:1) 104 Fig. 18 : The effect of fineness on lime-Poozzolana strength (L/P=1:2) 105 Fig. 19 : The effect of fineness on lime-Pozzolana strength (L/P=1:3) 106 Fig. 20 : The effect of Lime-Pozzolana ratio on strength 113 Fig. 21 : The effect of Lime-Pozzolana ratio on the strength 114 Fig. 22 : The effect of type and quality of Pozzolana on strength 118 Fig. 23 : The effect of type of curing on the strength of lime-Pozzolana cement 124 Fig. 24 : XRD-pattern of indirectly cured sample of lime –Pozzolana cement 126 Fig. 25 : The variation of strengths with temperature variations of lime- 129 Pozzolana cement Fig. 26 : The effect of use of torona on the strength of Lime-Pozzolana 132 Cement

14 Chapter One

1-1 Introduction: The Greeks (pre-400BC) followed by the Romans were the first to use Pozzolanas in lime mortars. The Romans used not only crushed pottery bricks and tiles as artificial Pozzolanas but also found that some volcanic soils were excellent for producing hydraulic mortar when mixed with lime. The development of hydraulic cements based on lime – Pozzolana mixtures led to radical change in Building during the Roman era. The increased strength of lime- Pozzolana mixtures , their hydraulic properties and good resistance to seawater, permitted the construction of not only arches and vaults but also marine structures. Lime- Pozzolana mortars were also used as water-proofing renders in the lining of baths, tanks and aqueducts. The durability of materials is attested to by the many remains of Roman structures still in evidence today. Lime mortar does not harden under water and for construction under water the Roman ground together lime and volcanic ashes or finely ground burnt clay tiles. The active silica and alumina in the ash and the tiles combined with the lime to produce what became known as Pozzolanic cement, from the name of the village Pozzolana, near Vesuvius, where the volcanic ash was first found Neville (1981). 1-2: Objective of the Work:

The objectives of the present investigations are summarized as follows: -To conduct geological survey with the intent discovering the most potential areas containing natural Pozzolanic materials in Sudan; using the field and geological technique.

15 -To characterize the natural Pozzolana in these areas using different experimental techniques. - To establish the degree of Pozzolanicity of these deposits. - To study the factors affecting the strength of lime – Pozzolana cement

16

Chapter Two Literature Review

2-1 What are the Pozzolanas: Lea (1938) defines Pozzolanas as siliceous materials which, though not cementitious in themselves, contain constituents which at ordinary temperature will combine with lime in the presence of water to form compounds which have a low solubility and possess cementing properties. In Srinivasan (1956) modified Lea’s definition by including ferruginous materials, and taking in consideration the mineralogical , and crystallographic conditions of the oxides and also the pressure at which the reaction should take place. The definition quoted by Neville (1995) is: The Pozzolana is a natural or artificial material containing silica in a reactive form. . A more formal definition of ASTM 618-94a describes Pozzolana as a siliceous or siliceous and aluminous material which in itself posses little or no cementitious value but will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperatures to form compounds possessing cementitious properties. However, Malquori suggested that materials, having Pozzolanic activity should be defined, in respect of their uses , cementitious materials quite a part from the interpretation of the chemical and physico-

17 chemical phenomena which are responsible for the hardening of the hydraulic binder Neville (1995). It is essential that Pozzolana be in finely divided state as it is only then the silica can combine with calcium hydroxide in presence of water to form stable calcium silicates which have cementitious properties. We should note that the silica has to be amorphous, that is, glassy, because crystalline silica has very low reactivity. Pozzolanic materials can be used either in conjunction with lime as Pozzolana-lime cements, or in replacement of up to 30% of Portland cement in Portland-Pozzolana cements. Pozzolana may be divided into two groups: - Natural Pozzolana such as tuffs, pumice, obsidian and scoria. The materials of sedimentary origins include certain diatomaceous earth and bauxite. -Artificial Pozzolana: these include; rice husk ash, pulverized fuel ash, si- steff and sugarcane bagasse ash.

2.2 Uses of Pozzolanas: The manufacture of Portland cement requires relatively sophisticated technology, equipment and expertise. However, the potentially low manufacturing costs of large plants will only accrue, if the plant operates at a high capacity utilization . The addition of Pozzolana to either a lime or OPC-based (OPC = Ordinary Portland Cement) product has two major advantages. Firstly; the properties of cement will be improved, such as reduction of permeability, low heat of hydration, sulphate resistance, resistance to

18 alkali aggregates reaction and workability improvement. Secondly as the cost of Pozzolanas are usually low and certainly well below that of lime or OPC the overall cost will be significantly reduced assuming that the Pozzolana does not have to be transported too far. [Lea (1956), (1970), Pozzolanas IT (1992)]

The use of low cost lime- Pozzolana cements in small-scale building works is common in many parts of Asia. In OPC-based concrete, Pozzolanas are used to replace up to 30% of OPC used in structural purposes. As OPC is an expensive and sometimes is a scarce commodity, this can represent a significant cost saving. In addition a Portland Pozzolana blended cement has a number of significant technical advantages over OPC. These are: Improved workability, improved water retention, reduced bleeding, improved sulphate resistance, improved resistance to alkali-aggregate reaction, lower heat of hydration and enhance long-term strength Subhi (1978), Pozzolanas IT (1992) The only disadvantage of these blended cements is that the early strength gain is slightly slower than that of OPC. This might mean that the dismantling of formwork on structural concrete may need to be delayed by a day or so, but this disadvantage is far outweighed by the advantages. These technical and economic advantages are well recognized by many engineers and Portland- Pozzolana blends are now commonly specified , particularly on major civil engineering works in both the developed and developing world.

19 2-3 Types of Pozzolanas: According to Lea (1956), Industrial Minerals-1(1995) and Hill et al (1992). Pozzolanas are classified into two groups i.e. natural and artificial Pozzolanas. 2-3-1 Natural Pozzolanas: The natural Pozzolanas include the materials that can be ground and used directly without any treatment, such materials include: i. Materials of volcanic origin. ii. Material of sedimentary origin.

i. Materials of volcanic origin: These represent the most and important part of natural Pozzolana. Deposits of volcanic ash, which are likely to be found are recently active volcanoes. Such as those found in the Mediterranean, the Pacific Region and Central Eastern, Africa Pozzolana IT (1992) and Bayouda desert north Sudan Almond et al (1969). The physical condition of volcanic ashes ranges from loose fine- grained materials to coarse deposits, sometimes quite large particles. Deposits may be loose, with appearance texture similar to compacted coal or wood ash. Other deposits are cemented, sometimes with appearance and properties similar to stone, and in such form they normally referred to as tuffs or trass. The colour of deposits can vary from off-white to dark-grey Lea (1956). The Pozzolanic reactivity of ash deposits can vary considerably. The quality of materials may also vary within a

20 single deposits or a single geologically consistent stratum with variations in the depth being common Lea (1956). The Pozzolanic materials of volcanic origin include:

-Obsidian: It is massive volcanic rock, glassy texture, sometimes it is of porphyritic textures with quartz and feldspar phenocrysts, brown to black in colour, rich in amorphous silica in addition to iron oxide and magnesia ( giving the black brown colour). It is of acidic nature (rhyolitic or granitic), formed due to the rapid cooling of magma at volcanic eruption Elturkey (1992), Industrial Minerals - 1 (1995).

-Scoria: Rusty black in color, glassy in texture with less amorphous silica than obsidian and it is the basic equivalent to the obsidian, formed by rapid cooling at end of volcanic eruption Elturkey (1992) , Industrial Minerals -1 (1995).

-Pumice: Light coloured ( White , grey, yellow , pink or brown), porous, vesicular volcanic glass, generally about 60-70% amorphous silica in acidic magma, 40-50% amorphous silica in basic magma, 12-

14% Al2O3 , 1-2% Fe2O3 plus alkalis Lea (1956), Elturkey (1992), Industrial Minerals -1 (1995).

-Pumicite:

21 It is fine-grained equivalent to the pumice, pumice and pumicite are extremely brittle with sharp concoidal fracture El Turkey (1992) Industrial Minerals -1 (1995).

-Volcanic Tuffs: These are also fine-grained equivalent to the pumice, but are very fine, they arise from the deposition of volcanic dust and ash, and may occur in pure consolidated massive rock from underlying material deposited subsequently, or in a more fragmentary and unconsolidated stage. El Turkey (1992), C. clays, V. ash IT (1992) Industrial Minerals- 1 (1995).

-Pyroclastic Rocks: These include ignimbrite and agglomerate rocks; of rhyolitic composition, light in colour formed of welded tuffs contain amorphous silica Allen (1992).

ii. Pozzolanic Materials of Sedimentary Origin: These types of Pozzolanas are formed due to the sedimentary processes which include the weathering of parent rock, and deposition of such materials, which are rich in amorphous silica. Unlike the volcanic Pozzolanas, they are friable soft formation light in colour easy for mining and extraction. These types of Pozzolanas include:

-Diatomaceous earth:

22 Diatomites are siliceous rocks made up largely from the skeletons of aquatic plants ( mainly planktonic) called diatoms which are first became abundant in the Cretaceous period ( about 65-75 million years ago), and they are still abundant in the present seas. Most of commercial deposits are of Tertiary age (i.e. from the end of Cretaceous to the start of the most recent geological period the Quaternary Lea (1956) Industrial Minerals (1979) Industrial Minerals -II (1995). There are many variations of diatoms bearing rocks from almost pure diatomite through diatomaceous shales to clays, shales and stiff-stones containing minor amount of diatom fossils. Diatomite deposits may be found in many varieties of environment from marine through brackish to Lacustrine, generally less than 65 million years old. Diatomite beds vary from inches to several hundred feet ; but because of length of time required for deposition very thick deposits of top quality diatomite with few impurities are rare. Deposition rates are thought to be very slow because of the microscopic nature of the tests (there may be over 40m. in each cubic inch of material). This is an enormous number when one considers that a standard sized diatomite insulating brick has a volume of 121.5 cubic inches, containing almost 5,000 million. fossil skeletons. Industrial Minerals (1979). The major requirement for deposit of a commercial scale depositions are as follows: Industrial Minerals (1979). -large shallow basin. -an abundant supply of soluble silica ( often supplied by volcanism). - an abundant supply of materials for the plants.

23 - no growth inhibiting constituents such as a high concentration of certain soluble salts. - very little depositions of clastic sedimentary materials. According to Turniziani, (1967) natural Pozzolana can be classified tentatively according to the nature of the constituents which react with calcium hydroxide as follows: i. volcanic glass. ii. Pozzolanic tuffs. iii. High silica Pozzolana ( a reactive form of hydrated silica). -Volcanic glass: Volcanic glasses having Pozzolanic activity may be either clearly or partly altered. They include the Italian Pozzolana found in the volcanic districts in Compania and Labium and probably the Santorin earth from Greece as well as certain rhyolitic deposits from the United States. Tavasci (1946) (1948) made a detailed microscopic study of the Pozzolanas of Sengi (Latium) and Bacoli ( Compania). The two materials are largely composed of vitreous phase of microporous texture together with varying percentages of minerals in clear crystals and minerals altered in varying degrees. On the basis of the data obtained from selective extraction of Latium and Compania Pozzolanas, Parravno and Catioti {1937) suggested that the glass composition approximates to that of laboratorite in the Latium Pozzolanas, but is near to that oligocase (Ca, Na) Al2Si2O8 or between that of orthoclase (KAL

Si3O8) and anorthite (Ca Al2 Si2 O8) in the Compania Pozzolanas. According to the hypothesis generally accepted, the reactive glass originates from explosive volcanic eruption. The fused

24 magma which is pulverized by the gases librated during the explosion, undergoes an abrupt cooling which prevents crystallization. Evolution of dissolved gases during solidification produces a fine textures of canals or bubbles, so that the consolidated vitreous particles have a high internal surface area. Parravano and Cotiolti (1937) described this particular physical stage as an “aerogel”. It should be noted that “aerogel” do not have the same meaning generally attributed to it in colloidal chemistry, namely a gel in which the liquid phase been replaced by a gas. Malaquori (1962) , Ferrari (1935); consider that the absence of Pozzolanic deposits in Enta region provides indirect support for view that Pozzolanic activity is dependent on explosive eruptions. Since the volcanism there has not been an explosive type. According to Daravano and Catioti (1937); the reactivity of the glass depends on the nature of the gases librated during solidifications. It has also been suggested by Penta (1954); that the a activity may be enhanced by peneumatolytic alteration preceded by gases and underground water which have removed some of the more soluble constituents. For certain Roman and Flegrean Pozzolana Maffei (1935) found that the heat of wetting and absorbent power for methyl violet diminished considerably after heating for 1hour at 750oC. Turriziani and Schippa (1954) studied the effect of heating on Roman Pozzolanas 400-750oC. At 400oC, heating for up to 300 hr had no effect. At 600oC the reactivity is much lower and the density is greater after 20 hr. The effects reaches a limit after 100 hr. At 750oC the effect is greater than at 600 oC and reaches a limit in 60 hrs; the density rises from 2.35 to 2.7 g/cm3. These results

25 show that thermal treatments of Pozzolanas in which the active component is a glass do not increases the reactivity.

- Pozzolanic tuff: Deposits of this kind are found in the Rhine-land and Baravia (Germany), in Compania and Latium (Italy), in Romania, in the and elsewhere. The tuffs from the Eiffel region are of similar constitution Malquori (1962). The trass from Andenach is even closer to the Neapoliton tuff. It has approximately the same chemical composition, mineralogical nature and appearance under the microscope. The geological conformity of the deposits are also similar. The tuffs from other localities are generally similar, but contain different minerals, in the tuff from Canary Island, the zeolite is philipsite while those from latium contain phillipsite, chapazite and herschelite. Mielenz, etal (1950); reported Pozzolanic activity for rhyolitic tuffs containing clinoptilolite and analcite. Investigations on the genesis of the volcanic tuffs were carried out with interesting results by Maquori et al (1950), Sersale (1960), Sersale (1961). These authors established that the formation of compact or semi compact tuffs was attributable to the process of zeolitization of the active vitreous phase contained in the incoherent pyroclastic materials ejected by volcanoes during explosive eruptions. The alteration of the glass is a process of autometamorphism produced in hydrothermal or pneum- atolytic action. Sersale (1961) reproduced in the laboratory the transformation of incoherent vitreous materials to zeolites by hydrothermal treatment of natural glasses.

- High heat silica: Pozzolanic materials belonging to this group include diatomite and some rocks that probably represent the siliceous residues of minerals from which the soluble oxides have been removed. Iler (1955) mentioned that Diatomite is very finely divided, hydrated amorphous silica, composed of skeleton shells of many varieties of microscopic aquatic algae; the silica content can be as high as 94%. The largest known deposits is found in California.

26 Gaize; soft rock containing active silica which occurs in Ardennes and Meuse village in France. As with Moler, it is generally calcined before use. Pozzolanas of high silica content occur in Italy mainly in Viterbo region of north Latium; these include Viterbo silica, Saerofano earth, and white earth, so called from its rather high colour. Turriziani (1959), Turriziani et al (1961). Spence (1980) reported that; the volcanic ash found in Indonesia is used as a rich source of Pozzolanic materials. It is coarse-grained material, loosely cemented and easily quarried. It is mixed with 20% hydrated lime for making blocks. Compaction is carried entirely by hand using a vibrating compaction machine. In Kenya ( Koru region), Allen (1992) reported that; the Koru field study showed that the deposit was formed of tuffs of pyroclastic origin, described in the literature as ignimbrites. It appeared that sorting of amorphous and crystalline material had occurred during initial depositions. Pozzolanic tuffs were also reported in Tanzania and Rwanda Spence (1980), Apers (1983), and in Uganda Tabbarro (1992), Hammound (1992).

