Utilizing Volcanic Ashes As Partial Replacement of Cement in Concrete Production

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ISSN 2278 – 0211 (Online)

Utilizing Volcanic Ashes as Partial Replacement of Cement in Concrete Production

Mwavita Samizi Assistant Lecturer, Department of Civil Engineering, Ardhi University, Tanzania Jonasia Josephat Civil Engineer, Department of Civil Engineering, Ardhi University, Tanzania

Abstract: Volcanic Ash (V.A) is one of Pozzolanas natural occurring material that has been tested for partial replacement of cement for production of concrete. With respect to reduction of cement consumption for sustainable construction (i.e. reducing gas emission), evaluation of the strength reduction is crucial as it has a severe impact on the structure under construction. Therefore, this paper examines the effects of replacing cement by using Tanzanian Volcanic Ash on the strength of concrete (i.e. concrete grade). The research aims to determine the optimal amount of V.A for production of high-grade concrete. The samples of V.A received from Holili, Kilimanjaro were prepared in five different proportions (0, 10, 20, 30 & 40 wt %) to make concrete cubes. Uniaxial compressive tests were used to examine the strength of concrete achieved after 7 and 28 days of curing. Results revealed the grade of concrete is significantly affected by adding more than 30 wt% of the V.A (i.e. optimal amount of V.A is 30%). For high-grade concrete, 20 wt% replacement provides less than 10% reduction in strength relative to reference concrete strength (i.e. 0% of V.A). This maintained the desired strength of concrete structure for construction. Hence, a partial replacement of cement can be allowed for 20 to 25 wt% of V.A.

Keywords: Volcanic Ashes, Concrete production, Cement replacement

1. Introduction Cement has been for many years used as a crucial ingredient in construction industry due to its efficiency and effective binding properties. Often cement is applied for making concrete and in mortar for plastering, masonry works, water tightness for structures as well as for making joints and pipes. Cement is one of the major material in construction hence as construction activities increase, the cement demands increase as well. One of the uniqueness features of cement is its ability to harden the surface of the structures that protect it against destructive agents such as weathering, organic or inorganic chemicals and others. Pozzolana and limestone are common materials used for production of a good cement product qualifying for that purposes. Ancient Roman concrete was one of the best concrete that did withstand loads, weather and other destructive element for more than 2000 years. Roman concrete consisted of volcanic ash, hydrate lime, pasty and few pieces of fist-sized rock (Moore, 1995). Pozzolanas are materials that have cementation properties in the presence of lime. A Volcanic Ash is one of such materials. Worldwide, more than 50 countries produce volcanic Ashes, and related products (pumice) in large amount. Italy is an example of the largest producer of volcanic ash materials. Other major producing countries are Chile, Canada, Spain, Turkey, and the United states. In Africa, natural Pozzolanas are present in five countries, which are Burundi, Cape Verde, Ethiopia, Rwanda and Tanzania (Habitat, 1985). In Tanzania, accurate statistical data is hard to be found but geological information have indicated that there are many stones of volcanic ash/pumice/scoria, approximately 1 billion tones are accessible in the country. In addition, there are existence of evaluated sites with substantial amount of Pozzolanas (Stulz, 1983; Allen, 1983; Makange & Massawe, 1986). Oldonyo Lengai (Arusha) is one of active volcanic mountain that shows there will be production of volcanic ash resources in years to come. The development donors e.g. Danish International Development Assistance (DANIDA) (1999), and Small Scale Development Organization (SIDO)(1970s) conducted studies on the use of volcanic ash in road construction. Samples were collected from Mbeya, Oldonyo sambu and Kilimanjaro. The Pozzolana materials were classified based on mineralogy (COWI, 2000; Olekambainei, 2005) and showed a mix ration of 1:2:9 by weight lime, Pozzolana and sand mixture respectively. These studies recommended water content of 15 percent. After 7day of curing, additional strengths in excess of six (6N/mm 2)was observed on 25 mm cubes. The results of the DANIDA study recommended the volcanic ash to be used for stabilizing road base and sub bases in gravel roads construction. However, the SIDO project ceased due to political economic and some of technical factors (Olekambainei, 2005).

