Discussion of “Evaluation of Mechanical and Microstructural Properties of Engineered Geopolymer Composites with Construction and Demolition Waste-Based Matrices”

In their research, the authors employed construction and demolition waste (CDW) materials, including roof tiles (RTs), red clay bricks (RCBs), hollow bricks (HBs), glass (G), and concrete (C), as alkali-activated materials for preparing geopolymer composites.These materials were also utilized as substitutes for natural aggregates, leading to a comprehensive assessment of the mechanical properties and microstructures of CDW-based geopolymer composites.The discussers highly appreciate the experimental study on CDW-based geopolymer composites as presented by the authors and would like to contribute some insights to the assessment of alkali-activated materials, the geopolymer polymerization process, and the correlation between the mechanical properties and microstructure of geopolymers.Typically, alkali-activated materials employed in the formulation of geopolymer composites should exhibit a high silicaaluminum content and, crucially, demonstrate a corresponding solubility effect in alkaline environments (Zhang et al. 2023).In this investigation, the authors utilized unconventional geopolymer raw materials (such as RT, RCB, HB, G, and C), and conducted a thorough analysis of the chemical composition and mineral crystallinity of these alkali-activated materials using X-ray diffraction (XRD).In the view of the discussers, the chemical composition and mineral crystallinity play a pivotal role in influencing the reactivity and degree of reaction in geopolymerization systems, imparting significant implications to this aspect of the study.Moreover, the alkali activation process initiates with the deconstruction of the glassy (or amorphous) structure of the aluminosilicate precursor under robust alkaline conditions.This implies that the dissolution of alkali-activated materials in alkaline environments directly governs the microstructure of the resultant geopolymerization products (Provis et al. 2015).While emphasizing the physical and chemical properties of the raw materials, the reactivity of these materials in the geopolymer system can be further characterized through leaching tests conducted on the alkali-activated materials in alkaline environments.Such tests can further evaluate the ability