Abstract
As a cementitious material, geopolymers show a high quasi-brittle behavior and a relatively low fracture energy. To overcome such a weakness, incorporation of fibers to a brittle matrix is a well-known technique to enhance the flexural properties. This study comprehensively evaluates the short and long term impacts of different volume percentages of polypropylene fiber (PPF) reinforcement on fly ash based geopolymer composites. Different characteristics of the composite were compared at fresh state by flow measurement and hardened state by variation of shrinkage over time to assess the response of composites under flexural and compressive load conditions. The fiber-matrix interface, fiber surface and toughening mechanisms were assessed using field emission scan electron microscopy (FESEM) and atomic force microscopy (AFM). The results show that incorporation of PPF up to 3 wt % into the geopolymer paste reduces the shrinkage and enhances the energy absorption of the composites. While, it might reduce the ultimate flexural and compressive strength of the material depending on fiber content.
Highlights
Geopolymers are inorganic aluminosilicate polymeric material which cure and harden at near ambient temperatures [1]
X-ray diffraction (XRD) analysis were performed on an Empyrean PANALYTICAL diffractometer with monochromated Cu Kα radiation (λ = 1.54056 Å), operated at 45 kV and 40 mA with a step size of 0.026 deg and a scanning rate of 0.1 deg s-1 in the 2θ range of 5 to 75 deg to verify the change in crystalline phases of fly ash based geopolymer because of the polypropylene fiber (PPF) incorporation
The ATR-Fourier transform infrared spectroscopy (FTIR) spectrum of PPF fibers showed four large peaks in the wavenumber range 2800– 3000 cm-1: the peaks at 2952 and 2872 cm-1 were allocated to the CH3 asymmetric and symmetric stretching vibration respectively, while the peaks at 2920 and 2839 cm-1 were attributed to CH2 asymmetric and symmetric stretching vibrations respectively
Summary
Geopolymers are inorganic aluminosilicate polymeric material which cure and harden at near ambient temperatures [1]. Polypropylene fiber (PPF) have been extensively used as a reinforcement in Portland cement based materials because of its high toughness and durability; while there was a conflict about the correlation of the PPF content and the corresponding compressive strength of the concrete. It was stated by Building Research Establishment (2000) that incorporation of PPF reduces the compressive strength of concretes significantly, some others reported that there was no tangible reduction on compressive strength because of the PPF content [23,24,25]. Flexural toughness was increased and mode of failure changed from brittle to ductile in high PPF content fly ash based geopolymer composites
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