Natural organic matter and the formation of calcium-silicate-hydrates in lime-stabilized smectites: A thermal analysis study

Processes accounting for the negative effects of soil organic matter on strength development in lime-stabilized soils are not clearly understood. We used heat-flow differential scanning calorimetry and thermogravimetry to elucidate how natural organic matter (NOM) content and source influences the formation of calcium-silicate-hydrates (CSHs) in lime-stabilized smectites. The formation of CSH, was strongly correlated with strength (r ≥ 0.95) and decreased with increasing NOM content indicating that organic matter influenced strength development in lime-stabilized soils largely by inhibiting the formation of pozzolanic reaction products such as the CSHs. The degree of inhibition was also dependent on the type of pozzolanic reaction product and the NOM source. For example, the formation of CSH2 was less inhibited by NOM, than was the formation of CSH1. Inhibitory effects of NOM sources followed the order fulvic acid > humic acid > lignite and could be explained by considering their acid–base properties.