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RESEARCH PRODUCT

Investigations on The Micro-Structure of Hardened Cement Pastes

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Abstract Creep is a mechanical property, that has to be taken into account in the design of concrete constructions. Earlier studies showed that creep of concrete, among other things, depends on the relative humidity of the environment and on the type of cement used. The origin of creep lies in the hydrated cement paste, which is present between the aggregates. This paper, based on a thesis of H.H. Willems (ref. 1) deals with the relation between the creep behaviour and the microstructure of hardened Portland (PC) and Portland-blastfurnace cement (PBC) pastes. At several relative humidities shrinkage and creep experiments have been performed with thin-walled hollow cylindrical specimens. Next the pore structure has been studied by means of the physical sorption of water using a microgravimetric apparatus. In addition some nitrogen adsorption experiments were performed. The silicate structure has been determined by means of trimethylsilyl-derivatives made from the silicates present in the hydrated cement pastes, which were analyzed by gas-liquid chromatography. Clear differences exist between both the pore and the silicate structure of hydrated Portland and Portland-blastfurnace cement pastes. The influence of the relative humidity and the pretreatment of the specimen (shrinkage or creep) on the microstructure of the hydrated cement pastes, appears to be minor. No clear relation could be found between the creep behaviour, isotherm shape and the microstructure of the specimens investigated.