Effect of Alkali Silica Reaction (ASR) on Fly Ash based Geopolymer Incorporating Microwave Incinerated Rice Husk Ash (MIRHA) M.F. Nuruddin, S.N.A. Razak & S.A. Saad Universiti Teknologi PETRONAS, Perak, Malaysia ABSTRACT: This research reports the findings of an experimental investigation for alkali silica reaction (ASR) between geopolymer matrix and reactive aggregate. Geopolymer specimens were prepared using Class F fly ash with incorporation of Microwave Incinerated Rice Husk Ash (MIRHA) to replace a few percentage of fly ash content. Mechanical testing conducted were potential reactivity of the aggregates via length change as per ASTM C1260 standard test method and compression test. Test results appeared that the extent of alkali silica reaction (ASR) due to the presence of reactive aggregate in geopolymer specimens is lower and below the threshold limit of ASTM standard 0.10%. Furthermore, exposure of geopolymer specimens in external sodium hydroxide (1M) solution increase the rate of polymerization and consequently, it increased the mechanical strength of geopolymer specimens. Utilizing reactive aggregate in the production of gepolymer concrete could contribute towards sustainable and economical construction approach. 1 INTRODUCTION Development of new environmental friendly construction material which possesses equal attributes as conventional concrete has been done for the past three decades. Durability is a major concern for conventional concrete made from Portland cement. Even though Portland cement has good strength, but its durability shows some concern in some of the exposure conditions. Alkali silica reaction (ASR) is one of the concerns mention above for Portland cement. Alkali silica reaction (ASR) is a chemical reaction which occurs in concrete between the highly alkaline cement paste and reactive silica in aggregate. This reaction lead to expansion of the aggregate by the formation of a swelling gel called alkali silicate gel. This gel can cause serious expansion as it imbibes water with a consequent tendency to increase in volume (Neville, 1996). While it increases in volume with water, it exerts an internal pressure inside the concrete matrix, causing spalling and loss of strength of the concrete. Hence, the concrete failed (Winter, 2009). Three requirements must be met for ASR to occur which are 1) reactive forms of silica or silicate in the aggregate, 2) sufficient alkali (sodium or potassium) from cement and 3) sufficiently available moisture in the concrete. If these three requirements are not met, expansion due to ASR will not occur (Helmut and Stark, 1992). The reactive aggregates can be found in many common aggregate which contains reactive amorphous silica such as opal, tuff, cristobalite, quartz and etc. In alkaline environments, these forms of silica are susceptible to attack and greatly lead to the dissolution of the aggregate (Swamy, 1992). Low alkali cements used to prevent ASR often contain fly ash and granulated blast furnace slag (GGBFS). Supplementary Cement Material (SCM) such as silica fume was found to be effective in mitigating the ASR. Class F and C fly ash pozzolan works effectively in mitigating or reducing expansive reaction resulting from ASR when 30% of Portland cement is replaced by mass. Research of SCM using rice husk ash has been developed to investigate its performance when being mixed with cement. The use of rice husk ash in combination with cement in appropriate mixture produces better concrete composite (Bakri et al., 2009). Rice husk ash has been used a reactive pozzolan material to enhance the concrete properties and it’s improved the strength and durability of the concrete. (Bakri et al., 2009). It has been reported that rice husk ash is beneficial in reducing n alkali silica reaction. This is due to rice husk ash produce less expansive alkali silica gel from the reaction with the alkalis released from the cement hydration (Sensale, 2010). In 1978, Joseph Davidovits, a french material scientist, had develop an amorphous three dimensional alumina-silicate materials, which called