Models For Predicting the Structural Characteristics of Sand-Quarry Dust Blocks

ABSTRACT

In this work, models for predicting six structural characteristics and cost of sand-quarry dust blocks were developed. Three model equations namely Scheffe’s simplex lattice design (pseudo component), Scheffe’s simplex lattice design (component proportion) and Osadebe’s model were developed for each property. The properties investigated were Compressive strength, Water absorption and Split tensile strength. The others are Static modulus of elasticity, Flexural strength and Shear strength. The models were fitted to data obtained from tests on various mixes of 140 sand-quarry dust hollow blocks of 450 x 225 x 225 mm, 66 beams of 600 x 150 x150mm and 66 cylinder specimens of 150mm diameter and 300mm long. Adequacy of the models were confirmed using F statistic and normal probability plot. Computer programs, were developed to determine the responses to a given mix and the mixes that give a desired response value. The effect of the partial replacement of sand with quarry dust on the characteristics of the blocks was also studied. Component interactions was studied using Cox response trace plots. Comparisons between the experimental and model predicted results and between the models were made. The percentage difference between the experimental and model predicted values were all below 5% for all the models and responses. The analyses also show that there is no significant statistical difference between the models. The minimum and maximum values of compressive strength predictable by Scheffe’s pseudo component model are respectively 2.74 and 5.22Nmm-2. The corresponding values for the water absorption of the blocks are 3.21 and 7.84%. For the Scheffe’s component proportion model, the predictable compressive strength values range from 2.77 to 5.23Nmm-2 . The corresponding range for water absorption is 3.20 to 7.84%. The minimum and maximum flexural strength predictable by the Scheffe’s pseudo component model are 2.40 and 4.34Nmm-2 respectively. The corresponding values for the Split tensile strength are 2.24 and 3.33Nmm-2 . For Scheffe’s component proportion model, the corresponding values are 2.45 and 4.35Nmm-2 for the flexural strength and 2.27 and 3.33Nmm-2 for the split tensile strength. Analyses of the pseudo component models show that there is binary synergy between sand and quarry dust for all the properties. Other binary combinations anti synergistic effects. Cement and water has the greatest effect on the properties. The structural properties of the blocks improved when 10 to 40% of the sand was partially replaced with quarry dust. The optimum replacement was at 40% with an increase in compressive strength of 27%. A list of 117 mixes that meet NIS 87: (2004) recommended minimum compressive strength of 3.45Nmm-2 for load bearing sandcrete blocks was established. It is recommended that the inclusion of quarry dust in sandcrete block production be encouraged especially in areas where quality sand for sandcrete block production is scarce and expensive.

 

TABLE OF CONTENTS

CONTENT PAGE

Title page i

Approval page ii

Certification iii

Dedication iv

Acknowledgement v

Abstract vii

Table of Contents viii

List of Tables xi

List of Figures xvii

List of Appendices xx

CHAPTER ONE: INTRODUCTION 1

1.1 General 1

1.2 Statement of the Problem 2

1.3 Statement of Objectives 5

1.4 Scope of the Study 5

1.5 Justification of Study 6

CHAPTER TWO: LITERATURE REVIEW 7

2.1 Blocks 7

2.1.1 Sandcrete blocks 8

2.1.2 Constituents of Sandcrete blocks 9

2.1.1.2 Strength and durability properties of hardened concrete/sandcrete 15

2.1.1.3 Manufacture of Sandcrete blocks 20

2.1.1.4 Factors affecting the strength of sandcrete blocks 23

2.2. Quarry dust 25

2.2.1 Physical and chemical properties of quarry dust 26

2.2.2 Use of quarry dust in concrete/sandcrete works 26

2.3 Application of statistical methods in concrete mixture optimization 29

2.3.1 Mixture experiment and model forms 31

2.3.1.1 Scheffe’s simplex lattice designs 33

2.3.1.2 Augmented simplex lattice design (ASL) 40

2.3.1.3Axial designs 41

2.3.1.4 Simplex-centroid design 42

2.3.1.5Osadebe’s model 45

2.3.2 Model selection and validation (Test for goodness) 46

2.3.2.1Model selection and test for goodness for the augmented simplex lattice model 46

2.3.2.2 Test of goodness for Osadebe’s model 51

2.4 Design and Analysis of mixture experiments using computer software 52

2.4.1 Design and Analysis of mixture experiments using Minitab 16 (2010) 53

CHAPTER THREE: MATERIALS AND METHODS 59

3.1 Materials 59

3.1.1 Cement 59

3.1.2 Water 59

3.1.3 Sand 59

3.1.4 Quarry dust 59

3.2 Methods 59

3.2.1 Design of experiments 59

3.2.1.1Scheffe’s augmented simplex lattice models 60

3.2 .1.2 Mix ratios for the Osadebe’s model 63

3.2.2 Experimental investigation 67

3.2.2.1 Field work 67

3.2.2.2 Laboratory Investigation 68

3.2.3 Cost of production of 1m3 of sand-quarry dust mixes 70

3.2.4. Mixture data Analysis and Regression Equations 72

3.2.5. Comparison of results 72

3.2.6 Computer Programs 73

CHAPTER FOUR: PRESENTATION AND ANALYSIS OF RESULTS 77

4.1 Presentation of Results 77

4.1.1 Physical property tests results 77

4.1.2 Chemical property tests results of cement and quarry dust 80

4.1.3 Characteristics tests results of blocks 81

4.1.4 Model equations and test of adequacy of models 95

4.1.4.1Model equations for Compressive strength 95

4.1.4.2Model equations for Water absorption 103

4.1.4.3Model equations for Flexuralstrength 110

4.1.4.4Model equations for Split tensilestrength 116

4.1.4.5 Model equations for Static modulus of elasticity 123

4.1.4.6Model equations for Shearstrength 129

4.1.4.7 Model equations for Cost 136

4.1.5: Model results and comparison of experimental and model results 143

4.1.6 Statistical comparison of models 150

4.1.7 Response trace plots 152

4.2. Discussion of Results. 156

4.2.1 Physical properties of Sand and Quarry dust 156

4.2.1.1 Specific gravity and Bulk density of sand and quarry dust 156

4.2.1.2 Gradation of sand and quarry dust 156

4.2.2 Chemical analysis of quarry dust and cement. 160

4.2.3 Effect of partial replacement of sand with quarry dust on some strength properties of the blocks 157

4.2.4 Analysis of model equations 159

4.2.4.1 Maximum model responses 159

4.2.4.2 Component interactions 160

4.2.4.3 Comparison of experimental and model results and between the models 161

4.2.4.4. Cox response trace plots (Component interactions) 161

4.2.5 Computer programs OPTIMIZER and RESPONDER 163

4.2.6. Cost of blocks 165

4.2.7 Relationships between compressive strength and other properties 165

CHAPTER FIVE: CONCLUSIONS AND RECOMMENDATIONS 172

5.1 Conclusions 172

5.2 Recommendations 175

5.3 Contribution to Knowledge 176

REFERENCES 178

APPENDICES 190