Conference Agenda

Carbonation tests of hardened cementitious materials are time-consuming even under accelerated conditions, presenting significant challenges for the design of experiments. It is widely acknowledged that utilizing a low CO2 concentration (< 3%) is critical to accurately replicate natural carbonation conditions. Hence, a model is called for to estimate the carbonation front during accelerated carbonation tests of the designed composition a priori. In this paper, we first introduce a Finite Element Method (FEM) implementation in COMSOL Multiphysics that models a one-dimensional (1-D) reactive-transport process for OPC-based materials. Secondly, an equivalent FEM model is implemented in MARS (Modeling and Analysis of the Response of Structure). After benchmarking this model against the COMSOL model, we establish a novel three-dimensional (3-D) meso-scale model using the dual-lattice Multi- physics Lattice Discrete Particle Model (M-LDPM) framework. A CO2 concentration of 1% is applied in both implementations, with a constant temperature field of 20 ◦C and a relative humidity of 65% to simulate accelerated carbonation tests in an environmental chamber. It is shown that the meso-scale model can predict the average carbonation depth while retaining the heterogeneity of concrete and, thus, the spatial variability in the carbonation front. Advantages and disadvantages of both implementations are discussed, providing insights into their applicability in simulating real-world carbonation processes that can help researchers in their design of experiments.

Reinforced concrete (RC) bridge deck slabs in cold regions are simultaneously subjected to freeze–thaw cycles (FTC) and fatigue loading, leading to premature deterioration. However, this issue is rarely considered in their design. This study employed multi-scale numerical simulations to investigate the fatigue performance of frost-damaged RC slabs. The proposed model was validated against experimental results, which successfully reproduced the coupled deterioration process involving pore ice pressure and wet fatigue. Based on the validated model, parametric analyses were performed to examine the influences of the water-to-cement (W/C) ratio, air content, and freezing temperature on the fatigue life of RC slabs. The results show the quanti-tative effects of a W/C ratio decrease, an air content increase, and a freezing temperature increase on the fatigue life of RC slabs. Meanwhile, inadequate concrete quality may cause severe damage under FTC. Finally, a strain energy-based damage factor, 𝐾_𝑈, is proposed to quantify material degradation under combined environmental and mechanical actions. 𝐾_𝑈 effectively captures the coupled deterioration mechanism and provides a rational and practical indicator for the durability assessment and maintenance management of RC bridge decks in cold climates.

Alkali-activated materials based on ground granulated blast furnace slag (GGBFS) are investigated as low-carbon hydraulic binders for immobilizing long-lived, low-activity nuclear waste (LL-LA) containing graphite. This study presents a multiscale approach to characterize the early-age behavior of sodium hydroxide-activated GGBFS mortars and ordinary Portland cement (OPC) mortars incorporating graphite. At the mesoscale, a Representative Volume Element (RVE) models the matrix and graphite inclusions, enabling the calculation of thermo-elastic deformations, hydration-induced chemical shrinkage, and the evolution of elastic modulus with hydration degree. At the macroscale, a 3D finite element simulation evaluates thermal gradients and early-age deformations, highlighting greater endogenous shrinkage and lower initial stiffness in alkali-activated mortars compared with OPC. The presence of non-hydrating, highly conductive graphite significantly alters heat dissipation, thereby reducing early-age stresses. This methodology provides a robust framework for optimizing the performance of confinement matrices for nuclear waste applications.

The production of ordinary Portland cement (OPC) results in some 8% of the world green house gas emissions. Partially replacing OPC with supplementary cementitious materials such as limestone and calcined clay is a promising approach for developing more sustainable alternatives. In this study, we model the compressive strength development of pastes made with limestone Portland cement (LPC) and limestone calcined clay cement (LC3) binders. We investigate whether or not the stiffness of microscopic binder constituents play a crucial role in the strength predictions, and we give polynomial formulae for approximating the tensorial strength model. To this end, three binders are investigated: one type each of OPC, LPC, and LC3. For the blended binders, the cement replacement ratio amounts to 30 %. The limestone-to-calcined clay ratio is set to 1.0. The water is dosed at an initial water-tobinder mass ratio of 0.45. Strength modeling is performed using a multiscale strength model which is based on methods of continuum micromechanics. The model is extended to account for inert limestone and calcined clay inclusions. Volume fractions are calculated using Powers’ hydration model. Elastic phase constants are taken from the literature. Qualitative input for the multiscale model is visualized using material organograms: spherical residual binder particles are embedded in a continuous matrix of hydrate foam, which itself consists of isotropically oriented hydrate gel needles in direct interaction with spherical capillary pores. A sensitivity analysis regarding the stiffness of binder particles is carried out. It is found that the strength predictions are virtually independent of the stiffness differences within the binder powder. This provides the motivation for developing a surrogate model which approximates the tensorial strength predictions by polynomial equations, based solely on the strength of the hydrate gel needles, the hydrate foam-related volume fractions of the capillary pores, and the cement paste-related volume fraction of the binder constituents.

The time-consuming nature of conventional shrinkage tests—which often extend over a year to approach ultimate shrinkage values and enable reliable extrapolation to structural scales—necessitates the development of accelerated approaches. This study investigates the shrinkage and moisture loss of specimens smaller than the recommended 75 × 75 mm or 100 × 100 mm prisms. In the experimental part, prismatic specimens of several sizes are prepared conventionally by casting or wet-cutting from a larger block of self-compacting concrete to mitigate the wall-effect caused by the mold. In the first 100 days of the experiment, behavior contradicting engineering expectations was observed, showing that the cut-out specimens tend dry and shrink faster and more. One-way coupled hygro-mechanical model was developed for both types of specimens. If the cut-out specimens are assumed as homogeneous, themodeling approach can accurately capture moisture loss, shrinkage evolution, and the development of internal relative humidity. The data support the credibility of the non-linear shrinkage coefficient recently introduced in the MPS theory. However, accurately reproducing the trends observed in the cast specimens remains challenging with the present modeling approach, indicating complexities that warrant further investigation.

The objective of this work is to develop a carbonation model for concrete incorporating recycled concrete aggregates (RCA), with the aim of predicting and assessing the progression of carbonation. The broader goal is to evaluate the relative influence of key parameters on carbonation and, more importantly, to determine the overall impact of replacing natural aggregates with recycled ones. Understanding carbonation is essential, as it is a critical precursor to reinforcement corrosion-one of the primary degradation mechanisms in concrete structures. The numerical model has been developed based on various approaches from the literature. It was first implemented at a macroscopic scale, then extended to a multiscale framework to account for the intrinsic heterogeneity of concrete. This heterogeneity is represented through a representative volume element (RVE), which includes the mortar paste, aggregates, and the adherent mortar surrounding them. The model considers several coupled processes, as well as the chemical reactions resulting from the carbonation process within the concrete matrix. The implementation was carried out using the nonlinear finite element software LAGAMINE, developed at the University of Liege.