PLS-MCDM-based evaluation of consolidation materials for earthen heritage sites: moisture regulation and overall consolidation performance of SAP

The deterioration of earthen heritage sites is highly coupled with moisture-related damage in earthen soils, underscoring the urgent need to identify soil moisture-regulating materials and to establish a corresponding evaluation system. In this study, superabsorbent polymer (SAP) is employed as a moisture-regulating material, and the effects of SAP type and content on nine performance indices are tested, including the drying delay factor (DDF), apparent diffusion coefficient (Dapp), evaporation reduction factor (ERF), and disintegration coefficient (DC). In parallel, a partial least squares structural equation modeling–multi-criteria decision making (PLS-MCDM) subjective–objective integrated evaluation framework is developed. The results show that a medium SAP dosage of 0.3%–0.5% markedly enhances drying delay, reduces effective diffusion and constant-rate evaporation, and maintains acceptable penalties in appearance and water vapour permeability. In contrast, a 0.1% dosage provides insufficient moisture control, while at 1% the penalties increase and marginal benefits diminish, with pronounced differences among SAP types. This work provides empirical data to support the application of SAP in moisture regulation for earthen heritage sites and, through PLS-MCDM, proposes a general comprehensive evaluation framework for conservation materials.