2-3-2. Artificial Pozzolanas: Artifacial Pozzolanas are produced after treatment of certain raw materials to obtain materials rich in active silica and alumina. The treatment is usually heating. Artificial Pozzolanas include; brick reject calcined clays ( burnt clays and shales), rice busk, pulverized fuel ash ( fly ash), burnt gaize, moler, si-stoff, sugarcane baggasse ash. These represent the most commonly used artificial Pozzolanas Grane (1980) . A brief description of each is given here under :-

i.Brick reject:

27 Grinding brick reject or broken clay tiles in at ball mill or hammer mill is traditional practice to make “Surkhi” in India, “Semen Morah” in Indonesia “Homra” in Egypt Siyam (1987). However, they are somewhat coarse but sufficiently reactive to enable masonry mortars to set and harden. In Indonesia red bricks which are not adequately burnt, or second class bricks, and bricks cleared from old mortars are used. They are ground to pass BS sieve 250µ but at least 50% passes BS sieve 75 µ. Hadinoto (1954). Indian specifications for “Surkhi” require that fully but not necessarily over-burnt bricks, or broken tiles and pottery are to be used. They must be perfectly clean and free from admixtures. P. W. D. Hand Book (1950). However, an alternative Pozzolana-lime cement known as “LYMPO” has been developed by KVIC Bombay. The Pozzolana is obtained from underfired bricks from rural bricks clamps, which is then. ground with lime and together with small proportion of mineral gypsum to control the setting and initial rate of hardening Spence (1980). Investigations carried out by Central Road Research Institute (CRRI), New Delhi and other research institutions in the country have shown that certain clays, when calcined at optimum temperature, give rise to good Pozzolanic reactivity Gupta (1992). The clay Pozzolana ( reactive surkhi) thus prepared when used as lime – Pozzolana- sand mortars has the same strength as cement– sand mortars. In addition tothat, the main advantage of surkhi is the simplicity of its operation resulting in low maintenance and repair cost. Moreover, the energy consumption compared to other

28 processes is also less and provides uniform quality of product at lower cost. In Sudan Hamid (1999) found that the Pozzolana of broken burnt bricks complied with the American standard regarding fineness and associated impurities. However, for the compressive strength of Lime/ Pozzolana mixes of 1:1 , 1:2 the results comply with the Indian standard IS 91905.With regard to the properties water absorption, consistency and workability, the same mixes gave better results than mortar containing Ordinary Portland Cement. ii. Burnt clays and shales: Clays or shales suitable for use as a Pozzolanas are very wide spread and are readily available in almost all regions of the world. They are used as partial cement replacement materials on large scale construction programmes in a number of countries. However, large utilization has declined in the last three decades due to the availability of Pozzolana which requires less processing such as volcanic ash and pulverized fueld ash. When these are not available., the calcined clay still has considerable potential [ Neville (1981), C. clays , V. ash- IT (1992), Basin News (1995) and Sayed etal (1992)]. Bain (1974) indicated that clay type, nature of impurities, and amount of clay present are the factors to be considered in evaluating clays for Pozzolanic process. He pointed out that heating above 600oC is sufficient to make kaolinite clay reactive but heating to 950oC must be avoided. For montmorillonite clay the maximum activity occurs at 700-750oC.

29 In research work carried out by Forrester (1974) on illite clay, reactive Pozzolana was produced by heating the clay at 800oC for 35 minutes. Hammond (1983) C. clays , V. ash- IT (1992) reported that, the temperatures for attaining maximum activity for the three main groups of clay minerals (montmorillonite, kaolinite and illite) are 600-800oC, 700-800oC and 900-1000oC respectively. Subhi (1978) showed that 700oC is the optimum temperature for a coloured kaolin to obtain a reactive Pozzolana. Hamid (1999) found that 700 and 750oC are the optimum temperature for production of Pozzolana from black cotton soil and kaolinite clay respectively. Grane (1980) and Taibi et al (1985) reported the same temperature i.e 750oC for kaolinite clay and pure kaolnite. However, Forester (1974) advocates that ; in order to optimize the formation of Pozzolana from a clay, it must be heated to a temperature between that required to remove lattice water i.e collapse of the structure, and that is when the crystallization begins. Simple methods of burning clays for manufacturing of burnt clay Pozzolanas were traditionally practiced in India Spence (1974), and in the Indonesian Island of Java Spence (1980). In the latter clay like soil made into blocks and fired in a simple clamp. The burnt blocks are disintegrated and the coarse materials are screened. The resulting red powder is used in conjunction with lime, and sometimes cement for masonry mortars. The Central Road Research Institute of India, CRRI in (1984) established certain procedure for firing and grinding clays in order to obtain a maximum reactivity.

30 -iii. Rice Husk Ash ( RHA): A wide variety of siliceous or aluminous materials may be Pozzolanic including the ash from a number of agricultural waste. Rich husk has the greatest potential because it is widely available and on burning produces a relatively large amount of ash which contains around 90 percent silica R. Husk and P. F. ash IT (1992). Because of the low capital cost per ton of product, the utilization of agricultural wastes as a Pozzolanic materials with time is highly considered as alternative cementing materials in developing countries. Rice Husk is the most agricultural waste used. The Pozzolana is obtained by burning rice husk at appropriate temperatures. Special burners or stoves are required. Much work has been carried out on using rice husk to make a reactive Pozzolana Chopra (1979). About one tone of husk is produced from five tones of rice paddy and it has been estimated that 60 million ton of husk could be available, annually on global basis for Pozzolana production. As the ash content by weight is about 20 percent, there are potentially 12 million tons of RHA available as Pozzolana. Rice is grown in large quantities in many Third World Countries inducing china, the India sub-continent, South East Asia and smaller quantities in some regions of Africa and South America, R. Husk and P. F. ash IT (1992). In an alternative way, equal quantities of clay and rice husk are mixed with water and shaped into cakes. The cakes are then sun dried, fired in an open clamp, and ground to fine powder that passes 200 mesh sieve AFRO (1978).

31 The CRRI of India has developed recently a basic technology for the manufacture of rice husk ash masonry cement. Chopra (1980) Smith (1992) studied the rice husk of many African and Asian countries and he concluded that; the differences in the quality of the product are due to the variations in the methods of production. Laboratory analysis shows that; temperatures below 750oC are appropriate to obtain good Pozzolana as manifested by the good compressive strength results. Arjum (1999) studied the Pozzolanic behavior of rice husk ash, using X –ray diffraction technique (XRD) at 500oC and 700oC. He observed only small peaks of quartz indicating that the major proportion of silica is amorphous. However with progress in firing to 900oC and above, sharp silica peaks were observed indicating the development of crystalline character, and this was associated with loss of the Pozzolanic activity indicated by the loss in compressive strength. Hence, it is quite evident that the degree of Pozzolanicity is associated with the amorphicity of the silica. iv. Fly Ash of Pulverized Fuel Ash (PFA): Fly ash or pulverized Fuel Ash (PFA) is a Pozzolanic material obtained by using waste byproduct from thermal power plants. It is the most widely used artificial Pozzolana in USA and Britain under numerous commercial names. It s essentially vitreous physical state and low alkali content makes it useful Pozzolanic material provided that it contains admissible amount of unburnt carbon matter Hammound (1983). Fly ash is extracted as a fine powder from fuel gasses and hence its other common name (Fly ash). The ash extracted from the

32 bottom of power station boiler, furnace bottom ash, is less suitable as Pozzolana R. Husk and P. F. ash IT (1992). There are two types of PFA Lea (1956); depending upon the type of coal used. These are high lime and low lime, with the former having lime content above 10 percent and therefore possessing cementing properties on its own. The latter i.e low lime, PFA can be used as Pozzolana. PFA is available in large quantities in counties or regions using coal fired electricity generating stations. These include most Europe, North America, the Indian sub-continent, China and South Africa. The chemical composition of PFA will depend on type of coal used, R. Husk and P. F. ash IT (1992). Physically PFA is fine (less than 75 micron) powder, with rounded particles shape and colourig range from cream to dark grey. It’s bulk density is approximately 800kg/m3 which is roughly two third of the OPC. As with all Pozzolanas, fineness is critical to the performance of PFA, with fine Pozzolanas giving faster Pozzolanic reaction. Electrically collected PFA will be finer than PFA collected mechanically and therefore normally preferred as Pozzolanas, R. Husk and P. F. ash IT (1992). v. Sugarcane Bagasse Ash (SCBA): The family of neo –Pozzolanas include, rice husk ash (RHA), rice straw ash (RSA), wheat straw ash (WSA) and others. Sugarcane Bagasse Ash (SCBA) can be classified as a new entrant to the clan of neo- Pozzolanas Sayed et al(1992). A case study of the development of CP40 Pozzolanic cement in Cuba edited in Basin ITDG (2001). The component of CP40 cement, is Pozzolana; silica or alumina based materials with

33 particular structure which reacts with hydrated lime to produce hardened material, the reaction with water is in a similar manner to hardening OPC. The Pozzolana is extracted from bagasse ash which is taken from industrial boiler used in sugar production. The bagasse ash has a silica content about 70%; fineness 200- 300m2/kg; and has been used in a variety of applications particularly as mosonary mortar , stabilizer in earth construction, in mortars, concrete blocks, and in mass concrete applications CP40 has substituted up to 50% of OPC.[ Martinrena (1994), Martinrena (1998), Martinrena I (1999) L/P cement IT (1992) and (Martinrena II 1999)]. vi. Pozzolana from Bauxite ore:

The bauxite is an ore of Al2O3(alumina) formed by the chemical weathering of a granite basement rich in potash feldspar (KAlSi3O8- feldspar), but of course the use of bauxite is more beneficial and valuable for Al-concentration Lea (1956). The use of bauxite as Pozzolana in some ancient mortars was reported by Ciatelie. He found mortars made from pulverized bauxite and lime in the rains at Baux in the Rone valley in France (Lea 1956). In tropical climate, clay deposits are often subjected to a form of chemical weathering which leaches out the silica and light alkalis resulting in accumulation of ferric and aluminum hydroxide. The soils produced are bauxite (aluminum bearing) and Lateritic (iron bearing) Atia (1998). Although these soils are low in silica, they are normally considered essential for a Pozzolanic reaction, both exhibit some Pozzolanic reactivity when calcined. clays , V. ash IT (1992).

34 vii. Pozzolana from basaltic rock: Basalt is one of the most popular Pozzolanic materials used in Vietnam. Typical basaltic rock, shows a good Pozzolanic reactivity. The lime absorption has maximum value at burning temperature of 800oC. The other metamorphic basalt has the highest degree of lime absorption after burning at temperature of 500oC. Due to the Pozzolanic reactivity, all tested types of metamorphic basaltic rocks can be ground and mixed with lime to become binders of low grade.Addition of 4% gypsum increases remarkably the strength of lime basalt binders.Ngo (1992) In Sudan, both natural and artificial Pozzolanas were reported Whiteman (1972), Siyam {1978). The pumice was found in the northern part of the Sudan (Bayouda desert), and in the Western part at Marra Mountains. Another source for natural Pozzolana materials is diatomite earth which occurs at Gregrieb area North Wad Madani at the Western bank of the Blue Nile. Artificial Pozzolanas are thought to be the most widely available type. The clay plains almost dominate the central part of the Sudan. Brick reject is found at all clamp kill sites, resulting from the poor technology of moulding, drying and burning of bricks. The rejects are estimated to reach 30% of the total burnt bricks , low cost housing-Sudan (1984). The first attempt to use Pozzolana in Sudan dates back to the period 1919-1925, during the construction of Sennar dam. Amortar of 70% cement, + 30% crushed brick had been used. subsequently series of research works on Pozzolana were carried out by many investigators using the burnt clays as artificial Pozzolana Siyam (1987) ,Hamid (1999). On the other hand , Sulieman (1999); studied the natural Pozzolana of Quaternary lake deposits from Abu Hadied area (North Kordofan).

35 2-4 Types of Pozzolanic Cement: Pozzolanas can be used with cement to produce Portland – Pozzolanic cement (PPC), and with lime to prooduce Lime- Pozzolanic cement (LPC)

2-4-1 Portland – Pozzolanic cement (PPC): As the name suggests, this type of cement is produced by blending or intergrinding OPC with a Pozzolanic cement. The Pozzolana to be used has to be dry and in fine powdered form. Some Pozzolanas such as pulverized fuel ash, will directly meet these requirements while others require processing. The Indian standard 1S1489 specifies a minimum fineness of 320 m2 /kg measured by the Blaine air permeability test. This is recommended for blended Pozzolanas , P/B cement IT (1992).

2-4-2 Lime – Pozzolanic cement (LPC): As the name suggests Lime Pozzolana cements are produced by blending or intergrinding (lime normally as dry hydrated lime i.e calcium hydroxide) with a Pozzolanic material. PFA will be used directly, whereas other Pozzolanic materials may need processing. In any case the Pozzolana to be used must be dry and in fine powdered form . In general fineness similar or slightly greater than that of OPC is usually recommended. However, some have to be ground to considerably finer powder. The minimum fineness recommended by the Indian standards for Pozzolana 1S 1344-(1981) of calcined clay and (IS 38812- (1981) Fly ash is 320 m2/kg and 250 m2/kg respectively . The proportions of lime and Pozzolanas depend on the required proportions of the cement and on the type and quality of the lime and

36 Pozzolana used. Most researchers have adopted that the Lime Pozzolana ratio of 1:1 ,1:2 , 1:3 and 1:4 i.e. from 1:1 to 1:4 .

2-5 Properties of Pozzolanic Cement:

2-5-1 Setting time: `The setting times of Pozzolanic cements are some what longer than that for OPC. Indian standard, IS 4098 specifies initial and final setting times as a minimum of two hours and maximum of 24 hours respectively, measured by the vicat apparatus. The final set period is extended to 36 and 48 hours for lower grades of lime Pozzolanic cements. P/B cement IT (1992).

2-5-2 Permeability: The permeability of concrete made with a Portland Pozzolanas cements and lime-Pozzolanas cements will be reduced due to a reduction of pore size in the concrete. Reduced permeability is important in the hydraulic structures and contributes to the increased sulphate and acid resistance of Portland- Pozzolana cement ( P/B cement IT 1992).

2-5-3 Heat of hydration: When OPC hydrates it produces heat, known as heat of hydration. With Portland Pozzolana cements, this is considerably reduced, resulting in reduced thermal expansion and shrinkage and therefore less cracking on cooling. This is of particular advantage with mass concrete structures. P/B cement IT (1992). 2-5-4 Workability: Workability is a term used to describe the cohesiveness and water retaining ability of a concrete or mortar. A high workable

37 mix will have the desirable quantities of good cohesion, higher water retention and low amount of bleeding ( grout loss). Poor workability is often associated with ( Low cement) concrete or mortar mixes. In general the use of Portland Pozzolana cements and lime – Pozzolana cements will improve workability particularly for lean mixes P/B cement IT (1992).

