Interaction of Hardened Cement Paste and Water

ADSORPTION OF WATER VAPOR ON A CLEAN SURFACE CHANGES THE SURFACE FREE ENERGY. IT IS SHOWN THAT, USING THE GRIFFITH CRITERION, THE CHANGE OF STRENGTH AS FUNCTION OF MOISTURE CONTENT CAN BE EXPLAINED BY ASSUMING A CHANGE OF SURFACE ENERGY. IN COLLOIDAL PARTICLES SURFACE ENERGY CREATES CONSIDERABLE HYDROSTATIC PRESSURE. A CHANGE IN ELASTIC MODULUS AND SHRINKAGE AS WELL AS SWELLING CAN BE RELATED TO A CHANGE IN HYDROSTATIC PRESSURE IN INDIVIDUAL GEL PARTICLES. CREEP IS AFFECTED PRIMARILY AT THE HIGHER RELATIVE HUMIDITIES. THE MAIN PARAMETERS OF A PROPOSED MODEL FOR HYDRATED PORTLAND CEMENT ARE SURFACE FREE ENERGY AND DISJOINING PRESSURE. ON THIS BASIS THE MECHANICAL BEHAVIOR OF HARDENED CEMENT PASTE IS DISCUSSED. A PHASE TRANSITION OF ADSORBED WATER NEAR 90 DEGREES C IS DISCUSSED. THE INFLUENCE OF THIS EFFECT ON THE MECHANICAL BEHAVIOR OF HARDENED CEMENT PASTE CAN BE UNDERSTOOD WHEN A CHANGE IN INTERFACIAL ENERGY IS TAKEN INTO CONSIDERATION. /AUTHOR/

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