Rheological Property and Extrudability Performance-Assessment of Construction and Demolition Waste-Based Geopolymer Mortars with Varied Testing Protocols (2022-12)¶

This study investigated fresh properties of 100% construction and demolition waste (CDW)-based geopolymer mortars providing innovative solutions for waste upcycling in favor of continuously transforming sustainable construction applications. Mortars were produced by utilizing hollow brick, red clay brick, roof tile, glass and concrete wastes as precursors and crushed concrete waste as aggregates. For activation, different combinations of NaOH-(molar concentrations of 7.5-10-12.5-15) and Ca(OH)2-(0-4-8%, by weight of binder) were used. For rheological assessments, different protocols including flow curve, constant shear rate, varied shear rate and three interval thixotropy testing (3ITT) were implemented. Ram extrusion was performed to investigate the extrudability performance of the mixtures. The study showed that the mortars’ rheological properties can be driven by arranging alkaline activator content. Although empirical approaches of flow curve, constant shear rate, and varied shear rate were able to verify the existence of thixotropy behavior, they were not capable of quantifying the viscosity recovery level of the mixtures, as opposed to 3ITT method. The 3ITT results showed that the viscosity recovery performances of geopolymers with varying activator content were between 65 and 82%. Ram extrusion demonstrated that mixtures were extruded without showing any types of failures, although some of them had different types of failures on the extruded specimen with the increased resting time beyond 60 min. However, except for 15M-activated mixtures, each mixture was extrudable even after 120 min. In general, this study presents a comprehensive investigation of assessing the rheological properties and extrudability performance of the CDW-based geopolymers via performing various testing methods.