Effects of slag content on the residual mechanical properties of ambient air-cured geopolymers exposed to elevated temperatures

This paper presents the effects of various slag contents on the residual compressive strength and physical properties of ambient air-cured fly ash-slag blended geopolymers after exposure to various elevated temperatures up to 800°C. The results showed an increasing trend in the compressive strength of ambient air-cured geopolymers with increase in the slag contents after exposure to 400 and 600°C temperatures. This trend deviated, however, at 800°C. Nevertheless, all the geopolymers showed reductions in control compressive strength at ambient temperature after exposure to elevated temperatures. The reductions were much higher at 600 and 800°C compared to 400°C. All the geopolymers exhibited significant damage in terms of cracking after exposure to a temperature of 800°C compared to 400 and 600°C and significant damage occurred at slag contents of 15–30%. Scanning electron microscopic (SEM) images of the above geopolymers also showed higher porosity at 800°C compared to 400 and 600°C. Traces of calcite/calcium silicate hydrate (CSH) peaks are observed in the X-ray diffraction (XRD) analysis of fly ash-slag geopolymers, and the intensity of those peaks increased with increases in slag contents. After exposure to elevated temperatures, the calcite/CSH peaks disappeared and new phases of nepheline and gehlenite were formed at 800°C in all the fly ash-slag geopolymers

Mechanical properties of cotton fabric reinforced geopolymer composites at 200-1000 °C

Geopolymer composites containing woven cotton fabric (0–8.3 wt%) were fabricated using the hand lay-up technique, and were exposed to elevated temperatures of 200 °C, 400 °C, 600 °C, 800 °C and 1000 °C. With an increase in temperature, the geopolymer composites exhibited a reduction in compressive strength, flexural strength and fracture toughness. When heated above 600 °C, the composites exhibited a significant reduction in mechanical properties. They also exhibited brittle behavior due to severe degradation of cotton fibres and the creation of additional porosity in the composites. Microstructural images verified the existence of voids and small channels in the composites due to fibre degradation

Pull-out Behaviour of Hooked End Steel Fibres Embedded in Ultra-high Performance Mortar with Various W/B Ratios

This paper presents the fibre-matrix interfacial properties of hooked end steel fibres embedded in ultra-high performance mortars with various water/binder (W/B) ratios. The principle objective was to improve bond behaviour in terms of bond strength by reducing the (W/B) ratio to a minimum. Results show that a decrease in W/B ratio has a significant effect on the bondslip behaviour of both types of 3D fibres, especially when the W/B ratio was reduced from 0.25 to 0.15. Furthermore, the optimization in maximizing pullout load and total pullout work is found to be more prominent for the 3D fibres with a larger diameter than for fibres with a smaller diameter. On the contrary, increasing the embedded length of the 3D fibres did not result in an improvement on the maximum pullout load, but increase in the total pullout work

Microstructure and Nanoscaled Characterization of HVFA Cement Paste Containing Nano-SiO₂ and Nano-CaCO₃

This paper presents the effects of nano-SiO2 and nano-CaCO3 on the microstructure of high-volume fly ash (HVFA) cement paste. The microstructures of HVFA cement pastes containing 40 and 60% Class F fly ash were evaluated at 28 days using nanoindentation, X-ray diffraction (XRD), thermogravimetric (DTA/TGA), and mercury intrusion porosimetry (MIP) analyses. A reduction of calcium hydroxide (CH) was seen in XRD analysis of HVFA pastes containing nanoparticles. This observation was also confirmed in the DTA/TGA analysis. The nanoindentation results also showed the evidence of pozzolanic reaction in the HVFA pastes, where the addition of 2% nano-SiO2 and 1% nano-CaCO3 increased the volume fractions of high-density and low-density calcium silicate hydrate (C─ S─ H) gels and confirmed the ability of nanoparticles to reduce the porosity of HVFA pastes, which was consistent with the MIP analysis. The improved nanostructure and microstructure of HVFA pastes due to the addition of nano-SiO2 and nano-CaCO3 in this study show that high-strength and highly durable sustainable concrete can be produced with lower repair and maintenance requirements for the concrete structures

Strain hardening behaviour of polyethylene fibre reinforced ambient air cured geopolymer composite

This paper presents experimental investigation on strain hardening and deflection hardening behaviour of polyethylene (PE) fibre reinforced ambient air cured geopolymer composite. Comparison is also made with its counterpart ordinary Portland cement (OPC) based composite. The effect of different volume fractions of PE fibre on compressive strength, strain hardening and deflection hardening behaviour of above two composites is evaluated and a critical volume fraction of PE fibre for strain hardening and multiple cracking behaviour is identified. Results show that ambient air cured geopolymer composites exhibited better strain hardening, deflection hardening and multiple cracking behaviour than its counterpart OPC based composite containing same volume fraction of PE fibre. Compressive strength of OPC composite is higher than that of geopolymer composite. PF fibre volume fraction of 0.75–1.0% exhibited optimum fibre content for strain and deflection hardening behaviour of both composites

Behaviour of Carbon and Basalt Fibres Reinforced Fly Ash Geopolymer at Elevated Temperatures

© 2018, The Author(s). This paper presents the behaviour of potassium activators synthesized fly ash geopolymer containing carbon and basalt fibre at ambient and elevated temperature. Six series of fly ash based geopolymer were cast where carbon and basalt fibre were added as 0.5, 1 and 1.5% by weight of fly ash. One extra control series without any fibre was also cast. Each series of samples were tested at ambient temperature and also heated at 200, 400, 600 and 800 °C and thus a total of 35 series of samples were tested in this study. The result shows that the geopolymer containing 1 wt% basalt and 1 wt% carbon fibre exhibited better compressive strength, lower volumetric shrinkage and mass loss than other fibre contents. Among two fibres composites, the carbon fibre geopolymer exhibited better performance than its basalt fibre counterpart regardless of temperature. The microstructure of carbon fibre reinforced geopolymer composite is more compact containing fewer pores/voids than its basalt based counterpart at elevated temperatures. The results also support the fact that carbon fibre is better than basalt fibre at elevated temperature and showed better bonding with geopolymer at elevated temperature