A new low carbon cementitious binder for stabilising weak ground conditions through deep soil mixing

Soft alluvial soils present unfavourable conditions for engineering developments due to their poor bearing capacities and high potential for experiencing shrinkage and swelling. This paper focusses on deep dry soil mixing (DDSM), which introduces cementitious binders to soft soils via a rotating auger drill, thereby producing soil-cement columns. Ordinary Portland cement (CEM-I) is globally used across the construction industry and is the most commonly used binder for DDSM applications due to its high strength performance. However, CEM-I production is one of the world׳s most energy intensive and expensive industrial processes, contributing 5-7% of the world׳s total CO2. There is now significant pressure on the cement and construction industries to greatly reduce their CO2 emissions by developing “greener” alternatives to CEM-I, which are both more environmentally and financially sustainable in the long-term. Alkali activated industrial by-products (IBP׳s) such as ground granulated blast furnace slag (GGBS), known as geopolymers have been identified as potential alternatives. These are advantageous due to negating the need to transfer IBP׳s to landfill, their abundance, negligible or zero production costs. Geopolymers are capable of reducing greenhouse gas emissions by up to 64%. Calcium-bearing slags have also been found to possess potential for carbon capture and storage (CCS). Comparisons with the strength and durability of untreated and stabilised soils have been made in this study. Results indicate that stabilising an alluvial soil with sodium hydroxide (NaOH) activated GGBS produced significant strength and durability improvements surpassing CEM-I. The addition of NaOH allowed pozzolanic reactions to occur, leading to improved mechanical properties with time, with a particularly marked improvement in strength.