Pore structure evolution and strength development of hardened cement paste with super low water-to-cement ratios

In the current study, the ice particles instead of liquid water was firstly utilized as mixing water to prepared cement pastes with super low water-to-cement (w/c) ratios and homogenous structures. The effect of w/c ratio on the properties, especially the pore structure evolution and strength development, of hardened cement pastes were investigated. Mercury intrusion porosimetry (MIP) was introduced for the evolution of pore structure of hardened cement paste. Hydration heat-evolution was employed for characterising the hydration process of cement paste with super low w/c ratios. Experimental results suggested that the water absorption rate decreased by 49.3% while its open porosity decreased by 43.5% with the increase of w/c ratios from 0.08 to 0.16. The initial porosity of cement paste compact reached up to 36.6%, and the pores were mainly capillary pores of diameter in range of 0.1-8 mu m. When hydrated for 3 days, the capillary pores with diameter more than 1 mu m were vanished totally. Furthermore, 28-days total porosity of samples with w/c ratio of 0.16 decreased by up to 46.1% compared to that of samples with w/c ratio of 0.08. With the w/c ratio increased from 0.08 to 0.16, the 28-days compressive strength increased by 68.9% to a value of 127.5 MPa. Additionally, the total porosity was the mainly factor that determined the compressive strength of hardened cement paste with super low w/c ratios. (C) 2019 Elsevier Ltd. All rights reserved.