The influence of guanidinium hydrochloride on Enzyme Induced Carbonate Precipitation

Abstract

In order to enable the use of Enzyme Induced Carbonate Precipitation (EICP) as a ground im-
provement technique in fine grained soils, the use of guanidinium hydrochloride (GndHCl) as a clay swelling inhibitor has been explored recently by Wennubst-Pedrini (2022). Guanidinium aggregates the clay by binding to the double layer of clay minerals. In that way, the particles become chemically and physically stable. However, it has been suggested that GndHCl as an additive has an effect on the calcium carbonate crystal sizes and polymorphs produced during EICP. However, the exact effect of guanidinium on calcium carbonate precipitation remains unclear. This study sets out to elucidate these effects. This study shows that the addition of GndHCl into the system strongly alters its starting pH from 8 to 4, leading to some samples not precipitating any calcium carbonate as the carbonate equilibrium was towards bicarbonate (HCO 3 ). However, the samples that did produce crystalline calcium carbonate, produced a comparable amount of about 0.65g per sample of the same polymorph (calcite), although crystal size was smaller. The morphology of the produced crystals suggested that guanidine altered the calcite production pathways. This study could not reproduce the promising results found by Wennubst-Pedrini (2022) and as such more research into the role of guanidinium in the EICP process is recommended. The promise that guanidine may hold in order to make EICP a market-ready technique in finer grained soils is worth further exploration.