This research explains the results of an investigation carried out to understand the influence of a microwave incinerated rice husk ash (MIRHA) powder on foamed concrete (FC) hydration. The experimental work was designed using the Taguchi approach. This method was selected to have a target for the optimum working conditions of the parameter that affects some physical properties of concrete mixtures. The loss on ignition (LOI) method was used to establish the nonevaporable water ( ) content at all selected ages of hydration. It was observed that the MIRHA powder showed lower nonevaporable water contents than the normal FC, indicating that MIRHA powder facilitated enhancement in FC hydration. The optimum FC properties were achieved at 10% MIRHA composition as proven from the highest compressive strength. This level corresponds to the highest values in change in nonevaporable water and degree of hydration. 1. Introduction Rice husks are by-products of paddy milling industries that attract attention due to their environmental issues [1]. Large amounts of rice husks are being produced annually in Malaysia almost reaching 2.2 million tons and the total annual world production is about 710 million tons [2]. Rice husk has large dry volume due to its low bulk density (90–150？kg/m3) and possesses rough and abrasive surfaces that are highly resistant to natural degradation. That is why disposal of rice husks has become a challenging problem [1]. Therefore, from the viewpoint of environmental issues, how to improve rice husk and how to recycle rice husk have become very important environmental protection subjects. In recent years, various researchers [3–5] have investigated the use of microwave incinerated rice husk ash (MIRHA) in construction materials. Improper burning of rice husk cannot extract maximum amount of amorphous silica; therefore a correct burning procedure is vital to obtain good quality RHA that can contribute to the strength development and durability of concrete. In order to increase the reactivity, MIRHA was ground and sieved to a specific particle size. It was obtained that the inclusion of MIRHA could significantly improve the compressive strength of hardened concrete [4] while reducing the workability of fresh concrete [5]. MIRHA had positive effect in interfacial transition zone (ITZ) between aggregate and cement paste [4]. MIRHA decreases in the total porosity [6] caused the change occurring in the pore size distribution as a result of using RHA which could react with the calcium hydroxide to form C-S-H gel [7]. Controlled incineration of
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