Effect of Mortar Spacers of Different Grades on the Performance of Concrete
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EFFECT OF MORTAR SPACERS OF DIFFERENT GRADES ON THE PERFORMANCE OF CONCRETE MOHAMED ALI MOHAMOUD A project report submitted in partial fulfillment of the requirements for the award of the degree of Master of Engineering (Structures) Faculty of Civil Engineering Universiti Teknologi Malaysia JANUARY 2017 iii This project report is dedicated to my beloved family; Father, Mother, Siblings and Relatives. iv ACKNOWLEDGEMENT In the name of Allah, the Most Gracious, and Most Merciful. Praise be to Allah S. W. T, Peace and blessings of Allah be upon His Messenger, Muhammed S.A.W, and all his family and companions. I would like to express my sincere appreciation to my supervisor, Associate Professor Dr. Abdul Rahman Mohd. Sam for his encouragement, guidance, critics, friendship and help during the development of this project. Thanks to all other lecturers for helping me either directly or indirectly in the completion of this report project. My special appreciation goes to my father, my mother and siblings, whom their love and care have brought me to this level. Their substantial encouragements and support have helped me to succeed in finishing my program here at Universiti Teknologi Malaysia. Last but not least, I would like to express gratitude to my colleagues and seniors their help is really appreciated and will be remembered forever. Also, I would like to thank the staff of Structure and Materials Laboratory, Faculty of Civil Engineering, University Teknologi Malaysia for their assistance in the experimental works. v ABSTRACT Rebar spacers are crucial component in reinforced concrete structures. Their purpose is to provide and maintain cover for the reinforcement bars. Since rebar spacers are permanent part of the member their quality must be taken into consideration, failure to do so will jeopardize the durability of the whole reinforced concrete member. In this research project, the effect of mortar spacers on the durability and strength of concrete is investigated by examining the penetration of moisture and other corrosive agents such as chloride through the mortar spacer or through the concrete-spacer interface, assuming that the concrete is in good condition dense and durable. For lab experimentation, cube and prism specimens with different curing ages and conditioning were cast, the specimens were embedded with mortar rebar spacers and tested in terms of strength and durability. Strength tests have been conducted such as compressive strength and flexural, also durability tests for cube specimens were conducted including water absorption, expansion and shrinkage, chloride penetration and carbonation. Results showed that the presence of rebar spacer in concrete increases the ingression and transporting of moisture and other corrosive agents, especially at the concrete-spacer interface and when the quality of the spacer is lower compared to the quality of the concrete. Moreover, the spacer will negatively affect the flexural strength of prism specimens by initiating cracks. The spacers might seem small and hold low value during construction, but because they are permeant part of the structure and they are placed every ≤1 m along the rebars, their overall effect on ingress of corrosive agents might be significant, and that must be considered by the concrete designers and practitioners. vi ABSTRAK Alas rebar adalah komponen penting dalam struktur konkrit bertetulang. Tujuan mereka adalah untuk menyediakan dan mengekalkan perlindungan untuk bar tetulang. oleh kerana alas rebar adalah sebahagian tetap ahli kualiti ia perlu diambil kira, kegagalan berbuat demikian akan menjejaskan ketahanan keseluruhan anggota konkrit bertetulang. Dalam projek penyelidikan ini, kesan alas rebar mortar pada ketahanan dan kekuatan konkrit disiasat dengan memeriksa penembusan kelembapan dan agen menghakis lain seperti klorida melalui alas rebar mortar atau melalui antara konkrit-alas rebar, dengan anggapan bahawa konkrit adalah dalam keadaan baik padat dan tahan lama. Untuk uji kaji makmal, kiub dan spesimen prisma dengan peringkat umur pengawetan yang berbeza dan pengawetan dibuat, alas konkrit dimasukkan ke dalam sampel dan diuji dari segi kekuatan dan ketahanan. Ujian kekuatan telah dijalankan seperti kekuatan mampatan dan lenturan, juga ujian ketahanlasakan untuk spesimen kiub telah dijalankan seperti penyerapan air, pengembangan dan pengecutan, penembusan klorida dan pengkarbona tan. Hasil kajian menunjukkan bahawa kehadiran rebar dalam konkrit meningkatkan serapan dan pengangkutan kelembapan dan agen menghakis lain, terutama di antara muka konkrit-alas rebar apabila kualiti alas rebar adalah lebih rendah berbanding dengan kualiti konkrit. Selain itu, alas rebar juga