Low tensile strength in older concrete structures with alkali-silica reaction

During an extensive investigation of some 25 concrete bridges and other structures suffer-ing from alkali-silica reaction it has been found that the uniaxial tensile strength of the concrete was extremely low in relation to both the compressive strength and the splitting tensile strength. It is known that concrete with damage due to ASR has reduced mechanical properties. The literature indicates that with an expansion of 1.0 0/00 a reduction of 30 °A may occur. The reduction found in some of the bridges was, however, up to 85 % with an expansion between 0.5 and 1.0 °/00. There was no clear reduction of the tensile splitting strength and the compressive strength. Previous research on older concrete structures without ASR showed that low tensile strengths are not exclusively connected to the presence of ASR. Although not conclusive, Petrographic Fluorescence Microscopy (PFM) research and visual inspection of the struc-tural damage of the concrete structures with ASR indicate that at least part of the damage must be due to ASR. The structural damage due to ASR and due to other causes can not be di stingui shed. Tests on reinforced beams taken from two of the ASR affected structures and tested in shear proved that the concrete had a reduced tensile strength, though the reduction was less than indicated by the uniaxial tensile tests. The orientation dependency of the tensile strength as found for these two structures can partly account for this difference. On the other hand, positive structural effects of ASR such as prestressing of the concrete due to the swelling within the reinforcement net can also explain this difference