CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
Concrete is a composite material which consists of cement, fine aggregate (sand), coarse aggregate (gravel or granite) and water in a certain prescribed proportion. The most dominant construction material is concrete and the most collapse structures are concrete structures. A number of researches (Ayininuola and Olalusi, 2004; Ede, 2010 and 2011) have identified the use of substandard materials, particularly concrete as the leading cause of building collapse in Nigeria. Concrete failure still occurs despite adequate design and mix ratio. This advocates the existence of a breach in requirement for production of quality concrete. Previous works confirm the use of inferior concrete aggregates materials as among the causative elements of structural concrete failure in buildings. Gollu et al. (2016) mentioned unsuitable materials, unsound aggregate, reactive aggregate, and contaminated aggregate as part of the sources of concrete failure in buildings. Akinleye and Tijani (2017) stated that the use of low quality aggregates also affect the performance of asphalt concrete in Southwest Nigeria. Concrete will only become a quality material for construction when its constituents are properly sourced. The quality of aggregate can vary significantly due to the geographic location and environmental condition (Ajagbe et al., 2018).
Fowler and Quiroga (2003) reported that aggregates are expected to have important effects on the properties of concrete since they occupy 70-80% of it. Concrete aggregates and paste are the major factors that affect the strength of concrete (Shetty, 2005), the properties of aggregate greatly affect the durability and structural performance of concrete as aggregate with undesirable properties cannot produce strong concrete (Neville, 2011). It is not necessarily true that aggregate whose properties all appear satisfactory will always make good concrete, and this is why the criterion of performance in concrete has to be used. According to Mehta and Monteiro (2001), the aggregates exercise a significant influence on strength, dimensional stability, and durability of concrete. Ajagbe and Tijani (2016) stated that assessment of concrete aggregate is vital to overcome the problem of structure collapse due to concrete failure in a certain environment. De Larrard (1999) and Dewar (1999) agreed that the aggregate source has an impact on concrete strength. Concrete strength is govern by aggregate size, type and source (Hassan, 2014: Aginam et al., 2013; Jimoh and Awe, 2007; Abdullahi, 2012).
Compressive strength is the most significant mechanical property of concrete. It is obtained by measuring concrete specimen after curing for 28days. Some of the factors that influence the concrete strength include aggregate quality, cement strength, water content and water/cement ratio (Noorzaei et al., 2007).
The incessant collapse of building in Nigeria and its associated loss of life, loss of properties and injuries to the survivors of collapsed building incidents have become worrisome to the extent that the Council for the Regulation of Engineering Practice in Nigeria (COREN) has recently advocated for a death penalty for the owners of collapsed buildings. Poor quality of materials has accounted for more than 50% of causes of building collapse in Nigeria (Oke, 2011). Ajagbe et al. (2015) stated that provision of necessary information to local concrete industry and practitioners regarding the application of aggregates from different sources will prevent selection of substandard aggregates for concrete. According to Ayininuola and Olalusi (2004) and Ede (2011), the use of substandard materials for concrete is the leading cause of building collapse in Nigeria. Therefore, an examination of the strength of concrete made from aggregates obtained from different sources in Nigeria is required to overcome the problem of building collapse due to concrete failure.
Investigation of the compressive strength of concrete produced from aggregates obtained from different quarries from different locations in Nigeria is the main focus of this paper. The study will use the aggregate of the same size, utilize cement of the same strength, water content and water/cement ratio in order to determine the influence of aggregate source quality on concrete strength.