akan memberi kesan negatif terhadap kekuatan lenturan spesimen prisma dengan memulakan retak. Alas rebar mungkin kelihatan kecil dan tidak kritikal semasa pembinaan, tetapi kerana mereka akan menjadi sebahagian daripada struktur dan diletakkan setiap ≤1 m di sepanjang tetulang, kesan keseluruhan mereka pada kemasukan agen menghakis mungkin menjadi penting, dan perlu dipertimbangkan oleh pereka dan pengamal konkrit. vii TABLE OF CONTENTS CHAPTER TITLE PAGE DECLARATION ii DEDICATION iii ACKNOWLEDGEMENT iv ABSTRACT v ABSTRAK vi TABLEOF CONTENTS viii LIST OF TABLES xii LIST OF FIGURES xiii LIST OF ABBREVIATION xiv 1 INTRODUCTION 1 1.1 Background of the study 1 1.2 Problem statement 2 1.3 Research Objectives 3 1.4 Research Scope 3 1.5 Significance of Research 5 2 LITERATURE REVIEW 6 2.1 Introduction 6 2.2 Spacers Development 7 2.2.1 Spacers Types 8 2.2.2 Use of spacers 14 2.3 Effect of Rebar Spacers on the Microstructure and Properties of Concrete 18 2.4 Conclusion for Literature Review 25 viii 3 METHODOLOGY 27 3.1 Introduction 27 3.2 Experimental Program 28 3.3 Experimental Framework 29 3.4 Material Used 30 3.4.1 Cement 30 3.4.2 Fine aggregate 31 3.4.3 Coarse Aggregate 32 3.4.4 Water 33 3.4.5 Silver Nitrate 33 3.4.6 Phenolphthalein 34 3.5 Mix Proportions 35 3.5.1 Concrete Mix Design 36 3.5.2 Mortar Mix Design 36 3.6 Specimen Preparation 37 3.6.1 Molds 37 3.6.2 Concrete and Mortar Mixing 38 3.6.3 Number and Types of Specimen 40 3.6.4 Specimen Details and Specifications 42 3.6.5 Curing Condition 44 3.7 Experimental Tests 45 3.7.1 Sieve Analysis 45 3.7.2 Slump test 46 3.7.3 Density of Hardened Concrete 47 3.7.4 Compression Test 48 3.7.5 Ultrasonic Pulse Velocity Test 50 3.7.6 Water Absorption Test 51 3.7.7 Chloride Penetration Test 52 3.7.8 Carbonation Test 53 3.7.9 Expansion and Shrinkage Test 54 3.7.10 Flexural Test 55 3.7.11 Modified Compression Test 56 4 RESULT AND DISCUSSIONS 58 4.1 Introduction 58 ix 4.2 Sieve Analysis 58 4.3 Slump Test 60 4.4 Density of Hardened Concrete 61 4.5 Compressive Strength Test 62 4.5.1 Mode of Failure 64 4.6 Ultrasonic Pulse Velocity Test for Cubes 66 4.7 Water Absorption Test 68 4.8 Chloride Penetration Test 69 4.9 Carbonation Test 72 4.10 Ultrasonic Pulse Velocity Test for Prisms 73 4.11 Expansion and Shrinkage Test for Prisms 74 4.12 Flexural Test 78 4.13 Modified Compression Test 80 5 CONCLUSION AND FUTURE RECOMMENDATION 84 5.1 Introduction 84 5.2 Conclusion 85 5.3 Recommendations 86 REFERENCES 87 x LIST OF TABLES TABLE NO. TITLE PAGE 2.1 Summary of various codes of practice on spacer classification and placement 12 2.2 Causes of concrete cover defects and their influence on spacers 20 3.1 Concrete mix proportions according to DoE method 36 3.2 Mortar mix proportions 37 3.3 Number of prisms 40 3.4 Number of cubes 41 4.1 Fine aggregate sieve analysis data 58 4.2 Coarse aggregate sieve analysis data 59 4.3 Slump test data 61 4.4 Average density of hardened cubes 62 4.5 Average compressive strength of cubes 63 4.6 Average pulse velocity for cubes, (km/s) 67 4.7 Water absorption for different types of specimens 68 4.8 Average chloride penetration depth for the specimens 70 4.9 Average pulse velocity for prims, (Km/s) 73 4.10 Expansion and Shrinkage results 76 4.11 Flexural strength for prism specimens 78 4.12 Compressive strength of prisms 81 4.13 Compressive strength for Prism and cube specimens, (MPa) 83 xi LIST OF FIGURE FIGURE NO. TITLE PAGE 2.1 Examples of clip-on spacers: a) A-spacers, b) wheel spacers and c) tower spacers 8 2.2 Some types of cementitious spacers: single spacers with centre opening for tie wire (a & b) and line spacer (c) 10 2.3 Steel wire chairs types: (a) single chair, (b & c) continuous chair and lattice (d) circular chair 11 2.4 Placing of plastic spacers 17 2.5 Causes of concrete cover defects observed in 25 construction sites in the UK 19 2.6 Local chloride induced corrosion adjacent to plastic spacer location 21 2.7 Corrosion at the interface between the mortar spacer and the concrete, the red circles indicates the locations where the corrosion started 22 2.8 Significant corrosion spotted at the plastic spacer location (left) but no corrosion spotted near the mortar spacer (right) 23 2.9 A-shaped spacer still attached to reinforcement with no sign of corrosion after 36 years of use in car park 24 2.10 Close look at reinforcement steel bar after ten years of weathering 24 2.11 Difference between A shaped plastic spacers used in pervious study 25 3.1 Flow chart of research stages 28 3.2 Ordinary Portland cement 31 3.3 Fine aggregate (sand) 32 xii 3.4 Coarse aggregate 32 3.5 Water 33 3.6 Sliver nitrate and distilled water used 34 3.7 Measurement of the depth of carbonation with phenolphthalein 35 3.8 Steel molds used a) cube molds b) spacer’s molds c) prism molds 38 3.9 (a) Mixing machine, (b) vibration table 39 3.10 Cubes