2-5-5 Alkali aggregate reaction: The alkali-aggregate reaction is caused by reaction between alkali from cement and certain types of aggregates containing a form of silica which reacts with the alkali. It causes expansion which can result in various damages to concrete structures. The use of Portland- Pozzolana cements and lime- Pozzolana cements will reduce alkali aggregate reaction. In recent years, an increasing number of deleterious chemical reaction between the aggregate and the surrounding hydrated cement paste has been observed. The most common reaction is that between the active silica constituents of the aggregate and the alkalis in cement. The reactive forms of silica are opal (amorphous), chalcedony (crysptocrystalline fibrous), and tridymite (crystalline). These reactive materials occur in opaline or chalcedonic cherts, siliceous limestone, rhyolites and rhyolitic tuffs, dacite and dacite tuffs, andesite and andesite tuffs, and phyllites. Goldbeck (1956). The reaction starts with the attack on the siliceous minerals in the aggregate by the alkaline hydroxides in pore water derived from the alkalis (Na2O and K2O) in the cement. As a result, an alkali-silicate gel is formed, either in planes of weakness or pores in the aggregate ( where reactive silica is present) or on the surface of aggregate particles. In the latter case, a characteristic altered surface zone is formed. This may

38 destroy the bond between the aggregate and the surrounding hydrated cement paste. The gel is of the “unlimited’ swelling type, it imbibes water with consequent tendency to increase in volume. Because the gel is confined by the surrounding hydrated cement paste, internal pressures results and may eventually lead to expansion, cracking and disruption of hydrated paste. Thus, expansion appears to be due to hydraulic pressure generated through osmosis, but expansion can also be caused by swelling pressure of the still solid products of the alkali –silica reaction Powers (1955). For this reason, it is believed that it is the swelling of soft gel is later leached out by water and deposited in the cracks already formed by the swelling of the aggregate. The size of the siliceous particles affects the speed with which reaction occurs, fine particles (20 to 30 µ) leading to expansion withi9n a month or two , larger ones only after many years (Diamond 1974). Reviews of the mechanisms involved in the alkali-silica reactions have been presented by Diamond (1989) and by Helmuth (1993). It is believed that the gel formation takes place only in the presence of Ca++ ions Chalterji (1979) . This is of importance with reference to the preventation of expansive aggregate-silica reactions by the inclusion in the mix of Pozzolanas, which remove (Ca (OH)2). The progress of reactions is complex, but it is important to bear in mind that it is not the presence of the alkali-silica gel, but the physico-chemical response to the reactions that leads to the cracking of concrete. Diamond (1989)) . They concluded that; the rate of release is affected by the temperature and the fineness of grinding of the Pozzolana and by how well the solid is dispersed in the solution. They also concluded that; the increase in temperature probably causes some of the crystalline minerals to react appreciably and so contribute to the release of alkali.

39

2-5-6 Sulphate Resistance: Sulphate resistance is the ability of Pozzolanic cements to resist the sulphate attack. The sources of high sulphate content may either be ground water, or soil containing sulphates such as gypsum or when sea water comes into contact with continent. Sulphate resistant cement has a C3A (tricalcium aluminate or 3CaO.Al2O3) content below 3.5% BS 4027: (1980) Neville (1981). The calcium hydroxide produced by hydrating OPC is readily subject to sulphate attack which can cause a serious deterioration of the concrete, due to the reaction of C3A with sulphate to produce ettringite causing swelling and failure as a consequence of the associated expansive forces. In Portland – Pozzolana cements calcium hydroxide combines with the Pozzolana to form more stable silicate or aluminate hydrates and therefore sulphate resistance is increased. Concrete made with Portland Pozzolana cement is also resistant to sulphate attack probably due to a reduction in permeability rather than any chemical reaction, Lundwing (1960), Taylor (1964), Manning (1995). The subject of suphlate attack was studied by many investigators using different methods [Turriziani and Rio (1957), Rio and Cedani (1961), Turriziani and Rio (1962) , Turiziani and Rio and Celanic (1962), Turriziani (1964) and Ansteft (1964)].

2-5-7 Compressive strength: The strength of Pozzolanic cement is the direct tool for measurement and assessment of Pozzolanic activity , in other

40 words the degree of Pozzolanicity of Pozzolana is assessed by measuring compressive strength of Pozzolanic cement. The compressive strength is an important physical property, the higher compressive strength of Pozzolana, the higher degree of Pozzolanicity, which positively influences the reaction between calcium oxide (CaO) and silica (SiO2). In general Portland- Pozzolana cements will produce relatively low strength at early ages but higher long-term strength once the contribution of the lower and secondary Pozzolanic reaction takes place Swamy (1986), Lea (1970). As a general rule up to 30 percent will produce concretes with lower early strength, particularly during the first seven days , where loss in strength of approximately 23-30 percent can be expected. Much of this loss will be compensated for at 28 days and by 90 days a comparable strength to that OPC will be achieved. After one year the strength of Portland Pozzolana cements is normally at least equal or probably greater than OPC. [Spence (1980) Spence (1983), P/B cement IT 1992)]. The strength gain of Lime Pozzolana cements is very slow in comparison with OPC and it may be several days before any measurable strength is developed. However their strength gain does not drop off after a few months in the same way as OPC and they will continue to gain strength gradually for many years. P/B cement IT (1992). The compressive strength achieved by Portland-Pozzolana cement and lime-Pozzolana cement can be upgraded by taking into consideration the following factors:- type and quality of Pozzolana; proportion of the mix; fineness of Pozzolana; firing temperature for artificial Pozzolana; curing conditions ( type of curing; time of

41 curing and temperature of curing); addition of additives and type of lime Siyam (1987), P/B cement IT (1992).

2-6 Factors affecting the development of the Strength of Pozzolana: 2-6-1 Type and quality of Pozzolana: The ability of Pozzolanas to react with lime varies greatly from type to another. Some are excellent while others have hardly any Pozzolanic activity. However the differences of quality may even occur within the same deposition of Pozzolanic materials Siyam (1987), Stulz (1981). Quality of Pozzolanas is primarily dependent on the presence of reactive silica and alumina which react with lime in the presence of water to form cementitious compounds. This in fact further depends on the physical and chemical properties, and/on their preparation processes from their raw materials Stulz (1981). In case of the burnt clay Pozzolnas; the quality depends on clay type and its chemical compositions; amount of clay present; nature of impurities, and the optimum temperature of calcinations ASTM C- 593 (1970). The Pozzolanic quality of fly ashes which may varies from day to day production, depends on the coals burnt and the efficiency of the combustion process Stulz (1981). Different countries have different standards for controlling the Pozzolanic qualities. These include both chemical and physical requirements. For fly-ash ASTM standard requires a minimum of 70% of the sum of SiO2 and Al2O3 and Fe2 O3 content; whereas Japanese (JISA 6201) and USSR (GOST 6269) standards specify a minimum of 45% and

40% SiO2 content respectively Kawiches (1983).

Spence and Allen (1981) have pointed out that as Pozzolanas are always used in conjunction with other materials, it is not so important for standards to define chemical and physical properties of Pozzolana. However out of the various methods proposed for assessing the Pozzolanic quality , one based on a strength test has been generally claimed to be the most suitable method .

42 Different types of natural and artificial Pozzolanas show wide variation in compressive strength depending upon the type and quality of Pozzolana. Rafeel (1992) determined the Pozzolanic strength of various Kenyan natural Pozzolanas. The results are summarized in Table (1).

Table (1) characteristics of natural Pozzolana:

Type of SiO2+Al2O3 Concrete cubes compressive strength natural + Fe2O3 (OPC only :100% )

Pozzolana ( % ) 15% 15% 30% 30% Pozz. Pozz. Pozz. Pozz. 28 days 60 days 28 days 60 days Pumice 82% 92% 94% 79% 83% Diatomite 84% 109% 94% - - Phonolite 67% 67% 88% 77% 82% Yellow tuff 53% 120% 124% 102% 106% Athi tuff 76% 100% 102% 82% 89% OPC = Ordinary Portland Cement

In Table (1); some selected characteristics of the natural

Pozzolanas are listed. The combined values of SiO2 + Al2O3 +

Fe2O3 vary between 53 and 84%. The concrete cubes strength, as compared to OPC only as binder, shows that three of the five Pozzolanas have systematically higher strengths than OPC when mixed in a 15:85 ratio. For the 30:70 ratio, still one sample gets higher values than OPC. The other Pozzolanas reach between 82% and 89% of the control value. The diatomite sample could only be tested up to 25% because, with richer diatomite mixes, the water

43 requirement becomes very high. It can also be seen that the relative strength of all Pozzolana samples (as compared to the control sample) is higher at 60 days and 28 days, which confirms the characteristics long-term strength increase of Pozzolanic binders. Gupta (1992); reported a 30 kg/cm2 for the 28 days strength when using burnt clay and 45 kg/cm2 when using RHA, in both cases the lime / Pozzolana ratio was kept the same. Subhi (1978) studied the effect of type of Pozzolana on the compressive strength of natural and artificial Pozzolana keeping the other factors constant. He showed that; the strength of Pozzolana can be classified to high and low compressive strength type , such as: - Pozzolana from burnt clay to 700oC. - Pozzolana from burnt clays to 800oC. - Pozzolana from reject brick . - Pozzolana from volcanic tuffs. The above data is arranged in descending manner i.e from high compressive strength to low compressive strength. In Sudan Hamid (1999) ; studied the effect of type of Pozzolana on the compressive strength of different types of artificial Pozzolana, keeping the other factors constant, he showed that the strength of lime- Pozzolana can be classified in descending manner (from high to low compressive strength ) , according to the following sequence: - Pozzolana from burnt black cotton soil. - Pozzolana from burnt clay at 700oC. - Pozzolana from reject bricks. - Pozzolana from burnt kaolinitic clay

44 2-6-2 Pozzolana/Lime ratio: The proportion of lime to Pozzolana depend on both the quality of Pozzolana and lime used. Unfortunately in many countries the commercial building limes available are of poor quality and therefore suitable lime will have to be imported. Ideally, the lime content should be just sufficient for all the Pozzolana to react fully. In practice somewhat higher lime content is used to allow for inadequate mixing. Spence etal (1981) ; who have studied Pozzolanas of varying types from Tanzania, found that the optimum strength occurs at Pozzolana lime ratios between 2.5:1 and 4:1. however, it was pointed out by Hammound (1983); that at early stages the maximum strengths are obtained with ratios of about 4:1 (Pozzolana : lime ), but for longer periods lower ratios gave higher strengths. Thus ratio of 2:1 and 3:1 give maximum strengths at one year. In the methods developed in Tanzania for the production of a Pozzolana-lime cement, slightly hydraulic lime which contains about 70% calcium hydroxide is used. The lime was dry-mixed with a volcanic ash in a ratio 1:1 by weight and then the mixture passed through a 3mm sieve before packing ATCE (1980). In Pakistan, where an experimental low-cost house has been built, Lime with rice husk ash in the proposition of 1:2 by weight was used in mortar, in plaster , and in the fabrication of load bearing hollow blocks. The mixture form only 8.55% by weight of the block. Taibi et al (1985); produced synthetic Pozzolanic binder by mixing (50/50 by weight) a thermally activated pure kaolinite and pure lime having 96% calcium hydroxide. They found that

45 stabilization with 5% cement or 8% of this new Pozzolanic binder led to the same 56 days strength when the specimens were subjected to wetting and drying cycles. Moreover with higher curing time ( 90 to 180 days) the Pozzzolanic binder tended to give higher strength than when cement was used. Nagarkar (1977); carried out a comprehensive study on the effect of replacing lime by Pozzolana from zero to 100% on the strength properties of lime mortar cubes. He used two Pozzolanas; surkhi and fly ash and two lime samples; fat and hydraulic lime, with CaO content of 90% and 60% respectively. He concluded that 40 to 60 percent replacement of lime by Pozzolana gave the maximum strengths. On his study of artificial Pozzolana prepared from burnt clay and brick rejects, Hamid (1999) found in production of lime : Pozzolana 1:3 gave higher strength than 1:2 (lime : Pozzolana).

2-6-3 Fineness: The hydration of Pozzolanic cement ( Portland- Pozzolana cement or lime- Pozzolana cement) starts at the surface of the cement particles. It is the total surface area of the cement particles that represents the materials available for hydration. Thus the rate of hydration depends on the fineness of the cement particles, and for a rapid development of strength high fineness is necessary. Thus fineness of Pozzolana is a vital property, and has to be carefully controlled. Neville (1981). Generally the strength of Lime- Pozzolana increases with increasing degree of fineness.

46 The effect of grinding of Pozzolana, on Pozzolanic quality has been studied by many researchers. Robertson (1974) recommended grinding finer than 300 mesh for pumice and only 100 mesh for volcanic ash. Moreover he emphasized that the lime must be freshly calcined. Some countries measure fineness by determining the maximum retained on a certain sieve, whereas others adopt specific surface tests. For instance, the ASTM standard C-593 (1970) specifies the maximum percentage retained on 74µ and 95µ sieves as 30% and 2% respectively based on wet sieving. In Indonesia, where the brick powder is used for mortars, plasters and concrete, the minimum percentage retained on BS sieve 75 µ is specified as not to be greater than 50% Siyam (1987). Subhi (1978) studied four different types of Pozzolana in Iraq; he concluded that the strength of four types increases with increase in fineness. This was also confirmed by the work of Hamid (1999).

2-6-4 Temperature of firing: The presence of amorphous silica is very important for both the natural and artificial Pozzolana to react with lime for production of cementitious compounds. For artificial Pozzolana such as burnt clay , rice husk ash, sugar bagasse the firing temperature should be controlled in order to produce materials with enough amorphous silica. The optimum calcining temperatures for clay Pozzolanas are slightly below those for clay bricks or tiles and therefore better results are likely to be obtained if the moulding and firing process are designed specially for Pozzolana production. The Indian standard IS 344 (1981) ,specifies the following range of temperatures for different types of clays. Montmorillonite type 600-800oC. Kaolnite type 700-800oC.

47 Illite type 900-1000oC. In practice most clay soils consist of a mixture of minerals and a calcination temperature of 700-800oC is normally considered suitable. The optimum period of calcination will vary with clay type but normally at around one hour or less. Smith (1992) reported that controlled calcination of rice husk resulted in gain of strength of mortar or concrete compared to uncontrolled calcination . On the other hand he showed that high temperatures during the incineration of rice husk resulted in the formation of crystalline phases of silica in RHA and in low strength RHA. In his study of the Pozzolanic behavior of RHA using XRD analysis. Arjum (1991) obtained very small quartz peaks when firing at 500oC and 700oC. This indicates that most of ash is amorphous. However firing at 900oC and above resulted in formation of crystalline silica with consequent loss of Pozzolanicity of RHA. Subhi (1978) studied clay burnt at different temperatures 600oC, 700oC, 900oC, 1000oC. He came to conclusion that the clay brunt at 700oC, 800oC produced good quality of Pozzolana than that burnt at temperatures 600oC, 900oC and 1000oC.

Basin Cp40 (2001) confirmed that the husk produced in the incinerator cinder controlled conditions would produce better Pozzolana than that obtained from boilers, where burring conditions were largely not controlled. He suggested that incinerator ash would likely be more active and softer, and so easy to grind.

2-6-5 Curing conditions:

48 The curing conditions include: a. Humidity. b. Time c. . Temperature Moisture is known to be an essential factor for the development of Pozzolana lime reaction. It is necessary for the Pozzolana lime based products to be kept moist for a considerable length of time, preferably for at least 28 days . Colonial Building Notes (1954). Beside Humidity the Pozzolana–lime reaction increases with curing time. Many investigators verified this statement. On the other hand the rate of strength development is very sensitive, to the curing temperature, such development is very slow below 10oC, moderate at 15oC, and considerably increased above 20oC as long as the mix is kept moist . Colonial Building Note (1954). Apers, et al (1983); reported that an increase of 20oC (20-40oC) accelerates the process of Pozzolana lime reaction by approximately five times. In experiments conduced by Spence and Allen (1981) on different Pozzolanas, it was found that when Pozzolana mortar cubes were cured at elevated temperatures such as 50oC for 7 days, they approximately attained twice strength for the sample cured at 20oC.

2-6-6 Use of additives: Investigations have been carried out by many researchers with the aim to improve the early strengths of Pozzolana lime mixtures. These include use of additives such as cement, gypsum, salts, e.g. Na2 CO3 Apers (1983) and certain additives in the form of water emulsions, suspensions or solutions Mehta (1985).

