Conference Agenda

The existing models of concrete degradation are being challenged by the sustainability-driven emergence of new chemical compositions and exposure conditions, such as from high fractions of cement replacements in new concretes or from service life extension of existing structures. This article identifies three challenges to address for concrete degradation models to become relevant also for unconventional compositions and exposure conditions: (i) being able to draw physical predictions of macroscale behaviours starting from chemo-mechanical processes at the microscale; (ii) conceiving experiments that are model-oriented, away from the current paradigm where full degradation experiments are run first, and then models are calibrated and validated on them without feeding back to the experiments; (iii) distilling the complexity of the microscale simulations into simpler, engineering-oriented tools describing the constitutive behaviour of the concrete. The first challenge, on modelling micro-chemo-mechanical processes, is discussed in detail, presenting the structure and capabilities of a recently developed simulator, MASKE, based on off-lattice, coarse-grained, kinetic Monte Carlo. Sample results are presented, from simulations of stress-induced dissolution, dissolution-induced strain-rate dependence of stress, crystallisation pressure, and cement paste carbonation. Potential solutions to the other two challenges are then discussed, envisaging a possible interplay between reverse-engineered experiments and short-term model predictions, and the use of machine learning to surrogate the results of the microscale simulations.

This paper presents a three-dimensional analytical framework for evaluating the structural behavior of box girder bridges, with particular emphasis on long-term effects such as creep, shrinkage, and shear lagfactors often neglected in traditional one-dimensional analyses. The proposed methodology integrates advanced material models and numerical strategies to simulate sustained loading and environmental influences, thereby improving the accuracy of stress and deformation predictions crucial for reliable bridge assessment. A rate-type creep formulation is developed based on the continuous retardation spectrum, removing the need to recompute Kelvin-chain stiffness parameters at each time step. Both EuroCode 2 and Model Code 2020 creep laws are incorporated, with approximate creep functions obtained through the PostWidder inversion technique. Cracking is represented using a continuous damage mechanics framework, enabling the gradual simulation of concrete degradation and crack evolution. The implementation is carried out in Abaqus/Standard through user subroutines and implicit time integration. The framework accurately models both reinforced and prestressed concrete structures, accounting for nonlinear creep, cyclic loading, shrinkage, cracking, and steel relaxation. A detailed case study of a three-span rigid-frame bridge further demonstrates the enhanced predictive performance of the model and confirms its consistency with experimental observations.

This paper presents preliminary numerical simulations of the gap test for plain concrete using
an advanced damage-plastic constitutive model. A few fundamental model parameters are calibrated against standard bending tests of geometrically similar specimen sizes of three different sizes. The primary objective is to trace the evolution of the stress and damage distributions during the two loading stages of the full gap test, and to reveal the mechanisms underlying the observed increase and decrease in peak bending load. The results show that the non-uniform, multiaxial stress state and the resulting damage pattern induced during the initial compressive stage critically affect the specimen’s performance in the subsequent bending stage. Such structural effects are suggested to play a more important role than the specific material behavior under tension combined with transversal compression.