Preparation and Properties of Alkali Activated Metakaolin-Based Geopolymer.

Liang Chen,Yuanyi Wang,Jing Feng,Zaiqin Wang

doi:10.3390/ma9090767

Abstract

The effective activation and utilization of metakaolin as an alkali activated geopolymer precursor and its use in concrete surface protection is of great interest. In this paper, the formula of alkali activated metakaolin-based geopolymers was studied using an orthogonal experimental design. It was found that the optimal geopolymer was prepared with metakaolin, sodium hydroxide, sodium silicate and water, with the molar ratio of SiO2:Al2O3:Na2O:NaOH:H2O being 3.4:1.1:0.5:1.0:11.8. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) were adopted to investigate the influence of curing conditions on the mechanical properties and microstructures of the geopolymers. The best curing condition was 60 °C for 168 h, and this alkali activated metakaolin-based geopolymer showed the highest compression strength at 52.26 MPa. In addition, hollow micro-sphere glass beads were mixed with metakaolin particles to improve the thermal insulation properties of the alkali activated metakaolin-based geopolymer. These results suggest that a suitable volume ratio of metakaolin to hollow micro-sphere glass beads in alkali activated metakaolin-based geopolymers was 6:1, which achieved a thermal conductivity of 0.37 W/mK and compressive strength of 50 MPa. By adjusting to a milder curing condition, as-prepared alkali activated metakaolin-based geopolymers could find widespread applications in concrete thermal protection.

Highlights

Alkali activated geopolymers have attracted increasing attention in recent years for their potential uses as construction materials and environmentally cementitious binders that would partly replace ordinary Portland cement (OPC) [1,2]
It can be concluded from the range analysis that the optimal mass ratio of alkali activated metakaolin-based geopolymer was sample #5, with the highest compressive strength of 37.4 MPa
The results suggest that the best curing condition was 60 ◦ C for 168 h, where the alkali activated metakaolin-based geopolymer showed the highest compressive strength at 52.26 MPa

Summary

Introduction

Alkali activated geopolymers have attracted increasing attention in recent years for their potential uses as construction materials and environmentally cementitious binders that would partly replace ordinary Portland cement (OPC) [1,2]. Studies have shown that geopolymers have excellent mechanical properties [3], such as high early strength and low shrinkage [4,5]. Geopolymers can be used as construction panels and fire resistant materials [6] for their characteristic light weight and thermal insulation properties [7,8,9]. The initial reaction process and performance of alkali activated metakaolin-based geopolymer is influenced by the chemical composition [13], Materials 2016, 9, 767; doi:10.3390/ma9090767 www.mdpi.com/journal/materials

Methods

Results

Conclusion