RELATIONSHIP BETWEEN CHARACTERISTIC STRENGTH AND CEMENT CONTENT IN CONCRETE MIXES
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ABSTRACT
Cement as one of the constituents of concrete is always considered as the most valuable constituent as far as the strength of concrete is concerned. Although cement constitutes only 7 to 15 percent of the volume of a concrete mix, it is however regarded as the most active portion of the binding medium and therefore must be considered to be the most important ingredient of the concrete. Most of the time it is difficult to ascertain the quantity of cement that will yield a concrete of a particular strength because of other parameters that are involve in the determination of the strength of the concrete. In this study, an investigation was carried out to determine the relationship between strength and cement content in concrete mixes. Five different mixes with a constant water/cement ratio of 0.5 were prepared and cast to ascertain the strength development at 7 and 28 days. The materials used included 5-15 crushed stone as coarse aggregate, plastering sand (0-4mm) as fine aggregate and cement. Results showed that as the quantity of cement increases in a mix, the characteristics strength also increases. For example, when the cement content was 250kg, the strength was 24.15N/mm2. When the cement content was increased to 450kg, the strength was 47.26N/mm2. Equations relating these two parameters were also determined. These equations can be used to determine the cement content needed in a mix depending on the strength required. This study will be of help to concrete producers, consultants and contractors in determining the actual cement content needed to attain a required strength in a particular concrete mix during the design and construction stages of projects.
TABLE OF CONTENT
CONTENT PAGES
Abstract — — — — — — — — — — i
Table of Content — — — — — — — — — ii
CHAPTER ONE
1.0 Introduction — — — — — — — — — 1
1.1 Statements of the Problem — — — – — — — 3
1.2 Aims and Objectives of the Study — — — — — 4
1.3 Scope of Limitations of the Study — — — — — 4
1.4 Significance of the Project — — — — — — 5
CHAPTER TWO: LITERATURE REVIEW
2.0 Introduction — — — — — — — — — 6
2.1 History of Concrete — — — — — — — 6
2.2 Properties of Concrete — — — — — — — 8
2.2.1 Workability of Concrete — — — — — — — 9
2.2.2 Cracking of Concrete — — — — — — — 10
2.2.3 Segregation — — — — — — — — — 10
2.2.4 Water/Cement Ratio — — — — — — — 11
2.2.5 Bleeding — — — — — — — — — 12
2.2.6 Durability of Concrete — — — — — — — 12
2.3 Cement History — — — — — — — — 13
2.4 Composition of Portland Cement — — — — — 14
2.5 Hydration of Portland Cement — — — — — — 15
2.6 Storage of Cement — — — — — — — — 16
CHAPTER THREE: MATERIALS AND METHODS
3.0 Introduction — — — — — — — — — 19
3.1 Materials — — — — — — — — — 19
3.1.1 Cement — — — — — — — — — 19
3.1.2 Aggregates — — — — — — — — — 19
3.1.3 Water — — — — — — — — — — 20
3.2 Test Equipment and Apparatus — — — — — — 20
3.2.1 Slump Apparatus — — — — — — — — 20
3.2.2 Weighing Machine — — — — — — — — 20
3.2.3 Compression Machine — — — — — — — 20
3.3 Concrete Mix Proportioning — — — — — — 21
3.4 Test Methods — — — — — — — — 22
3.4.1 Sieve Analysis — — — — — — — — 22
3.4.2 Slump Test — — — — — — — — — 22
3.4.3 Cubes Casting — — — — — — — — 23
3.4.4 Compressive Strength Test — — — — — — 23
CHAPTER FOUR: RESULTS AND DISCUSSIONS
4.0 Introduction — — — — — — — — — 24
4.1 Sieve Analysis Results — — — — — — — 24
4.2 Slump Test — — — — — — — — — 25
4.3 Compressive Strength — — — — — — — 26
CHAPTER FIVE: CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion– — — — — — — — — 28
5.2 Recommendations — — — — — — — — 28
References
CHAPTER ONE
1.0 INTRODUCTION
Concrete can be considered as an artificial conglomerate stone. The generally used term of Portland cement concrete (Pcc) was named because the hardened cement resembles the color of natural limestone quarried near Portland, England (Neville, 2003). Such artificial stone is assembled from stone particles, that is, aggregates (fine and course), by a special adhesive, cement paste comprised of Portland cement powder and water. The main compositions of concrete are cement, water, fine aggregates (sands), coarse aggregates (rocks). The process of concrete typically includes proportioning, batching, mixing, placing, consolidating, finishing and curing. Then, the hardened concrete becomes a strong, non combustible, durable, abrasion-resistant and practically impermeable building material that requires little or no maintenance.
