Rice husk ash (RHA) is a by-product of rice millingindustry.
It is obtained by burning the husks of rice paddy The controlledburning of rice husks between 500 and 800°C produces non-crystalline amorphousRHA (Mehta and Monteiro, 1993; Malhotra, 1993). It is whitish or grey in color.The particles of RHA possess cellular structure with a very high surface area.RHA has 90–95% amorphous silica (Mehta, 1992). It possesses excellentpozzolanic activity due to high surface area and high silica content.After Mehta’s findings in 1973 (Mehta, 1992), the useof RHA in construction materials was accelerated.
According to Givi et al.(2010), RHA can be used in mortar and concrete with a good workability. Ismailand Waliuddin (1996) made high-strength concrete with RHA.
Moreover, Zhang andMalhotra (1996) produced highperformance concrete using RHA as a supplementarycementing material. As a part of composite cement, RHA can be used to producenormal-strength selfconsolidating concrete (Nehdi et al., 2004). It can also beused for producing self-consolidating high-performance concrete with improvedhardened properties and durability (Safiuddin, 2008). The use of RHA decreasesthe porosity, and thus improves the compressive, tensile and flexural strengthsof concrete. RHA also improves the corrosion resistance and freeze-thawdurability of concrete (Zhang and Malhotra, 1996). RHA can also be usedsuccessfully in other construction materials such as bricks and blocks withoutany degradation in the quality of products (Nasly and Yassin, 2009).
Rahman(1988) reported that the compressive strength of bricks is increased in thepresence of RHA and therefore recommended the use of RHA bricks in load-bearingwalls. He also showed that the absorption capacity of RHA bricks lies withinthe permissible limit (Rahman, 1988). Nasly and Yassin (2009) used RHA to develop innovative interlocking blocks for use insustainable housing. They also obtained good compressive strength for theblocks incorporating RHA. Furthermore, Lertsatitthanakorn et al.
(2009) showedthat the RHA based sand-cement blocks reduce solar heat transfer, and thusresult in a decreased room temperature due to lower thermal conductivity thanthe commercial clay bricks.