Mechanistic insights into alkali-silica reaction mitigation using fly ash and rice husk ash: An integrated experimental and multi-scale simulation approach

Abstract

The alkali-silica reaction (ASR) poses a persistent durability threat in concrete structures containing reactive aggregates. This study combines experimental testing with a calibrated numerical modeling framework to evaluate the synergistic mitigation of ASR through combined use of fly ash and rice husk ash (RHA) as supplementary cementitious materials (SCMs). Aggregates from the Chichali and Lumshiwal formations classified as highly and moderately reactive, respectively, were characterized by Petrographic, X-ray Diffraction, and Scanning Electron Microscopy analyses, and incorporated into mortar bars following ASTM Standard. Experimental results revealed that individual additions of FA or RHA reduced expansion relative to the control; however, the binary blend containing 20%FA + 10%RHA achieved the most significant improvement, lowering 56-d expansion from 0.25% (control) to 0.08%, well below deleterious limits, while simultaneously increasing compressive strength from 25–27 to ≈ 30 MPa. Microstructural observations confirmed a denser, crack-free matrix with discontinuous ASR gel films. Finite-element and voxel-based simulations, calibrated against the measured expansion data, were used to interpret stress-indicator distribution and gel connectivity trends within the mortar microstructure. Control mixes exhibited continuous, high-stress gel networks, whereas the FA–RHA blend generated diffuse, low-stress voxel morphologies, indicating stable, non-percolating gel structures. Extended-time simulations up to 365 d suggested reduced expansion trends for the FA–RHA blend; however, these long-term results represent model extrapolations based on calibrated parameters rather than direct experimental validation. The combined experimental–modeling approach provides an interpretative framework for relating SCM incorporation to reduced ASR expansion through alkali consumption and altered gel connectivity. The findings contribute to the evaluation of binary SCM systems for mitigating ASR in regionally sourced reactive aggregates.

Graphical abstract

Keywords

ASR / SCMs / finite-element and voxel simulation / concrete durability

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