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This paper compares the hydration characteristics and microstructures of cement pastes with water-cement ratios (w/c) of 0.35 and 0.435, cured under saturated and sealed conditions. Degree of hydration is quantified by loss on ignition measurements. The microstructure, and specifically the pore structure, of the hydrated pastes are evaluated using both scanning electron microscopy with image analysis and low temperature calorimetry. Low temperature calorimetry is found to be particularly valuable as an indicator of the percolation state of the capillary pore network in the hydrating specimens. The w/c=0.35 specimens cured under sealed conditions first form a depercolated capillary pore system that later reconnects due to self-desiccation and autogenous shrinkage. In the w/c=0.435 specimens, conversely, there is some indication that sealed curing leads to an earlier depercolation of the remaining capillary pores than when saturated curing is applied, but without a subsequent repercolation. The results indicate the criticality of proper curing for both w/c, suggest that curing for strength and curing for transport properties or durability may require different practices, and may provide the impetus for innovative curing strategies to produce concretes with mechanical and transport properties optimized for their intended application.
Keywords: curing; hydration; low temperature calorimetry; microstructure; porosity; scanning electron microscopy.