Evaluation of slag/fly ash based geopolymer concrete with steel, polypropylene and polyamide fibers

Geopolymer composites have become an essential product to reduce CO2 emissions, which is an important problem today and ensures green sustainability. With the increasing concerns with global climate change, studies on geopolymer have also increased. The addition of different fibers also has essential potential for increasing the performances of geopolymer composites. Within the scope of this study, it is aimed to produce a green sustainable product as an alternative to traditional concrete by producing different fiber-reinforced geopolymer concrete. In this study, slag-fly ash-based geopolymer concretes reinforced with three different fiber types (Polypropylene (PP), steel (ST), and polyamide (PA)) were produced and the mechanical properties such as compressive, tensile, drying shrinkage and flexural behavior were investigated. Furthermore, elevated temperature (300, 600 and 900-celsius degrees) and freeze-thaw (250 cycles) tests were carried out within the scope of durability properties. Microstructural analyzes were also carried out to understand the matrix composition. Experimental test results revealed that fiber reinforcement improved some of the strength properties, but was ineffective for some properties. The addition of polypropylene and steel fibers significantly improved the flexural toughness factor value (1469% and 566%, respectively) of geopolymer concretes, while this rate of improvement remained quite low (46%) in the polyamide fiber reinforced geopolymer series. According to shrinkage test values, 50S50FA08ST sample ranged from 264 to 297 microstrains. Also, PP fibers increased the initial crack load from approximately 4500 N to 6750 N and the deflection values significantly improved by reaching the deflection values of 7.5 mm. Moreover, the compressive strength values after 900 degrees C was obtained as 11-12 MPa for steel fiber reinforced geopolymer concretes. But the freeze-thaw experiments generally revealed that fiber addition did not contribute to the improvement of strength properties