Concrete is a composite engineering material made from the mixtures of cement, water, fine aggregate (sand), coarse aggregates (such as crushed stones or rocks and granite) and a small amount of air in a specific proportion that hardens to a strong bony substance or become ossified. The cement always serves as a binder for the aggregate.
The uniqueness quality of concrete makes it desirable as a building material, because it can be moulded into virtually any shape or form. Concrete provides a wide latitude in surface textures, such as large buildings, bridges, dams, highways, roadways hydraulic structures, silo, farm building etc.
Concrete can be broadly classified as normal weight aggregate concrete and light weight aggregate concrete based on the density of the concrete. The density of concrete varies with the amount and density of its constituents (the coarse aggregate, fine aggregate, water cement ratio and sometimes entrapped air). A normal weight aggregate concrete has a density of approximately 2400kg/m3 while a light weight aggregate concrete contains natural or artificial aggregate unit with density usually less than 2000kg/m3. Light weight concrete has been successfully used in buildings for over 80 years. However, as report of moisture- related flooring problems have escalated in the past
decades, the drying time of light weight concrete has attracted much attention. A key issue is the volume of water in light weight concrete. It is a standard practice to pre-soak light weight aggregate before batching
Concrete has relatively high compressive strength, but much and significant lower tensile strength and such is usually reinforced with material that are strong in tension. There are different types of concrete mix design. The mix design depends on the types of structure been built, how the concrete will be mixed and delivered and how it will be placed to form this structure. As concrete matures it continues to shrink, due to the ongoing reaction taking place in the material, although the rate of shrinkage falls relatively quickly and keeps reducing over time (for all practical purpose, concrete is usually considered not to shrink due to hydration any further after thirty years). The relative shrinkage and expansion of concrete and brick work require careful accommodation when the two forms of construction interfere. Generally concrete has a very low coefficient of thermal expansion and shrinks as it mature.
Concrete mixes are usually specified in terms of dry volume ratios of cement, sand (fine aggregate) and coarse aggregate used. A 1:1:1 mixes for instance, consist of one part by volume of cement, one part of sand and one part of coarse aggregate. Depending on the applications, the proportion of the material in the concrete can be altered to produce specific changes in its properties, particularly strength and durability. The mix ratio of 1:2:4 by dry weight not by dry volume and the amount of water cement ratio added to this mixes are, 0.3, 0.4, 0.5, 0.6, and 0.7 times the weight of the cement. For high strength concrete, the water content is kept low with just enough water added to wet the entire mixture. In general, the more water in a concrete mix, the easier it is to work with, but the weaker the harden concrete becomes. (Microsoft Encarta premium, 2009)
Large amount of agricultural waste was disposed in most of tropical countries, for countries like Thailand, Philippine, Nigeria and Malaysia. If the waste is not disposed properly, it will lead to social and environmental problems. The high cost of conventional construction materials is a major factor in the delivery of construction in the country. To limit the cost of construction in Nigeria, the government has advised the use of local materials in the construction industry. This has necessitated research into alternative materials of construction. Recently the use of recycled materials as concrete ingredients has been gaining popularity because of increasingly strict environmental legislation.
The most popular way of achieving light weight concrete production is by using lightweight aggregate (LWA) (Polat et al, 2010). Lightweight aggregate concrete (LWAC) is not a new invention in concrete technology; it has been used since ancient times. LWA may be subdivided into two groups: those that occur naturally and those that are manufactured. The main natural LWAs are diatomite, pumice, scoria, volcanic cinders and tuff (Neville and Brooks, 2008). An alternative LWA in tropical region and countries that have a palm oil industry is oil palm shells (OPS), sometimes called palm kernel shells (PKS). The use of PKS as a lightweight aggregate or porous aggregate in producing lightweight concrete was researched early in 1985 by Salam and Abdullah (1985) in Malaysia. The oil palm industry is important in many countries such as Malaysia, Indonesia and Nigeria. Malaysia is one of the world leaders in the production and export of palm oil (Subramanian et al, 2008) and contributes about 57.6 percent of the total supply of palm oil in the world (Ahmed et al, 2010).