Microstructure, 3-chemical moduli (3CM) and micro-spectral analyses of HSDA-treated black cotton soil for sustainable subgrade construction

Abstract

Microstructural, 3-chemical moduli (3CM) and micro-spectral analyses has been carried out in this research work on HSDA-treated black cotton soil for sustainable subgrade construction. Black cotton soil (BCS) is considered problematic and incapable of withstanding axial load due to its erratically swell-shrink behavior on exposure to moisture. Sadly, hydraulically bound structures like the subgrade of highway pavement foundations are seasonally exposed to moisture through suction or capillary rise as the water table rises. So, the effect of treatment on the surface configuration, oxide composition and micro-graphical arrangement of the BCS has been studied. The BCS was characterized and classified as A-7 group soil with high plasticity and poorly graded condition. Sawdust ash was obtained by combusting sawdust and sieving through 2.35 mm aperture sieve. It was further activated by blending it with pre-formulated activator material (a blend of 8 M NaOH solution and NaSiO2 in 1:1 ratio) to generate HSDA. The HSDA was further used in wt % of 3, 6, 9, and 12 to treat the BCS. The treated samples were studied to their structure changes, 3-chemical moduli, and micrograph changes. XRF and SEM tests were conducted to determine the pozzolanic strength via the chemical oxide composition, 3-chemical moduli (3-CM) and the microstructural arrangement of the experimental materials and the treated BCS. The XRF tests showed that the experimental materials had less pozzolanic strength, which improved with the treated blends thereby forming stabilized mass of BCS. Also, it showed the silica moduli of the 3-CM dominated the stabilization of the soil with HSDA. SEM tests showed increased formation of ettringite and gels with the addition of the HSDA. Also, the ED-XRF chemical oxide and XRD micro-spectral studies showed great outcome at 12 wt% of HSDA and BCS blend with high formation of aluminosilicates above 70% and the formation of quartz and calcite, which showed HSDA potential as good supplementary cement.