Properties of modified engineered geopolymer composites incorporating multi-walled carbon Nanotubes(MWCNTs) and granulated blast furnace Slag(GBFS)

Engineered cementitious composites (ECC) are widely used owing to their high tensile capacity and strainhardening behavior; however, the use of large quantities of cement require huge amount of resources and pollutes the environment. Fly ash-based geopolymer has been considered as a promising alternative for the development of high-ductility eco-friendly engineered materials. To improve the tensile capacity of engineered geopolymer composites (EGC), an ultra-high-ductility engineered geopolymer composite has been developed with the incorporation of functionalized multi-walled carbon nanotubes and polyvinyl alcohol fiber. This paper reports the mixture process and mechanical tests on EGC with different mixtures. Fourier transform infrared spectroscopy (FT-IR) and X-ray powder diffraction were used to investigate the characteristics of the reaction products in the geopolymer matrix. The microscopic morphology of the geopolymer matrix were characterized using field emission scanning electron microscopy. The excellent saturated multiple cracking properties and strain hardening of the ultra-high EGC (UHEGCs) were demonstrated by uniaxial tension testing. At the maximum limit, the residual crack width and crack spacing of UHEGCs were generally less than 70 ?m and 2 mm, respectively. Tensile strain-hardening behavior with an ultimate tensile strain greater than 8% was experimentally demonstrated for the UHEGC. Meanwhile, the compressive strength of the UHEGC was greater than 45 MPa. The pseudo-strain hardening (PSH) indexes of UHEGC were used to determine the tensile capacity formation. Analysis demonstrated that the tensile capacity of UHEGC can be quantified using the classic PSH criterion, whereas ultra-high crack-bridging capacity was attributed to the ultra-high-ductility of UHEGC. The XRD studies demonstrated that for the reaction products of the geopolymer matrix, new crystalline phases are insignificant. The FT-IR analyses revealed that the amorphous aluminosilicate phases were mainly reaction products, i.e., N-A-S-H. Most importantly, the multi-scale (micro- and meso-scale) modification mechanisms of the material through the addition of two fibers were revealed.

Automated summary

Engineered cementitious composites (ECC) are widely used for their high tensile capacity and strain-hardening behavior, while fly ash-based geopolymer is considered a promising eco-friendly alternative. This study developed an ultra-high-ductility engineered geopolymer composite (UHEGC) with excellent multiple cracking properties and strain hardening. Various tests, including FT-IR and XRD, were used to investigate the characteristics of reaction products in the geopolymer matrix.