Waste-derived incense stick ash as a SCM: Linking multiscale gel-pore evolution, strength, and eco-efficiency via 1H LF-NMR and nanoindentation

Journal article, 2026

Effective utilization of incense stick ash (ISA) as a supplementary cementitious material requires a mechanistic understanding of its effects on pore evolution and performance. This study evaluates multiscale pore characterization by ¹H low-field nuclear magnetic resonance (LF-NMR), mercury intrusion porosimetry, nitrogen adsorption, and backscattered electron imaging using ISA-blended cementitious materials as a case study. LF-NMR matched nitrogen adsorption for gel pores and MIP for capillary pores, while covering a wider pore-size range. Its intraglobular, small gel and large gel pores tracked C-S-H development and corresponded to nanoindentation-derived low-, high- and ultra-high-density C-S-H, establishing a pore-phase-mechanical bridge. A Bayesian-regularized backpropagation neural network using these parameters predicted performance with errors below 10.60%. Strength-normalized cost and carbon analyses identified 5% ISA as most eco-efficient. These results support ISA as a cleaner SCM and offer a cross-scale framework for data-driven design of waste-derived cementitious materials.