The making of Class C fly ash as high-strength precast construction material through geopolymerization
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The making of Class C fly ash as high-strength precast construction material through geopolymerization Jinhong Zhang 1
&
Qingming Feng 1
Received: 13 April 2020 / Accepted: 4 August 2020 # Society for Mining, Metallurgy & Exploration Inc. 2020
Abstract A study has been carried out to apply fly ash as a high strength, water-resistant precast construction material through geopolymerization. Experiment results show that the working conditions such as water content, the concentration of NaOH, curing temperature, and curing time significantly affect the mechanical property of geopolymer matrix. Through optimization, an above-100 MPa compressive strength has been achieved with the geopolymerization products. The optimum working conditions involves 10 M NaOH concentration, 14–15% water content, and curing at 90 °C in an oven for 1 day or at ambient condition for 3 weeks. Adding Ca(OH)2 does not help to increase the compressive strength of the specimen. Water soaking tests show that the geopolymerization product has a very high water resistance without losing noticeable compressive strength, even after a 1-month soaking time. To elucidate the geopolymerization mechanism, microscopic techniques such as SEM/EDS (scanning electron microscopy and energy-dispersive X-ray spectroscopy), XRD (X-ray diffraction) and ATR-FTIR (attenuated total reflectance Fourier transform infrared) are also applied to investigate the microstructure, the elemental and phase composition of geopolymerization products. The findings of the present work provide a novel method for applying fly ash as a high-strength water-resistant precast construction material. Keywords Fly ash . Geopolymerization . Alkali activation . Compressive strength . Water-resistant
1 Introduction Geopolymerization is a process of obtaining a polymeric structure from aluminosilicate by dissolving aluminosilicate sources in a strong alkali (NaOH) solution and condensation of free [SiO4] and [AlO4] tetrahedral units [1–3]. After being cured at an elevated temperature for a specific time, the geopolymerization product shows a greatly increased compressive strength. Therefore, the product can be used as construction material such as bricks and road pavement. It provides a very promising method for applying aluminosilicate sources such as fly ash as a construction material for a sustainable development. Fly ash is a major industrial waste which needs to be carefully impounded because of its potential impact on environment. Many efforts have been tried to utilize fly ash as
* Jinhong Zhang [email protected] 1
Department of Mining and Geological Engineering, The University of Arizona, 1235 E. James E. Rogers Way, Tucson, AZ 85721, USA
construction materials, substituting for Portland cement, because of the following reasons [4, 5]. First, fly ash is a silica/ alumina-rich aluminosilicate source, which makes the specific material an ideal source for the geopolymerization process. Secondly, the particle size of fly ash is usually very small (< 50 μm), and this saves a lot
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