49 Ngo (1992) studied Pozzolana produced from firing basalt; and he found that the addition of gypsum to the Lime - Pozzolana cement improved the strength considerably; as illustrated in Table (2). Table (2): improvement of the strength by addition of gypsum to lime Pozzolanic cement. Proportions of Compressive Strength (Kg/cm2) Pozzolana 14 days 20 days 60 days 90 days 76% basalt + 20% lime + 5% 173 219 233 239 gypsum 66% basalt + 30% lime + 4% 146 147 189 285 gypsum 53% basalt + 40% lime + 4% 212 220 264 291 gypsum 70% basalt + 30% lime 72 93 111 120 Reference: Ngo (1992) 2-7 Mechanism of lime- Pozzolana reactions:

The fundamental property of Pozzolana is its ability to combine with lime to form cementitious materials. Many theories were postulated in order to explain the mechanism of Lime-Pozzolana reactions. A brief survey is given here under:

2-7-1 Old theories: Two main theories have been advocated: -The base exchange theory. -Direct combination theory. The idea that natural Pozzolanas are zeolitic compounds and owe their properties to base exchange, runs through much of the older literature. The zeolites are group of insoluble hydrated alumina silicates of the alkalis and alkaline earth which have the property of exchanging some of their base constituents for others when immersed in solutions. This property utilized water softening in the permitute process. Lea (1938) , (1956), reported that when

50 volcanic ash Pozzolanas are shaken with solutions of calcium nitrate a small amount of alkalis are librated into solution. A more advance work came with Startling (1940); who showed that hydrated calcium aluminum silicate (2CaO. Al2O3- o SiO2 aqua.) was formed from burnt kaolin and lime water at 20 C. The compound which had a distinctive X-ray pattern formed weakly birefringent plates with a reactive index 1.50-1.505. In addition, evidence was obtained from the presence of 3CaO. SiO2 aqua.

Startling suggested the following reactions:

2(Al2O3. 2SiO2) + 7Ca(OH)2 3CaO.2SiO2aqu. +2(2CaO.Al2O3-

SiO2aqu).

The hydrated gehlenite compound dissolved in water to give a solution containing 0-00lgm SiO2, 0. 003gm Al2O3, 0.008gm CaO per 100ml.

The problem has been pursued further by Italian worker ( Turriziana and Schippa (1954) using differential thermal analysis and X-ray examination. The results obtained showed that the active silica in a Pozzolana reacts to form either Taylor’s calcium silicate hydrate

(0.8-1.50 CaO.SiO2 aqu. ) or Starling’s compound.

2-7-2 Recent Theories: Theory of silica –lime reactions: Five basic reactions were suggested for the theory of silica-lime reaction. UNIDO (1987). These are: water absorption; cation exchange; flocculation and aggregation; carbonation; and silica lime Pozzolanic reaction

51 a. Water absorption: Quick lime undergoes hydraulic reaction in the presence of water or moist silica. This reaction is strongly exothermic with release of about 300 K cal for every Kg of quick Lime UNCHS (1984).

b. Cation exchange: When lime is added to moistened montmorillonite or kaolinite clay, it will be flooded with calcium ions. Cation exchange then takes place, (giving the clay a lower affinity for water ), with Ca ions being replaced by exchangeable cations in the soil compounds, such as Mg++, Na+, K+, and H+. Thus the resulting mix is characterized by a lower moisture movement, i.e. lower liquid limit and plasticity. The volume of this exchange depends on the quantity of the exchangeable cations present in the over all cation exchange capacity of the soil. The general order of replacibility of the common cations associated with soils is given by the lytropic series, Na+ < K+ < Ca++ < Mg++ . Cations tend to replace cations to the left in the series and monovalents are replaceable by multivalent cations. [UNCHS (1984), Hilt etal (1960) and TRB (1976)].

c. Flocculation and aggregation: As the result of the cationic exchange and the increase of the quantity of the electrolytes in the pure water, the soil or clay grains flocculates and tend to accrete. UNHS (1984). This makes the mix more viscous or stiff UNIDO (1987). The size of accretions in the fine fractions increases.

52 Both structure and grain size distribution are altered. According to Herzog and Mitchell (1963), the flocculation and agglomeration are caused by increased electrolyte content of the pore water and result of ion exchange Diamond and Kinter (1965) suggested that the rapid formation of calcium aluminate hydrate is significant in the development of flocculation and agglomeration tendencies in soil-lime stabilization. The basic mechanisms involved have been explained by Davidson (1963). He postulated that: Calcium ions cause a reduction in the plasticity of cohesive soil. The mechanism is either a cation exchange or crowding of additional cations onto the montmorillonite or kaolinite clay mineral. Both processes change the electrical charge density around the clay particles. Then these particles become electrically attracted to one another, causing flocculation. Whereas Davidson et al (1963) stated that: the crowding of additional Ca onto the clay must be the more important of the two mechanisms, since when they have tested the soil already had an excess of carbonates present (16.6%), yet the (Plastic Limit) of the soil was decreased from 40% to 18% with the addition of less than 3% lime. d. Carbonation: Lime added to the silica reacts with the carbon dioxide

(CO2) from the atmosphere to form weak carbonated cements. This uses part of the

53 lime available for Pozzolanic reactions; which give rise to hardening effects El gallad

(1997).

e. Soil-lime Pozzolanic reaction; The reaction between hydrated lime and various sources of silica and alumina to form cementing type materials are referred to as soil-lime Pozzolanic reactions. These reactions by far are the most important reactions involved in lime stabilization. Possible sources of silica and alumina in typical soils include clay minerals quartz, feldspar, micas, and other similar silica or aluminosilicate minerals either amorphous or crystalline in nature. TRB (1976). With respect to a study submitted by the Transportation Research Board (TRB), when a significant quantity of lime is added to a soil, the PH is elevated to approximately 12.4, which greatly increases the solubility of silica and alumina TRB (1976). In an early study of silica lime reaction Eades (1962), suggested that the high pH causes silica to react forming a positive charged ion [Si

(OH)2] and becoming available to combine beside alumina with Ca to form a water insoluble gel of aluminum and calcium silicates ( similar to some of those found in Portland cement UNIDO (1987). This reaction will continue as long as Ca (OH)2 exists in the presence of silica and alumina, i.e in time this gel gradually crystallizes into a well defined

54 calcium silicate hydrates such as tobermorite and hillebranite, the micro- crystals of which can also interlock mechanically; and thus cementing the grains together Hilt etal (1960). Recent work conducted by TRB (1981) gave an over simplified quantitative view of some typical soil lime reactions as follows:

+2 Ca(OH)2 Ca + 2(OH-) (i) +2 Ca 2(OH-) + SiO2 CSH (ii) +2 Ca + 2(OH-) + Al2O3 CAH (iii)

A wide variety; of hydrated forms can be obtained, depending on the quantity and the type of lime, clay characteristics, curing time and temperature TRB (1976).

Typical clay-lime reactions are:

55 Kaolinite + Lime CSH

+ CAH = CASH (iv)

Kaolinite + Lime CSH (prehnite) (v) Montmorillonite + Lime CASH (gel) (vi) Montmorillonite + Lime CSH (gel)+ hydrogarnet CAH (vii) Montmorillonite + Lime CSH (gel) +CSH(1) + tobermorite + hydroygarnet (viii) Clay + lime CSH(gel)+

CSH(1) + C4AH13 + C3AH6

(ix) Chapter Three

3- Experimental Techniques

3-1 Introduction:. The objectives of this study are to characterize some natural Pozzolanas, and to determine their Pozzolanicity through determination of compressive strength of Lime Pozzolana cement and to study the factors affecting the compressive strength of lime-Pozzolana mortar. Therefore, the experimental work comprises two parts, the first deals with the characterization techniques, and the second is the determination of the degree of Pozzolaniciy. Hence the following experimental techniques were used, namely:

56

3-2: Geological field work: The Geological field investigation covered five locations; which are: Quaternary lake deposits at Abu Hadied ( northern Kordonfan), diatomites earth at Gregrieb (Gezira area along Blue Nile,), obsidian or pitchstone deposits at Ban Gadied area (Sabaloka northern Khartoum), natural burnt clay at Mindraba ( southern Bayouda desert) and northern Bayouda volcanic comprising pumice and volcanic tuffs deposits (northern Bayouda desert).. The objectives of the investigations are; - To locate exactly the site of natural Pozzolanic deposits in Sudan. - To study the host rocks and soils in order to determine thier types, structures and genesis. - To estimate roughly the reserve of Pozzolanic deposit in each site. - To collect samples for further laboratory tests. Different field tools were used during the field trip. These include; compasses, global positioning system (GPS), geological hammers, aerial photographs at scale 1:20000 and 1:40000, measuring tapes ( 50 and 100), bags with different sizes for samples collection, and hand lenses. The fieldwork was preceded by extensive data collections and examination of geological and topographical maps and reports . Finally appropriate samples were collected for further laboratory tests, such as chemical analysis, X-ray diffraction and compressive strength tests.

57 3-3: Chemical analysis: Chemical analysis was carried out according to the standard methods [ see Bennett et al (1971)] “Methods of silica analysis”. The loss on ignition was determined by heating the sample to 1000oC for 30 min. the main part of the sample was fused in sodium hydroxide, the melt was extracted with hot water, dissolved in nitric acid and the solution made up to volume. Aliquos were taken for silica, alumina and titania determination by spectrophotometric procedure, silica was determined by measuring the yellow silicomolybdate colour and alumina by the addition of solochrome cyanine, and measuring against a control solution. The iron was one aliquot was complexed with thioglycolic acid, and the iron and aluminum in the control with EDTA. Titanium was determined with hydrogen peroxide, using phosopric acid to bleach the yellow colour of the iron. Ferric oxide was not normally determined on this solution as there was a tendency to lose some of the iron in the sample into the nickel crucible. The alkalis in the solution were determined by flame - Photometry and the ferric oxide in an aliquot was determined spectrophotometrically with 1:10 phenanthroline after reduction with hydroxyammonium chloride. Further aliquots were used for the compleximetric determination of lime, and magnesia, the ammonia group oxides being complexed in each case, with triethanolamine. Lime was determined by adjusting the pH with potassium hydroxide and titerating with EDTA using screened calcium as indicator and lime plus magnesia was determined by adjusting the pH with ammonia solution and titrating with EDTA using methylthymol blue complex one as indicator.

58

3-4: X-ray diffraction: X-ray diffraction technique is one of the most effective tools which is widely used as rapid method in the mineralogical analysis of rock formations. The main purpose of using X-ray diffraction in this study is to differentiate between crystalline and non crystalline or amorphous silica, this criterion is used for detection of Pozzolanic formations. A diffractometer is an instrument for studying crystalline ( and non crystalline) materials by measurements of the way in which they diffract X-rays of known wavelength. In the diffractometer, the intensity of a diffracted beam is measured directly either by means of the ionization it produces in a gas or the florescence it produces in a solid. The diffractometer comprises [See Zamzami (1979)] a powder specimen in the form of flat plate supported on a table, which can be rotated about the diffactometer axis; and X-ray source ( producing monochromatic radiation) situated parallel to the diffractometer axis. X – rays diverge from this source and are diffracted by the specimen to form convergent diffracted beam which comes to a focus at a slit and then the counter. The receiving slit and the counter are supported on a carriage which may be rotated around the diffractometer axis and whose angular position 20 may be read on a graduated scale . The diffraction patterns of unknown substances may be obtained either continuously or intermittently. In the former the counter is set near 2O = 0 and connected to accounting-rate meter which is then driven at constant angular velocity through

59 increasing values of 2 O until the whole angular range is a scanned, at the same time, the proper chart on the recorder moves at constant speed, so that distances along the length of the chart are proportional to 2 O. In the latter, the counter is connected to a scaler and set at fixed value of 2 O for a time sufficient to make an accurate count of the pulses obtained from the counter. The counter is then moved to a new angular position and the operation is repeated. The whole range of 2 O is covered in this fashion and curve of intensity Vs. 2O is finally plotted by software diffract-AT. In this study a SIEMENS, 500 diffractometer was used. It was operated at generator voltage of 45-60 KV and 35 m. A current using nickel filtered Cu K radiation. The samples were scanned at 2 O range of 4-60o and at a speed of 2O 2 O /min.

3-5 Compressive strength test: The compressive strength test was used as a tool for the charcterization and determination of degree of Pozzolanicity. The test procedure was described in the BS-12-1978. The materials used are natural Pozzolanas, lime and standard sand.

3-5-1 Pozzolana: Samples were collected from different localities in Sudan; they were crushed, ground and sieved so as to obtain the following fractions: -Fraction greater than 250µ (> 250 µ ) -Fraction between 250-150 µ -Fractions between 150-90 µ

60 -Fraction between 90-63 µ -Fraction less than 63 µ (<63 µ ).

3.5.2 Lime: The source of raw material for the production of lime (CaO) is the Blue Nile marble (about 60 km south of Damazin) in which the purity is about 98% (CaCO3) The raw material was calcined at 1000oC for six hours. The produced lime (CaO) was ground to pass a 90 µ sieve.

3.5.3 Sand: Standard sand was prepared according to BS No. 12-(1978); the sand was sieved to pass 880 µ but retained on a 600m sieve. The sieved fraction was washed to get rid off fine materials such as clays, salt and organic impurities. It was then dried under the sun for 24 hours.

3.5.4 Preparation of Lime.- Pozzolana Mortar: The lime Pozzolanic cements were prepared using different lime – Pozzolana ratios (1:1, 1:2 and 1:3) at different degrees of fineness i.e (>250µ, 250-150 µ, 150-90 µ, 90-63 µ and < 63 µ). In the mortar test 1:3 Lime- Pozzolana : sand. mortar was used. The water in the mix corresponds, to 0.52 by weight (expressed as water cement ratio). The proportions were mixed thoroughly in dry and wet conditions. The tests were carried out according to BS 12-(1978) using

61 70.7mm (2.78 in) cubes, which were vibrated for two minutes, and then demoulded after 24 hours. Curing was carried in humid condition for a predetermined periods after which the cubes were tested after, 7, 14, 28, 60, 90, and 120 days.

Chapter Four Results and Discussion (Part 1)

4. Characterization of Natural Pozzolana in Sudan

4. 1. Introduction: The natural Pozzolanic materials in Sudan can be characterized by using many different techniques which include; geological and field observation, chemical analysis, X-ray diffraction, (XRD) and compressive strength test to determine the degree of Pozzolanicity. The geological studies depend on the field survey in order to locate exactly the site of natural Pozzolanic deposits and to study the mother rock bearing Pozzolana, its mineralogical composition, structural controls, and rock genesis.

62 In the field Pozzolanic depositions reserve can be roughly estimated, further petrographic examination may be needed to determine the mineralogical composition of Pozzolanic material. Since we are dealing with natural Pozzolanas the geological characterization is very significant especially as key guide for identification of the deposit in the field, which are found in very complicated formations associated with different types of rocks and soils. In order to identify certain minerals such as silica (SiO2) alumina (Al2O3) etc… quantitative analysis was carried out using chemical analysis to give the amount of oxides constituting the minerals components.

On the other hand the most fundamental tool in the identification of minerals is the X-ray diffraction (XRD) technique. With regard to this study it is used to differentiate between amorphous and crystalline silica

(SiO2) i.e between Pozzolanic and non Pozzolanic materials. However

63 the degree of Pozzoanicity is determined by the compressive strength of lime Pozzolana mixes.

4.2. Gregrieb diatomite deposits:

4.2.1 Geology: The Gregrieb deposit is located at western bank of the Blue Nile near Gregrieb and Fadasi villages, about 160 km south of Khartoum and about 20 km north of Wad Madani along the asphaltic road Fig. (1) . The deposit is grey to buff in colour, has low bulk density, high water absorption. It is siliceous rock materials and is largely made up of aquatic plant algae (fresh water planktons) known as diatomites. The deposits are composed mainly of silica (SiO2), calcium carbonate (Ca CO3), silt, mica, with very thin layers of clay. They contain also micro-fossils (radiolaria), trace fossils, in the form of burrows in addition to traces of manganese (Mg). The reserve of the Gregrieb and Fadasi deposits is estimated to be about three million m3 . The deposits are also found as traces at Abu Furua village- [See Figs. (1A) and (2)] . The favorable conditions for the formation of diatomites are prevalent in this area. These include: - the presence of large shallow basins of the banks of the Blue Nile. - An abundant supply of soluble silica probably from Ethiopian plateau. - An abundant supply of materials for plants from the fresh water deposits of the Blue Nile.

