The effect of polypropylene fiber additive on fly ash and blast furnace slag based geopolymer composite material properties

In this study, mechanical and physical properties of geopolymer composites based on fly ash (FA) and ground granulated blast furnace slag (GGBFS) were investigated. Fly ash (FA) and ground granulated blast furnace slag (GGBFS) mixtures with polypropylene (PP) fiber addition by weight (0.5 %, 1.0 % and 1.5 %) were activated by 10 M sodium hydroxide (NaOH) and sodium silicate solutions (Na2SiO3) (2 and 3 module). Geopolymer composite samples were placed in 4 x 4 x 16 cm metal molds with the help of a vibrating table. The relevant samples were subjected to heat curing for 5 hours in a laboratory oven at 90 °C, and then stored at room temperature for 7 days. Subsequently, in order to determine their physical properties, the relevant samples were kept in the water tank for 24 hours, and then the physical properties of the samples such as water absorption by weight, apparent porosity, unit volume weight and apparent density were determined according to Archimedes principle. Then the flexural and compressive strength values of the samples were determined. The obtained physical and mechanical properties were evaluated and experiments were continued on the sample groups (geopolymer mortars with 50 % FA and 50 % GGBFS content), which were thought to provide ideal values. On these sample groups, phase contents with XRD analysis, surface morphology with SEM-EDX analysis, and sample properties were examined with findings obtained from durability tests such as freezing-thawing, exposure to high temperature and sulphated environments (with 5 % of NaSO4 and 5 % of MgSO4 solutions). Flexural strength of reference samples varied between 0.1 MPa - 5.6 MPa, and between 2.4 MPa - 11.4 MPa in fiber reinforced samples. The compressive strength values of the reference samples varied between 15.3 MPa - 60.9 MPa, while this value varied between 21.4 MPa - 77.60 MPa in fiber reinfoeced samples. Therefore, it has been observed that positive developments occurred in the mechanical properties of the samples with the increase in the fiber ratio in the mixtures. Consequently, when all the findings obtained in the prepared geopolymer composite materials are evaluated; It has been determined that mixtures prepared with 50 % FA and 50 % GGBFS are activated with 3 modules of sodium silicate solution and 10 M NaOH, and it has been concluded that they can be used in structures. For this reason, samples with the same content were also used in durability tests and experiments. When the findings obtained from the durability tests are evaluated, it is thought that 1.5 % PP fiber added geopolymer composite mortars have better durability properties.