Chemical stabilization of rammed earth using calcium carbide residue and fly ash

Rammed earth has been considered as a sustainable construction technique that uses local soil to build structural walls. However, some natural soil do not have adequate strength and must be treated in order to improve their engineering properties. Chemical stabilization is a recent technique for this purpose and Portland cement is the most commonly used binder material. In the current study, industrial by products such as calcium carbide residue (CCR) and fly ash (FA) are investigated as binders instead of hauling them to landfills. Two different ratios of binders (CCR:FA = 40:60 & CCR:FA = 60:40) at five different binder contents (3%, 6%, 9%, 12% & 15%) were utilized to investigate strength properties of a model soil. Based on the CCR and FA ratios, soil specimens were grouped as A and B. The unconfined compressive strength (UCS) for both groups was tested after four different curing times (3, 7, 28 & 60 days). The UCS values of Group A specimens showed better performance at 12% binder content, whereas, Group B specimens showed an improved strength behavior at 15% binder content for all curing conditions. Also, results of SEM images for Group A specimens at 12% binder content indicated formation of a more integrated soil matrix with reduced soil voids and therefore, significant improvement of the soil strength.