THEORY OF VOLUME CHANGES IN HARDENED PORTLAND-CEMENT PASTE DURING FREEZING

NEW EXPERIMENTAL DATA ARE PRESENTED ON THE FREEZING OF HARDENED PORTLAND-CEMENT PASTES WITH AND WITHOUT ENTRAINED AIR. THEY ARE EXPLAINED IN TERMS OF TWO MECHANISMS: (1) THE GENERATION OF HYDRAULIC PRESSURE AS WATER FREEZES IN CAPILLARY CAVITIES AND (2) THE GROWTH OF THE BODIES OF ICE IN THE CAPILLARY CAVITIES OR AIR VOIDS BY DIFFUSION OF WATER FROM THE GEL. AIR VOIDS LIMIT THE HYDRAULIC PRESSURE AND SHORTEN THE PERIOD DURING WHICH THE ICE IN THE CAVITIES CAN INCREASE. THE CLOSER THE AIR VOIDS ARE TO EACH OTHER THE MORE EFFECTIVE THEY ARE IN CONTROLLING EITHER MECHANISM. /AUTHOR/