The Influence Of Bagasse Fly Ash Particle Size In Controlling Expansive Soils In Combination With Hydrated Lime

Thang Le, Sachit Desa and Hadi Khabbaz

Sugarcane is the second largest export crop in Australia. Industrial production of sugar, from sugarcane, results in bagasse fly ash (BFA), a by-product from the cogeneration in sugar milling operations that generate electricity by steam. The chemical and physical properties of BFA highlight its potential as a promising pozzolan for the stabilization of expansive soils, due primarily to a high content and surface area of the amorphous silicate found in BFA. Silicate in bagasse fly ash reacts extensively with calcium hydrate in lime to produce hydrated products via pozzolanic reactions, this results in a hardening of the material to which BFA and lime have been added. This reaction has been studied to be a function of the size of BFA particles and conditions of the curing process.

This study explored the variables that influence the reaction and evaluated shrinkage and compressive strength of the mixtures to which bagasse fly ash, in the form of different particle size distributions, and hydrated lime are added. The maximum BFA particles sizes considered within this study include 75, 150 and 425 μm; curing times of 7 and 28 days are also explored. A suite of testing, including Atterberg limits, linear shrinkage (LS), and unconfined compressive strength (UCS) tests were completed on the prepared mixtures. The findings indicate that bagasse fly ash with a maximum size of 425 μm yields a higher UCS and lower LS, compared to finer BFA particle mixtures. The ash with a maximum particle size of 425-μm also improves the ductility of treated soils and accelerates their strength gain, compared to soil- lime stabilized samples. The results of the study build towards a better understanding of BFA, and the ways in which such a material maybe engineered to replace concrete in road work projects and other applications involving expansive soils.