Pore structure of cement pastes through NAD and MIP analysis

Two cement pastes (water to cement ratio, w/c = 0·5, 0·3) were investigated through mercury intrusion porosimetry (MIP) and nitrogen adsorption/desorption (NAD) methods at different hardening ages. The pore structure is characterised by specific surface area, pore volume and pore size distribution. The results show that: (a) the pore structure has strong scale dependence and NAD–MIP joint measurement helps to identify the different pore structure patterns; (b) MIP total pore volume captures the global process of the hydrates filling process with curing age, the mesopore (2–70 nm) volume is dominated by hydrates filling for w/c = 0·5 but countered by high-density calcium-silicate-hydrate growth for w/c = 0·3; (c) specific surface area is sensitive to calcium-silicate-hydrate growth and specific surface area values are likely to confirm that high w/c (0·5) favours low-density calcium-silicate-hydrate growth whereas low w/c (0·3) facilitates high-density calcium-silicate-hydrate formation.