Red clay brick and tungsten mining waste-based alkali-activated binder: Microstructural and mechanical properties

Abstract

This paper illustrates the study on the synthesis of alkali-activated binders based on the combination of tungsten mining waste mud (TMWM) with red clay brick waste (RCBW) with the use of sodium hydroxide (SH) and sodium silicate (SS) solution as alkaline activators; with a solid/liquid weight ratio = 3, and the SS:SH weight ratio = 2:1. The synthesis of TMWM-RCBW alkali-activated binders was conducted at 60 ± 2 °C curing temperature for 24 h, by using different TMWM and RCBW volume proportions, namely (90:10, 80:20, 70:30, 60:40 and 50:50 vt.%). Mineralogical and microstructural characterisation was carried out by X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX), simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC), mercury intrusion porosimetry (MIP) and Fourier transform infrared spectroscopy (FT-IR). The FT-IR spectra and EDX analysis demonstrated that the higher dosage of RCBW content in the samples, the higher the formation of N–A–S–H and/or C–A–S–H and/or K–A–S–H and the combination (N,C)–A–S–H and/or (N,K) –A–S–H gels during the alkaline activation process. By SEM image analysis it was also verified that more gels are formed for more denser structure of the alkali-activated materials. The increase in the dosages of RCBW in the mixtures was also followed by an increase in compressive strength for all the tested ages. It developed from 25 to 59 MPa for samples with RCBW volume content dosage of 10% and 50% respectively. Also, the binder matrix becomes denser and compact by gradually increasing the RCBW dosage.