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COMPARISON ON THE DURABILITY OF DIFFERENT PORTLAND CEMENTS AFTER FIVE YEARS EXPOSURE TO SULFATE AND TO SEA WATER ATTACK

Experimental research has been performed to relate specific cement characteristics to deterioration due to sulfate and sea water attack after five year exposure, and to study different test method suitability for sulfate and marine resistance. Sulfate resistance testing have been performed on mortar specimens made with fifteen cement types of statistically diverse chemical composition according to European standard EN 197-1, most of them with sulfate resistant properties according to Spanish regulations. Chemical and mechanical characteristics were studied to determine the variation in properties of selected cements. SO3 content, type and amount of additions, C3A, and C4AF content were used to examine relationships between these characteristics and the results of sulfate resistance. Mortar specimens testing using Na2SO4 as the aggressive medium according to ASTM 1012 (with w/c ratio adapted to prENV 196-X:1995) was performed using each type of cement; identical specimens were also stored in sea water, and in lime saturated water (blank condition), up to five year age. Additionally these cements were tested conforming ASTM 452 and Koch and Steinegger test. Recommended acceptance limits for sulfate resistance of cements concerning to each used test method were evaluated in order to explore their suitability. Relationships between cement characteristics, degradation, expansive products obtained by X-ray diffraction techniques and maximum expansion after applied storage treatments, were correlated at final age, to redefine cement characteristics for sulfate resistant and marine resistant Portland cement. Originality In the last century many studies had been developed with traditional Portland cements to provide meaningful discrimination between sulfate resistant or non-sulfate resistant cements. In this investigation fifteen real trading common cements (EN 197-1) have been tested. Different C3A contents, variable types and proportioning of constituents (limestone, pozzolanic additions, blastfurnace slag ...) with or without the same clinker type were investigated. Present theories about accelerated test procedures adopt that the mechanism of deterioration in the accelerated test should be representative of those observed in service. In this study linear expansion and external damage of mortar specimens with a w/c ratio of 0,5 have been tested, and both have been analysed after five years of immersion in a sulfate solution and also in seawater (and in lime saturated water, as a blank condition). None of the prepared mortars was blended with gypsum or any other non realistic condition. Additionally these european common cements were tested following ASTM standards (modified to EN 196-1 mortar compositions) to evaluate if ASTM specifications were applicable to both cement families of such different characteristics. Chief contributions The development of a prescriptive European Standard (EN) for sulfate resisting cements has been a difficult task due to differences in the types of cements that are considered sulfate resisting. Many countries have national specifications for sulfate resisting cements, most of them only specifying the cement chemical composition, but these regulations do not exactly coincide. This research provides newer information and proposes criteria taking into account the behaviour of common cements, useful to unify the different values established in various national european regulations, which probably were mainly based on traditional Portland cements. These results are in agreement with a broad spectrum of sulfate expansion theories and can provide a better way to specify sulfate resistant cements, establishing a relationship between some accelerated laboratory test and field performance after five year exposure. Durability behaviour in common cements conforming to EN 197-1 exposed to sulfate attack are explained, and also the correlation between sulfate resistance and seawater resistance has been studied.