A low-temperature DSC investigation of hardened cement paste subjected to chloride action

Differential scanning calorimetry (DSC) was used to investigate the freezing behaviour (−175°C to 20°C) of hardened cement paste (hcp) subjected to NaCl and CaCl 2 solutions containing up to 5.4 mol Cl/l. Thermograms were also recorded for samples dried to relative humidities (RH) between 61 % and 96 %. The low-temperature phase transition at −38°C exhibited the freezing behaviour of an aqueous solution in gel pores of ≈ 4 nm radius. Chloride ions strongly reduce the coupling forces between gel particles and structure the gel pore water. On desorption critical behaviour of the low-temperature transition energy was observed at 0.52 mol Cl/l which is the concentration most damaging to hcp. Above 1.3 mol Cl/l freezing of supercooled bulk water in macropores was observed at more than one temperature.