Potential application of Portland cement-calcium sulfoaluminate cement blends to avoid early age frost damage

This paper aims to investigate mechanical strength and hydration behavior of Portland cement (PC) and calcium sulfoaluminate (CSA) cement mixtures when exposed to different temperatures from -5 degrees C to 20 degrees C. Setting time and compressive strength were evaluated for mixtures with different PC-CSA ratios. The exothermic hydration heat flow, hydration products, pore size distribution and microstructure for typical samples were determined by using isothermal calorimetry measurement, TG/DTG, XRD, MIP and SEM facilities. The results indicate that the setting time of PC-CSA blends decreases with the higher dosage of CSA cement. Compressive strength of cement mortar is increased by the higher incorporation of CSA cement (5-10%) at early ages, but it is decreased by CSA cement at late ages. This negative effect on late age strength is alleviated by the lower curing temperature. The compressive strength degradation of Portland cement induced by early age exposure to -5 degrees C is improved by the addition of 5-10% CSA cement. Moreover, the negative effect can be avoided by the incorporation of 20% CSA cement due to the achievement of critical strength after 6 h pre-curing. The hydration of CSA cement during the first several hours is accelerated by the existence of PC and this is favorable for improve the resistance to early age frost. The pore structure and porosity of cement paste under room temperature is aggravated when the incorporation of CSA is higher than 5% due to the fast formation of massive AFt crystals. But the pore structure and microstructure is improved after exposure to early age frost due to the higher resistance to frost damage. Therefore, the incorporation of suitable content CSA provides a potential method for avoiding early age frost damage for cement concretes under minus temperatures. (C) 2018 Elsevier Ltd. All rights reserved.