Among the construction materials; concrete, steel, timber and glass, concrete has gained popularity all over the world due to its durable properties in normal environment and easiest construction procedure. Compare to others constituent, cement performs a vital role for the production of concrete. Due to continuous increasing demand and the cost of cement, recently, the utilization of supplementary cementing materials such as industrial by-product (fly ash, silica fume and slag) and agricultural wastes (rice husk ash, palm oil fuel ash, bagasse ash and ash from timber) has become an important issue for the researchers in concrete industry. Fly ash (FA), one of these valuable industrial wastes, is generated as by-product from power generating industry. The production of FA increases every year, it is disposed for landfills without any commercial gain and now becomes a trouble. It contains a non-crystalline silicon dioxide with high specific surface area and high pozzolanic reactivity. Huge researches have been carried out for the use of pozzolans, mainly waste pozzolans such as FA, slag and rice husk ash, as a supplement of ordinary portland cement (OPC). Test results of compressive strength and durability of concrete from those previous researches ensured the use of FA as a pozzolanic material for cement replacement in concrete. In this paper, a critical review on the strength development of concrete as influenced by the use of FA as a supplement of cement in concrete has been presented on the basis of available information in the published literatures of utilization of FA in blended cement and concrete. The compressive strength of mortar and concrete as varied by the percent replacement and fineness of FA is discussed here. Physical and chemical properties, pozzolanic activity, normal consistency and setting time, strength activity index, advantages and disadvantages of using FA in concrete are also pointed out. Proper consumption of FA as pozzolanic material in concrete would be a useful step for the production of cost effective and more durable concrete. Besides, utilization of FA in cement and concrete could reduce negative environmental effect, and also would be the appropriate solution for the disposal of this waste.
Key words: Fly ash, mortar, concrete, compressive strength.
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