Mechanical properties and microstructure of metakaolin-based geopolymer compound-modified by polyacrylic emulsion and polypropylene fibers

Abstract

Geopolymer belongs to brittle or quasi-brittle materials, and the improvement of its mechanical properties especially the flexural strength and toughness has recently been attracted increasing attention due to its great potential as a green building materials. In this work, a new type of metakaolin-based geopolymer (MKG) compound-modified by polyacrylic emulsion (PAA) and polypropylene fiber (PPF), named PF-MKG, was developed, and the mechanical properties of PF-MKG, P-MKG (MKG modified only by PAA), F-MKG (MKG modified only by PPF) and MKG were measured to explore the compound-modification effect and mechanism. Mercury intrusion method (MIP), scanning electron microscope equipped with energy dispersive spectrometer (SEM+EDS), Fourier transform-infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) were employed to investigate the microstructure of PF-MKG. The results indicated that 5 wt% of PAA or 0.2 v/v% of PPF could improve the flexural strength of MKG by 39.4% or 32.3% respectively in the compound-modified of PF-MKG, but only by 22.2% or 18.5% respectively in the single-modified system. Compared with that of MKG, the flexural toughness of PF-MKG was enhanced by 569.3% whereas that of P-MKG or F-MKG was enhanced only by 202.5% or 245.9% respectively. In the microstructure of PF-MKG, geopolymer matrix adhered to PPF through PAA, and PAA could form C-O-Si bonds with geopolymer and reduce the polymerization degree of [SiO4] and [AlO4], thus promoting the formation of geopolymer gel. As a result, the adhesion between the geoploymer and the polymer was strengthed, and the pore structure was improved, finally producing a significant compound-modification effect in the compound-modified system.