An Investigation Into Quality of Aggregate in Road Construction
Chapter One
AIM AND OBJECTIVES OF THIS STUDY
THE GENERAL AIM AND OBJECTIVES OF THIS STUDY IS AS FOLLOWS
1. To identify the key factors affecting the strength of aggregate structure which are aggregate shape, angularity and texture.
2. To ensure that the specifications for aggregate angularity are included in the super pave mixture design system.
3. To obtain a material sufficiently durable to last the design life of the road so that its performance is not affected by deterioration or degradation of the material.
4. To determine the aggregate abrasion resistance and breakdown of particles and tests that address aggregate weathering when exposed to freezing and thawing.
5. To determine the different properties of aggregates
6. To examine the different quality plans or system for controlling the sources of aggregate.
CHAPTER TWO
LITERATURE REVIEW
INTRODUCTION
The literature review is presented in this chapter to show the originality and relevance of the research problem. This literature review has created a rapport with existing information by sharpening its research focus on literature that has maximum research output value. The key areas chosen are affiliated to:
- Understanding of the pavement structure, load conditions and pavement designing procedure
- Review the classification test methods to define the properties of pavement material
- Understand the behaviour of pavement materials under repeated loading conditions and influencing factors on the performance characteristics
- Review the specifications for pavement materials and the development of using recycled materials in pavement industry
- Develop an understanding of recycled concrete aggregates, discuss the sustainable outcomes by using recycled concrete aggregates in constructions
Different pavement types and the role of each layer in pavement structures are detailed in sections 2.2 and 2.3 to develop an understanding the base of the research field. The laboratory classification methods of determination of the properties of pavement materials and their performance evaluation tests are discussed in sections 2.4 and 2.5. The industrial practice in recycled materials and recycled concrete aggregates are discussed together in Sections 2.6 to 2.8.
The summary is drawn in section 2.6 with an understanding of the research gap, and the requirements for investigation of the capability of using recycled concrete aggregates in the road construction industry.
PAVEMENT TYPES
Pavement is a layered structure that consists of selected materials in different layers. Pavements perform as an engineering structure to meet functional requirements of traffic loads. Thickness of the layers, quality of the materials, and load sustained are considered as structural performance of a pavement to facilitate a comfortable ride under various loads of vehicles (Sharp and Group 2005).
Pavements are being constructed under two categories, as either rigid or flexible. Rigid pavements typically consist of a high strength concrete layer placed over the subgrade (natural ground or man-made earth works) with or without middle layers. Figure 2.1 illustrates a typical section for a rigid pavement. Rigid pavements are substantially stiffer than flexible pavements due to the high modulus of elasticity of the concrete material, resulting in very low deflections under loading(Youdale and Sharp 2007).
The literature covers more on flexible pavements in detail, in the following sections, since the studied materials are to be used as granular materials in flexible pavements.
CHAPTER THREE
RESEARCH METHODOLOGY
The research design was a cross-sectional descriptive survey type. The study plan involved the use of both qualitative and quantitative method of data collection.
AREA OF STUDY
Enugu, usually referred to as Enugu State to distinguish it from the city of Enugu, is a state in Southeastern Nigeria, created in 1991 from part of the old Anambra State. its capital and largest city is Enugu, from which the state derives its name, the principal cities in the state are Enugu, Ngwo, Agbani and Awgu.
Materials and test specimens
ASTM C150 Type I Portland cement, with the chemical composition shown in Table 1, was utilized in preparing the concrete specimens. Four types of coarse aggregates, namely calcareous limestone (CC), dolomitic limestone (DL), quartzitic limestone (QZ), and steel slag (SS), were utilized to prepare the concrete mixtures. The physical properties of the coarse aggregates selected for this study and their grading are shown in Tables 2 and 3, respectively, while the quantity of clay lumps in the selected coarse aggregates are shown in Table 4.
CHAPTER FOUR
RESULTS AND DISCUSSION
Effect of aggregate quality on compressive strength of concrete
The effect of aggregate quality on the compressive strength of concrete was evaluated by testing concrete specimens prepared with CC, DL, QZ and SS aggregates. Fig. 2 shows the variation of compressive strength with age for the concrete specimens prepared with the four types of aggregates selected for this study. As expected, the compressive strength increased with age in all the concrete specimens. Further, the data in Fig. 2 indicate that the type of coarse aggregate has a significant effect on the compressive strength of concrete. The highest compressive strength was measured in the concrete specimens prepared with the steel slag aggregates while the lowest compressive strength was noted in the concrete specimens prepared with calcareous limestone aggregates.
CHAPTER FIVE
Conclusions
The quality of coarse aggregate has a significant effect on the compressive strength of high strength concrete. The compressive strength of steel slag aggregate concrete was more than that of crushed limestone aggregate concrete. The compressive strength of concrete prepared with calcareous limestone aggregate was the least. These data indicate that in a high strength concrete, i.e. concrete prepared using a low water– cement ratio and high cement content, the compressive strength is dependent on the quality of aggregate. In such concrete, the bulk of the compressive load is borne by the aggregate rather than the cement paste alone.
The failure in such concretes is often through the aggregates. Since the calcareous limestone is known to be weaker than the dolomitic and quartzitic limestone aggregates, its low load carrying capacity is understandable.
Split tensile strength increased with age in all the concrete specimens. The type of aggregate also influences the split tensile strength of concrete. The split tensile strength of steel slag aggregate concrete was more than that of limestone aggregate concrete. The least split tensile strength was noted in the calcareous limestone aggregate concretes. The quality of coarse aggregate also influences the modulus of elasticity of concrete. Weaker aggregates tend to produce a more ductile concrete than strong aggregates do, in the construction of roads.
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