Study on the preparation, performance, and mechanism for solid waste cementitious materials

Using granulated blast furnace slag (GGBS) as the volcanic ash material and fly ash (FA) as the supplementary material, the study was conducted to investigate the mix proportions of an alkali-activated solid waste cementitious material under the stimulating effect of alkali activator carbide slag (CS). This type of cementitious material could serve as a substitute for a portion of cement usage, contributing to resource conservation and mitigating environmental pollution caused by solid waste. This facilitates green and sustainable development. Firstly, an analysis of three raw materials was conducted, and the mix proportions were designed with reference to the CaO-Al2O3-SiO2 system of Portland cement. Then 28 groups of specimens were prepared based on the designed mix proportions. The flowability and setting time of each group of specimens were tested. It was observed that an increase in the amount of CS and a decrease in the amount of GGBS resulted in decreased flowability and earlier setting times of the specimens. Additionally, FA exhibited a retarding effect on setting time. Compressive strength tests were conducted on these specimens, revealing that the optimal CS content ranged between 20 % and 40 %. Overall, FA had minimal impact on compressive strength, but it contributed to increased compressive strength in the specimens at later ages. Subsequently, microscopic characterization of the hydration products was performed using X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR), Differential Thermal Analysis (DTA), Scanning Electron Microscope (SEM), and Energy Dispersive Spectrometer (EDS). The hydration products were identified as predominantly composed of calcium silicate hydrate. The quality and defects in the microstructure of gel products from various specimen formulations were compared to elucidate differences in macroscopic performance. Finally, the hydration process mechanism diagram of alkali-activated materials was presented to illustrate the stimulation and formation of gel products, primarily composed of C-S-H. This diagram revealed the principles behind the action of alkali-activated cementitious materials. The proposed design and testing methodology for the GGBS-FA-CS system in this study had certain reference significance for research in the direction of alkali-activated solid waste cementitious materials.