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Production of cement usually involves mixing of different materials that undergoes several processes including mining, crushing and grinding (milling) in order to achieve a suitable product size before heating in the kiln. These processes involve high production costs because they requires intensive amount of energy. In recent years, Portland cement has been a dominant type of cement product produced for construction. This type of cement is expensive and known for emission of greenhouse gases (i.e. carbon dioxide gas). Mixing of fresh volcanic ash material to aggregates and cement is an alternative approach that can partially replace the amount of cement in making concrete. Studies that investigated different proportions of volcanic ashes to construction, concluded that, the link between utilization of volcanic ashes and minimization of costs of using cement is still missing for concrete making. Therefore, a blending technique for utilization of volcanic ash is suggested for Tanzania construction industry, which is characterized by the following requirements: Reducing the cost for cement use in construction industry; Minimize production of gas emission from Portland cement production; and Minimize the amount of energy per unit weight of cement produced. The above economic and environmental factors will result into challenge in construction industry based on sustainable development concept. Sustainable development concept can be fulfilled under the use of high technical performance materials, which are environmental sound. This research focused on replacement of cement partially by using volcanic ash from Holili, Kilimanjaro in production of concrete. The performance of the concrete made of reduced cement and addition of volcanic ash was tested based on compressive strength of hardened concrete after 28days of curing.

2. Description of Application of Volcanic Ash in Construction Volcanic ashes are materials formed from eruption of volcanic events. The material formed consists of fragments(sometimes called tephra) of igneous rock material (Rose &Durant, 2009). During the formation, volcanic ash may be in form of slurry or mud and later on can dry into solid i.e. concrete-like mass. The density of individual fragments are less dense compared with other rock fragments but can vary (from 700 to1200 kg/m 3 for pumice)depending on eruption rate (Wilson et a l., 2011). Rose& Durant (2009) classify fragments of volcanic ash into Pyroclasts (diameter < 2mm) and Lapilli (diameter > 2mm).In facts, these properties are crucial for the quality of concrete in construction activities but are limited because of the process of extracting volcanic ash and blending approaches as well as evaluation of blending ratios. The common properties of volcanic ash and functional role in the construction applications are:

• Pozzolanic properties: Volcanic ash is one of natural Pozzolana and has pozzolanic properties. Silica oxide (SiO 2) content plays a great role in the strength of the designed concrete. The chosen volcanic ash for the investigation has approximately 46wt% SiO 2which fall into first category of common Pozzolana materials (i.e. basic Pozzolana). The commoncategory of Pozzolana materials based on chemical compositions are: I. Basic Pozzolana ( 45 – 52 wt% of SiO 2 ); II. Ultrabasic (< 45 wt% of SiO 2); and III. Intermediate Pozzolana (52 – 66 wt% of SiO 2). • Strength development: A mixture of volcanic ash and aggregate develop the strength of concrete depending on initial consumption of lime, fineness of content, curing, and testing conditions. The amount of lime ensure the initial consumption of lime and sufficient to permit modification for complete cementation orpozzolanic action (Ballantine &Rossouw, 1989). The reactivity of Pozzolana depends on fines contents of the reactingfragments (i.e. Pozzolana and lime). The fineness of the natural Pozzolana has a significant effect on early strength development (Shi& Day, 1993). Curing plays an important role for strength development of any binding material (Vandewalle & Mortelmans, 1992). Longer curing time and curing type provides higher strengths when compared with shorter curing time for the same mix. Lime Pozzolana mixtures are mostly affected by curing due to their slow strength gain as compared to cement. Curing also influences the permeability of pozzolanic mixtures that reflects in the durability of the structure (Saricimen et al ., 1992). Water content affects pozzolanic stabilized aggregate. According to Pylkkanen (1995), when immersion doubled the water content of the specimens to 9% the strength reduced to 40%.

