Inner relative humidity and degree of saturation in high-performance concrete stored in water or salt solution for 2 years

The inner relative humidity (RH) and degree of saturation (S) of high-perfo rmance concrete cured for 2 years in water or 3% NaCl solution were measure d 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 inc rease in silica fume content; 2) RH and S values of the outer layer of conc rete 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 expect ed, 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 value s 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 concre te cured in water; and 5) theoretical calculations indicate that the increa se in molar concentration of soluble ions in concrete and the fractions of interlayer water, absorbed water, and gel water in the evaporable water cou ld be the main factor behind the decrease of RH values or so-called self-de siccation of concrete with low w/c ratio and concrete with silica fume cure d in water. (C) 1999 Elsevier Science Ltd. All rights reserved.