Research on mechanical properties and micro-mechanism of Engineering Geopolymers Composites (EGCs) incorporated with modified MWCNTs

Fly ash-based geopilymers have been considered as a promising alternative for the development of high-ductility and eco-frindly engineered materials. In this study, high ductility EGCs were prepared with the incorporation of polyvinyl alcohol (PVA) fiber and modified multi-wall carbon nanotubes (MWCNTs). The compression, flexural and four-point bending tests were used to evaluate the mechanical behaviors of EGCs. The relationship between the ultimate tensile strain and the mid-span displacement was discussed. Meanwhile, the micro-structure and morphology of EGCs were researched using the field emission scanning electron microscopy(FESEM) analysis. The experimental result showed that the compressive and flexural strength of modified geopolymers containing 0.10% modified MWCNTs and 2.00% PVA fiber at curing age of 28d reached maximal value(38.43 MPa and 7.75 MPa). Meanwhile, the uniaxial tensile strain of EGCs also reached maximal value(8.02%), and the corresponding cracking strain, cracking stress and ultimate tensile stress were 0.08%, 2.00 MPa and 4.70 MPa, respectively. In addition, the computing result of ductility indexes and residual strength indexes were well related with corresponding requirements of the deal elastoplastic material. And the four-point bending test could be employed to evaluate the special mechanical properties of uniaxial tensile test. Most importantly, the mechanism of anti inferiority of EGCs was explained and analyzed from the point of view of microscopic perspective and mesoscopic perspective, and a new mechanism for the modification of PVA fiber and modified MMWCNTs was revealed.