Multicriteria sustainability assessment of nano-silica–modified high-strength ECC with fly ash cenosphere: Environmental, economic, service life, and mechanical considerations

Fly ash cenosphere (FAC) is a promising additive for engineered cementitious composites (ECC) because it reduces density and improves ductility, thermal insulation, and sustainability. However, replacing conventional components with FAC can reduce mechanical performance and thus weaken ECC ' s strength-normalized environmental benefits. This study evaluates whether adding nano-silica (NS) at 0.5 wt% and 1 wt% of binder can offset that drawback by improving mechanical properties and extending structural service life. Experimental results showed that incorporating FAC increased the tensile strain capacity of ECC (water to binder ratio of 0.2) to 4.26% (versus 2.34% for the reference mixture, Ref.-ECC), but reduced compressive strength from 85.6 MPa to 67.4 MPa. Adding NS raised compressive strength to 80.1 MPa and substantially improved tensile properties: tensile strain capacity and tensile strength increased by 80% and 58%, respectively, resulted in the increased strength- and strain-normalized sustainability. NS also reduced crack width, which is expected to extend the predicted service life from 11.83 years to about 15.0 years and to promote self-healing. Finally, the multicriteria assessment (environmental, economic, service life, and mechanical dimensions) indicated that the sustainability index decreased with FAC alone but improved when FAC was combined with NS, relative to the reference ECC.