64

65

66

67

The Key:- 1. Northern volcanics fields (Northern Bayouda). 2. Natural burnt clay (Southern Bayouda). 3. Obsidian or pitchstone deposits (Sabaloka-Nothern Khartoum). 4. Diatomite deposits (Gregrieb-Gezira). 5. Quaternary lake deposits (Abu Hadied-Northern Kordofan). 6. Gadarif volcanics. 7. Miedob volcanics. 8. Tagabo volcanics 9. Marra volcanics. *Occurences(6—9); contain Pozzolanas and are not covered by this work.(Personal communications with GRAS (2000))

68 - No growth inhibiting constituents such as high concentration of certain soluble salt. - Very little deposit of clastic sedimentary materials. - Certain climatic condition (cold weather condition} Therefore the deposition of Gregrieb area is diatomite deposit is formed in stagnant fresh water by growth and accumulation of diatomites which are aqueous planktonic algae whose their cell walls are formed from amorphous silica. Since this deposit is rich in amorphous silica it is considered as Pozzolanic materials. However, the degree of its Pozzolanicity is determined by determination of strength tests, other tests are used to characterize the deposits.

4.2.2 Chemical Analysis: Table (3) shows the chemical analysis of Gregrieb diatomite deposit.

Table (3) chemical analysis of Gregrieb deposit;

Constituent CaO MgO Fe2O3 MnO Na2OK2O L.O.I. SO3 SiO2 Al2O3 % 12.5 0.52 4.00 0.14 1.16 1.65 15.4 0.28 54.27 4.7

According to Table (3); the main constituents of Gregrieb deposits are the silica (SiO2) (54%), and CaO (12.5%). L.O.I. is

15.4% indicating the presence of calcium carbonate (CaCO3). The presence of silica (SiO2) and alumina (Al2O3) indicates the presence of clay, and since Al2O3 is very small the clay content is expected to be small. It is well known that the chemical analysis alone does not give conclusive evidence about the Pozzolanicity of the materials

69 concerned. However, there is a rough guide, which correlates between the chemical analysis and Pozzolanicity of the materials.

It advocates that the sum of SiO2 + Al2O3 + Fe2O3 shall not be less

than 70%; but the silica (SiO2) alone shall be greater than 45% and the other oxides not greater than 15% .IS 1344-(1981). Accordingly taking into consideration the first criterion, the deposit will not be Pozzolanic. But the content of silica alone indicates some

Pozzolanicity of the material (SiO2 > 45%).

4.2.3: X-ray diffraction analysis (XRD): In contrast to chemical analysis, the XRD analysis gives a conclusive evidence regarding the Pozzolanicity of the materials. The absence of crystalline silica from the XRD pattern is strong evidence of the Pozzolanicity of the material. X-ray diffraction analysis was performed between the angles range of 0-60o for five samples from the diatomite deposit. The results are shown in the Figs. (3,4). In Figs. 3a-c, 4a and c, the XRD patterns show distinct peaks at 3.07, and traces at 1.88Å , 1.9Å. However in Fig. 4(b) the distinct peaks at 3.07, 1.88 and 1.9Å almost disappeared. According to the data reported in the literature [Hardy et al, Grimshow (1971)], these peaks are assigned to mineral calcite (CaCO3). The most striking feature is the disappearance of the peak at 3.36 Å, but only small traces are observed in Fig. 3(a), 3(b), 3(c), 4(a), 4(c) and disappearing completely from Fig. 4(b). The appearance of prominent peak at 3.36A is assigned to crystalline silica. The disappearance of the peak is a conclusive evidence of the presence of amorphous or non- crystalline silica, a phenomenon associated with Pozzolanic materials.

70 Hence it would be expected that Gregrieb Pozzolanic deposit would give high degree of Pozzolanicity, a suggestion to be verified by the determination of compressive strength of lime- Pozzolana mortars.

71

72

73 4.2.4: Compressive strength: The mechanical strength of hardened Pozzolanic cement is the property of the material that is perhaps most obviously required for structural use. It is not surprising, therefore, that strength tests are prescribed by all specifications for Pozzolanic cement. The strength of mortar or concrete depends on the cohesion of the Pozzolanic cement (i.e. the degree of Pozzolanicity) and its adhesion to the sand and aggregate particles. The strength reflects the hydration and rate of the reaction between the active silica and the lime, and hence the formation of cementitious compounds which creates the strength property.The compressive strength tests were carried out on the mortar cubes of lime- Pozzolana ratio of 1:3 Lime-Pozzolana sand. The Lime-Pozzolana cement was prepared after blending of Pozzolana with lime in the ratio 2 :1;The degree of fineness of Pozzolana is < 63µ. The mortar cubes were cured in humid atmosphere and tested after 7 days, 14 and 28 days. Curing for 3 days or less resulted in the disintegration of the mortar cubes. The results are shown in Table (4).

74 Table (4); the compressive strength of lime-Pozzolana mortar cubes of diatomite (Gregrieb): Compressive strength (kg/cm2) 7-day 14-day 28- day Test No. 1 22.99 38.68 62.69

2 24.03 33.44 65.83

3 25.08 33.44 63.83

24.08 35.18 64.09 Average

The average compressive strength reported after 7, 14, and 28 days were 24 , 35, and 64 kg/cm2 respectively. This confirms that the strength increases with curing time. The reported results comply statifactorily with the requirements of the Indian standard IS 4098-(1967), where the minimum requirements are 20 kg/cm2 after 7 days and 40 kg/cm2 after 28 days. ASTM C-95 also specifies a minimum of 41 kg/cm2 after 28 days. Hence the strengths obtained are far beyond that specified by IS and ASTM. The Gregrieb Pozzolana gives high degree of Pozzolanicity, this is probably due to the presence of high percentage of enough amorphous

silica (SiO2) (approximately 54% for hydration and reaction with lime (CaO) to form cementitious compounds leading to the development of strength. Thus the obtained results verify the X-rays diffraction result regarding the presence of amorphous or non-crystalline silica which is responsible for the Pozzolanic property.

75

4.3: Obsidian (pitchstone) of Sabaloka:

4.3.1: Geology: The occurrence of pitchstone (obsidian ) lies near Ban Gadied village east of Sabaloka just north and north-west of Jebel , Duhr-El humar (see Fig. (1) and ( Fig. (5, 6)) , Almond et al (1993) Ban Gadied area is part of Sabaloka inlier in which the older Sabaloka basement complex rocks are surrounded by younger rocks of Nubian sandstone formation. This area provides access to variety of basement complex rocks, including several types of grey gneiss of granulites facies as well as granites and gabbros.

76

77

The small village of Ban Gadied lies south-west of and along strike of the exposures of grey gneiss and migmatite.

78 The Ban Gadied area is much richer in the older and higher grade varieties of grey gneiss. The thing of interest in the Ban Gadied is the swarm of felsite dykes which trend ENE through the hills south and west of the village. The age of these dykes is not clear. Within this dyke swarm natural glass dykes of pitchstone or obsidian was found. The obsidian is found as dykes in a small side valley at coordinates; N 16o 59.5, E 32o55.1, 2.00m wide trend E-W and can be traced for several hundred meter. Adjacent to it are parallel dykes of normal felsite type. The age of this obsidian or pitchstone was found to be 69.6 + 2 Ma (end of Cretaceous. According to K-Ar dating done by Almond et al (1989), Almond (1993). Based on the field visit the estimated reserve is about 500.000m3. The obsidian (pitchstone), is dark colour, glassy porphyritic texture, formed of potash feldspar with few quartz as phenocrysts embedded in glassy silica. Petrographic examination under the microscope showed that the rock was composed mainly of phenocrysts of the potash feldspar with few crystal of quartz, iron oxide and biotite embedded in glassy groundmass of non crystalline silica. From the geological study the rock obsidian which is composed mainly of glassy formation seems to be non crystalline even under the microscope. Hence this glassy groundmass constitutes an amorphous active silica (SiO2). Conclusive evidence that Sabaloka obsidian is a Pozzolanic material is obtained using XRD techniques. However the degree of its Pozzolanicity is established by determination of the strength test.

4.3.2 Chemical Analysis:

79 The result of chemical analysis for Sabaloka obsidian are shown in Table (5).

Table (5): Chemical Analysis of Obsidian Deposit:

Constituent CaO MgO Fe2O3 MnO Na2OK2OL.O.ISO3 SiO2 Al2O3

% 0.577 0.032 1.16 0.00 1.38 1.38 5.95 0.169 75.15 6.64

It can be seen that, the obsidian is mainly composed of silica SiO2

(75%), The other major oxide is alumina (Al2O3), which approximates to

7% , whereas the rest of oxides (CaO + MgO + Fe2O3 + Na2O + K2O +

SO3) are about 4%.

According to the rough guide for Pozzolanicity, which is based on IS 344 (1981) and ASTM- 6118-78 and STM C-593-95, the obsidian complies satisfactorily with the requirements of the above standards and consequently shows a strong indication of very good Pozzolanicity.

4.3.3 X-ray diffraction analysis: It has been stated previously that, the XRD analysis gives a conclusive evidence regarding the Pozzolanicity of the materials. The absence of the crystalline silica from the XRD patterns are strong evidence of the Pozzolnicity of the material. The results are presented in Figs. (7 (a--e), and 8 (a--d), The most striking features in Figs. 7(a and b) and 8 (a, b, and c), are: the disappearance of the distinct peaks at (3.36 Å), but small peaks are observed at (d) values 3.50, 3.02, 4.29, 4.05 3.82 and 3.27 Å). On

80 the other hand Fig 7c and 8d show distinct peaks at 3.36Å. Other small peaks are also observed at 4.3, 4.05, 3.85, 3.50, 3.25 Å). XRD pattern 7d, and 7e are characterized by the complete disappearance of all peaks. According to the data reported in the literature (Hardy and Tucker), (Grimshaw 1971); the prominent peak at 3.36Å is assigned to crystalline silica (Quartz), whereas the peaks at (4.30, 3.85, 3.50 Å) are assigned to potash feldspar mineral. The disappearance of the peak at 3.36Å is a conclusive evidence of the presence of amorphous or non crystalline silica which is a perquisite for a Pozzolanic materials. Hence it would be expected that samples (7a, 7b, 7d, 7e, 8a, 8b, and 8c) would give a high degree of Pozzolanicity compared to samples (7e) and (8d) which contained small amount of crystalline silica (quartz) appearing as phenocrysts under the microscope.

81

82

4.3.4 Compressive Strength:

83 In determining the compressive strength of mortar cubes, the ratio of 1:3 (cement : sand) is chosen. The fraction of Pozzolana passing 63µ sieve is used. The results of compressive strength tests of obsidian Pozzolana are presented in Table (6).

Table (6): the compressive strength of Lime- Pozzolana mortar cubes of obsidian (Sabaloka): Compressive strength kg/cm2 7-day 14-day 28- day

Test No. 1 24.03 39.71 77.32 2 24.03 43.89 78.28 3 22.99 43.89 81.50 Average 23.68 42.50 79.02

The average compressive strength after 7,14 and 28 days are 24, 43 and 79 kg/cm2 respectively, i.e the strength increases with increasing curing time. It is interesting to note that the rate of strength gain is almost constant factor 1.8. Referring to Indian standard 1S4098-67, the minimum requirement of strength is 40 kg/cm2 at 28 days, for a good Pozzolana. Similarly the American standard ASTM 593-95 minimum requirement is 41 kg/cm2 after 28 days. Accordingly the obsidian is a good Pozzolana and complies with the Indian and American requirements. Not only this, but the 28 days strength of obsidian Pozzolana is almost double that required by the Indian and American standards. 4-4 Quaternary Lake Deposit at Abu Hadied:

84

4-4-1 Geology: Abu Hadied Poazzoanaic deposits occur in northern Kordofan at coordinates N 14o 43.68; E 30o 14.50 about 7km east of Abu Hadied village (Fig. (1)), the deposit is located at the eastern part of the basement rocks. It includes marble which is grey in colour and with high

CaCO3 content , granite which is mainly composed of quartz, potash feldspar, and iron oxide. In addition to these the basement rocks include light colour ignimbrite which is formed of quartz and potash feldspar as phenocrysts emerged in glassy groundmass of felsic composition ( see Fig. (9)). Abu Hadied deposit is a lake deposit formed in a depressed topography, it is rich in siliceous materials (SiO2), calcium carbonate

(CaCO3), with clayey silt contamination. The reserve which is of Quaternary age is estimated to be about 10 million m3. The deposit was formed at stages:

The first stage; is the formation of sand dunes due to the updoming in the northern parts of the desert in dry climate, succeeded by weathering and transportation of weathering products, by the wind forming a sand dune. Later due to the rainfalls the sand dunes were stabilized and became fossil dunes . Subsequently the climate became humid and hot.

The second stage: the deposits of fine siliceous material, with

85 high CaCO3 content were deposited in the depressed area due to water penetration through the fossil dunes. This led to the formation of lake deposits, which was rich in siliceous materials (amorphous silica (SiO2), CaCO3, and contaminated with clayey silt, in addition to gastropods fossils and shell fragment of

Quaternary age (see Fig. (10).

The Pozzolanic lake deposit at Abu Hadied varies in colour from light grey to whitish grey, soft, friable in some parts and compact in others ranging from a massive to laminated compact area.

86 The carbonate (CaCO3) was found as calcareous clay, highly biturbated in some parts. In some parts the deposits show vertical cracks about 50 cm thick filled with clay.

The active amorphous silica (SiO2) is possibly eroded from the ignimbrite rock which is a pyroclastic rock rich in glassy materials (see Figs. (9) and (10). Such geological conditions provide evidence for Pozzolanicty, but to what extent, is a question to be answered subsequently.

87

88

89 4.4.2: Chemical Analysis: The result of chemical analysis of Abu Hadied Quaternary lake deposit are reported in Table (7).

Table (7): chemical analysis of Abu Hadied Deposit: constituent CaO MgO Fe2O3 MnO Na2OK2OL.O.ISO3 SiO2 Al2O3 14.13 3.66 3.56 0.177 0.48 0.06 23.21 0.029 40.85 2.27 % 21.05 4.11 3.39 0.173 0.42 0.10 26.35 0.016 35.79 2.27 14.09 4.05 4.59 0.074 0.602 0.05 21.86 0.025 39.67 4.07 15.53 4.28 4.88 0.410 0.560 0.10 23.34 0.38 39.37 5.25

The deposit is composed mainly of silica (SiO2) , ranging between

36 to 41%, and carbonate (CaCO3 + MgCO3) approximately 41-51%.

Other constituents comprise (Al2O3) 2.5-5.5%, iron oxide (Fe2O3) about

4-5% and minor oxides such as MnO, K2O, Na2O and SO3.

According to the chemical

rough guide Abu Hadied lake

deposit shows an evidence of

moderate Pozzolanicity.

4.4.3 : X-ray diffraction:

X-ray diffraction was carried out on four samples. The results are shown in the Fig. (11).

90 XRD patterns, 11 (a, b, c, and d) show distinct peaks at 3.06Å and 3.3Å. other small peaks are observed at 4.30, 2.1 , 1.92 and 1.88 Å. According to the data reported in the literature ,Hardy et al, Grimshaw (1971) the peaks at 3.06, 1.92, 1.88 Å are assigned to mineral calcite

(CaCO3), whereas the peaks at 3.38 Å and 4.30o are assigned to minerals quartz (SiO2) and tridymite (SiO2) respectively, however, the peak at 2.10

Å is assigned to mineral magnesite (MgCO3). The X-ray results show that the main constituent is the crystalline silica and no sign for amorphous silica is observed0. Therefore , the

deposit is expected to be non-Pozzolanic.

91

92

4.4.4. Compressive Strength: The results of compressive strength are shown in Table

(8).

