Studies on the Properties of Fly Ash–Rice Husk Ash-Based Geopolymer for Use in Black Cotton Soils

Expansive soils are found in many parts of the countries like India, Australia, Ethiopia, Sudan and USA in the form of black cotton soil (BCS). The distress induced by swelling and shrinkage behavior of black cotton soil results in millions of dollars of damage to the construction industry each year. In this study, experimental investigations are carried out for the stabilization of BCS using fly ash (FA) and rice husk ash (RHA)-based geopolymer. For this purpose, a mixture of sodium silicate (SS) and sodium hydroxide (SH) mixed in the ratio of 1.5 is used as the alkaline activator solution. A mixture of FA and RHA (mixed in weight percentage of 100:00, 75:25, 50:50, 25:75, 00:100) is used as the precursor and is referred as blended ash (termed as FARHA) in this paper. Stabilization potential of the geopolymer is determined by conducting unconfined compressive strength test, free swell ratio (FSR) test and shrinkage limit test on the stabilized specimens. Attempts are also made to establish the effects of varying the quantity of FARHA (5, 10, 15, and 20%) and curing period on strength properties of BCS. X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier Transformed Infrared Spectroscopy (FTIR) studies were conducted to analyze the micro-level changes due to geopolymerization. Results obtained from the experiments indicate that the geopolymerization significantly improves the strength of BCS and at the same time makes it less prone to swelling and shrinkage. Thus, BCS stabilized with blended ash geopolymer can be used as a sustainable alternative to conventional stabilizers.