Impact of field conditions on the strength development of a geopolymer stabilized marine clay

A soft marine clay was stabilized with fly-ash (FA) and slag (S) based geopolymers. FA and S with combined contents of 10, 20 and 30% were added to the soft clay and activated with a liquid alkaline activator (L) at various contents. The clay was a marine clay which was dominated by quartz, illite and feldspar. The effect of a number of preparation and curing factors including water content and temperature variation, wetting-drying cycles and mixing time and method were evaluated. The objective of this research was to evaluate the effect of these factors that are likely to occur in ground improvement applications, such as deep soil mixing, on the unconfined compressive strength (UCS), microstructure and mineralogy of the mixtures. Results showed that increasing the FA + S content increased the UCS values significantly through the geopolymerization process, which was evident when increasing the FA + S content from 10% to 20%. Moreover, higher UCS values were achieved when the curing temperature was increased and the strength development was accelerated as a result of accelerated precipitation of FA and S. Furthermore, strength development was enhanced when the L/(FA + S) ratio was increased from 0.75 to 1.0, followed by a decrease at L/(FA + S) ratio of 1.25. Similar trends of strength development were observed by varying the water contents of 0.75, 1.0 and 1.25 liquid limit (LL) of the soil. The increased amount of liquid, L and water, caused less favorable environment, such as lower L molarity and less particle contact, for proper strength development. The UCS values decreased for up to 6 cycles of wetting and drying, where the geopolymeric network was not sufficiently stable, and remained almost constant afterwards. Increasing the mixing time caused more dissolution of FA and S, which resulted in enhancement of the UCS values. Adding FA + S and L to the soil separately resulted in higher UCS values compared to when FA + S and L were mixed together initially and then added to the soil. The microstructure and mineralogy analyses indicated that increasing the curing temperature, as well as the L/(FA + S) ratio resulted in more dissolution of FA and S and formation of calcium sodium aluminum silicate hydrate (CNASH) products.