Table (8): The compressive strength of lime-Pozzolana mortar cubes of lake deposit (

Abu Hadied):

Compressive strength (kg/cm2) 7-day 14-day 28- day Test No. 1 6.26 9.40 22.99 2 5.22 10.45 21.99 3 5.22 9.40 22.99 Average 7.57 9.75 22.04

It can be seem that the average strength results of mortar cubes after 7,14 and 28 days are approximately 8, 10 and 22 kg/cm2 respectively. During the first 14 days the strength gain is very low, which

93 means that the rate of formation of cementitious compound is very slow. However , during the second 14 days i.e. after 28 days, a clear increase in the strength gain has been observed. Referring to the Indian standard 1S 4089 – 1967 the minimum requirements for the strength are reported as 20 kg/cm2 at 28 days for a moderate Pozzolana. Therefore this deposit marginally complies with the requirement. The gain in strength during the second 14 days may be associated with presence of tridymite , and the formation of CaCO3 due to reaction of Ca (OH)2 and atmospheric CO2.

4.5 Natural Burnt Clay (Southern Bayouda):

4.5.1 Geology: This deposit occurs at southern part of the Bayouda desert in Mindraba area. The occurrence of natural burnt clay is found at coordinates N 17o 30.3 , E 33o 13.8 Fig. (1). It was formed by basaltic flow overlying the clay bed which resulted in the heating and burning the underlying clay layer completely. The succession of the profile from the top to bottom is shown in Fig. (12). The upper most layer is formed of fragments of basalt, black in colour, fine - grained formed of dark Fe-Mg - silicates (pyroxenes ) iron ore in addition to plagioclase feldspar. - The second layer is weathered zone of burnt clay mixed basalt fragments about 40 cm thick. The bed is soft and loose. - The third layer is formed of dark brown burnt clay relatively compact, with whitish nodules of CaO. 70cm thick.

94 - The fourth layer ( down word), brick-red colour burnt clay relatively compact with whitish nodules. The exposed part is more than 3.00m thick. In this locality the reserve was estimated to be 500.000 m3. - It can be seen that this clay formation is naturally burnt, but whether or not the product is suitable for use as Pozzolana is a matter to be confirmed later.

95

4.5.2 Chemical Analysis:

96 The results of chemical analysis of natural burnt clay at Mindraba ( southern Bayouda) are given in Table (9).

Table (9): chemical analysis results of natural burnt clays:

Constituent CaO MgO Fe2O3 MnO Na2O K2O L.O.I SO3 SiO2 Al2O3 % 3.92 1.51 8.33 N.O 0.19 0.241 12.90 0.177 59.68 8.12 1.78 1.37 9.59 N.O 1.73 0.261 12.70 0.250 55.47 8.99

The natural brunt clay is composed mainly of silica (SiO2) 55-

60%, alumina (Al2O3) 9%, and iron oxide about 10%. The loss on

ignition is about 13%. The minor oxides are CaO, MgO, Na2O,

K2O and SO3.

The SiO2 content of the natural burnt clay is more than 45% and

at the same time the sum of SiO2 + Fe2O3 + Al2O3 is more than 70% . This result complies satisfactorily with the requirements of the rough chemical guide, IS 1344-1981 .

4.5.3: X-ray diffraction: X-ray diffractogram of natural burnt clay are shown in Fig. 13 (a and b).Both diffracograms (13a, 13b) show distinct peaks at 3.38

and 1.8 Å which are assigned to mineral quartz (SiO2). The small

peak at 4.5Å is assigned to mineral tridymite (SiO2) (Hardy et al, Crimshaw (1971). The X-ray results show that the deposit contains mainly

crystalline silica (SiO2). However, if there is any sign of Pozzolanicity, it may related to the presence of minute non crystalline silica associated with main crystalline silica or due to the presence of tridymite. In any case the XRD result does not conform with the chemical analysis. However, the contradiction

97 may be reconciled if we realize that chemical analysis alone does not give a conclusive evidence regarding the Pozzolanicity of materials.

98

4.5.4: Compressive Strength: The results of compressive strength of natural burnt clay are given in Table (10).

99

Table (10): the compressive strength of lime-Pozzolana mortar cubes of natural burnt clay : (Southern Bayouda) Compressive strength 7-day 14-day 28- day (kg/cm2)

Test No. 1 4.18 6.27 14.63 2 4.18 9.40 16.99 3 6.27 8.36 15.67 Average 4.88 8.01 15.70

It can be seen that, the strength of mortar cubes containing Pozzolana of natural brunt clay after 7,14 and 28 days are approximately 5, 8 and 16 kg/cm2 respectively. The strength increases slowly with time but the gain in strength is very slow. The strength reported after 28 days is only 16 kg/cm2 whereas the requirements of Indian and American standards are 40 and 41kg/cm2 respectively for good Pozzolana and 20 kg/cm2 for medium and only 7 kg/cm2 for weak Pozzolana. Hence natural burnt clay is classified a weak Pozzolana

4.6 Pozzolanic deposits at Northern Bayouda volcanic fields:

100 Geology of Northern Bayouda volcanic fields: The Tertiary volcanicity at Bayouda was characterized by multiplicity of short-lived centers of eruption, none of which was active long enough to create a major volcano. About 100 of these centers which are present in the area are shown on the general map (Fig. 14), Almond et al (1969 ).Many of these centers are small composite volcanoes and all are composed of basaltic lava and tephra . Each of the composite volcanoes passed through a stage of pyroclastic cone-building followed by period of lava extrusion which usually resulted in the breaching of the cone. Unconformities exposed on the flanks of eroded cones and overlapping of craters on well preserved cones showed that small shifts of the active vent was common at the pyroclastic stage . When lava followed , they were erupted through the crater vent rather than the flanks of the cone. This simple sequence was rarely repeated at the same center , Almond et al (1969) The main volcanic field is 48km long and 11km wide extending in a north - westernly direction from 180 17 N , 320.55 E to 180 26 N , 32 o 29 . Within this area the close spacing of eruptive centers has resulted in a more or less complete cover of volcanic rocks, while isolated volcanoes are scattered over the plain beyond the limits of the field . These isolated centers may be used to illustrate the basic morphology of the volcanoes . Thus ; Jebel Mazrub (16 km west of Sani ) and twin hills of Sergein (6km west of Sani ) are typical composite volcanoes , each comprising a breached and eroded remnant of pyroclastic cone rising some 180 m above the plain skirted by a sub-circular lava field about 3 km in diameter .

101 The cones are built of thin- bedded ashes (tuffs) and thicker beds of cinder-breccia and agglomerate. These materials are largely of basaltic composition although basement derived fragments became noticeable where erosion has reached the deeper levels of the cone. The cinder breccias are well- graded rocks, composed of externally reddened, sub- angular fragments of finely

102 circular basalt up to 10-15 cm in diameter. The agglomerate on the other hand show a wide range of grain size from convoluted bomb to roppy lava up to 1.00m across in a matrix of ash, lapilli and cinders,

Almond et al (1969 ).

Explosion craters are also represented among the volcanoes out side the main field , as at Jebel Habeish (east of Sani ) and El Muweilih (west of Khor El Eide ). The Habeish crater measures 800 m in diameter and is bounded by a rim of out ward dipping tephra reaching hight of 60m above the crater floor to the north-west , but only 20m high in the south . The El Muweilih crater show notable asymetry in its structure related to its position astride the ring-dyke of the complex . Moreover , Housh Ed Dalam is an impressive example of volcanic cones of northern Bayouda volcanic field . Meseasuring 1300m in diameter and 300m in depth , it extend down with sub- vertical walls to the base of the volcanic succession and some way

103 into the underlying granites . The succession as observed from the northern rim is as follows : from the bottom to the top ; basememt granite (190m) , bedded tuffs (30m) , agglomerate (135m) and bedded tuffs (45m) . Generally the volcanics within the main field show similar charcteristics to those out side the volcanic field . The total volume of volcanic rocks of the northern Bayouda field about 18 km3 , and the total volume of the pyroclastic formations (agglomerates , breccia and tuffs ) are estimated to be nearly 9 km3. The age of Bayouda volcanics are

Byouda volcanic field is composed Pleistocene (Almond et al 1969) of two types of Pozzolanic deposits: - volcanic tuffs - and pumice.

104

105

4.6.1: Volcanic tuffs deposits: 4.6.1.1 Geology: The volcanic tuffs (ashes) are part of the cones which are built of bedded tuffs , cinder breccia and agglomerates. The bedded tuffs vary form grey to yellow, formed mainly of siliceous materials which on the petrographic examination under the microscope, does not show any sign or evidence of crystals development, which is an evidence of Pozzolanicity. This deposit represents the important source of Pozzolana. The reserve of the pyroclastic rocks which include three formations agglomerates, breccia and volcanic tuffs, is estimated to be nearly 9 km3 according to Almond et al (1969 ).

4.6.1.2 Chemical analysis: The chemical analysis results of Bayouda volcanic tuffs (ashes) are reported in Table (11).

Table (11); the chemical analysis of Bayouda volcanic tuffs:

Constituent CaO MgO Fe2O3 MnO Na2O K2O L.O.I SO3 SiO2 Al2O3 % 2.26 12.19 9.70 0.10 0.070 0.53 12.99 0.556 36.68 6.65 9.65 5.31 5.56 0.10 0.76 1.17 7.80 0.152 53.68 9.39 6.63 6.41 7.61 0.10 0.82 1.08 10.80 0.424 56.40 9.12

According to Table (11); the deposit is composed mainly of silica which ranges between 36-56%. Sample 1 contains an

106 appreciable amount of MgO (MgCO3), whereas the second and third samples contain CaO more than MgO. An appreciable amount of Fe2O3 has been noticed. According to the geological studies and the rough chemical guide based on the Indian and American standards the volcanic tuffs deposits of Bayouda show a sign of Pozzolanicity.

4-6-1-3 X-ray diffraction analysis:

The X-ray diffraction was carried out on four samples of Bayouda volcanic ashes. The results are shown in XRD patterns (15) (a, b, c and d). XRD patterns 15 (a and b) show small peaks at 3.37, 3.23 and 3.02Å, which are assigned to minerals quartz, potash feldspar and calcite respectively. In the X-ray diffractograms 15 (b and c) the most striking feature is the disappearance of all peaks, in particular the disappearance of the peak at 3.37 Å. This is a conclusive evidence of the presence of amorphous or non crystalline silica (SiO2), which is a prerequisite for a Pozzolanic material. Hence the deposit of Bayouda volcanic tuffs is composed mainly of amorphous or non crystalline silica (SiO2) ,which indicates a sign of good Pozzolana.

107

108

4-6-1-4 Compressive strength: The results of compressive strength of Lime-Pozzolana mortar are shown in Table (12).

Table (12); The compressive strength of lime-Pozzolana mortar cubes of volcanic tuffs (Northern Bayouda):

Compressive strength 7-day 14-day 28- day kg/cm2

Test No. 1 19.85 34.48 58.51 2 16.71 34.48 60.60 3 17.76 33.44 65.83 Average 18.11 34.18 61.65

It can be seen that, the average compressive strength results of mortar cubes after 7, 14 and 28 days are approximately 18, 34 and 62 kg/cm2 respectively. It is noticeable that the strength increases remarkably with curing time. The 28-day strength is more than three times greater than the 7- day strength and almost double that of the 14-day strength. At any stage the reported strength is far beyond that specified by 1S and ASTM standards. The 28-day strength (61, kg/cm2)

109 exceeds the minimum (40 kg/cm2) by a factor of 1.5. Accordingly Bayouda volcanic tuffs can be classified as good Pozzolana.

4.6.2 Pumice deposits:

a. 4.6.2.1 Geology: The pumice in northern volcanic field of Bayouda is found associated with basaltic lava and contaminated in some occurrences with the basalt of Bayouda volcanic field. It is not found in separate beds and this is difficult for quarrying and extraction. The pumice varies in colour, ranging from black to red colour and black, it has a low density, and is composed of siliceous materials with pores and cavities. In the petrographic examination under the microscope, the rock shows siliceous glassy groundmass without any sign of crystallization. The rock is composed of empty cavities, but only very few of them are filled with calcite mineral. According to the field survey the pumice is limited in occurrence, and therefore contain a limited reserve. In some parts the pumicite basalt is found beside the pumice. It is composed of pyroxenes, plagioclase feldspars, siliceous materials and cavities. In the latter stages the cavities are filled with secondary minerals such as calcite and zeolite. Generally the geological field survey and petrograhic examination, reveal that the pumice shows good indication of Pozzolanic material.

110

4.6.2.2 Chemical analysis: The results of chemical analysis of pumice are shown in Table (13)

Table (13) the chemical analysis of pumice:

Constituents CaO MgO Fe2O3 MnO Na2OK2O L.O.I SO3 SiO2 Al2O3 % 7.37 5.31 9.04 1.89 1.39 1.05 12.95 0.177 49.8 10.35 7.79 6.63 9.67 0.13 1.57 1.06 11.41 0.198 51.89 10.13 8.46 6.22 9.78 0.13 1.75 0.83 13.07 0.419 49.50 10.35 8.67 6.63 9.36 0.12 1.84 0.83 11.80 0.136 50.10 10.42

The pumice is composed mainly of silica (SiO2) 50-52% , with

other constituents; carbonate (CaCO3 + MgCO3) about 29% ; alumina

(Al2O3) 10% and iron oxide (FeO) 10%. The presence of high carbonate contents indicate the presence of calcite and dolomite . The high alumina

content is associated with the minerals feldspars, whereas the high Fe2O3 content indicates the presence of iron ores . The minor constituents are

K2O, Na2O, SO 3 and MnO . According to the rough chemical guide based on the Indian and American standards, and with regard to the geological investigations, the pumice deposit shows an evidence of Pozzolanicity.

4.6.2.3 X-ray diffraction: The results of the X-ray analysis of pumice are shown in Fig. 16 (a, b, c, d). The XRD patterns of Fig.16 (a, b, c and d ) are more or less similar. Small peaks are observed at 3.25, 2.52 and 3.06Å, which are

111 assigned to minerals: orthoclase (K-feldspar) (KALSi3O8), calcic feldspar

(anorhtite) (CaAlSi2O8) and calcite (CaCO3). The most striking feature in all these patterns is the complete disappearance of the peaks at 3.36Å. This gives a conclusive evidence of the presence of the non crystalline silica, a phenomenon always associates with Pozzolanic materials. However, the presence of other materials such as orthoclase, and anorthite may reduce the degree of Pozzolanicity.

112

113

4.6.2.4 Compressive Strength: The results of the compressive strength of pumice are shown in Table (14).

Table (14): compressive strength tests of lime-Pozzolana mortar cubes of pumice (Northern Bayouda) Compressive strength (Kg/cm2) 7-day 14-day 28- day No Test. 1 16.71 22.99 36.37 2 16.71 17.76 34.37 3 15.67 22.99 31.35 Average 16.36 21.24 34.67

It can be seen from Table (14) average strengths after 7, 14 and 28 days of Pozzolana are approximately 17, 21 and 35 kg/cm2 respectively. The IS classifies the Pozzolana into good, medium and weak, according to the 28-day strength, 40 kg/cm2 for the former and 7 kg/cm2 for the latter. The 20 kg/cm2 strength is considered as medium type. Accordingly this deposit may be considered of medium type. Inspite of the fact that the XRD data revealed a complete disappearance of crystalline silica, the degree of Pozzolanicity did not match the degree of amorphosity. This discrepancy could be associated with the presence of the minerals orthoclase and anorthite feldspars.

114

Chapter Five Results and Discussion (Part II)

5. Factors Affecting the Compressive Strength of Lime- Pozzolana Mortar

5.1. Introduction: There are many factors which affect the lime-

Pozzolana mortar strength.

These factors affect the rate of the reaction which is manifested in the enhancement and improvement of the early and late strengths.

