On the mechanical performance of K- and Na-based strain-hardening geopolymer composites (SHGC) reinforced with PVA fibers

Strain-hardening cementitious composites (SHCC) are known by their high deformation capacity due to a multiple cracking tolerance under increasing tensile loading. While SHCC have been well investigated, the design of geopolymer (GP) composites in the same context is not sufficiently understood, mainly due to varying precursor materials used in previous studies. In this work, two metakaolin-based GP mixtures were produced, using K and Na as alkali sources. The incorporation of fine-grained sand was extensively investigated to evaluate its compatibility with both strain-hardening geopolymer composites (SHGC) reinforced with short polyvinyl-alcohol (PVA) fibers. Their mechanical properties were analyzed by means of compression, bending, and tension tests. Digital Image Correlation (DIC) was used to evaluate the fracture mechanisms under uniaxial tension. Particle size distribution (PSD), X-ray diffraction (XRD), Thermogravimetric analysis (TGA) and mercury intrusion porosimetry (MIP) were conducted. Additionally, single-fiber pullout tests with subsequent Environmental Scanning Electron Microscopy (ESEM) were carried out. NaGP composites, reinforced with fine-grained sand, yielded improved mechanical responses, reaching a strain capacity of approximately 4.5%, with enhanced multiple cracking, as opposed to the lower performance observed for KGP composites, that did not present a typical strain-hardening curve when in presence of fine-grained sand, but a strain-softening one. When compared to typical SHCC responses, Na-based SHGC showed a mechanically improved multiple cracking behavior, indicating the potential of this material for a wide range of applications, such as dynamic loading and requirements of long-term durability. (C) 2020 Elsevier Ltd. All rights reserved.