3. Material and Method

3.1. Material In this study, various material was used for set up of experiment and making the concrete cubes. The major materials used for concrete casting were ordinary Portland cements (Twiga Cement), Volcanic Ash, fine and course aggregates and water. The details of material are as follows: • Volcanic Ash Samples (Volcanic ash) for the study come from Holili located in Kilimanjaro. In Holili, the Ministry of Energy and Minerals monitor volcanic ash and therefore the author arranged the permit to access the materials from one of the V.A dealers. The extracted V.A materials were parked into two bags of about 50kg each and transported by truck to University of Dar es Salaam (UDSM)–College of Engineering and Technology (CoET) laboratory for investigations. In the laboratory, they were naturally (i.e. under shade) dried for 24hours in order toreduce the moisture content. V.Afrom Holili is granular in nature and hence they were grinded and sieved to 0.075mmsieve size. From the characterization, the moisture content of V.A is approximate 6.8 %. In addition, the oxides composition of the V.A sample was measured at Tanzania Portland Cement Company (TPCC) laboratory, which showed

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www.ijird.com June, 2017 Vol 6 Issue 6 the amount of oxides content to be more than 70% and Ioss on ignition was not exceeding 15% as recommended by Otto Ruskulis (2009) for qualifying to have pozzolanas properties (See Table 1)

Measured Components Composition ( % ) Remarks Silicon oxide, SiO2 45.83 Total Oxides content is Aluminum oxide, AL2O3 12.35 76.56% sample qualify as a Iron oxide, Fe2O3 15.38 pozzolanas material Loss on ignition 6.03 Sample qualify Table 1: V.A Sample Qualification • Fine Aggregate The fine aggregate sample from Mpiji was characterized by particle size ranging from0.15mm to 4.75mm. During the investigation, representative samples were prepared by Riffle splinter sampling techniques. The properties of fine aggregate (sand) were tested at UDSM-CoET laboratory before they were used to make concrete (see Table 2). • Coarse Aggregate The coarse aggregate sample comes from Lugoba Coast Region and the representative samples were prepared by using quartering technique. The particle size for coarse aggregates ranges from 4.75mm to 19.5mm.Other properties of coarse aggregate were tested in the same way as in fine aggregates (see Table 2.)

Test Parameters Fine aggregates Course aggregates Average Bulk Density 1.46g/cm 3 1.39g/cm 3 Average Gross Density 2.67g/cm 3 2.50g/cm 3 Aggregate Impact Value Not applicable 11.50% Aggregate Crushing Value Not applicable 19.90% Water of Absorption of Coarse Aggregate Not applicable 0% Table 2: Fine and course aggregate material properties

3.2. Method The V.A, sand, course aggregate and ordinary Portland cement were mixed together to make concrete.M25 was used as a benchmark based on designed CP 110 – 1993 guidelines for research. The proportional of material for concrete was 1: 1.7: 4.5 of Cement, Sand and Coarse Aggregate respectively with Water to cement ratio of 0.56.Experiments were conducted to replace cement by changing the composition of concrete mixture in the series of 10, 20, 30 and 40% of V.A (i.e. percentage of V.A. added in the mixture).Apart from the benchmark mix, there were four-mix type as shown in Table 3with six cubes (of 100mm cube size) for each type, three cubes for 7days and 3 cubes for 28days after curing tests.

Type V.A No of Cement V.A (gm) Fine Aggregate Coarse Aggregate Water (gm) (W + Contents cubes (gm) (gm) (gm) 6.8%V.A) ( % ) I 0 6 2250 0 3825 10058 1260 II 10 6 2025 225 3825 10058 1276 III 20 6 1800 450 3825 10058 1290 IV 30 6 1575 675 3825 10058 1306 V 40 6 1350 900 3825 10058 1321 Table 3: Summary of weight requirement for concrete mix cube types

Mixing process was performed by rotary mixer machine where by each batch contained not less than 17393gm of mass to make 6cubes.Mixing by rotary machine ensure homogeneous mixture of all ingredient used for the investigations. After mixing, the paste (i.e. concrete)was casted into 100mm cubes steel mold and were properly fixed and smeared with oil. For efficacy compaction, vibration was introduced to the cubes through vibrating table. The concrete cubes were then left in the mold overnight. The following morning concrete cubes were removed from the mold and their weight was recorded. They were then deepened into curing sink for 7days and 28days (see Figure 1).

