Hybrid effect of carbon nanotubes and basalt fibers on mechanical, durability, and microstructure properties of lightweight geopolymer concretes

• Hybrid effect of CNTs and BFs on LWGC was investigated. • GGBFS and CNTs were utilized as raw material in LWGC. • BFs improved the mechanical properties, especially splitting tensile strength. • LWGC containing BFs and CNTs were suitable for structural applications. • Reinforced LWGC beams containing BFs and CNTs had a suitable flexural performance. In this research, a combination of basalt fibers (BFs) and carbon nanotubes (CNTs) were used to improve the engineering attributes of lightweight geopolymer concrete (LWGC). A combination of ground granulated blast furnace slag (GGBFS) and CNTs was utilized as the binder. The experiments consisted of slump, equilibrium density, compressive and splitting tensile strengths, ultrasonic pulse velocity, water absorption, water penetration depth, electrical resistivity, fourier-transform infrared spectroscopy, energy dispersive X-ray microanalysis, and scanning electron microscope. Also, reinforced LWGC beams containing different percentages of BFs and CNTs were fabricated and subjected to four-point loading. The experimental outcomes demonstrated that CNTs could be used as a replacement for a part of GGBFS to obtain structural LWGC with suitable mechanical and durability attributes. The combined use of CNTs and BFs increases the compressive and splitting tensile strength by 32.2% and 43.7%, respectively. Due to greater participation in the geopolymerization process and the formation of hydrated gels, mixes containing CNTs fill the voids and form a dense and cohesive structure. Moreover, the presence of BFs in the binder texture of LWGC strengthens the bond between the binder and the aggregates and prevents the development of capillary cracks. It was observed that the reinforced LWGC beam containing BFs and CNTs had higher flexural strength and better ductile performance than the control specimen.