Investigation on physical behavior, impermeability and micromechanism of engineering geopolymer composites modified with MWCNTs

Abstract

As a green cementing material, geopolymer solves the problems of environment pollution and building resource waste. The working performance, including setting time and flowability, were firstly evaluated to select a basic mix proportion of geopolymer. Then, the study was aimed at assessing the effect of PVA fibers (1.50 %, 2.00 % and 2.50 % by the volume of sample) and MWCNTs contents (0.05 %, 0.10 %, 0.15 % and 0.20 % by the mass of blinders) on the impermeability and mechanical strength of engineering geopolymer composite(EGC). Meanwhile, the pore structure, polymerization products and microscopic morphologies of geopolymers incorporated with different MWCNTs contents were researched by micro-structure analysis. The experimental results show the 0.1 % functionalized MWCNTs effectively improve the compressive strength, bending strength and impermeability of modified geopolymer by 9.4 %, 23.6 % and 63.2 %, respectively, and the corresponding relative permeability coefficient of modified geopolymer is decreased by 63.24 % compared to that of control geopolymer. Importantly, the incorporation of the functionalized MWCNTs can refine the pore structure and enhance whole compactness of the internal structure, meanwhile limit the extension and expansion of micro-cracks owning to its nano-nucleation, nano-filling and nano-laying effect. Furthermore, the introduction of functionalized MWCNTs improves the geopolymerization reaction of Si-O-Si bands by means of FT-IR analysis. The MIP analysis show that the addition of functionalized MWCNTs can increase the proportion of harmless pores but decrease the quantity of harmless pores. Significantly, the effective porosity(rather than total porosity) should be adopted to evaluate the impermeability of geopolymer because of the appearance of ink bottle pores.