Long-Term Physical and Mechanical Properties and Microstructures of Fly-Ash-Based Geopolymer Composite Incorporating Carbide Slag.

Xianhui Zhao,Boyu Zhou,Lingchao Meng,Jiashuo Zhang,Haoyu Wang,Linlin Jiang

doi:10.3390/ma14216692

Xianhui Zhao, Boyu Zhou + Show 4 more

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https://doi.org/10.3390/ma14216692

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Abstract

The long-term property development of fly ash (FA)-based geopolymer (FA–GEO) incorporating industrial solid waste carbide slag (CS) for up to 360 d is still unclear. The objective of this study was to investigate the fresh, physical, and mechanical properties and microstructures of FA–GEO composites with CS and to evaluate the effects of CS when the composites were cured for 360 d. FA–GEO composites with CS were manufactured using FA (as an aluminosilicate precursor), CS (as a calcium additive), NaOH solution (as an alkali activator), and standard sand (as a fine aggregate). The fresh property and long-term physical properties were measured, including fluidity, bulk density, porosity, and drying shrinkage. The flexural and compressive strengths at 60 d and 360 d were tested. Furthermore, the microstructures and gel products were characterized by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The results show that the additional 20.0% CS reduces the fluidity and increases the conductivity of FA–GEO composites. Bulk densities were decreased, porosities were increased, and drying shrinkages were decreased as the CS content was increased from 0.0% to 20.0% at 360 d. Room temperature is a better curing condition to obtain a higher long-term mechanical strength. The addition of 20.0% CS is more beneficial to the improvement of long-term flexural strength and toughness at room temperature. The gel products in CS–FA–GEO with 20.0% CS are mainly determined as the mixtures of sodium aluminosilicate (N–A–S–H) gel and calcium silicate hydration (C–S–H) gel, besides the surficial pan-alkali. The research results provide an experimental basis for the reuse of CS in various scenarios.

Highlights

In recent years, geopolymer materials have obtained much focus, interests, and developments, owing to their environmentally friendly materials that act as an alternative to ordinary Portland cement (OPC) materials [1,2,3]
The square areas (40 mm × 40 mm) at the middle positions of side surfaces were uniformly taken out, and the pore distributions were observed by naked eye, as mentioned in the literature [23], in order to analyze the correlation with tested porosity
The aim of this paper is to evaluate the effects of carbide slag (CS) on the fresh, physical, and mechanical properties of fly ash (FA)-based geopolymer (FA–GEO) composites, and to further characterize the microstructure and gel products of CS–fly-ash-based geopolymer (FA–GEO) composites

Summary

Introduction

Geopolymer materials have obtained much focus, interests, and developments, owing to their environmentally friendly materials that act as an alternative to ordinary Portland cement (OPC) materials [1,2,3]. Geopolymer materials tend to be prepared using industrial waste by-products as an aluminosilicate source (fly ash, red mud, blast furnace slag, etc.) rather than natural materials (including metakaolin, etc.) due to the economic and evenly available characteristics [5,7,8,9]. Low-calcium fly ash (active CaO, lower than 10.0% by mass) is regarded as one of the main industrial solid aluminosilicate by-products, which is employed to synthesize geopolymer materials through alkali activation under a NaOH or/and Na2 SiO3 solution [10]. It is emphasized that, when the concentration of the NaOH solution with less than 10.0 mol/L was used to manufacture the low-calcium fly-ash-based geopolymer (FA–GEO) materials at room temperature, it obtained a lower mechanical strength at a

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