Chemical stabilization of soft Bangkok clay using the blend of calcium carbide residue and biomass ash

The blend of calcium carbide residue (CCR) and biomass ash (BA) required as a stabilizing chemical additive which causes a pozzolanic reaction was investigated. The dissolution of CCR in water generated calcium hydroxide, Ca(OH)2. This high pH solution (pH=12.6) dissolved the amorphous Si from BA and resulted in pozzolanic products. Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD) analyses indicated the existence of ettringite and non crystalline phase calcium silicate hydrate (C-S-H) after 7 days of curing. The strength development of stabilized clay with a CCR and BA blend is influenced by the interrelationship of various factors, including the binder content, the water content and curing time. From two factorial experiments, the strength of stabilized clay at specific curing time and initial water content was the function of the CCR content, the BA content and their combined effect. When the initial soil water content was constant at 1.2 and 1.4 times the optimum water content (OWC) and the binder contents ranged from 5% to 30% of the dry weight of soil, the strength depended on the clay water–binder ratio(wc/B)(wc/B) and the curing time. The plot of the strength development ratio and curing time on a logarithmic scale revealed that the blend of CCR and BA rendered a different chemical reaction from cemented clay and fly ash (FA) and BA blended cement admixed clay. The strength development ratio of stabilized clay with a CCR and BA mixture exceeded those of cemented clay and FA and BA blended cement admixed clay after 28 days of curing due to the progress of the pozzolanic reaction.