Improved mechanical and thermal properties of sustainable ultra-high performance geopolymer concrete with cellulose nanofibres
Yuekai Xie, Chenman Wang, Yingying Guo, Hanwen Cui, Jianfeng Xue
Abstract
Although the application of the cellulose nanofibre (CNF) on the mechanical performance of conventional ultra-high performance concrete (UHPC) and geopolymer materials have been extensively studied, the effects of CNF on the mechanical and thermal behaviour of ultra-high performance geopolymer concrete (UHPGC) have not been well understood. This paper presents a laboratory study on the mechanical properties, thermal resistance, and microstructures of CNF-incorporated UHPGC prepared under the ambient (23 °C) and elevated (80 °C) temperatures and volumetric contents of CNF from 0 to 0.4 %. The precursors included fly ash (19 %), ground granulated blast-furnace slag (76 %), and silica fume (5 %). The volumetric contents of the steel fibres (length of 13 mm and diameter of 0.2 mm) ranged from 0 % to 3 %. The flowability, compressive and flexural strengths, and residual compressive strength after the thermal exposure to 200, 400, and 600 °C were determined. The flowability of CNF-UHPGC dropped with CNF proportions. For the specimens cured under the ambient temperature, the highest compressive strength (143.6 MPa) and flexural strength (22.3 MPa) were determined with 0.2 % and 0.4 % CNF, respectively. For the specimens cured under the elevated temperature, the maximum compressive strength (156.4 MPa) and flexural strength (21.5 MPa) were determined with 0.1 % and 0.2 % CNF, respectively. Furthermore, the residual compressive strength of UHPGC with 0.1 % CNF cured under the ambient temperature was 6.2 %–6.8 % and 2.4 %–4.4 % higher than that without CNF after being exposed to 200 and 400 °C, respectively. Systematic microscopic investigations, including X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA), revealed that the addition of the CNF enhanced geopolymerisation reactions and promoted calcium (aluminate) silicate hydrate (C-(A)-S-H) gel formation, enhancing the strength. Based on the experimental results, adding 0.1 % v/v CNF not only enhanced the mechanical performance but also improved the thermal resistance of UHPGC. • CNF-UHPGC reached compressive and flexural strength of 156.4 and 22.3 MPa. • CNF-UHPGC exhibited higher residual strength after heat exposure of 200 and 400 °C. • CNF enhanced the production of calcium (aluminate) silicate hydrate gels. • CNF of 0.1 % and 0.2 % v/v was feasible for enhanced strength and thermal resistance.