An Austrian experience with identification and assessment of alkali-aggregate reaction in motorways

Abstract

Drilled cores from two different Austrian concrete motorways suspected to be damaged by Alkali Aggregate Reaction (AAR) were investigated. The aim of the investigation was to reveal the cause of cracking and thereby apply published methods for investigating AAR and adapt them to Austrian needs. More specific, visual examinations of the cores after wetting-drying cycles as well as microscopic investigations of thin section and polished sections and SEM examinations were performed. For mechanical testing, ultrasonic pulse velocity and resonant frequency were measured and dynamic Young's modulus determined. Additionally static Young's modulus and compressive strength measurements were conducted and an extensive statistical analysis was carried out with the data from mechanical testing. Damage Rating Indices developed by Dunbar and Grattan-Bellew were determined and adapted to improve the correlation with the results from mechanical testing. The overall chemical analysis of the cores and the water-soluble alkali, silicon and chlorine content were surveyed for hints for an ongoing AAR. It could be shown that for the cores from one motorway AAR was clearly the cause of the damage, whereby the damage was most severe in the area of the first lane. The cores from the other sampling site showed few to no signs for AAR damage so far. But, the samples showed a potential for AAR in the future since the preconditions for AAR could be observed. Two motorways situated in the region in the south of the Austrian province Styria are subject of the present study. The first motorway (A2) was built in 1976/78 and then reconstructed in 2000. During the recon- struction the concrete was recycled and used for the subconcrete. First early damages became visible only three years after the reconstruction. The second motor- way (A9) was built in 1985 and showed first signs of map cracking after 13 years. Alkali-aggregate reac- tion was not considered as major reason for the dam- age at first, as the opinion was that in Austria there are few to no reactive aggregates. Only two major AAR damage cases have been reported until then in Austria (Sommer et al. 2001): A concrete road surface with carbonate aggregate built in 1990 showed signs of damage in 1994. Investigations confirmed the suspect of AAR. The second AAR damage case was a dam in north Tyrol. Built in 1942 severe damage occurred decades later so that another dam had to be installed in 1993/94 with the old one acting as lost shuttering. Nevertheless, after first investigations of the motorways in 2003 it became more obvious that AAR could be the reason for the damage. Thus, investiga- tions were carried out in order to reveal the cause of