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Aggregate prepared for concrete making Volcanic ashes in the field

Mixture of aggregate and binder (i.e. cement & Concrete cubes deepen in curing sink Volcanic ashes) for making concrete Figure 1: Materials used for testing the replacement of cement in concrete making.

After curing, the concrete cubes were tested to identify the achieved quality of mechanical properties of the concrete based on percentage changes of V.A. in the mixture of concrete. Figure 2 shows machine set up for compressive strength test.

Figure 2: Machine (uniaxial compressive test) set up for testing the strength of different concrete cubes with varying amount of volcanic ashes

4. Results and Discussions

4.1. Results The particle size distribution of the aggregate used to make concrete is very narrow for both fine and coarse aggregate (see Figure 3).The selected aggregate was appropriate for making concrete because fine aggregates produce stronger concrete when mixed with cement and other materials.

100

50 Fine aggregate Coarse aggregate 40

Percentage passing (%) passing Percentage 30

10 0.01 0.1 1 10 Aggregate size (mm) Figure 3: Particle size distribution for coarse and fine aggregates

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The concrete cubes from 7 and 28 days of curing were analysed with respect to the strength development. In the first place, the strength of concrete made without addition of V.A was measured (strength at zero percent of V.Ai.e. reference) aiming at determining the relationship between percentage of added V.A. and strength of concrete. Figure 4 shows the results from the compressive test for different proportions of V.A. materials added in the concrete. As expected, it can be seen that all the curing curves were monotonously decreasing with increasing percentage of V.A. Comparing the strength of concrete for seven (7) days curing with that of twenty-eight (28) days, the twenty-eight days of concrete curing curve run below the curve received from seven (7) days. This indicates lower strength development for the concrete in seven days curing but the strength progressively improved after reaching 28 days of curing.

7 days curing 15 28 days curing Measuredcompressive strength (N/mm2)

10 0 10 20 30 40 Percentage volcanic ash (%) Figure 4: Variation of compressive strength of concrete mix types

The difference of compressive strength from control mix, 0% and 30% of volcanic ash replacement as the optimal content, results into maintenance of desired strength with reduction of about 10% compressive strength from reference concrete mix sample shown in Table 4.

Samples V.A contents % Compressive strength Deviation Deviation Remarks N/mm 2 at 28day curing compressive strength compressive N/mm 2 strength in % I 0 32.6 Reference mix II 10 30.8 1.8 5% III 20 30.5 2.1 6% IV 30 29.2 3.4 10% Optimal mix Table 4: Variation of Compressive Strength with Volcanic Ash Contents (%)

As an estimate to the strength of the relationship between percentage decrease in strength of concrete and percentage increase in V.A., the coefficients of determination are high, and for 28 days of curing is approximated to 99.9 % (see Figure 5).

0 y = -0.001x 3 + 0.083x 2 - 1.249x + 0.087 R² = 0.999 -5

-10

-15 y = -0.002x 3 + 0.097x 2 - 1.641x + 0.852 -20 R² = 0.962 -25

-30 7 days curing -35 28 days curing -40

-45 Perncentage decrease ofconcreate stregth (%) -50 0 5 10 15 20 25 30 35 40 45 Percentage composition (%) Figure 5: A plot showing the effects of varying amount of volcanic ashes on reduction of strength of a concrete

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Comparing the results from the two compressive strength development, curing tests revealed that there is a non-linear correlation between the strength reduction of a concrete and addition of V.A. When taking into account the power of prediction, strength reduction can very well be predicted with 28 days curing condition with empirical model given by: = − × 3 + × 2 − × + % RCS 0.002 (%VA ) 0.08 (%VA ) 1.25 (VA ) 0.09

Where, %RCS=Percentage Reduction Concrete Strength %VA=Percentage of Volcanic Ash added to the concrete The relative error is estimated within the range of 1% to maximum 9% with average of 5 %. This is within the acceptable experimental errors.

