Reinforcing efficiency of nanomaterials on mechanical and interfacial characteristics of green concrete incorporating fly ash cenosphere

Abstract

As part of coal-burning ashes, fly ash cenosphere (FAC) has not been extensively used on account of its negative impact on the mechanical performance of concrete. Hence, nanomaterials, i.e., nano-silica (NS) and carbon nanotubes (CTNs), were adopted in this study to enhance the performance of green concrete containing FAC. A chemical etching procedure was presented to arouse the internal curing and pozzolanic activity of FAC and was validated by comparing the physical and chemical properties of raw and treated FAC. The reinforcing efficiency of NS and CNTs on concrete containing raw and treated FAC was evaluated by investigating cement hydration, fresh and mechanical properties, microstructure and interfacial performance. Results showed that nanomaterials had higher enhancing efficiency when they were added to the concrete incorporating treated FAC, as an increase of up to 72.22%, 15.32% and 30.18% in 28-d non-evaporable water, 28-d compressive strength and 28-d split-tensile strength, respectively, was achieved. The internal curing and pozzolanic effects made treated FAC have superior interactions with NS and CNTs, thereby contributing to a denser microstructure and better interfacial performance. With the addition of NS and CNTs, a stiffer ITZ was identified between the treated FAC and mortar given a higher Si/Ca ratio, which alleviated the negative impact of FAC on the mechanical properties of concrete.