ABSTRACT STRUCTURAL ADEQUACY OF RECYCLED COARSE AGGREGATES IN CONCRETE PRODUCTION
This work presents experimental investigations on structural adequacy of recycled coarse aggregates in production of structural and non-structural concrete. Natural coarse aggregate used was crushed stones with 20mm maximum size. While recycled coarse aggregates used were extracted from concrete box culverts. The culverts were barely six (6) months old when the alignment of the road was slightly changed due to other
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development or plans. Part of the culverts was carefully demolished for extension works. The debris was gathered and the coarse aggregates were extracted manually using hammer. The maximum size of recycled coarse aggregates extracted was 20mm. Both natural and recycled aggregates were from the same source. Concrete mixture of 1:1.5:3 by mass was used in this investigation. The 28-day compressive strength of concrete cubes of the recycled coarse aggregates and natural coarse aggregates were 21.30N/mm2 and 24.66N/mm2 respectively with a corresponding reduction in strength of 13.30%. The workability test showed that natural coarse aggregates concrete was more workable than recycled coarse aggregate concrete (81.3mm and 77.33mm respectively). Water absorption capacities of natural and recycled coarse aggregates were 3.5% and 4.9% respectively. Both recycled and natural aggregates concrete showed the same trend, their densities and compressive strengths increased with time. The compressive strength and densities of recycled coarse aggregates concrete were lower than that of natural coarse aggregates. The results proved that Recycled coarse aggregates could be used in production of structural and non-structural concrete, but more cement and surface treatment may be required for the strength to measure up with natural aggregates. The differences in the results were due to high porosity, high water absorption, changes in the physical and chemical states of the recycled coarse aggregates.
TABLE OF CONTENTS
Title page i
Certification ii
Approval page iii
Dedication iv
Acknowledgement v
Abstract vi
Table of contents vii
List of tables xii
List of figures xiv
List of plates xv
CHAPTER ONE
INTRODUCTION
- Preamble 1
- Statement of problems 3
- Aim and objectives of the project 3
- Scope of the project 3
- Significance of the study 4
CHAPTER TWO
LITERATURE REVIEW
2.1 Concrete constituents 5
2.1.1 Aggregates 6
2.1.2 Characteristics of aggregates 9
2.1.2.1 Strength 9
2.1.2.2 Stiffness 10
2.1.2.3 Bond of aggregate 10
2.1.2.4 Shape and texture 11
2.1.2.5 Specific gravity 11
2.1.2.6 Particle size 11
2.1.2.7 Water absorption 12
2.1.2.8 Bulky density and void ratio 12
2.1.2.9 Porosity 13
2.1.2.10 Soundness of aggregates 14
2.1.3 Cement 14
2.1.4 Water 15
2.2 Defects in concrete 15
2.2.1 Cracks 16
2.2.1.2 Alkali aggregate reaction 16
2.2.1.3 Steel 16
2.2.1.4 Freeze and thaw 16
2.2.2 Crazing 16
2.3 Concrete production 17
2.4 Curing 18
2.5 Water-cement ratio 29
2.6 Properties of Concrete 20
2.6.1. Compressive strength 20
2.6.2 Workability 23
2.6.3 Durability 24
2.6.3.1 Factors affecting durability of concrete 24
2.6.3.2 Permeability 24
2.6.3.3 Sulphate attack 24
2.6.3.4 Carbonation 25
2.6.3.5 Mineral oils 25
2.6.3.6 Organic acids 26
2.6.3.7 Sugar 26
2.6.3.8 Cracks 26
2.6.4 Shearing strength 26
2.6.5 Creep 26
- Shrinkage 27
- Bleeding 27
- Segregation 27
- Density 27
- Sieve analysis (gradation test) 28
CHAPTER THREE
METHODOLOGY
Selection of materials 30
Tests and Experiment 31
3.2.1Slump test 31
3.2.2 Sieve Analysis 33
3.2.3 Compressive Strength 34
3.2.4 Water absorption 37
CHAPTER FOUR
COMPUTATIONS, RESULTS AND DISCUSSION
4.1 Results 39
4.1.1Result of slump test 39
4.1.2 Discussion of slump test results 39
4.1.3 Result of sieve analysis 40
4.1.4 Discussion of sieve analysis test 43
4.1.5 Result of compressive strength and density tests 44
4.1.6 Discussion of compressive strength and density test results 49
4.1.7 Result of water absorption capacity of coarse aggregates 51
4.1.8 Discussion of water absorption capacity tests 51
