Method for determining the moisture condition in hardened concrete

A method for studying the moisture conditions inside hardellcd concrete and cement paste is described. An electric hygrometer developed by the National Bureau of Standards was used to measure the relative humidity in cavities at various locations in the material. The relat ive humidity inside 12-inch concrete cubes stored at 50 percent rehtive humidity for 300 days was found to range from 50 percent near the surface to 66 percent near the center of the cube. For cubes stored at 20-percent relative humidity the corresponding range was from 20 t o 60 percent. The relative humidity over cement paste of approximately normal consistency and cured in hermetically sealed bottles fo r 28 days was found to be 88 percent for a m oderate heat-oI-hardening cement a nd 79 percent for a highearly-strength cement. CONTENTS Page