1.1 Introduction
The effects of aggregate type, size, and content on the behavior of normal and high-strength concrete, and the relationships between compressive strength, flexural strength, and fracture energy are discussed. The role of coarse aggregate in concrete is central to this report. While the topic has been under study for many years, an understanding of the effects of coarse aggregate has become increasingly more important with the introduction of high- strength concretes, since coarse aggregate plays a progressively more important role in concrete behavior as strength increases.
In normal-strength concrete, failure in compression almost exclusively involves debonding of the cement paste from the aggregate particles at what, for the purpose of this report, will be called the matrix-aggregate interface. In contrast, in high-strength concrete, the aggregate particles as well as the interface undergo failure, clearly contributing to overall strength As the strength of the cement paste constituent of concrete increases, there is greater compatibility of stiffness and strength between the normally stiffer and stronger coarse aggregate and the surrounding mortar. Thus, microcracks tend to propagate through the aggregate particles since, not only is the matrix-aggregate bond stronger than in concretes of lower strength, but the stresses due to a mismatch in elastic properties are decreased. Thus, aggregate strength becomes an important factor in high-strength concrete.
Flexure test results show that high-strength concrete containing basalt yields higher flexural strengths than concrete with similar compressive strength containing limestone. The flexural strength of high-strength concrete containing limestone is limited by the strength of the rock and the matrix. The flexural strength of high- strength concrete containing basalt is controlled by the strength of the rock and the interfacial strength at the matrix-aggregate interface. The flexural strength of normal- strength concrete containing the basalt or limestone used in this study is not affected by aggregate type, and is limited by the matrix strength and the strength of the interfacial transition zone. The flexural strength of normal and high-strength concrete is not affected by aggregate size. Normal and high-strength concretes containing basalt yield higher flexural strengths with higher coarse aggregate contents than with lower coarse aggregate contents.
As a prelude to other parts of this study, this chapter will discuss the background upon which this study was initiated, the statement of problems that led to this study, the Aim and Objectives of the study. Others are Significance of the study, Scope of work, Research hypothesis and questions, Limitations of the Study and Definition of technical terms.
1.2 Statement of Problems
Compression test results show that high-strength concrete containing basalt produces slightly higher compressive strengths than high-strength concrete containing limestone, while normal-strength concrete containing basalt yields slightly lower compressive strengths than normal-strength concrete containing limestone. The compressive strength of both normal and high-strength concrete is little affected by aggregate size. High-strength concrete containing basalt and normal-strength concrete containing basalt or limestone yield higher compressive strengths with higher coarse aggregate contents than with lower coarse aggregate contents. The compressive strength of high-strength concrete containing limestone is not affected by aggregate content.
1.3 Aim and Objectives of Study
The aim of the study is to examine the Effect of Coarse Aggregate Sizes on Concrete. In achieving this aim, the following specific objectives were laid out as follows:
- To determine the aggregates in concrete and the variables considered which are aggregate type, aggregate size, and aggregate content in normal and high-strength concretes.
- To examine the role that coarse aggregate plays in the compressive, tensile, and fracture behaviors of concrete.
1.4 Significance of Study
This study will be of immense benefit to civil engineers, and other researchers who intend to know more on this study and can also be used by non-researchers to build more on their research work. This study contributes to knowledge and could serve as a guide for other study.
1.5 Scope of Study
The study focuses on the Effect of Coarse Aggregate Sizes on Concrete in Nigeria Construction Site.
1.6 Limitations of the Study
During the course of this study, many things militated against its completion, some of which are:
- Time Constraint: The time frame given to accomplish this project was very short due to school academic calendar and it was carried out under pressure which made the researcher not to implement some necessary features.
- Research material: availability of research material is a major setback to the scope of the study.
- Frequent power failure: This made the researcher append more money on fuel to ensure sustainable power.
- Financial Constraint: Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet).
