Abstract
Aluminosilicate minerals have become an important resource for an emerging sustainable material for construction known as geopolymer. Geopolymer, an alkali-activated material, is becoming an attractive alternative to Portland cement because of its lower carbon footprint and embodied energy. However, the synthesis process requires typically a two-part system for alkali activation wherein the solid geopolymer precursor is mixed with aqueous alkali solutions. These alkali activators are corrosive and may be difficult to handle in the field-scale application. In this study, a one-part geopolymer in which coal fly ash was mixed with solid alkali activators such as sodium hydroxide and sodium silicate to form a powdery cementitious binder was developed. This binder mixed with soil only requires water to form the soil-fly ash (SO-CFA) geopolymer cement, which can be used as stabilized soil for backfill/foundation. This geopolymer product was then evaluated for chemical stability by immersing the material with 5% by weight of sulfuric acid solution for 28 days. Indication suggests that the geopolymer exhibited high resistance against acid attack with an observed increase of unconfined compressive strength even when the immersion time in acidic solution was increased to 56 days. The mineralogical phase, microstructure, and morphology of the material were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), respectively. Results not only confirmed the formation of gypsum due to acid attack but also indicated the dissolution of anorthite and albite that may have caused the microstructure to be composed of sodium aluminosilicate hydrate (N–A–S–H) and calcium (alumino) silicate hydrate (C(–A)–S–H) with poly(ferro-sialate-siloxo) and poly(ferro-sialate-disiloxo) networks. A column leaching test with deionized water was also performed on the soil-fly ash geopolymer to study the leachability of metals in the material. Results showed that arsenic exhibits higher mobility in the geopolymer as compared to that of cadmium, chromium, and lead.
Highlights
The construction industry contributes to about one-third of the energy-related global CO2 emissions which makes it a significant sector often targeted as part of the mitigation strategies to Minerals 2018, 8, 411; doi:10.3390/min8090411 www.mdpi.com/journal/mineralsMinerals 2018, 8, 411 reduce carbon footprint [1]
This study has evaluated the acid resistance and leachability of geopolymer from soil-fly ash mixture using a one-part geopolymer binder system
The soil-fly ash geopolymer cement showed a promising result in terms of compressive strength considering that the strength further increased after acid exposure, from 1.0 MPa to 2.6 MPa (28-day immersion) and 3.2 MPa (56-day immersion)
Summary
The construction industry contributes to about one-third of the energy-related global CO2 emissions which makes it a significant sector often targeted as part of the mitigation strategies to Minerals 2018, 8, 411; doi:10.3390/min8090411 www.mdpi.com/journal/mineralsMinerals 2018, 8, 411 reduce carbon footprint [1]. The construction industry contributes to about one-third of the energy-related global CO2 emissions which makes it a significant sector often targeted as part of the mitigation strategies to Minerals 2018, 8, 411; doi:10.3390/min8090411 www.mdpi.com/journal/minerals. One of the important materials in the construction industry is Portland cement where it is used as a binder. The production of cement accounts for 5–8% of global anthropogenic emissions [2]. Carbon dioxide emissions from cement production come from the calcination process to produce clinker and from the combustion of fuel used for heating. Several efforts have been made to reduce its consumption such as blending of other pozzolanic and cementitious materials to reduce clinker consumption, and utilization of agricultural waste as an alternative source of fuel
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