Use of Rhenish trass in Marine concrete : A microscopic and durability perspective

Use of Rhenish trass in (historic) lime mortars is well known. However, its application to concrete has not been investigated elaborately. In the past, trass was used as a pozzolanic addition to concrete for marine structures in the Netherlands. Recent investigations of several structures have shown that identification of trass in aged concretes by polarization-and-fluorescence microscopy is difficult. In order to facilitate PFM studies, historic mixtures were recast. Two mixtures have been recast, viz. a mixture of 300 kg m-3 ordinary Portland cement (CEM I) and another mixture of 310 kg m-3 ground granulated blastfurnace slag cement (CEM III/B), both with an addition of 10 % trass by cement mass. Concrete mixes were originally designed for a major lock, built in the 1920’s, and a quay constructed in Rotterdam harbour in the 1970’s, respectively. Difficulties of recognizing trass in aged concretes by PFM and apparent effects of trass on both microstructure of the concrete and durability are discussed. Durability in a maritime environment has extensively been studied in the case of Rotterdam harbour. It is shown that addition of 10 % of trass to CEM III/B has no effect on the durability of concrete