Synthesizing and Assessing Fire-Resistant Geopolymer from Rejected Fly Ash

Abstract

Ordinary Portland cement is a widely favored construction material because of its good strength and durability and its reasonable price; however, spalling behaviour during fire exposure can be a serious risk that can lead to strength degradation or collapse of a building. Geopolymers, which can be synthesized by mixing aluminosilicate source materials such as metakaolin and fly ash, and alkali activators, are resistant to fire. Because the chemical composition of geopolymers controls the properties of the geopolyers, geopolymers with various Si:Al ratios were synthesized and evaluated as fire resistant construction materials. Rejected fly ash generated from a power plant was quantitatively analyzed and mixed with alkali activators to produce geopolymers having Si:Al ratios of 1.5, 2.0, and 3.5. Compressive strength of the geopolymers was measured at 28 days before and after heating at 900 o C. Geopolymers having an Si:Al ratio of 1.5 presented the best fire resistance, with a 44% increase of strength from 29 MPa to 41 MPa after heating. This material also showed the least expansion-shrinkage characteristics. Geopolymer mortar developed no spalling and presented more than a 2 h fire resistance rating at 1,050 o C during the fire testing, with a cold side temperature of 74 o C. Geopolymers have high potential as a fire resistant construction material in terms of their increased strength after exposure to fire.

Optimal Design of Ferronickel Slag Alkali-Activated Material for High Thermal Load Applications Developed by Design of Experiment

“…The compressive strength The calculated coefficients of determination between the Si/Al ratios and compressive strengths for ferronickel slag low-calcium AAM were found to lie below 0.22 and indicate very poor correspondence. The lack of correlation between the compressive strength and Si/Al ratio has also been reported in other studies [35]. The addition of silica fume in the mixture likely had a strong influence on the mechanical properties of the mix, which obscures the role that the Si/Al ratio has on the measured responses.…”

“…Previous works (between 800 • C and 1000 • C) associated lower Si/Al ratios with higher residual strengths [14,35]. On the contrary, other authors like Kong [12] correlate higher Si/Al ratios with smaller reductions in strength after a high thermal load, or even with increases in residual strength [67].…”

“…All prisms programmed for heating were exposed to a thermal load comprising a ramp of 5 • C/min up to 900 • C, followed by a constant temperature step spanning 2 h; then, the oven was turned off and the specimens were left to cool down in the oven (with the door shut) until the next day. For heating, an electrical 500 mm 3 oven was used, with a maximum heating capacity of 1100 • C. This heating regime was adopted to allow for comparison with previous studies that followed the same protocol [32,33] and others varying only the ceiling temperature, which was kept constant for 1 h [34][35][36]. The specimens' dimensions were measured with a vernier caliper, and the shrinkage/expansion was evaluated as the difference between pre-and post-high temperature exposure measurements.…”

A Review on Geopolymer Technology for Lunar Base Construction

“…Above all, geopolymer is a material with excellent fire resistance that can withstand temperatures up to 900~1000 • C without spalling. Depending on the formulation, the compressive strength of some geopolymers was observed to increase at high temperatures [13,26]. The superior physical and chemical properties of geopolymer compared to OPC makes it a promising prospect to be manufactured from lunar regolith and is thus an ideal construction material for the purposes of ISRU.…”

Scientometric Analysis of Global Research on the Utilization of Geopolymer Composites in Construction Applications

“…The effect of alkaline activator ratio [131], Si to Al ratio [132], additives such as aluminum powder and calcined clay [133], nanomaterials such as nano titanium dioxide [60,134], and fibers such as polypropylene [135] fibers on the fire resistance of geopolymer composites.…”