Impact of sand surface coating on biocementation mechanisms

In biocementation, the overall degree of cementation achieved is constrained by the successful completion of four individual, potentially rate-limiting steps: (i) adsorption of the biocatalyst urease onto the soil grains, (ii) retained enzymatic activity of adsorbed urease, (iii) calcium carbonate (CaCO 3 ) precipitation, and (iv) soil strengthening. Failure in any single step can result in no or limited cementation thus limited strength gain. This study conducted a thorough analysis of each step and how they translated to the degree of cementation achieved in mixtures of uncoated, iron-coated, and hydrophobically treated sand. Our results showed that higher levels of protein adsorption and urease activity were found in columns containing 10% hydrophobic sand, but that did not translate to higher amounts of calcium precipitate produced. Approximately 23% more protein mass adsorbed onto the iron-coated columns compared to 100% sand columns, but the overall urease activity was similar among these columns. However, the strength gain was 100% higher in the iron-coated columns when compared to 100% sand columns, suggesting that CaCO 3 bridging was highly effective in the iron-coated columns. Overall, the results from this study highlight the importance of considering each underlying mechanisms behind biocementation, especially when the goal is to optimize the technique for field applications.