Effect of Steel Fiber Additive on High Temperature Resistance in Geopolymer Mortars

In this study, the effect of steel fiber additive on high temperature resistance in geopolymer mortars was investigated. Sodium hydroxide (NaOH) was used as activator. Geopolymer mortar samples were produced by mixing fly ash, limestone sand, water, NaOH and steel fiber in different proportions. Samples placed in 40 x 40 x 160 mm standard prism molds were kept in a 100 degrees C oven for 24 h. Before high temperature effect, unit weight, apparent porosity, water absorption ratio, ultrasound pulse velocity (UPV), flexural strength and compressive strength tests were performed on the samples. Then samples were exposed to 200 degrees C, 400 degrees C, 600 degrees C and 800 degrees C temperature. After the effect of high temperature, UPV, weight loss, flexural strength and compressive strength tests were performed on the samples and compared with the samples kept at room temperature. As a result of the experimental studies, before the temperature effect, an increase in flexural and compressive strength was observed in all of the fibrous samples compared to the fiberless. While 44.81 MPa compressive strength were determined in the fiberless samples, 51.70 MPa compressive strength were determined in the samples containing 1.5% steel fiber. After the effect of high temperature, decrease in flexural strength and compressive strengths of all samples was determined. After the temperature effect of 800 oC 12.09 MPa strength was determined for the fiberless samples and 13.67 MPa for the samples containing 1.5% steel fiber. As a result of the examination of scanning electron microscope images (SEM), the formation of ettringite was observed in the samples with the effect of high temperature.