The shrinkage behavior of alkali-activated materials (AAMs) is governed by the combined effects of precursor type, activator chemistry, and curing conditions, which control microstructure development and hydration gel formation. The synergistic interaction between these two factors ultimately dictates the material’s shrinkage behavior. Due to the varying reaction kinetics of raw materials, short-term shrinkage measurements often fail to capture the long-term effects of these influencing factors on the material’s dimensional stability. In this work, slag/fly ash-based AAM with varying alkali contents were cast and subjected to different durations of sealed curing before long-term drying shrinkage tests (up to one year). Pore structure and gel chemistry were analyzed to decouple their roles in shrinkage behavior. Results show that prolonged initial curing drastically reduces shrinkage, while early exposure to drying accelerates shrinkage kinetics. When exposed to drying at an early age, mixes with higher fly ash content exhibited the greatest shrinkage after one year, whereas if cured for a longer duration, mixes with higher slag content exhibited the highest shrinkage strain. Shrinkage–mass loss relationships followed a three-stage S-curve, reflecting the combined effects of pore structure and gel characteristics. By isolating specimens with comparable pore structures at the time of exposure, gel characteristics were shown to directly govern shrinkage, with higher Na/Si ratios disrupting the C-(N)-A-S-H gel network and increasing shrinkage. Thus, this work bridges microstructural insights with practical mix design, enabling the development of AAM binders with reduced shrinkage and improved durability. ... Read more

While ensuring the long-term integrity of wellbore sealants is critical for the success of geological carbon storage (GCS), the chemical degradation of conventional materials under CO₂-rich conditions remains a major challenge. This study investigates the carbonation behavior of a one-part granite-based geopolymer, integrating a novel pore-scale simulation framework with experimental validation. A new model, ReacSan, is developed to simulate CO₂ transport and carbonation reactions within the evolving microstructure of the geopolymer under GCS-relevant conditions. The framework incorporates CO₂ dissolution using the Redlich–Kwong equation of state, gel dissolution via transition state theory, ion transport using the Lattice Boltzmann Method, and chemical reactions through thermodynamic modeling. The model was validated through experiments exposing equivalent geopolymer samples to CO₂ under in-situ conditions. The experimentally observed rapid carbonation, leading to a decrease in pore fluid pH and the precipitation of CaCO₃ matched the numerical simulations well, demonstrating the ability of the novel ReacSan framework to capture both temporal and spatial variations in the microstructure and carbonation mechanisms of alkali-activated materials (AAMs) exposed to supercritical CO₂. Based on the demonstrated validity of the model, the model is capable of providing detailed predictions of carbonation progression of AAMs or any other sealants over longer time- and length-scales required to ensure long-term GCS integrity. ... Read more

This study focuses on the numerical modeling of the reaction and microstructure development of a one-part granite-based geopolymer, which is often used for carbon capture and storage (CCS) applications. This work extends the capabilities of GeoMicro3D to model one-part geopolymers containing different precursors and activators (solid and in solution). The model considers the particle size distribution of different solids and the real shape of particles to prepare the initial simulation domain. Further, the dissolution rates of different solids estimated from the experiments were used to model the dissolution of different elements in the pore solution. Subsequently, the model utilizes classical nucleation probability modeling coupled with thermodynamic modeling to estimate the precipitation of products in the microstructure. Experiments were performed to study the pore solution, reaction degree, and amount of products in the microstructure, which were further compared with the simulation results to check the rationality of the model. ... Read more

This study presents an extended numerical approach based on GeoMicro3D to simulate the reaction kinetics and three-dimensional (3D) microstructure evolution of alkali-activated fly ash (AAFA). Dissolution experiments were conducted under varying NaOH concentrations and temperatures to formulate predictive rate functions for Si and Al release. These experimentally derived kinetic functions, alongside a thermodynamic dataset for N-(C-)A-S-H gels, were incorporated into the GeoMicro3D model to capture the chemical reactions and 3D microstructure evolution of AAFA. The model well captured reaction degree of fly ash, formation of solid products, evolution of pore solution compositions, and porosity over time. Notably, it is the first to predict the time-dependent spatial distribution of phases within the 3D AAFA microstructure by integrating kinetic and microstructural modeling. Dual validation using both dissolution data and microstructural metrics demonstrates the model's reliability and robustness. This integrated framework provides new insights into the coupled chemical–microstructural evolution of alkali-activated materials. ... Read more