4.2. Discussion The findings of this investigation provide an insight about a threshold (limit) of addition of V.A. when partially replacing the cement for making concrete. Based on achieved compressive strength of a concrete, cement can be replaced up to 30-wt% by V.A. Beyond this value, the concrete grade significantly decreases irrespective of the curing period. Small reduction of strength require a lower amount of cement replacement and 20wt% is a suitable amount of V.A. required to replace cement for better concrete grade. The magnitude of the strength reduction is very small for 28 curing days compared to the 7 days. In practice,28 days of curing is crucial in order to achieve a high strength concrete. According to Schoener and Mwita (1987), comprehensive strength of concrete at 7days should be greater or equal to 60% of designed concrete grade. For example, the design concrete grade of 25N/mm 2 should provide a minimum strength 15N/mm 2 for 7days of curing. This is concurrent with the measured concrete grade for 7days data achieved in this study. Analysis of 28days results show that all samples reached the desired strength of 25N/mm 2 at 30% volcanic ash content. Alsoin the investigation, it was observed that 99.9 % variations of concrete grade for 28 days of curing can be described by content of V.A by using an empirical equation obtained from experimental data. Advantages of using Pozzolana in construction (i.e. for making concrete) were reported by other researchers e.g. reducing permeability and voids(Meddah&Tagnit, 2009) specially when improved strength and the effect of Supplementary Cementations Material (SCM’s) in concrete porous structure is strongly related with the composition of SCM and water cement ratio (Diamond, 2000). On the other hand, it reduces expansion and heat of hydration. Replacing 57.5 % Portland cement by natural Pozzolanas can reduce the expansion and heat of hydration up to 40 % (Al-chaar et all ., 2011). In addition, Pozzolana materials tend to reduce the potential for alkali aggregate distress in concrete due to its ability to react with the alkalis in the pore solution more quickly than the larger aggregate particles hence reduce deleterious expansive reaction on products (Alchaar et all., 2011; Diamond, 1983).These are useful knowledge but they require comprehensive experiments that may lead to high cost. The missing picture of modeling is crucial for generating similar kind of knowledge with less number of experiments and low costs. The approach used here requires more data from different cases (i.e. different aggregates, different V.A with different properties) but it has provided a platform for further development. The uncertainty from other cases in the empirical model limits wide application of the model to provide knowledge about how the properties of material affect the concrete grade, and how flexible and easy they can be used for blending the V.A with other materials in order to produce high-grade concrete.

5. Conclusion Based on experimental results of the V.A from Holili, it has been revealed that volcanic ashes can be used to reduce the amount of cement in the concrete mix for acceptable required strength of a concrete. The 30 wt% of V.A is an optimal value for cement replacement. The 20 wt% value of V.A. in the mix (blending) is suitable for high grade concrete. Within blending techniques, a further study is suggested to investigate the cost implication of using volcanic ash in concrete mix although it has indicated the possibility of reducing energy and gas emission in the context of sustainable construction. Besides blending techniques, more data is required for the modeling of mix design for various concrete grades.

5.1. Acknowledgement We thank all people who supported us in carrying out this research, specifically the University of Dar es Salaam, College of Engineering and Technology for allowing us to use their laboratory.

