Origin and mobility of alkalies in two Dutch ASR-concretes. II: Microscale element distribution around sandstone and chert. Implications for the mechanism of ASR
conference paper
River gravel used as aggregate for concrete in the Netherlands contains several potentially deleterious components with respect to alkali-silica reaction (ASR), viz. porous chert, chalcedony, and impure sandstones (greywackes. mica- and sericite-rich sandstones, siltstones, arkoses etc.). Whereas cherts and chalcedonies are virtually free from alkalies prior to their incorporation in concrete, impure sandstones are not. Current regulations therefore impose a cumulative limit in terms of Na2O-equivalents on concrete. i.e. the sum of bulk Na20-equivalents of individual Components (cement, aggregate. Mier. additives, etc.). However, for understanding the fundamental mechanism of alkali-silica reaction itself, knowledge of the internal relationships within concrete, i.e. exchange between different types of aggregate (chert, impure sandstone), cement paste and fluid phase, is essential.
To study these, samples from two structures showing deleterious ASR have been studied by electron microprobe techniques. In both cases. ASR affected concrete produced from Portland cement (with minor PFA in one case), river gravel and river sands. Microscale element distribution maps have been
obtained for Si. Fe. Ca, Na, K and S. showing distributions of these elements between different types of aggregate and cementpaste. These show a depletion of alkalies in impure sandstone aggregate, and an ingress of these elements into porous chert. Implications of these relationships with respect to the mechanism of ASR and its prevention will be discussed.
To study these, samples from two structures showing deleterious ASR have been studied by electron microprobe techniques. In both cases. ASR affected concrete produced from Portland cement (with minor PFA in one case), river gravel and river sands. Microscale element distribution maps have been
obtained for Si. Fe. Ca, Na, K and S. showing distributions of these elements between different types of aggregate and cementpaste. These show a depletion of alkalies in impure sandstone aggregate, and an ingress of these elements into porous chert. Implications of these relationships with respect to the mechanism of ASR and its prevention will be discussed.
TNO Identifier
329964
Source title
Proceedings of the 8th Euroseminar on Microscopy Applied to Buildings Materials, Athens, Greece, 4-7 September
Pages
85-92
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