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The inner relative humidity (RH) and degree of saturation (S) of high-performance concrete cured for 2 years in water or 3% NaCl solution were measured at three different levels from the concrete surface (outer layer 0 to 16 mm, middle layer 16 to 32 mm, and inner layer 32 to 50 mm). The effects of many factors, such as water-to-cement (w/c) ratio, content of silica fume, and air content, were investigated. Results show that 1) inner RH values of high-performance concrete decrease with decrease in w/c ratio and with increase in silica fume content; 2) RH and S values of the outer layer of concrete are higher than those of the inner layer, and the difference increases with decrease in w/c ratio and with increase in the silica fume content; 3) air content has little influence on RH of the inner layer, but, as expected, because air pores do not readily absorb water, the air content reduces S of the concrete; 4) for concretes cured in 3% NaCl solution, the RH values of the inner layer are higher than for concrete cured in water, and the S values of the three layers of concrete are markedly higher than for concrete cured in water; and 5) theoretical calculations indicate that the increase in molar concentration of soluble ions in concrete and the fractions of interlayer water, absorbed water, and gel water in the evaporable water could be the main factor behind the decrease of RH values or so-called self-desiccation of concrete with low w/c ratio and concrete with silica fume cured in water. |
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