Combination of Slag and Fly Ash to Prepare Engineered Cementitious Composite: A Study on Mechanical Properties and Gas Permeability

The global coal plants are gradually decreasing to improve sustainability, resulting in the possible resource shortage of fly ash (FA) as the main raw material of engineered cementitious composite (ECC). In order to seek good candidates, this paper systematically studied the possibility of using ground granulated blast-furnace slag (or slag, GGBS) as the partial FA replacement for preparing ECC (i.e., GGBS-ECC). Using the uniaxial tensile and compressive tests, the macromechanical properties were achieved; at mesoscale, the three-point bending, single crack tensile, and single fiber pullout tests were performed to explain the tensile ductility; the microscopic techniques including gas permeation and mercury intrusion porosimetry (MIP) were applied to measure the permeability and pore structure. The results revealed that adding GGBS into ECC increased the tensile and compressive strength at either 7 days or 28 days and changed little (reduced) the tensile and compressive strain capacity at 7 days (28 days). The calculated pseudo strain hardening indices based on the mesoscale experimental results were higher, accompanied by the higher tensile strain capacity; incorporation of GGBS could improve the interfacial chemical bonding between fiber and matrix. Moreover, the GGBS-ECC exhibited a lower gas permeability and a smaller average pore size than the ECC without GGBS. Based on these findings, it was concluded that GGBS could be utilized in the development of ECC with appropriate ductility and facilitate the compactness of the matrix.