Shear strengthening of RC deep beams with cement-based composites

The effectiveness of cement-based composite systems for strengthening reinforced concrete (RC) deep beams was compared to an epoxy-based carbon fiber reinforced polymer (CFRP) system. Two types of cement-based systems were investigated: carbon fabric reinforced cementitious mortar (CFRCM) and carbon fiber reinforced polymer (CFRP) grid embedded in mortar. Experimental results revealed that the cement-based strengthening systems performed better compared to the epoxy-based system in terms of the observed increase in shear capacity relative to the ultimate strengths of the strengthening system. This is possibly due to the bi-directional fabric used in the cement-based strengthening systems compared to the unidirectional sheets used in the epoxy-based strengthening system as well as their improved bond to the concrete substrate; the beams strengthened with CFRP sheets failed by debonding of the CFRP sheet, whereas no debonding was observed in beams strengthened with cement-based systems. The failure loads of tested beams were predicted using a simple strut and tie model by incorporating the effect of the strengthening system in the diagonal strut capacity.