Mechanical and microstructural study of slag based alkali activated concrete incorporating RHA

The objective of the present research is to evaluate the effect of incorporation of rice husk ash (RHA) into ground granulated blast furnace slag (GGBS) based alkali activated concrete (AAC) at ambient temperature to develop a cement free binder that composed of waste products. The hardened properties of AAC have been evaluated in accordance with Indian Standard code in terms of destructive tests such as compressive, splitting tensile and flexural strength, as well as non-destructive tests such as rebound number, ultrasonic pulse velocity (UPV) and dynamic modulus. Using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR), the microstructural characteristics of AAC mixes were evaluated. The outcomes of the test indicate that the compressive strength of AAC achieves maximum strength when RHA component of up to 10% is incorporated into the AAC mixture. The compressive strength declined beyond 10% RHA, however the AAC has lower strength of 39.5 N/mm2 (M7 mix at 7 days) among all mixes, which was adequate for the structural applications. Corresponding to compressive strength, the split tensile and flexural strengths exhibit similar performance. Statistical analysis also carried out to determine the correlation between different parameters. The SEM test shows the formation of dense microstructure at a lower percentage of RHA content in the mix, whereas cracks and voids were detected in case of a higher percentage of RHA. Therefore, using GGBS with lower RHA content as binder cured at ambient temperature enhances the performance of AAC and also facilitates the use of AAC instead of ordinary concrete.