COMPARATIVE ANALYSIS OF THE COMPRESSIVE STRENGTH OF CONCRETE WITH GRAVEL AND CRUSHED BURNT BRICKS AS COARSE AGGREGATES

CHAPTER ONE

1.0     INTRODUCTION

1.1     RESEARCH BACKGROUND

Concrete is a versatile engineering material consisting of cementing substance, aggregates, water and often controlled amount of entrained air. It is initially a plastic, workable mixture which can be moulded into a wide variety of shapes when wet. The strength is developed from the hydration reaction between cement and water. The products, mainly calcium silicates, calcium aluminates and calcium hydroxide are relatively insoluble which bind the aggregate in a hardened matrix. Concrete is considerably stronger in compression than in tension. For structures required to carry only compressive loads such as massive gravity dams and heavy foundations, reinforcement is not required and the concrete is consequently called plain concrete. When the structure is to be subjected to tensile stresses, steel bars are embedded in the concrete.

The requisite quantities of material for a given grade of concrete are usually obtained from mix design. The constituent materials, when properly batched and thoroughly mixed, set through the process of hydration and harden into a mass of concrete capable of resisting compressive stresses. The extent to which a given concrete resists the compressive stresses to which it is subjected depends largely on the compressive strength of the concrete which in turn depends on the quality of

the concrete. Since seventy five per cent of concrete is made up of aggregates, its types, quality and general properties determine the quality of concrete (Neville,

1995, Troxel et al, 1968).

1.2     RESEARCH PROBLEM

Concrete  is  one  of  the  most  widely  used  construction  materials.  The  raw material from which it is prepared: cement, aggregates and water affect both the quality and cost of construction. Aggregates are usually cheaper than cement and constitute over 70% of the volume of concrete. The availability and proximity of aggregate to the construction site also affect the cost of construction.

At present, the most commonly used coarse aggregates for concrete production in Benue State of Nigeria is river washed gravel due mainly to the presence of River Benue and its deposits. But these are not readily available in some local government areas which are not serviced by the river. Thus the cost of transporting gravel to the areas outside the catchment of the river tends to increase the cost of construction even at relatively low labour. This necessitates the use of alternative coarse aggregates which are locally obtained. One such coarse aggregate is crushed burnt bricks obtained from the production of burnt bricks (Maher, 1987).

1.3     SIGNIFICANCE

In many countries, the need for locally manufactured building materials can hardly be overemphasized because there is an imbalance between the demands for

housing and expensive conventional building materials coupled with the depletion of  traditional building materials.  To  address  this  situation,  attention has  been focused on low – cost alternative building materials (Agbede and Manasseh, 2008 and Waziri et al, 2011).

This research is  therefore important as it tries to compare the compressive strength of concrete made with the conventional gravel and crushed burnt bricks as coarse aggregates.

1.4     AIM AND OBJECTIVES

This research is aimed at finding out whether crushed burnt bricks can be substituted for gravel as coarse aggregates in the production of concrete. The objectives include:

i.     To determine the compressive strength of concrete with gravel and crushed burnt bricks or brick bats as coarse aggregates.

ii.     To determine the optimum mix ratio.

iii.     To compare the compressive strength of concrete with gravel and crushed burnt bricks as coarse aggregates.

iv.     To determine the effect of partial substitution of gravel with crushed burnt bricks as coarse aggregates on the compressive strength of concrete.

v.     To  develop  a  model  for  predicting the  compressive strength of  gravel- crushed burnt brick concrete.

1.5     SCOPE AND LIMITATIONS

This research is carried out on crushed burnt bricks produced from Naka, Benue State and river washed gravel from River Benue as coarse aggregates. The investigation is limited to the workability and compressive strengths of concrete cubes made from different mixes of sand, gravel and/or crushed burnt bricks, Benue Cement and water. The study does not cover the temperature at which burnt bricks will give optimum strength; neither does it cover the effect of admixtures on the compressive strength of crushed burnt bricks-concrete.

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