Porosity of cement paste cured at 45 °C as a function of location relative to casting position

Abstract The influence of location relative to the casting position, on porosity and pore size distribution of cement pastes, was investigated. Three different pastes were prepared at a constant water/binder ratio of 0.45. The pastes were the control paste (CP) in which Portland cement was used and no cement replacement materials were added, pastes with 22% and 9% replacement (by mass) of cement with fly ash (FA) and silica fume (SF), respectively. Paste specimens were cast in cube moulds and were either cured in air at a temperature of 45 °C and relative humidity of 25% for 28 days or moist cured for 14 days after casting at 45 °C, followed by air curing at 45 °C and 25% relative humidity for further 14 days. Samples were taken from various locations of the cube specimens. Porosity and pore size distribution were conducted on the paste samples using the mercury intrusion porosimetry technique. The results show that large differences in porosity and pore size distribution exist between samples taken from different locations relative to casting positions. These differences are larger in pastes subjected to dry curing as compared to pastes subjected to some initial moist curing. The influence of sample location relative to casting position on porosity and pore size distribution of paste is compared with absorption of concrete performed in a previous investigation. The correlation between pore volume of paste and water absorption of concrete is also conducted.

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