6. References i. Al-chaar, G.K; Alkadi, M; Yaksis, D.A and Kallemeyn, L.A, (2011), The use of natural pozzolan in concrete as an additive or substitute for cement, Engineer Research and Development centre, US Army corps of Engineering, Washington DC.USA. ii. Allen, W.J. and Spence, R.J.S.,(1983), A study of the activity of a volcanic pozzolana in Northern Tanzania, Appropriate Building Materials for Low Cost Housing, E & FSpon, New York, pp 34-42 iii. Ballantine, R. and Rossouw, A., (1989),Stabilization of Soils - A practical manual Detailing. Pretoria Portland Cement Limited, Johannesburg, South Africa. iv. COWI Tanzania Ltd, (2000). Pilot Study for Possible Use of Locally Available Pozzolan in Tanzania, summary report for Ministry of Works, CoWI Tanzania Ltd, the United Republic of Tanzania.

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v. Diamond, S. (2000), Mercury Porosimetry: An Inappropriate Method for the Measurement of Pore Size Distribution in Cement-Based Materials. Cement and Concrete Research, 30(10): p. 1517-1525. vi. Diamond, S., (1983), Alkali Reactions in Concrete-Pore Solution Effects - Alkalis in Concrete, Research and Practice, Proceedings, 6 th International Conference, Copenhagen, G. M. Idorn and Steen Rostam, pp. 155-166. vii. HABITAT, (1985),The Use of Selected Indigenous Building Materials with Potential for Wide Application in Developing Countries, United Nations Centre for Human Settlements, Nairobi. viii. Makange, A.A. and Massawe, N.M., (1986), Investigation of Natural Pozzolan-Portland Cement Mortars in Tanzania, Journal of Ferrocement (Bangkok), 16(3), pp 255-262 ix. Meddah, M.S. and. Tagnit-Hamou, A., (2009), Pore Structure of Concrete with Mineral Admixtures and Its Effect on Self- Desiccation Shrinkage. ACI Materials Journal, 106(3): pp. 241-250. x. Moore, D., (1995), The Riddle of Ancient Roman Concrete,http://www.romanconcrete.com/docs/spillway/spillway.htm, (accessed: June, 2016) xi. Olekambainei, A K E, (2005), The Influence of Moulding Moisture Content on the Engineering Properties of Aggregate- Lime-Natural Pozzolan Mixes, Master’s dissertation, Faculty of Engineering, Built environment and Information Technology, University of Pretoria, Pretoria. xii. Pylkkanen K. (1995). Granulated Blast Furnace Slag in Base Course of Low-Volume Roads, Proceeding. 6 th International Conference on Low-Volume Roads, vol. 2, Minneapolis, Minnesota, USA. xiii. Rose, W. and Durant, A., (2009). Fine Ash Content of Explosive Eruptions, Journal of Volcanology and Geothermal Research,pp 32–39. xiv. Saricimen, H.; Maslehuddin, M.; Shamim, M.; Khan, M. and Al-Tayib, A., (1992),Effect after curing on the Permeability of Plain and Pozzolanic Concrete. Proceeding. 4 th CANMET / ACI International Conference on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, Istanbul, Turkey. xv. Schoner, W. and Mwita, N.,(1987), Building Materials. Part 4. Concrete. Dar es Salaam, Tanzania: Faculty of Engineering, University of Dar es Salaam (UDSM). xvi. Shi, C. and Day R., (1993),Acceleration of Strength Gain of Lime-Pozzolan Cements by Thermal Activation. Cement and concrete research, 23(4), USA. xvii. Stulz, R., (1983).Fundamental information on building materials", Appropriate Building Materials, Intermediate Technology Publications Ltd., SKAT publication Vol.12, pp 321 xviii. Vandewalle, L. and Mortelmans, F., (1992),The Effect after curing on the Strength Development of Mortar Containing High Volumes of Fly Ash, Proceeding,4 th International Conference on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, vol. 1, Istanbul, Turkey. xix. Wilson, T.; Stewart, C. ; Sword, D. ; Leonard, G. ; Johnston, D.; Cole, J.; Wardman, J.; Wilson, G. and Barnard, S., (2011). Volcanic Ash Impacts on Critical Infrastructure, Physics and chemistry of the earth, Part A/B/C, Vol. 45-46, pp5-23

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