Enhancing effect of carbon nanotubes on the performance of concrete containing surface-treated fly ash cenosphere

Abstract

Fly ash cenosphere (FAC) has been reported to lessen concrete properties due to its poor load-bearing performance. To address this issue, a surface treatment process is presented herein to improve the characteristics of FAC. In addition, carbon nanotubes (CNTs) are adopted to enhance the interfacial performance of the surface-treated FAC (STFAC) and the overall performance of STFAC-incorporated concrete, considering promising interactions in the cement-STFAC-CNTs system. Results show that the surface treatment process makes STFAC exert an internal curing effect and enhanced early-age pozzolanic activity since good water desorption properties and enhanced migration of Si and Al are identified, which is responsible for increased cement hydration. Adding CNTs at a dosage of less than 0.10% positively affects the hydration process and mechanical properties of STFAC-incorporated concrete at both early and later ages, but it decreases the workability of the fresh mix. A higher CNTs dosage of 0.20% has a damaging impact on concrete performance due to the secondary agglomeration but it can be alleviated by a higher internal-water to binder ratio of 0.248, since the excessive internal water favors the transfer of CNTs and leads to uniform distribution. Furthermore, the reinforcement of CNTs on the interfacial performance of STFAC is confirmed by characterizing the morphology and hydrate phases near the STFAC interface.