Factors influencing relative humidity in concrete

The effects of water/cement ratio, cement type, curing and exposure condition on time-dependent relative humidity profiles in drying concrete are examined. The water/cement ratio of the concrete and the period of initial moist curing were found to have little effect on the measured relative humidities for laboratory exposure, but the latter dropped more rapidly in concretes made with pulverized fuel ash or ground granulated blastfurnace slag than in those made with ordinary Portland cement. The relative humidities in the concretes subjected to laboratory exposure were represented concisely by a set of simple equations. High relative humidities were measured in concretes exposed outdoors, although these were less high when the exposed surface was sheltered from rain. The effects of moisture on several aspects of concrete performance are briefly reviewed, and the benefits of relative humidity measurements are indicated.