Strain monitoring of CFRP wrapped RC columns damaged by alkali aggregate reaction

One method of repairing structural elements damaged by alkali-aggregate reaction (AAR) is confining them by wrapping with epoxy-impregnated carbon fibre reinforced polymer (CFRP) material. This paper presents the results of experimental investigations involving strain measurements in reinforced concrete (RC) columns, damaged by AAR, before and after the application of CFRP. Square and circular RC columns were cast, incorporating fused silica as reactive aggregate, and stored at 38 degrees C and 100% relative humidity for periods of one and two months. They were then wrapped with one or two layers of normal modulus (240 GPa) CFRP. Various types of strain gauges were used to monitor strain development in the horizontal and vertical direction in the concrete and in the longitudinal and transverse bars in the columns. The strain measurements continued after the columns were repaired. Strains were also measured on the CFRP wrapping for another 250 days. For comparison, expansion measurements were also carried out on concrete prisms, according to ASTMC1293, using the same mixture as that used in the columns. The results of the strain measurement were analyzed with respect to the effect of internal and external reinforcement, provided by the reinforcement bars and the applied CFRP on the strain developments in the columns before and after CFRP wrapping. The results show that the effectiveness of CFRP wrapping depends on the shape of the columns and the number of CFRP layers used for wrapping them. Most importantly, the time of CFRP wrapping has a major influence on the effectiveness of CFRP in confining the expansion of the AAR-affected columns, earlier application being more effective