Optimizing mechanical performance of geopolymers produced from construction and demolition waste: A comparative study of materials from different origins

Abstract

Construction and demolition wastes (CDW) are promising sources for geopolymer production; however, the great variability of CDWs arising from their origin causes an abstention from implementation. As one of the key challenges in the CDW management and recycling practices, origin-depended variations in the waste materials and their reflection on the final product performance can be overcomed through in-depth waste characterization and design optimization. To this end, this paper aims to characterize CDWs collected from five different demolition zones with regard to their physical-, chemical-properties and the mechanical performance of geopolymer pastes produced with them. The compressive strength of geopolymer pastes was found to be significantly influenced by the chemical composition, crystalline nature, and fineness of CDWs. Optimization of precursor characteristics resulted in consistent mechanical performance ranging from 54.5 to 68.0 MPa after curing at 115 °C for 48 hours, regardless of the CDW origin. The aluminosilicate and calcium content of the precursor heavily influenced the ultimate gel structure in a positive manner, which determined material strength. The optimized use of CDWs from the same source increased the compressive strength of geopolymer pastes by up to 64%.