Durability analysis of the bridge B7 on the railway line Bitola-Kremnica

Abstract

Cases of unsatisfied duration of structure service life turn not to be so rare. In concrete structures, one of the key reasons for that is corrosion of embedded reinforcement that can be either chloride- or carbonation-induced. The later one has been reported to be a major durability problem for any infrastructure object exposed to carbon dioxide CO2. Such an example is the case study bridge considered in this paper - recently built RC bridge B7 on the railway section Bitola-Kremenica. The subject bridge is located in extremely CO2 rich environment. Thus, environmental conditions as well as in-built concrete quality were taken into account in order to examine if the recently built bridge meets the durability requirements, i.e. if the target service life of 100 years can be achieved. In order to quantify the key parameters in the numerical model for service life prediction, several laboratory and in-situ investigations were organized: (1) on-site measurement of CO2 concentration in the air; (2) compressive tests on concrete cores and (3) determination of carbonation resistance of concrete through accelerated carbonation tests (ACC). Direct phenolphthalein test showed that the samples were carbonated prior to placing in the carbonation chamber. Based on the results from the conducted ACC tests, the concrete represented by the two cores, was classified as low to moderate in terms of carbonation resistance. Using the collected results, durability analyses based on partial factor and probabilistic method were carried out to determine the required concrete cover from carbonation point of view. The outcomes of each analysis have shown that a hundred-year service life of the bridge can be achieved only with relatively thick concrete cover (more than 60mm). Additionally, the carbonation process can be minimized and slowed down by application of waterproof and vapor-permeable concrete coatings on the exposed concrete surfaces.