Optimization of mechanical properties and pore structure of lightweight geopolymer concrete using GGBFS based on LF-NMR technology

Lightweight geopolymer can combine good physical and mechanical properties, good thermal and chemical stability, low CO2 emission and low energy. The development of high strength lightweight geopolymer concrete for load-bearing structures is important to expand the application range of geopolymer. This paper presents an improvement study on the mechanical properties and pore structure of lightweight geopolymer concrete (LGC) by adding ground granulated blast-furnace slag (GGBFS). The effect of GGBFS content on the mechanical properties of LGC was analyzed, including ultimate compressive stress and elastic modulus. The variation in the microscopic pore structure of LGC with different GGBFS content was further analyzed by low-field nuclear magnetic resonance (LF-NMR) technology. The lightweight geopolymer concrete with different strength grades was proposed including LC20, LC30 and LC40. The results show that as the GGBFS content increases, the ultimate compressive stress and specific strength of LGC increase while the strain corresponding to peak stress decreases, which means that the mechanical properties and deformation resistance of LGC are improved. The CO2 emissions of LGC are lower than that of cement-based lightweight concrete, which shows good sustainability. The results also show that the addition of GGBFS can produce more gel and reduce the volume proportion of capillary pores and air pores, resulting in the densification of the LGC. The recommended GGBFS contents corresponding to the strength grades of LC20, LC30 and LC40 are 0 similar to 12.7 %, 12.7 % similar to 24.6 % and 24.6 % similar to 30%, respectively. The LGC has the characteristics of lightweight and high-strength, which has a potential application in civil engineering. Highlights Mechanical properties and pore structure of LGC were improved by adding GGBFS. The effect of GGBFS content on geopolymer concrete properties was discussed. Effect of slag content on pore structure of geopolymer concrete were studied. GGBGS content of geopolymer concrete with different strength grades was proposed.