Eco-mechanical synergy in low-cement CLSM from MSWIBA and TBM slurry : a Ca(OH)₂-activated cross-scale engineering approach

Abstract

In this study, a low-cement controlled low-strength material (CLSM) was designed by synergistically incorporating municipal solid waste incineration bottom ash (MSWIBA) and tunnel boring machine (TBM) waste slurry, with Ca(OH)₂ as an activator. The roles of Ca(OH)₂ in reaction pathways, multi-scale pore structure evolution, and carbon intensity were systematically investigated through rheological tests, mechanical measurements, XRD, TG/DTG, SEM-EDS, MIP, X-CT, and carbon footprint analysis. Results show that the exogenous Ca(OH)₂ is completely consumed via pozzolanic reaction, clay adsorption, and early carbonation, shifting from a conventional alkaline activator to a direct reactant that governs gel chemistry while maintaining satisfactory flowability (> 180 mm). Cross-scale characterization reveals that the strength enhancement originates primarily from topological fragmentation of the defect architecture rather than from a mere reduction in total porosity. Despite a modest increase in embodied carbon due to Ca(OH)₂ addition, the disproportionate strength gain reduces the carbon intensity of the CLSM by 26%. By integrating mechanistic insight, cross-scale structural engineering, and eco-mechanical assessment, this work establishes a new framework for transforming disparate solid wastes into low-carbon CLSM through rationally designed activation.