Calcium-silicate-hydrate seeds as an accelerator for saving energy in cold weather concreting

Cold weather concreting is well-known for its high energy consumption and carbon emissions because it needs to take various measurements to prevent the frost damage of concrete. Effectively promoting the strength of concrete developed rapidly in cold weather is a crucial way to solve this problem. In this study, the chloride-free and green calcium-silicate-hydrate (C-S-H) seeds were used to modify the performance of Portland cement (PC) at the negative temperature. The results showed that the strength of PC adjusted by C-S-H seeds developed rapidly at negative temperature (-5 degrees C) within 28 d after several hours pre-curing; its strength value at 28 d (74.2 MPa) was comparable with that of PC cured at room temperature for 28 d (75.3 MPa). The addition of C-S-H seeds significantly accelerated the early hydration of PC during pre-curing and the subsequent hydration at negative temperature. The freezing point and the frozen water of cement paste were significantly reduced by C-S-H seeds and pre-curing, which can help to prevent the cement matrix from frost damage at -5 degrees C. This advantage was further demonstrated by the improvement of the microstructure caused by ice. The easy-operate and green method can significantly decrease energy consumption and CO2 emissions in cold weather concreting. (C) 2020 Elsevier Ltd. All rights reserved.