Abstract
This paper deals with the effect of initial curing conditions on the hydration process of Portland pozzolan cements. Experiments were performed on pastes made with Canadian Standards Association (CSA) Type 10 (ASTM Type I) Portland cement (PC) and Portland pozzolan cement (PPC) containing 30% natural pozzolan by mass. PC pastes are more sensitive than PPC pastes to the period of initial water curing because the hydration of PC occurs more quickly than does the pozzolanic reaction in PPC pastes. The hydration of Portland cement and the pozzolanic reaction continue after specimens are removed to a dry environment (relative humidity ≈ 20%). The presence of natural pozzolans retards the normal hydration of PC before an age of 1 day but accelerates it after 1 day. For the tests reported here, an excellent correlation exists between strength and the quantity of “hydrate” water. The measurement of pore structure shows that the measurable total pore volume is significantly decreased for specimens that are water-cured and then dried, compared with those that are water-cured only. The period of initial water curing does not have a significant effect on total pore volume at 28 days (measured by Hg porosimetry), but does affect the pore size distribution. Examination of strength is not a good indicator of the effect of initial water curing.
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