EFFECT OF REPEATED WETTING AND DRYING ON PHYSICAL PROPERTIES OF A CLAY BODY*

Specimens of fine-grained, red-firing clay, which had been fired to temperatures corresponding to various stages of vitrification, were subjected to 200 cycles each of wetting at 100°F. and drying at 100°F. and 60% of relative humidity. This treatment, simulating weathering in mild climates, caused (1) a permanent gain in weight which was greater for the softer specimens; (2) a moisture expansion for the softer specimens but none for those near vitrification; (3) a fairly uniform decrease in modulus of elasticity for all specimens; and (4) a decrease in modulus of rupture for the softer specimens but an increase in strength for those that were completely vitrified. The data indicate that moisture expansion and a decrease in strength of soft-fired clay bodies, caused by repeated wetting and drying, may be eliminated by proper vitrification.