Experimental Investigation of Mixture Design and Durability Performance of Alkali-Activated Rammed Earth

Abstract

This study investigates the utilization of alkali-activated granular blast furnace slag (GBFS) and fly ash (FA) for stabilizing rammed earth materials and assessing their mechanical and durability properties. Twenty mixtures were designed using the central composite design (CCD) of response surface methodology (RSM). The clay content of the soil, NaOH molarity, and GBFS to the binder ratio were selected as independent variables. Density, water absorption, 28-day compressive strength, and compressive strength loss after 60 days of exposure to sulfuric acid were measured as responses. Also, the microstructure of the specimens and the effects of the sulfuric acid attack were investigated by SEM and XRD analysis. The results revealed that an increase in the clay content of the soil reduced the compressive strength of specimens. Also, higher content of FA than GBFS in binder led to more acid-resistant specimens for mixtures containing a low amount of kaolin clay. On the other hand, for specimens with a high amount of kaolin clay, a higher proportion of GBFS than FA in binder resulted in more acid-resistant specimens. In addition, an increase in NaOH molarity and GBFS content in the binder was accompanied by an improvement in compressive strength. SEM investigations showed more homogenous and compact reaction products for these mixtures. Finally, a numerical optimization method was implemented to obtain mixtures with the highest compressive strength and minimum compressive strength reduction after acid exposure.