The factors comprise the following: -fineness. -lime- Pozzolana ratio.

115 -type and quality of Pozzolanic materials. -curing conditions. -use of additives. The study of the effects of those factors on the compressive strength were carried out using the obsidian Pozzolana at Sabaloka area. The choice depends upon the homogeneity of the material and its high Pozzolanic effect.

5.2. Fineness

The hydration of Pozzolanic cement (lime- Pozzolana and Portland- Pozzolana cement), starts at the surface of the particles. Hence it is the total surface area of cement that represents the materials available for hydration, and consequently the rate of hydration depends upon the fineness of the cement and Pozzolana particles. For rapid development of strength high fineness is necessary. Therefore fineness of Pozzolana is a vital property, and it has to be carefully controlled. On the other hand the fineness influences most of other factors which affect the strength of lime- Pozzolana cement, such as lime- Pozzolana ratio, type and quality of Pozzolana, and curing conditions, as will be seen later in this study. The effect of fineness of Pozzolana on strength of lime- Pozzolana mortar was studied using the following rang of fineness.

-fineness greater than 250 µ (>250µ ), classified as very coarse-grained, and denoted here after as (P1).

-Fineness ranges between 250 and 150µ (250-150 µ ), classified as coarse- grained and denoted a here after as (P2).

-fineness ranges between 150 and 90µ (150-90 µ ), classified as medium- grained and denoted there after as (P3).

-Fineness ranges between 90 and 63µ (90-63 µ), classified as fine –grained and denoted as (P4).

116 -Fineness less than <63 (<63µ ), classified as very fine-grained, and denoted as (P5). The lime- Pozzolana is denoted as LP1, LP2, LP3, LP4 and LP5.

The results obtained , are shown in Tables (15), (16), (17), (18) and Figs. (17), (18), (19). From Table (15) and Fig. (17) it was evident that the very coarse and coarse fractions (> 250µ,( 250-150µ), had no effect on the compressive strength even after 7 days. The first sign of strength development starts at medium fineness fraction (150-90µ). With increase in fineness the compressive strength increases as shown in the fine and the very fine fractions (90-63µ and < 63µ). The increase in strength was observed to be consistent during the 14 and 28 days. However the strength obtained after 28 days at fineness (< 63µ) was nearly twice that reported for the fraction at 90-63µ. (75 and 35

117 kg/cm2). The effect of fineness was markedly observed at later ages when strength rose markedly from 75 kg/cm2 after

28 days to 126 kg/cm2 after 60 days and 164 kg/cm2 after 120 days.

Similar trend was observed when using 1:2 and 1:3 Lime Pozzolana ratios; however , the magnitude of the strength development increased with the increasing lime/ Pozzolana ratio for the same degree of fineness and curing time (see Tables 16, 17, 18 and Figs. 18, 19). The fact that the degree of fineness outweighs lime- Pozzolana ratio, is clearly shown in Table (19), where the coarse-grained fraction (250-150µ) gave strength of 38 kg/cm2 afer 120 days at 1:3 lime- Pozzolana ratio compared to 164 kg/cm2 at 1:1 lime- Pozzolana ratio with very fine-grained fraction (< 63µ). On the other hand at the same lime- Pozzolana ratio (1:3), the strength obtained after 14 days (52kg/cm2 ) with < 63µ fraction was not attained even after 120 days with 250-150µ fraction. The impact of fineness also affect the curing time (Table 20). Even at the same lime/ Pozzolana ratio, the finer fraction gave higher

118 strength than coarser fractions e.g at 120 days, finer fractions gave strength of 206 kg/cm2 compared to only 38 kg/cm2 for the very coarse fraction. In brief we can conclude that the compressive strength of lime- Pozzolana is directly proportional to the degree of fineness, the higher the degree of fineness the higher strength attained and vice versa.

Table (15) : The effect of fineness on the compressive strength of lime- Pozzolana mortar ( at lime:Pozzolana ratio 1:1).

Compressive strength kg/cm2 7-day 14-day 28-day 60-day 120-day

Degree of fineness > 250µ Zero - 5.33 - 10.80

250-150 µ Zero 5.52 5.52 14.63 26.65

150-90 µ 5.57 9.20 16.77 63.04 110.24

90-63 µ 7.66 20.55 35.53 88.04 129.59

<63 µ 16.02 35.02 75.23 126.78 164.74

119

Table (16): The effect of fineness on the compressive strength of lime- Pozzolana mortar, (at 1:2 lime : Pozzolana ratio) Compressive strength kg/cm2 7-day 14-day 28-day 60-day 120-day

Degree of fineness > 250µ zero - 5.80 - 13.58

250-150 µ zero 4.52 7.82 15.32 35.18

150-90 µ 5.57 9.05 21.60 68.44 117.55

90-63 µ 9.40 27.17 39.31 92.65 134.10

<63 µ 23.68 42.50 78.02 142.11 189.82

120

Table (17): The effect of fineness on the compressive strength of lime -Pozzolana mortar (at 1:3 lime : Pozzolana ratio) Compressive strength 7-day 14-day 28-day 60-day 120-day kg/cm2

Degree of fineness > 250µ Zero - 5.49 - 13.58

250-150 µ Zero 3.66 4.53 21.95 37.97

150-90 µ 4.87 9.05 21.08 76.28 131.31

90-63 µ 11.21 31.35 42.5 92.92 161.43

<63 µ 23.34 52.24 93.00 153.95 206.35

121

Table (18) Summary of compressive strength results for different fineness and lime- Pozzolana ratios.

Compressive strength Lime/ 7 days 14 days 28 days 60 days 120 days kg/cm2 Pozzolana ratio Degree of fineness > 250µ 1:1 Zero - 5.33 - 10.30

122 (LP1) 1:2 Zero 5.80 13.58 1:3 Zero 5.49 13.58 250-150 µ 1:1 Zero 4.52 5.22 14.63 26.65

(LP2) 1:2 Zero 3.13 7.82 15.32 35.18 1:3 Zero 3.66 4.52 21.95 37.97 150-90 µ 1:1 5.57 9.20 16.72 63.04 110.24

(LP3) 1:2 5.57 9.05 21.60 68.44 117.55 1:3 5.82 9.05 25.08 76.28 131.31

90-63 µ 1:1 7.66 20.55 35.53 88.04 129.59

(LP4) 1:2 9.40 27.17 39.31 92.65 134.10 1:3 11.21 31.35 42.15 92.95 161.43 <63 µ 1:1 16.02 35.53 75.23 126.78 164.74

(LP5) 1:2 23.68 42.50 78.02 142.11 189.82 1:3 30.50 52.24 93.00 153.95 206.35

123

124

125

126

Table (19) Effect of fineness on compressive strength at different lime-Pozzolona ratio. Curing time Lime/ Compressive strength kg/cm2 Degree of Pozzolana ratio 7 days 14 days 28 days 60 days 120 days fineness

LP2 Zero 3.66 4.53 21.95 37.97 1:3 L/P

LP5 16.02 35.53 75.23 126.78 164.74 1:1 L/P

LP: Lime Pozzolana ratio

LP2: fraction 150-250 µ

LP5: fraction < 63 µ

127

Table (20) Effect of fineness on compressive strength at different curing time.

Curing time Lime/ Compressive strength kg/cm2 Degree of Pozzolana ratio 7 days 14 days 28 days 60 days 120 fineness days

LP2 Zero 3.66 4.53 21.95 37.97 1:3

LP5 30.50 52.34 93.00 153.95 206.35 1:3

L/P Lime : Pozzolana ratio = 1:3 LP2: fraction 250-150 µ LP5: fraction <63 µ

128

The explanation for the increase in the strength with increase in the degree of fineness could be found in the definition of Pozzolana. It is defined as reactive siliceous or siliceous and aluminous materials which react with lime in presence of moisture at the room temperature to produce cementitious materials. The silica should be amorphous (non crystalline), and in a very fine powder form. The increase in fineness is therefore associated with the increase in surface area, ie increase in points of contact (reaction points). Hence the rate of the reaction increases leading to formation of more cementitious materials and consequently high strength. The effect of fineness on the strength of Lime-Pozzolana has been investigated by many researchers, some of them determine the fineness by the maximum amount retained on certain sieves, whereas others adopt the method of specific surface area. For instance , to obtain high strength, the (ASTM) standard 1970 specifies the maximum percentage retained on 74 µ and 95µ sieves as 30% and 2% respectively . In Indonesia, where the brick powder is used for mortar, plasters and concrete, the minimum percentage retained on BS sieve 74µ should not be greater than 50% in order to give higher strength. Elgallad (1997) and Robertson (1974) recommended grinding to finer than 300 mesh for pumice and only 100 mesh for volcanic ash.

129 The results obtained in this study are in conformity with the work of Subhi (1978). He studied four different types of Pozzolana, and came to conclusion that the strength is directly proportional to the degree of fineness. A similar trend was observed by Hamid (1999). Although he used artificial Pozzolana (kaolinite, balck cotton soil and reject brick), he found that in every case

the strength was closely related to degree of fineness.

5.3 Lime/ Pozzolana Ratio: The proportion of lime- Pozzolana depends upon both the quality of Pozzolana and lime used. The lime-Pozzolana used in this study comprised 1:1, 1:2 and 1:3 respectively, the compressive strength was determined in each case at various degree of fineness, such as > 250 µ, 250-150µ, 150-90µ, 90-63µ, and < 63µ and at different curing times. The results obtained were reported in Tables (21), (22) and Figs. (20), (21). From Table (21) and Fig. (20) it was evident that at different lime/ Pozzolana ratios, the first sign of development of strength was observed after 14 days , where the strengths reported were almost similar ranging between 3 and 4 kg/cm2. However slight development in the strength was observed after 28 days ( 5, 7 and 4 kg/cm2 respectively) for lime/Pozzolana ratio (1:1, 1:2 and 1:3). The reported results were inconsistent with the increase in lime/Pozzolana ratio after 14 and 28 days strength. After 60 days the effect of lime/Pozzolana ratio was clearly indicated by the increase in strength with the increase in lime/Pozzolana ratio (14, 15 and 22 kg/cm2 at 1:1, 1:2 and 1:3) respectively. Similar results were observed after 120 days (26, 35 and 38 kg/cm2 respectively). With finer fractions (< 63µ), the effect of lime/ Pozzolana ratio was very pronounced, (Table (22)). The compressive strength increased

130 remarkably with the increase in lime/Pozzolana ratios even at early ages (16,23 and 30 kg/cm2 at 1:1, 1:2 and 1:3 respectively) after 7 days and 35, 42 and 52 kg/cm2 after 14 days). This pattern persisted consistently thereafter specially after 120 days, where a dramatic increase in strength was observed (164, 189 and 206 kg/cm2 respectively at 1:1 , 1:2 and 1:3 lime /Pozzolana ratios).

Table (21): The compressive strength of lime/Pozzolana mortar at different lime/ Pozzolana ratios. Average compressive 7 days 14 days 28 days 60 days 120 days

strength (kg/cm2) lime/ Pozzolana ratio

1:1 Zero 4.52 5.22 14.63 26.65

1:2 Zero 3.13 7.85 15.32 35.81

1:3 Zero 3.66 4.53 21.95 37.97

- fraction 250-150µ

131

Table (22): The compressive strength of lime/Pozzolana mortar at different lime/ Pozzolana ratios Average compressive 7 days 14 days 28 days 60 days 120 days

strength (kg/cm2)

lime/ Pozzolana ratio

1:1 16.02 35.53 71.05 126.78 164.74

1:2 23.68 42.50 76.62 142.11 189.82

1:3 30.50 52.24 93.00 153.95 206.35

- fraction < 63µ

132

133

134 Summering up, the results obtained showed inconsistency with coarse fractions (250-150µ) especially at the early ages. However regular increase in strength with increase of lime/Pozzolana ratio was obtained at very fine fractions (< 63µ). There are two explanations for the above-mentioned results: (i) The impact of Lime/ Pozzolana ratio on the strength can be explained by formation of more cemntitious products through the

reaction of active silica of Pozzolana with Ca(OH)2 obtained from the hydration or slacking of lime in presence of water with the result of formation of calcium silicate gel as a cementitious materials). The formation of calcium silicate gel definitely increases with the increase of Pozzolana content. (i.e increase Lime/ Pozzolana ratio). (ii) It is worth mentioning that the previous reaction is greatly enhanced by the increase of the surface area (i.e finer particles), it is evident that the degree of fineness surmounts the impact of he lime/ Pozzolana ratio. The results obtained in this study are in conformity with the work of many investigators. Spence and Allen (1981) found that the optimum strength occurred at Pozzolana lime ratio between 2.5:1 and 4:1. However it was pointed by Hammound (1993); that at the early stages the maximum strengths were obtained with ratios about 4:1, but for longer periods higher ratios gave higher strength. Thus ratio 2:1 and 3:1 gave maximum strengths at one year. Similar results were reported by Hamid (1999), although he used artificial Pozzolana in the form of brunt clay, and bricks reject he found that the strength increased with the increase in lime / Pozzolana ratio. The strength reported for the 1:3 ratio was always higher than that reported for the 1:2 ratio. On the other hand Taibi et al (1985); produced synthetic Pozzolanic binder by using (50/50) ( by weight) of a thermally activated

135 pure kaolinite and pure lime having calcium hydroxide of 96%. They found that stabilization with 5% or 8% cement of this new Pozolanic binder led to the same 56-day strength, when specimens were subjected to wetting and drying cycles. Moreover with long curing period (90-180 days) the Pozzolanic binder tends to give higher strengths than when cement is used.

5.4 Type and quality of Pozzolana : The ability of Pozzolanas to react with lime varies greatly from one type to another, some are excellent while others have hardly any Pozzolanic activity. However differences in quality may even occur within a single deposit of Pozzolanic materials. Quality of Pozzolana is primarily dependent on the presence of reactive silica or silica and alumina which react with lime in the presence of water to form cementitious compounds. In this study the main method used for assessing the Pozzolanic quality is the compressive strength test, which is determined at degree of fineness < 63µ ( very fine-grained ) and at 1:2 Lime Pozzolana ratio. The effect of quality of Pozzolanas on the compressive strength is shown in Table (23) and Fig. (22). It was evident that the obsidian of Sabaloka showed higher strength values; ( approximately 24, 42 and 78 kg/cm2 respectively) at various curing time (7, 14 and 28 days), the diatomite at Gregrieb and volcanic tuff at Bayouda ranked second and third of the series with strength of 24, 35, 64 kg/cm2 and 18, 34 and 61 kg/cm2 respectively.

