Investigation of the effect of basalt fiber on some mechanical properties and high temperature behavior of structural geopolymer lightweight concrete

In this study, the effect of basalt fiber on the mechanical, thermal properties and high temperature behavior as well as the microstructure of structural geopolymer lightweight concrete was investigated. Blast furnace slag, metakaolin and cement were used as binders, pumice and limestone as aggregates, and basalt fiber was used as fiber. A mixture of sodium hydroxide and sodium silicate was used as the alkali activator solution. The mechanical, thermal and high temperature properties of the concretes, the microstructure and the products formed as a result of the reaction and the obtained data were statistically evaluated and interpreted. All concretes produced meet the criteria specified for structural lightweight concrete. In terms of mechanical properties, 0.2% basalt fiber structural geopolymer lightweight concrete gave superior results compared to all other geopolymer concretes. The thermal conductivity coefficients of geopolymer lightweight concretes ranged from 0.37 W/mK to 0.53 W/mK. At high temperatures, geopolymer lightweight concretes containing fibers show similar behavior to the reference geopolymer lightweight concrete, and the compressive strengths of all geopolymer concretes show a significant decrease up to 600°C, while they tend to increase after this temperature. Characterization analyses show that at 0.3% and higher fiber content, the paste phase-fiber interlocking is improved and, accordingly, the deformation of the concretes is increased. The loss in weight of the concretes observed through the thermal analysis becomes quite evident around 700°C.