Development and performance of ultra-lightweight engineered cementitious composite with eco-friendly lightweight fillers: Balancing strength and ductility

Ultra-lightweight engineered cementitious composite (ULW-ECC) offers broader potential than conventional ECC by reducing new building deadweight and minimizing additional loads during repair and rehabilitation of existing structures. However, this is typically achieved at the expense of mechanical properties, including strength and ductility. Therefore, the aim of this research is to develop a sustainable and cost-effective ULW-ECC that strikes a balance between strength and ductility. In this study, two eco-friendly lightweight fillers, fly ash cenospheres (FAC) and hollow glass microspheres (HGM), were used to reduce the density of the mixtures. The effects of completely replacing sand with FAC, and replacing 0 %, 30 %, and 60 % of fly ash (FA) with HGM, as well as replacing 30 % of FA and 30 % of cement with HGM, on the mechanical properties of ECC were discussed. A lower PE fiber content (1 % by volume) was chosen, as the incorporation of lightweight fillers reduced the fracture toughness of the matrix while enhancing strain-hardening behavior, thereby addressing the high cost associated with conventional ECC. Additionally, the enhancement of ECC properties by different concentrations of cellulose filament (CF) was explored. The high tensile ductility of the developed ULW-ECC was explained based on fracture micromechanics . Furthermore the mechanical properties, including compressive strength , tensile strength , and microstructure, were investigated through experimental studies. The results show that the developed ULW-ECCs, with densities ranging from 1196 kg/m 3 to 1414 kg/m 3 , compressive strengths of 38.5 MPa to 42.8 MPa, and a tensile strain capacity from 7.77 % to 10.28 %, exhibit significant potential for practical applications. • Replacing FA with HGM, on a full sand-to-FAC basis, improved ULW-ECC ductility without notably reducing strength. • The developed ULW-ECC, with a PE fiber content of 1 % (by volume), achieved a highest tensile strain capacity of 10.28 %. • The addition of 0.1 % CF by binder mass effectively improved performance of the mixture.