Mix design and flexural toughness of PVA fiber reinforced fly ash-geopolymer composites

The orthogonal experiment design method was employed to study the mix design of poly(vinyl alcohol) (PVA) fiber reinforced fly ash-geopolymer composites (FRGC) in this paper. The influence of major mix design parameters on the working performance, setting time and mechanical properties of fly ash-geopolymer was researched. Furthermore the effect of two different kinds of PVA fibers on the tensile properties and flexural toughness of FRGC was also investigated in this paper. The composition, morphology and structure of FRGC were analyzed by X-ray diffraction and scanning electron microscopy. Based on the orthogonal experiment results, it can be concluded that the optimal values of the water/binder ratio, the modulus of sodium silicate, dosage of alkali excitation agent and the GBFS/binder ratio are 0.28, 1.2, 14% and 40%, respectively. The toughening effect of samples with 12 mm PVA fiber is more obvious than that of samples with 8 mm PVA fiber. The flexural toughness index of samples with 12 mm PVA fiber is higher than that of the control sample by over 1300%. The results of microscopic tests uncovered that continuous geopolymer gel network structure formation presented in matrix contributes to the improvement of toughness and compact degree of interface transition zone (ITZ). Furthermore, the geopolymer gel covered on PVA fiber improves the interfacial bonding strength between the composite matrix and PVA fiber. (C) 2017 Elsevier Ltd. All rights reserved.