136

Table (23): The effect of type and quality of Pozzolona on the compressive strength of lime-Pozzolona mortar. Average Compressive Strength (kg/cm2) Type Pozzolona Location 7-day 14-day 28-day in Sudan Pumice Bayouda 16.36 21.24 34.07 Volcanic tuffs Bayouda 18.11 34.13 61.65 Natural burnt clay Bayouda 4.88 8.01 15.70 Obsidian Sabaloka 23.68 42.50 78.02 Diatomite Gregrieb 24.03 35.18 64.09 Quaternary lake deposit Abu 7.57 9.75 22.46 Hadied Using fraction < 63µ Lime/Pozzolana ratio(L/P) 1:2

137

138

Table (24): Relation between degree of fineness and the quality of Pozzolana ( at Lime/Pozzolana ratio 1:2)

Degree of Type of Quality of Compressive strength kg/cm2 fineness Pozzolana Pozzolana 7 days 14 days 28 days < 63µ Natural Weak 4.88 8.01 15.70 (LP5) Burnt clay Pozzolana 250- Obsidian V .good Zero 3.13 7.81 150 µ (Sabaloka) Pozzolana (L/P2)

139 Moderate values of compressive strength were reported for pumice at Bayouda; (16, 21 and 34 kg/cm2 respectively). The deposit at Abu Hadied of Quaternary Lake showed comparable results to that of the pumice. Weak Pozzolanic formation ( natural burnt clay) showed weak and low results of strength (5, 8 and 16 kg/cm2) respectively. The classification of Pozzolanas on the basis of Lime- Pozzolana strength was adopted by Indian standard IS 4098. The strength of 40 kg/cm2 after 28 days was considered as high grade Pozzolana, whereas the strength of 20 and 7 kg/cm2 were considered as medium and low grade respectively. According to this classification we can categorize the natural Pozzolanas in Sudan into three groups: (i) High grade Pozzolanas; include obsidian of Sabaloka (78kg/cm2). Diatomite of Gregrieb (64 kg/cm2) and volcanic tuffs of Bayouda (62 kg/cm2). (ii) Medium grade Pozzolanas; include, pumice of Bayouda (34 kg/cm2) and Quaternary Lake deposits of Abu Hadied (23 kg/cm2). (iii) Low grade Pozzolanas; include natural burnt clay of Bayouda (16 kg/cm2). It can be seen that the Pozzolana which exhibit high strength (e.g obsidian, diatomite and tuff) are usually associated with high silica content (SiO2). At the same time the X-ray diffractions show no sign of crystalline silica i.e no diffraction line for SiO2. This proves that the silica exists in amorphous state (active silica). The reactive silica has great ability to react with slacked lime Ca (OH)2 at room temperature to produce cementitious compounds. The variation of the strength is due to the degree of amorphosity of silica. On the other hand pumice and Quaternary lake deposits showed moderate strength and this might be related in some part to the

140 amount of SiO2 (< 40%) but the degree of the amorphosity or non crystallintiy is the decisive factor. Moreover the Quaternary lake deposits is contaminated with clayey material, which decreases the compressive strength. As stated previously the type and quality of Pozzolana are greatly influenced by the degree of fineness (Table (24)). The strengths reported for the weak fine grained Pozzolana are higher than that reported for good coarse-grained Pozzolana at all ages. The strength after 28 days (15.7 kg/cm2) is doubled that reported for coarse grained Pozzolana 7.81 kg/cm2). This indicates that fineness supersedes the effect of type and quality of Pozzolana. Similar results were obtained by Rafeel (1992) who studied different types of Pozzolana from Kenya. He found that volcanic tuffs and diatomites have higher strength than the others.

5.5 Curing conditions: The curing conditions include: a. Humidity. b. Curing time. c. Curing temperature.

5.5.1. Humidity: Moisture is known to be an essential factor for the development of strength. In order to study the effect of humidity, curing of

141 lime- Pozzolana cement was carried out under two different conditions. -The first is direct curing where the cubes or specimens are completely immersed in water. -The second is indirect curing where the cubes are not directly immersed in water, but placed over an iron-mesh situated 10 and 20 cm above water level.. The results obtained were reported in Table (25)., Fig. (23). It can be seen that the 7-day strength reveals a higher strength for the indirect curing compared with the direct curing. The effect is more pronounced with the finer fractions. The strength reported are 10.5 and 11.8 kg/cm2. Similar trend is observed after 14 and 28 days strength. It is interesting to point out that the strength reported for the finer fractions (63µ) is almost double that reported for the fractions ranging between (90-63µ). In all cases the indirect curing gave higher strengths than that for direct curing , as shown in Table (25) and Fig.(23), when we compare the strength values for fine fraction (90-63 micron) and very fine fraction (<63micron) after 7, 14 and 28 days for the two conditions of curing e.g. (18.5 and 10.5), (25.6 and 11.8), (30.3 and 15.7),(42 and 21), (64 and 27), (83 and 41) kg/cm2 respectively for indirect and direct curing . It seems that Lime/Pozzolana cement needs special conditions for curing. In every case as it is evident that indirect curing gives a higher strength than that for direct curing. The higher strength obtained by the indirect curing is probably due to reduction in porosity and due to carbonation. When the Lime/Pozzolana mortar cube is directly immersed in water, some fine particles may leach out, and thus create some porosity which is always associated with a reduction in strength.

142

Table (25) the effect of type of curing on the compressive strength of lime -Pozzolana cement

Type of curing Degree of Average compressive strength fineness (kg/cm2) (µ) 7 days 14 days 28 days Direct curing in 90 -63 10.45 15.67 27.17 water Indirect curing 90.-63 11.84 21.29 41.16 (indirect contact with water ) Direct curing in <63 18.46 30.31 64.43 water Indirect curing <63 25.60 42.15 83.20 (indirect contact with water Lime: Pozzolana ratio 1:2

143

144 Regarding carbonation, the possibility of absorption of CO2 from the atmosphere is greatly enhanced the indirectly cured Lime/Pozzolana cube. Atmospheric CO2 reacts with lime to produce CaCO3 which is accompanied by gain in strength. ;

Ca(OH)2 + CO2 CaCO3 + H2O

The formation of CaCO3 was detected by the XRD patterns

(Fig. 24), revealed the presence of mineral calcite (CaCO3), in the sample which was indirectly cured for 28 days. So we can conclude that the formations of carbonate may increase the strength of indirect-cured lime- Pozzolana cement. The fineness of Pozzolana also influences the type of curing. This was noticed from the slight difference between the strength values of indirectly and directly cured fine fraction after 7 days, however, a considerable difference between the two values was observed for the very fine fractions at the same curing time.

145

146 5.5.2 Time: It is necessary for the Pozzolanic-lime based products to be kept moist for a considerable length of time preferably for at least 28 days. Long curing time (60, 90, 120 days) may also be required. It has been established previously that strength increases with curing time.

5.5.3 Temperature: The rate of strength development is very sensitive to the curing temperature. The reaction between lime and Pozzolana to produce Lime-Pozzolanic cement is affected by change in temperature of curing and consequently the strength varies with change in temperature. In order to study the effect of temperature on the strength of lime- Pozzolana cement, compressive strength tests were carried out for mortar cubes with very fine fractions Pozzolana (< 63 µ) and at 1:2 lime/ Pozzolana ratio. The curing temperatures chosen were 28, 45 and 70oC to simulate room temperature, medium and high temperatures. The results obtained are reported in Table (26) and Fig. (25). It can be seen that at room temperature, the strength increases progressively from 25 kg/cm2 to 83 kg/cm2 after 28 days. With elevation of temperature to 45oC, the strength increases remarkably from 42kg/cm2 after 7 days to 115 kg/cm2 after 28 days. When comparing the strength obtained at 70oC to that at room temperature, a very pronounced difference can be observed. The strength attained after 7 days is more than four times that attained at room temperature, and more than three times for the 14-day

147 strength and nearly two times for the 28-day strength (see Table 26). It is clear that the strength increases remarkably with increase of temperature of curing. The reason is that elevation of temperature accelerates the process of lime- Pozzolana reactions, and consequently increase the strength. Therefore the effect of temperature of curing can be used to improve the early strength of Lime - Pozzolana cement. The work of Spence and Allen (1981) is a good example for the study of effect of curing temperature on the strength of Lime- Pozzolana cement. They obtained comparable results to that reported in this study. The strength obtained after 7 days at 50oC was almost twice that obtained at 20oC. Similarly Appears et al (1983) found that an increase of 20oC – 40oC accelerates the reaction of Lime-Pozzolana approximately five times.

Table (26) the compressive strength of lime- Pozzolana cement at various temperatures* Temperature Average compressive strength of curing oC kg/cm2 7 days 14 days 28 days 28 25.60 42.15 83.20 45 42.82 67.57 114.59 70 114.24 136.53 152.21 * At very fine fractions (<63µ), 1:2 lime: Pozzolana ratio.

148

149 5.6 Use of additives: In order to improve the early strength of cement Pozzolana- mixtures , certain additives were used such as cement, gypsum, salts (NaCO3…etc), water emulsions suspensions or solutions. Many of the research investigations concentrated on the use of cement and gypsum, but torona (Na2CO3-NaHCO3) was only mentioned as an additive. No systematic work has been carried out. Due to the availability of torona in Sudan, it was necessary to conduct preliminary investigation. With 1:3 lime- Pozzolana ratio, various amounts of torona

(Na2CO3, NaHCO3) namely 2, 5, and 10% were added respectively. Mortar cubes were prepared, cured and tested after 7 , 14 and 28 days. The results of average compressive strength were presented in Table (27) and Fig. (26).

Table (27) and Fig. (26) show that the addition of 2% Na2CO3

NaHCO3 has virtually no effect on strength compared to that of cement without additives. With addition of 5% an appreciable increase in the strength was noticed (15, 37 and 46 kg/cm2 respectively.) however, addition of 10% increased the strength remarkably. (25 , 41 and 53 kg/cm2). The reported 7-day strength is more than twice of the strength of the lime – Pozzolana cement alone. A similar trend was observed after 14 and 28 days, however, the rate of increase is not comparable to that observed after 7 days. The increase in the strength is probably associated with formation and drying out of CaCO3.

Ca(OH)2 + Na2CO3 CaCO3 + 2Na(OH)2

150

Table (27) The effect of torona additive on the compressive strength of lime- Pozzolana cement* torona Average compressive percentage strength kg/cm2 (%) 7-day 14-day 28-day 0% 11.21 31.35 42.15 2% 11.50 32.33 42.39 5% 14.63 36.71 46.32 10% 25.43 41.45 52.94

* fraction 90-63µ Lime/Pozzolana Ratio 1:3

151

152

Chapter six

6. Conclusion and Recommendations

In the present investigation, the method and techniques used for the characterization of Pozzolana gave consistent results. The geological investigation was used as key and guide method for the detection of deposits in the field. On the other hand, it is known that the chemical analysis alone does not give conclusive evidence regarding the Pozzolanicity of the material concerned, but it gives rough guide which correlates the chemical analysis and Pozzolanicity of the materials. In contrast to chemical analysis, the X-ray diffraction technique gives a conclusive evidence regarding the Pozzolanicity of the materials. The absence of the diffraction line of crystalline silica from the X-ray diffraction pattern is strong evidence of the Pozzolanicity of the materials. However the degree of the Pozzolanicity of the materials, is determined by the compressive strength method. The results of the study showed that the occurrences of most natural Pozzolanas in Sudan were associated with the Tertiary volcanics and Quaternary lake deposits. The Tertiary - Recent volcanics are rich in tuffs and glassy formation characterized by the presence of amorphous silica, whereas the Quaternary sediments are rich in active amorphous silica. Fields observations generally revealed clear variation in the quality of the Pozzolanas even for the same occurrence. This necessitats a selective mining process to obtain good quality Pozzolana. However in the case of dykes, the mode of occurrence of the deposits is homogenous i.e. the distribution of the concentration of amorphous silica is regular vertically and laterally. The results of the characterization of investigated occurrences revealed that best Pozzolanic deposits are the obsidian of Sabaloka; diatomite of Gezira and volcanic tuffs at Bayouda . The most promising deposit of Pozzolana is the volcanic tuffs at Bayouda .

153 On the other hand natural burnt clay was considered to be weak Pozzolana. The X-ray diffraction pattern showed that the deposits contained crystalline silica (SiO2) in the form of quartz and tridymite. The sign of Pozzolanicity reported might be related to the presence of minute non crystalline silica or due to strained quartz. The presence of tridymite might also be a cause of Pozzolanic behavior. However, the low compressive strength results obtained, confirmed the poor degree of Pozzolanicity. It is clear that the presence of calcium and potassium feldspars (anorthite and orthoclase) reduces the degree of Pozzolanicity as shown in the case of pumice . According to compressive strength results, the natural Pozzolanas in Sudan can be classified into three grades: high grade Pozzolanas represented by obsidian diatomite and volcanic tuffs; moderate grade Pozzolanas such as pumice and Abu Hadied deposits; and finally low grade Pozzolanas shown by natural burnt clay. The compressive strength of lime- Pozzolana cement is greatly affected by the degree of fineness of Pozzolana. The strength increases remarkedly with fineness irrespective of the degree of Pozzolanicity of the material. On the other hand the magnitude of the strength development increases with increase of Pozzolanna: lime ratio at the same degree of fineness. The type and quality of Pozzolanas are also important factors affecting the compressive strength of lime Pozzolana cement. It can be seen that the Pozzolanas which exhibited high strength e.g. obsidian, diatomite and tuffs are usually associated with the high amorphous silica content. The decrease in the amorphocity of silica is associated with decrease in strength as shown by moderate strength of pumice and Abu Hadied deposits, and low strength reported for burnt clay. The study also revealed that the Lime- Pozzolana cement needs special condition for curing. In all cases indirect curing (i.e not immersed in water) gave higher results than that reported for direct curing i.e

154 immersed in water. This might be associated with reduction in porosity and increase in carbonation. Not only the type, but the temperature of curing has an effect on compressive strength. Increase in temperature is remarkably accompanied by increase in strength, and this is because a rise in temperature accelerates lime- Pozzolana reactions with consequent increase in strength. Additives also affect the strength of lime- Pozzolana cement.

Addition of torona (Na2CO3. NaHCO3) up to maximum of 10% increased the compressive strength of lime Pozzolana cement, this is probably due to carbonation. The results of the study show that; the degree of fineness outweighs the effect of other factors such as; lime- Pozzolana ratio, type and quality of Pozzolana and curing condition. With regard to Tertiary volcanics and Quaternary lake deposit, there is evidence of occurrence of some additional deposits at Jebel Marra, Gadarif volcanics, Tagabo volcanics and Meidob Volcanics, and hence detailed investigation is recommended. Moreover diatomite deposits may occur as isolated lakes, along left and right banks of the Blue Nile extending from the Sudanese Ethiopian borders to Khartoum. The geological features which are associated with occurrence of obsidian dyke at Sabaloka may also be found in other areas with the same rock genesis. The waste of the products of mining works of bauxite can be used as Pozzolana; in Sudan bauxite ores occur at Twiga area (Northern Darfur), hence more investigations are needed for the study of the Pozzolanic uses. It has been established that the occurrence of volcanic tuffs of Bayouda is the most promising deposit both qualitatively and quantitatively. Hence it is recommended to carry out detailed investigation in order to identify exactly the bearing Pozzolanic layers

155 and occurrences. This should be followed by study of geological and engineering properties.

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156 5. Appers, J. Plentinck, M. Versohure, H. 1983 “A Pozzolana Lime Cement Industry in Rwanda”, Proceedings of Symposium on Appropriate Building Materials for low costing housing held in Nairobi, Kenya Vol. II. PP 86-92. 6. Appropriate Technology in Civil Engineers, 1980, Westminster, London, England, Refer 12. 7. Ansteff, F. 1964, “Rev. Mater. Csontr.” 162, 145. 8. ASTM Standards Designation C-593 - 1970. 9. ASTM 6118-78 “Chemical specification of Pozzolana “ 10. ASTM C-593-95 “Specifications for Lime-Pozzolana Cement”. 11. Atia M. G. 1998 “Bauxite Ore Deposits”, A Geological Mining View No. 1 Vol PP 5-9. 12. Arjum D. 1999 “Bozzolanic Behavoir of Ricke Husk Ash” UDC, 691. 39p. 309. 311. 13. Bain, J. A. 1974 “Mineralogical Assessment of Raw Materials for Burnt clay Pozzolanas “IT Publications , London. 14. Basin, ITDG. 2001 “Case Study; The Development of CP 40 Pozzolanic Cement in Cuba”. IT Publications. London,U. K. 15. Basin News, Mars 1995. “Natural Pozzolana”. Building Advisory Service and Information Network IT, U. K. 16. Bennet, G. (1971) “ Method of silicates analysis “. 17. BS-12-1978 “Standards Specifications of Cement” 18. BS-4027-1980 ” Standards Specifications of Cement “ 19. Chatterji, S. (1979) “ The role Calcium Hydroxide in the breakdown of Portland cement concrete due to alkali-silica reaction “ , cement and concrete research . 9 No.2, PP.185-8. 20. Central Road Research Institute, (CRRI), 1984 “ Pozzolanic Clays of India “ Special Report No. 1 Okhla New Delhi

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