Mechanical properties of graphene oxide modified ultra-high-performance concrete containing coarse aggregate

Abstract

This study investigates the use of graphene oxide (GO) to improve the mechanical properties of UHPC containing coarse aggregate (CA). Three different replacement ratios of CA (0%–40%) and five contents of GO (0%–0.05%) were added to UHPC mixture to evaluate the effects of CA and GO on the compressive, flexural and tensile behavior of UHPC. Compression, flexural and tensile tests were conducted on 24, 15 and 6 groups of specimens, respectively. Based on the test results, it was found that the incorporation of CA into UHPC significantly improves its compressive strength by 21.5%, 29.8% and 23.4% when the CA is replaced by 20%, 30% and 40%, respectively compared to the control UHPC. Conversely, it was observed that the addition of CA to UHPC decreases its flexural strength by 13.8% and 18.8% when the CA is replaced by 20% and 30%, respectively. It was also revealed that adding CA adversely affected the tensile performance of UHPC. In addition, the use of GO increases the compressive strength of UHPC. However, the optimum content of GO is up to 0.04%. When the GO content increases from 0.01% to 0.04%, the compressive strength increases from 8.9% to 26.1% and then it decreases to 24.4% when the 0.05% GO content is added. The flexural strength of UHPC seems to increase by 26.8%, 21.3%, 20.5%, 19.2% and 2.9% when GO contents are added by 0.01%, 0.02%, 0.03%, 0.04% and 0.05%, respectively. Adding GO also enhances the tensile strength of UHPC by 15.8% compared UHPC without GO. Moreover, increasing the GO content in UHPC with lower replacement ratio of CA increases the compressive and flexural strengths of UHPC-CA, while it adversely affects UHPC-CA with higher replacement ratio of CA, where the optimal content of GO affecting compressive strength decreases, while the optimal content affecting flexural strength increases. Additionally, whether it is compressive strength, flexural strength, or tensile strength, the optimal content of GO in GO-modified normal concrete is always greater than that in GO-modified UHPC. Similarly, it was observed that the addition of GO to the UHPC-CA specimens increases the tensile strength by 27.42% and 28.53% when the GO contents are incorporated by 0.01% and 0.02%, respectively. Finally, empirical formulas were proposed to predict the compressive strength and flexural strength, considering the content of CA and GO. A stress-strain model was also proposed for GO-modified UHPC-CA and verified by comparison with experimental results with error within 10%.