Evaluation of pozzolanic activity, heterogeneous nucleation, and microstructure of cement composites with modified bentonite clays

The use of bentonite clays as supplementary cementitious material (SCM) is limited because of their low pozzolanic activity, high hydrophilicity, and dramatic swelling nature. In this study the bentonite clay was modified by silane treatment, and its pozzolanic activity was compared with as-received bentonite (ARB) and calcined bentonite (CB) clays. Portlandite quantification by thermogravimetry and Rietveld analysis showed a higher pozzolanic activity of the silane-modified clay. The specific surface area (SSA) of silane-treated bentonite (STB) clay was increased by 314% than ARB clay which provides an additional surface for the heterogeneous nucleation of cement hydrates, thereby improving the microstructure of the cement paste. The hydrolysis and polycondensation of silane on the surface of the STB clay generates SiO₂ like structure which reacted with portlandite to produce an additional calcium silicate hydrate (C-S-H). The swell index and hydrophilicity of the STB clay were significantly reduced, which improved the mortar flow and mechanical strength.