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.@en

The early age expansion of cement paste/concrete due to expansive additives (EA) has a significant impact on the microstructure and early-age mechanical properties of cement paste and concrete. Moreover, external restraints owing to reinforcement and supports play a crucial role in reducing concrete expansion and may also affect the microstructure. In this study, a measurement technique to monitor the development of early age elastic modulus of paste (from casting to hardened stage) focusing on the effect of external restraints was established. The influence of external restraint on the microstructure and elastic modulus was examined using the Elastic Modulus Measurement Ambient Response Method (EMM-ARM) and mercury intrusion porosimetry (MIP). This study also focuses on the effect of water-to-binder (w/b) ratios and amount of EA on the early-age mechanical properties of cement paste. The experimental results revealed that under unrestrained conditions, the addition of EA caused the microstructure of the paste to become porous, resulting in a decrease in mechanical properties. Conversely, under restrained conditions, the elastic modulus of the paste with EA and the level of porosity were comparable to the paste without EA. These findings have significant implications for the utilisation of EA in concrete construction and provide potential avenues for enhancing the durability and performance of concrete structures.

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Expansion of concrete due to expansive additives (EAs) is greatly affected by the degree of external restraints in the form of reinforcements and supports. Furthermore, the presence of anisotropic restraints influences concrete expansion in different directions. In this study, a chemo-mechanical model was developed to estimate concrete expansion under the framework of poromechanics. The volume of expansive hydrates was obtained from the hydration model, which was used for estimating the stress on the cement paste using poromechanical formulations. An external non-isotropic state of stress affects the orientation of crystal precipitating inside the pores of the cement paste. Thus, anisotropy in concrete expansion due to external stress was considered by maintaining the chemo-mechanical equilibrium of crystals of expansive hydrates, which was reflected in the poro-elastic constants utilized to estimate the stress at the cement paste scale. Poroelastic coefficients were estimated using a micromechanical scheme reflecting the effect of crystal orientation. Dedicated experiments were performed to comprehend the anisotropic expansion of concrete under anisotropic external restraint conditions. Finally, the applicability of the model was verified by comparing the expansion in different directions estimated from the model and experiments performed in this study with available literature data. Thus, the developed chemo-mechanical model could benefit practitioners and engineers in evaluating the expansion behavior of restrained concrete for a given application.@en

Heterogeneities in concrete manifest at various scales, from aggregates and its interfacial transition zone (ITZ) at macroscale to various hydration products at the microscale. On the application of load, cracks initiate from ITZ and propagate to the bulk cement paste (BCP), leading to the nonlinear stress-strain behaviour of concrete. This paper proposes a novel multiscale analytical approach to simulate the uniaxial stress-strain behaviour of concrete. Initially, the heterogeneous microstructure of ITZ and BCP is simulated using a cement hydration microstructure model (μic). Considering the gradient of phases in ITZ, aggregate gradation and aggregate volume fraction, stresses in the different phases in the ITZ and BCP are calculated by step-wise stress downscaling using continuum micromechanics. The initiation and propagation of cracks in the ITZ and BCP are modelled using damage mechanics. The efficacy of the current analytical approach is validated by comparing with the experimentally observed stress-strain curve. The current model investigates the relation between the macroscopic strain increment with the distribution of strain and the progression of damage in different ITZ layers. Through a parametric study, the influence of w/c ratio (0.30–0.50), aggregate volume fraction (30% and 50%), and aggregate size distribution on the stress-strain behaviour of concrete are discussed.@en

Expansive additives in higher dosages induce chemical prestress in concrete by imparting higher early-age expansion. However, induced stress and concrete expansion can vary significantly, depending on different restraint conditions. In addition, concrete expansion can be highly anisotropic depending on the nature of external restraints and boundary conditions. Experimentations have been performed to study the effect of uniaxial (anisotropic) restraint on the concrete expansion (in both restraint and stress-free directions) and induced prestress. A higher degree of restraint resulted in a substantial decrement in the longitudinal expansion. In contrast, expansion in the stress-free (lateral) direction was not much affected by the restraint in other direction. As a result, an overall decrement in the volumetric expansion was observed with an increase in the reinforcement ratios. Stress induced in concrete due to the restraint expansion in the longitudinal direction was found to be higher for a higher reinforcement ratio. Data provided from the current work can be used for the comprehensive modelling of expansive concrete under external restraints.@en