A green ultra-high performance geopolymer concrete containing recycled fine aggregate: Mechanical properties, freeze-thaw resistance and microstructure

The shortage of natural aggregate poses challenges and offers new opportunities for the construction industry. Under this background, the emergence of recycled aggregates sheds new lights on building aggregate. In this study, a green ultra-high performance geopolymer concrete (UHPGC) containing recycled fine aggregate (RFA) was prepared. To assess the feasibility of RFA and reveal the reaction mechanism of UHPGC, the reaction process, mechanical properties, freeze-thaw resistance and microstructure were systematically studied. The heat evolution results indicate that the control of reaction process could be achieved by adjusting the precursor component. A compact microstructure with extremely low porosity could be formed in the UHPGC specimens, which contributes to their good mechanical properties and freeze-thaw resistance. Good compatibility in the interface transition zone between fiber, paste and RFA could be observed, indicating great potential in the manufacture of UHPGC by alkali-activation technology. A considerable environmental benefit could be obtained in UHPGC when compared to ordinary ultra-high performance concrete (UHPC). This study is expected to offer more insights into the application of recycled aggregate and the manufacture of green UHPC.