Sprayed strain-hardening cement-based composite overlay for shear strengthening of unreinforced load-bearing masonry

Strengthening of unreinforced masonry walls is realised by a bonded overlay of strain-hardening cement-based composite. In-plane shearing resistance is considered here, although out-of-plane resistance is also increased by the overlay. The strain-hardening cement-based composite mix is adjusted for sprayed application with low run-off and waste. Characterization of masonry joint shear-slip behaviour, interfacial response between the masonry substrate and the strain-hardening cement-based composite overlay and multiple cracking tensile response of the sprayed strain-hardening cement-based composite bond is described. Preferred failure of the composite by multiple cracking shearing in the strain-hardening cement-based composite overlay is achieved through structural mechanics-based design of the overlay. Drying shrinkage development and cracking due to restraint by the masonry substrate are reported. Finally, shear wall response is reported for single- and double-leaf masonry walls with a bonded strain-hardening cement-based composite overlay on one face only and compared with single- and double-leaf control masonry walls without overlays. An overlay of thickness similar to that of typical plaster rendering is shown to lead to significantly enhanced shearing response.