Relative humidity and deterioration of concrete under freeze–thaw load

• The w/c ratio essentially determines the steady RH in concrete.
• The freezing and thawing temperature can be identified from RH curves.
• Material damages were evaluated by the mechanical, visual rating and pore-structure tests.
• The effective crystallization pressure and the effective liquid pressure were estimated.

Evolution of internal relative humidity (RH) and deterioration of concrete under cyclic freeze–thaw (F–T) load were studied. RH values of concrete specimens were monitored upon freezing and thawing. Compressive strength, mass loss, visual ratings and porosimetry were used to evaluate changes in concrete. Decreasing water to cement ratio (w/c) decreased the steady-state internal RH. RH–temperature curves showed that freezing temperature was independent of F–T cycles, while thawing temperature varied with F–T cycle and w/c. More severe deterioration, but less alteration of pore structure, occurred in higher w/c concrete – increasing w/c increased ice formation in pores, and thus effective crystallization pressure and liquid pressure.