Conference Agenda

In recent years, monitoring of existing reinforced concrete (RC) structures, such as nuclear power plants (NPPs) and multi-story RC buildings, has revealed a decrease in natural frequencies over decades. Moisture loss in concrete emerges as a potential cause of stiffness reduction. Understanding the mechanism of drying effects on structural performance requires a multi-scale perspective, considering moisture loss and stiffness change at the material level, and drying shrinkage-induced cracking at the structural level. This study investigates how concrete structural performance is influenced by shrinkage due to moisture loss through hydration or dissipation, employing multiscale integrated finite element analysis. The thermo-hygral analysis for RC lifetime over decades is applied with monitoring data of existing multi-story buildings and nuclear power plants in service. The reduced natural frequency is numerically replicated, revealing cracking near junction planes between structural members of different dimensions and dispersed cracks close to the surfaces of thick members. To deepen understanding of the impact of drying shrinkage, a cyclic shear loading test on shear wall specimens subjected to drying in a previous study was also reproduced by the analysis. In addition, a parametric study, focusing on the member scale, mix proportion, and surface treatment of concrete was performed. Difference of the drying speed by member scale was highlighted. The dominance of autogenous shrinkage in the case of high-strength concrete was also confirmed. In such cases, protection against drying may be disadvantageous as it impedes moisture supply from ambient air. The mechanism of stiffness reduction due to shrinkage and the complex relationships among multiple factors are quantitatively elucidated.

In Belgium, disposal of high-level nuclear waste in a stable geological environment is considered as a suitable technological option. Such waste is planned to be disposed in disposal tunnels lined with concrete. The waste generates a significant amount of heat for an extended period, which may affect the stability of the disposal liners as well as influence the stresses around the adjacent connecting gallery concrete liners. The structure is designed for long-term use, spanning hundreds of years. Therefore, it is crucial to study the decay of concrete properties due to exposure to high temperatures. This research covers different aspects of concrete properties at various scales to provide a comprehensive understanding of time-dependent deformation behaviour at different temperatures. The temperatures considered are 23°C, 65°C, and 85°C, while the relative humidity is 65%. The research covers hydration kinetics, pore structure, moisture diffusivity, mechanical properties with particular focus on time-dependent deformation at the mesoscale for different curing ages. The mechanical properties of interest comprise compressive strength, static and dynamic modulus of elasticity, flexural strength, fracture energy, creep, and shrinkage for various sample sizes. The research provides a comprehensive analysis and a several findings on the effect of curing on the same concrete mixture over a period of one year. It is generally observed that temperature and drying have a significant impact on the physical and mechanical properties of concrete, particularly for concrete that is cured for less than 28 days and then exposed to elevated temperatures, which is confirmed and quantified in this contribution.

This work aims to investigate the influence of weather conditions and global warming on chloride transport in concrete structures. In regions prone to cold temperatures and frequent freeze-thaw cycles, this study considers the effect of the freeze-thaw induced damage on chloride transport. Utilizing a multiscale approach based on finite element solutions of chloride, moisture, and heat transfer equations, chloride ion profiles within concrete were predicted. The simulations incorporated real meteorological data from four diverse locations, selected for their distinct climatic characteristics: Mediterranean (Annaba, Algeria), Arid Subtropical (Abu Dhabi, UAE), Equatorial (Accra, Ghana), and Continental (Oslo, Sweden). The findings indicate that, among the climates examined and considering the impact of freeze-thaw induced damage, the continental climate of Oslo demonstrated the most favorable conditions for chloride penetration. Following closely behind, the equatorial climate of Accra ranked as the second most conducive environment for chloride ingress, exhibiting only a slight disadvantage compared to the continental climate of Oslo. Notably, relative humidity emerged as the predominant factor influencing chloride transport over temperature. Despite global warming potentially reducing the frequency of freeze-thaw cycles annually, its impact on chloride transport in cold regions was found to be negligible. Conversely, in the other locations, global warming was observed to accelerate chloride transport by approximately 5% – 7%. Furthermore, incorporating daily temperature variations led to higher chloride profiles compared to average daily temperatures. The former resulted in a 12.5% reduction in the time to corrosion initiation. Understanding the influence of weather conditions and climate change is crucial for implementing effective adaptation strategies to mitigate premature structural degradation.

Post-installed bonded anchors are used to connect structural and non-structural members in a variety of applications in concrete structures. The performance of bonded anchors can be influenced by several different parameters. One of the most important parameters that directly affects the bond strength of the adhesive anchor in both the short and long term, as well as various processes that occur at the material level of the adhesive, e.g. creep, curing, post-curing, is the temperature conditions during installation and over the design service life of the fastener. For this reason, different adhesive systems have different temperature ranges defined by the manufacturer. These temperature ranges include the maximum short-term temperature, which defines the highest temperature the adhesive fasteners can withstand for a short period of time, and the maximum long-term temperature, which represents the upper limit of the temperature range in which the fasteners can maintain their structural integrity and performance without significant degradation. Therefore, the service life of adhesive anchors is designed by considering the various environmental conditions of the region in which the structure is located. Typically, this is done by evaluating only the air temperature data at 2 m. However, this may not be appropriate in many cases since the concrete members may experience different temperatures influenced by the amount of solar radiation and wind speed. The present study proposes a method that calculates the temperature profiles of concrete members under different conditions where the adhesive anchors are to be installed, considering the heat flux due to i. solar radiation, ii. convection and iii. heat conduction. In this way, temperature maps are generated for different geographical regions based on their historical environmental measurements. Finally, the concrete temperatures are coupled with the mechanical properties of the adhesives and the concrete.

Cement is one of the largest global carbon dioxide emission sources worldwide. Replacing ordinary Portland cement clinker with silica fume, fly ash or other supplements can reduce the enviromental impact up to 50%. However, this contemporary cements show higher explosive spalling risks under fire loading in experiments. Although, the origin of this behaviour is still unclear, the pore pressure development of concrete under fire loading was identified as important influence on the spalling behaviour. Due to the variety of blended concrete compositions, experimental investigations of the pore pressures are very costly. Computational models offer a possible remedy to capture the pore pressure development for a variety of blended concretes and can lead to important insights into the problem’s specifics with its multiphysical nature.

Based on chemo-thermo-hygro-mechanical analyses, the drying front of blended concretes under fire loading is investigated, considering four primary state variables, i.e., gas pressure, capillary pressure, temperature, displacement and two internal variables, i.e., dehydration degree, chemo-mechanical damage. Within a microporomechanical framework the chemo-mechanical damage is calculated via Eshelby-type homogenisation techniques and the dehydration degree for the different blended concretes is predicted by Arrhenius equations for each cement constituent.

Blended concretes, namely CEM II/A-LL, CEM III/B, CEM II/B-V, CEM IV/A, with different water to cement ratios are analysed in the context of a sensitivity study comparing the different inital moisture states and dehydration behaviours regarding the pore pressure development. It was shown that high initial volume fractions of C-S-H and monosulfoalumiates and a high fineness of grinding increase the pore pressure development.