Effect of ternary cements containing thermally activated paper sludge and fly ash on the texture of C-S-H gel

The texture of the C-S-H gels formed in ternary cement blends containing thermally activated paper sludge (APS), fly ash (FA) from coal combustion and Ordinary Portland Cement (OPC) was studied by means of the specific surface area (SSA) and pore-size distribution (PSD), which were measured by the sorption isotherms of nitrogen gas and the BET method. Two differentiated zones in the PSD of the C-S-H gel at ∼10-20 nm and ∼5 nm were observed. The proportion of such zones depends on the age of hydration and amount of OPC replacement. The incorporation of the additions (APS and FA) clearly revealed an increase in both porosity and SSA. This effect decreased with the progress of hydration together with a refinement of the nano-porous structure of C-S-H. High correlations were found among these nanostructure characteristics of the C-S-H gel and mechanical strengths.