Evaluation of mechanical and durability properties of fiber-reinforced lightweight geopolymer composites based on rice husk ash and nano-alumina

In the current study, the physical and mechanical properties of polypropylene fiber-reinforced lightweight geopolymer concretes are assessed. Geopolymer synthesis consists of rice husk ash (RHA) and nano-Al2O3 (NA) as solid precursors and 10 M sodium hydroxide (SH) and sodium silicate (SS) with a ratio of SS/SH = 2.5 as alkaline solution. NA amount is 20% of total volume of the binder for all mixtures. Scoria particles are used as lightweight aggregates (LWA) with replacement ratio of 0, 10 and 20% by volume of the total aggregates. Polypropylene (PP) fibers is added to the mixture with the amount of 0, 0.5 and 1% by the volume of the binder. Compressive and flexural strength, density, water absorption and rapid chloride permeability test (RCPT) were evaluated. Results indicated that PP fibers improves the mechanical properties (especially flexural strength) while incorporation of LWA reduced the compressive and flexural strength slightly. Water absorption of geopolymer samples decreased by the incorporation of PP fibers which can compensate significantly the negative impact of LWA replacement. Replacement of 10% LWA does not have significant impact on water absorption and chloride permeability of composites; however, 20% replacement reduced durability. Introduced lightweight geopolymer concrete would be suitable for structural applications due to its relatively low density, high compressive strength and good flexural strength, which is improved by adding PP fibers.