CHAPTER FIVE
CONCLUSION AND RECOMMENDATION
5.1 Conclusion 52
5.2 Recommendation 53
References 54
Appendix 61
LIST OF TABLES
Table 2.1: Cement concrete constituents and their functions. 6
Table 2.2: Compressive strength of different grades of concrete at 7 and 28 days 21
Table 2.3: Types of slump 23
Table 2.4: Classes of slump 24
Table 4.1: Slump test values 39
Table 4.2: Sieve Analysis of fine aggregates 40
Table 4.3: Sieve analysis of natural coarse aggregates 41
Table 4.4 : Sieve analysis of recycled coarse aggregates 41
Table 4.5: Summary of sieve analysis of coarse aggregates 42
Table 4.6; Sieved materials classification 43
Table 4.7: Compressive strength of crushed concrete cubes 44
Table 4.8: Average compressive strength and densities 46
Table 4.9: Compressive strength of cubes at different days 47
Table 4.10: % reduction in strength of recycled coarse aggregates compared to natural
coarse aggregates concrete 48
Table 4.11: Relative strength of recycled coarse aggregates and natural coarse
aggregates concrete (%) 49
Table 4.12: Water absorption capacity values 51
LIST OF FIGURES
Figure 4.1: Particle size distribution curve of fine aggregates 40
Figure 4.2: Particle size distribution curve of natural aggregates 41
Figure 4.3: Particle size distribution curve of recycled aggregates 42
Figure 4.4: variation in strength of natural coarse aggregates concrete cube 45
Figure 4.5: variation in strength of recycled coarse aggregates concrete cubes 45
Figure 4.6: Graph of weight of cubes and age of recycled and natural coarse aggregates
concrete 46
Figures 4.7: Graph of density and age of recycled and natural aggregates concrete 47
Figure 4.8: Graph of compressive strength of natural and recycled coarse aggregates 48
Figure 4.9: Relationship between %strength of concrete and cubes age 48
Figure 4.10: Relationship between %strength ratio and concrete cubes age 49
LIST OF PLATES
Plate 1: Sample materials for slump test 65
Plate 2: Slump test 66
Plate 3: Fine aggregates on scale 66
Plate 4: Sample materials on the mechanical sieve machine 67
Plate 5: Arrangement of sieve pans 67
Plate 6; Coarse aggregates on scale 68
Plate 7: Concrete cubes 68
Plate 8: Concrete cube in compression testing machine 69
Plate 9: Coarse aggregates in oven 69
Plate 10: oven-dried sample on scale 70
CHAPTER ONE
INTRODUCTION
- Background of the study
Concrete is inert mass which grows from a cementing medium. Concrete is a product of two major components, one is the cement paste and another is the inert mass. In order to form the cement medium, cement would mix with water. Coarse aggregates and fine aggregates are the part of inert mass. In properly mixed concrete, these materials are completely surrounded and coated by cement paste filling all the void space between the particles (Raju et al,1979).
Strength is the design property of the concrete. Characteristics like, durability, impermeability, volume stability ay be important in some case of designing concrete structure but strength is the most important one. An overall picture of concrete quality is being reflected by the concrete strength.
Concrete mix proportioning, aggregate quality, aggregate gradation, type of cement, mixing and placing method, concrete curing and curing temperature and the most important one is the water cement ratio. Water cement (W/C) ratio has a critical impact on concrete strength characteristic. A minimum amount of water is necessary for proper chemical reaction in the concrete and extra amount of water increases the workability and reduces strength.
Natural aggregatesare aggregates which have not been used in any concrete works. They are obtained by crushing from quarries of igneous, sedimentary or metamorphic rocks.
Recycled aggregatesare natural aggregates which have been used in another engineering projects or concrete works, but extracted for another works.
Recycling of waste concrete for production of aggregates can be helpful in solving problems like depletion of natural resources, scarcity of land for waste disposal, and growing costs of waste treatment prior to disposal (Hosseini et al,2009).
