Tensile performance of eco-friendly ductile geopolymer composites (EDGC) incorporating different micro-fibers

Geopolymer composites are eco-friendly with lower carbon footprint than cementitious composites. In this paper, practical eco-friendly ductile geopolymer composites (EDGCs) with a reasonable mixing time and workability, using natural sand as fine aggregate are envisioned. The performance of EDGCs incorporating 1%, 2% and 3% volume fraction of different micro-fibers - namely polyvinyl alcohol (PVA), polypropylene (PP), high strength steel (HSS), and chopped steel wool (CSW) fibers is investigated. An alkaline solution containing sodium silicate and sodium hydroxide in the ratio 2.5:1 is used to activate fly ash to make dogbone shaped EDGC specimens to perform the tensile test. The effects of fiber type, fiber volume fraction, alkaline solution concentration, and sand content on the tensile performance of EDGCs is evaluated. HSS fibers had the least influence on workability of the EDGCs whereas CSW had the most detrimental effect. With exception of PP fibers in low-sand EDGCs, the compressive strength either remained the same or improved with addition of fibers in comparison to the unreinforced specimen. CSW and HSS fibers on the other hand demonstrated a notable improvement in compressive strength of EDGCs. Under tensile investigation, a pseudo-strain hardening response was observed with both PVA and HSS fibers in all cases. With PP fibers, a low post-crack bridging tensile strength was observed whereas the tensile strain capacity was very high (> 4%) due to the large elongation of PP fibers before fracture. The sizeable improvement in compressive strength with CSW fibers could not be replicated in the tension, and among the fibers investigated CSW had the poorest tensile response.