Design of Engineered Cementitious Composite Suitable for Wet - Mixture Shotcreting

An engineered cementitious composite (ECC) suitable for wet-mixture shotcreting (sprayable ECC) in the fresh state, while maintaining tensile strain-hardening behavior in the hardened state, has been developed by employing a parallel control of micro-mechanics-and rheology-based design. In the development concept of sprayable ECC, micromechanics is adopted to properly select the matrix, fiber, and interface properties to exhibit strain-hardening and multiple cracking behaviors in the composites. Within the predetermined micromechanical constraints, the fluid properties are controlled by the rheological process design to develop flocculations between cementitious particles at a proper rate. The pumpability and sprayability of the ECC mixture are then realized by the controlled rheological properties of fresh matrix and the uniform dispersion of fibers. A series of spray and deformability tests show the excellent pumpability, sprayability, and rebound property of the sprayable ECC. Subsequent uniaxial tensile tests demonstrate that the mechanical performance of sprayed ECC using wet-mixture shotcreting process is comparable with that of ECC cast with external consolidation for the same mixture design. INTRODUCTION An engineered cementitious composite (ECC) is a micromechanically designed cementitious composite that exhibits extreme tensile strain capacity while using a moderate amount of fiber, typically less than 2% in terms of fiber volume fraction V f. Recently, a special type of poly-vinyl alcohol (PVA) fiber was developed specifically for ECC reinforcement. 1 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.