EFFECT OF SORBED WATER ON SOME MECHANICAL PROPERTIES OF HYDRATED PORTLAND CEMENT PASTES AND COMPACTS

Abstract

THE EFFECT OF SORBED WATER ON MECHANICAL PROPERTIES OF PORTLAND CEMENT PASTES AND COMPACTS WAS OBSERVED. THIN DISCS OF NORMAL CEMENT PASTE WERE CUT FROM 1.25-IN. DIAMETER CYLINDERS WITH 0.3 TO 0.7 W/C RATIOS. COMPACTS OF SIMILAR SHAPE WERE PREPARED FROM BOTTLE-HYDRATED CEMENT AT PRESSURES OF 15,000, 40,000 AND 110,000 PSI. ALL SAMPLES WERE CONDITIONED TO DIFFERENT RH LEVELS BETWEEN O AND 98%. AT ALL LEVELS, THE MODULUS OF ELASTICITY OF ALL SAMPLES AND THE STRENGTH OF SOME WERE DETERMINED BY A MINIATURE TESTING MACHINE. SAMPLES WERE CONDITIONED OVER NAOH SOLUTIONS AND MEASURED IN GLOVED CONDITIONING BASES TO AVOID CARBONATION. INCREASES IN ELASTIC MODULUS WERE OBSERVED ONLY ABOVE 50% RH. THE INCREASE WAS MAINTAINED ON DESORPTION AND APPEARED TO BE ASSOCIATED WITH ENTRY OF INTERLAYER WATER IN THE TOBERMORITE GEL. MAXIMUM FRACTURE-STRENGTH FOR SAMPLES OF GIVEN POROSITY WAS ATTAINED AT 0% RH, AND LARGEST STRENGTH REDUCTION WAS OBSERVED FROM 0 TO 15% RH. PLOTS OF YOUNGS MODULUS VS POROSITY AND FRACTURE-STRENGTH VS POROSITY GAVE COMMON CURVES FOR COMPACTS AND PASTES.