Recycled Concrete Aggregates (RCAs) are obtained by crushing of concretes from demolition of concrete structural components in many structures such as: old buildings, concrete pavements, bridges & structures, at the end of their service life & utility, structures deteriorated beyond the possibility of repairs, structures that are turned into debris resulting from natural disasters (such as floods, earthquake, tsunami, manmade disaster/war, etc), structures not serving the needs in present scenario, old structures to be brought down to pave way for new construction for better economic growth ( Monjurul & Ahsanul, 2011).
Compressivestrength of the concrete made with 100% recycled coarse aggregates was found to be 25 % lower than that of natural aggregates Concrete. Major problems occurring while using recycled concrete aggregates in concretes are: higher porosity and hence higher water absorption, lower mechanical strengths, residual impurities on the surface of the recycled coarse aggregates creating weaker bond between cement paste and aggregates (Swapna, 2009).
The applications of recycled aggregation in concrete have started since end of World War 11. Demolished concretepavement was as recycled aggregate in stabilizing the base course for road construction (Olorusongo, 1999).
The mechanical process of breaking blocks of demolished concrete into relatively small grains may cause recycled aggregates suffering internal damage such as micro-cracks. Recycled coarse aggregates have relatively lower strength compared to natural aggregates concrete at the same water/cement ratio. Investigations found that a couple of approaches such as particle shaping, heating and grinding can considerably improve the quality of recycled aggregates (http://www.hindawi.com/journals/amse/2013/842929).
1.2 Statement of the Problems
Concrete is one of most consumed commodities in the world. Metric tons of it are being used on daily basis through-out the world. Almost its constituents are natural and depreciate everyday due to demands. Coarse aggregate constitutes 60-65% of concrete volume and contributes a lot to dimensional stability, strength and durability of concrete structures. Therefore, there is need to search for alternatives to natural coarse aggregates to reduce natural resources depletion and environmental disturbances and pollution due to quarry activities.
1.3 Aim and objectives of the project
The aim of the project is to determine the adequacy of recycled coarse aggregates as a complete replacement to natural coarse aggregates in the production of both non-structural and structural concrete.
The objectives are:
- To ascertain the density of recycled coarse aggregates.
- To determine the compressive strength of recycled coarse aggregates concrete.
- To determine the workability of a recycled coarse aggregates concrete.
- To determine the water absorption capacity of recycled coarse aggregates.
1.4 Scope of the project
In determining the structural adequacy of recycled coarse aggregates, slump test, sieve analysis and compressive strength tests shall only be carried out for both natural and recycled coarse aggregates concrete. Coarse aggregates of maximum size of 20mm from McDaniel Quarry,Ezza-Mgbo,Ohaukwu L.G.A, Ebonyi State shall be used with only 1:1.5:3:0.5mix ratio for both slump and compressive strength tests. Fine aggregates shall be river sand obtained from any river. Recycled coarse aggregates with 20mm maximum size must be obtained from old concrete works and must have same origin or source with natural aggregates.
The standard procedure for concrete cube test according to BS EN 12390-3:2009 shall be adopted. The work covers extraction of recycled coarse aggregates from old concrete work, batching of materials, mixing of materials, placing of concrete in the molds, curing of the cubes, weighing and crushing of cubes at various required ages. Portable water according to BS1348:part2:1980 must be used for the mixing and curing. Moulds made from mild steel, measuring 150mm x 150mm x 150mm internally which is one of the methods suggested by BS 1881: part 108:1983 for making test cubes from fresh shall be used.
All cubes must be cured in accordance with the standard of BS EN 12390-2:2009. For the sieve analysis, 300g of fine aggregates and 400g of both recycled and natural coarse aggregates shall be used. This work covers the procedures of the tests mentioned above and the results obtained and all tests shall be carried out in Nnamdi Azikiwe University, Awka, Anambra State except compressive strength of concrete cubes which shall be in Ebonyi State Ministry of Works and Transport, Abakaliki.
1.5 Significance of the Study
Adequacy of coarse aggregates is as important as concrete itself. Recycling of coarse aggregates, (if the strength is found satisfactory) will help in reducing the amount of construction debris disposal, rate of natural coarse aggregates depletion, environmental disturbances and pollution. It has potential of saving energy and cost.
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