Mechanical Performance of Sprayed Engineered Cementitious Composite Using Wet - Mix Shotcreting

This paper presents an experimental study on the fundamental performances of a sprayed engineered cementitious composite (ECC) in repair systems. ECC serving as a repair material has been expected to be highly effective in providing durable repaired structures because of the tight crack width control and high delamination resistance. For this study, a polyvinyl alcohol (PVA) fiber-reinforced ECC (PVA-ECC) that exhibits suitable properties for wet-mix shotcreting in the fresh state and strain-hardening behavior in the hardened state was sprayed and tested. The experimental results show that the sprayed ECC exhibits strain-hardening behavior with strain capacities comparable with the cast ECC with the same mixture proportion. It is also revealed that when sprayed ECC is used as a repair material, both load-carrying capacity and ductility represented by deformation capacity at peak load of repaired beams in flexure are obviously increased in comparison with those of commercial prepackaged mortar (PM) repaired beams. The significant enhancement of energy absorption capacity and tight crack width control in ECC repair systems using a wet-mix shotcreting process suggests that sprayed ECC can be effective in extending the service life of rehabilitated infrastructures. INTRODUCTION Engineered cementitious composite (ECC) is a high-performance fiber-reinforced cementitious composite designed with micromechanical principles. Micromechanics allows optimization of the composite for high performance represented by extreme tensile strain capacity while minimizing the amount of reinforcing fibers, typically less than 2% by volume V f. A variety of applications of this material ranging from repair and retrofit of structures, cast-in-place structures to precast structural elements requiring high ductility, are being developed. 1,2 The use of ECC as a repair material has been proposed Their works revealed that superior tensile ductility of ECC material appeared to provide significant enhancement of the performance of repaired structural systems resulting in tight crack width control and high delamination resistance. The potential advantage of using ECC as a repair material is further demonstrated in a numerical study by Lim et al. 6 In that work, the flexural performance of a repaired system with high ductility such as ECC showed improvement of post-peak behavior and total energy absorption compared with that of high-strength repair material with low ductility. Also, the crack width on the tensile surface and the stress distribution along the reinforcement in a flexural member were found to be dramatically reduced in the repair system with ECC.