Concrete has been used for construction since ancient times. Modern day concrete application includes dams, bridges, air-ports, swimming pools, homes, streets, patios, basement, balustrades, plain cement files, mosaic tiles, pavement blocks, kerbs, camp-posts, drain covers, benches and so on. It is interesting to note that over six billion tons of concrete produced each year, and it is the second most widely used substance (Neville; 2003). Since concrete combines cement, aggregates (fine & course), and water as ingredient, the proportioning of these ingredients should be considered as great important to ant concrete producer so as to attain the desired characteristic strength.
Basically, the problem of designing a concrete mix consists of selecting the correct proportions of cement, fine and coarse aggregates and water to produce concrete having the specified properties. There are many properties of concrete that can be specified, example workability, strength, density, thermal characteristics, and elastic modulus and durability requirements. The properties most usually specified are:
- The workability of the fresh concrete
- The compressive strength at a specified age
- The durability, by means of specifying the minimum cement content or the maximum water/cement ratio, and in some case restricting the type of material to be used.
The mix design process must take into account the factors which may affect the workability and strength of concrete such as w/c ration, segregation. A properly designed concrete should have minimum possible cement content without sacrificing the concrete quality in order to make it an economical mix. Although cement constitutes only 7 to 15 percent of the volume of a concrete mix, it is however regarded as the most active portion of the binding medium and therefore must be considered to be the most important ingredient of the concrete.
Most of the time it is difficult to ascertain the quantity of cement content that will yield a concrete of a particular strength because of other parameters that are involve in the determination of the strength of concrete. Some of these parameters include the type of aggregate, the slump of the proposed concrete and the standard deviation of the producer. In this study, effort was made to determine the relationship between concrete strength and cement in concrete mixes.
1.1 Statements of the Problem
The main problem concrete producers faced when producing concrete is how to dentine the amount of cement content that will yield a concrete of a particular strength. Most of the time, the producers do not take into account the purpose in which the concrete will be used for and the desired strength expected at a specified age. Another worrying fact is the general processing of concrete which includes proportioning, batching, mixing, placing, consolidating, finishing and curing. If these processes are not adequately taken care of when producing concrete, the desired strength of concrete will not be obtained thereby resulting in failure of any structure in which the concrete is being used for. Upon this background, it became necessary to investigate the relationship between strength and cement content in concrete mixes. At the end of this study, the cement content in concrete mixes will be compared to the strength obtained which can be used by concrete producers to determine the proportion of cement content required in a mix to attainted the desired strength.
1.2 Aims and Objectives of the Study
The objective of this investigation is to determine the relationship between characteristic strength and cement content in concrete mixes. The study also intends to determine the effects of cement content on the workability of a fresh concrete using the method of slump.
1.3 Scope of Limitations of the Study
This work was confined to the following:
- The maximum aggregate size of 15mm (coarse aggregate) and 4mm (fine aggregate).
- Crushed coarse aggregate and uncrushed fine aggregate
- Test strength at 7 and 28 days
- Ordinary Portland cement produced by Unicem industry was used.
- Water/cement ratio of 0.5
- Five mixes were produced
1.4 Significance of the Project
This study which is the determination of relationship between strength and cement content in concrete mixes will be of help to concrete producers, consultants and contractors in determining the actual cement content needed in a particular concrete mix to obtain the required characteristic strength of concrete during the design and construction stages of projects.
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