Exploring the role of thermal activation of cement exposed to the external environment on the improvement of concrete properties

Abstract

Since carbon dioxide generated by the cement industry raises environmental issues, attempts have been made to benefit from waste cementitious powder (WCP) as a supplementary cementitious material in order to reduce the adverse impact. In this study, an abandoned-and-unused cement (AC) exposed to an external environment for a long period of time (2 years) was used as a partial replacement for cement at 15 wt%. The effect of AC on various properties of concrete was investigated. Moreover, the performance enhancement of concrete was attempted by thermal activation of AC at 400 °C, 600 °C and 800 °C. The properties of concrete containing AC were compared with ones mixed with ordinary Portland cement (OPC) and ones with normally-hydrated cement paste (NHC). The TGA and XRD were used for the characterization of cementitious materials. For concrete, workability, mechanical strength, physical and durability properties were investigated. The results showed that the performance of both concretes containing AC and NHC without thermal activation was lower than that of the reference concrete made with OPC, but all the tested properties improved with increasing thermal activation temperature. Certain concrete mixtures with thermally-activated WCP exhibited better performance than the reference concrete. The minimum temperatures required to exceed the performance were 600 °C for AC and 800 °C for NHC, indicating that AC achieved higher performance at lower heating temperatures. Consequently, utilizing thermally-activated AC can result in favorable outcomes with respect to cost, energy efficiency, and environmental impact.

Keywords

• Recycled cement powder
• Waste cementitious powder
• Thermal treatment
• Cement rehydration
• Dehydrated cement waste