EFFECT OF HEAT EXPOSURE ON THE FLEXURAL STRENGTH OF REINFORCED CARBON AND GLASS FIBERS GEOPOLYMER MATRIX COMPOSITES

摘要

Geopolymer has been used as substitute for Portland cement in concrete. Heat resistance is one of the advantages of geopolymer compared to Portland cement. As with Portland cement concrete, flexural strength of geopolymer is less than 10% of its compressive strength. Fibers reinforcement of the geopolymer matrix was expected to increase flexural strength. In this experiment, 2.5, 5.0 and 7.5 wt% of chopped carbon and glass fibers are added to the geopolymer matrix which was made by mixing fly ash and sodium silicate solution. Heating of the cured specimens for 2 hours at 200, 400 and 600°C has been carried out to observe heat resistance. In general, fiber reinforcement did not significantly increase flexural strength but did increase heat resistance. The addition of 5 wt% carbon fibers to the geopolymer matrix gave a slight increase in flexural strength from 13.530 MPa to 15.998. Aside from that, the flexural strength decreased slightly with the addition of fibers. The flexural strength of the cured geopolymer matrix dropped to 1.780, 1.256 and 0.880 MPa after exposure to200, 400 and 600°C respectively. The best heat resistance was provided by the glass fiber reinforced composite. The strength of cured composite was 11.263 MPa. After exposure at 200, 400 and 600°C, the strength was sustained to 10.518, 12.234 and 10.518 MPa respectively. Although not as good as glass, carbon fibers reinforcement sustained the after exposure strength from 15.998 MPa to 14.152, 12.279 and 6.841 MPa with the respective exposure temperatures.