The serviceability of reinforced concrete beams is evaluated by the criteria of crack width and deflection according to the design codes. However, depending on the environment in which the reinforced concrete beam is located, it may not be possible to directly measure the crack width or deflection. Also, the calculation methods provided by the ACI 318 building code require the current load level to calculate crack width and deflection even though the load cannot be accurately determined. This study aimed to correlate the crack width and deflection of reinforced concrete beams and provide a method to calculate them with crack width or deflection measured in the field. For this purpose, an experimental study was conducted for reinforced concrete beams with key variables such as tensile reinforcement ratio and cover thickness. During the experiment, the digital image correlation (DIC) method was utilized to measure deflection and crack width. The results were compared with those measured using LVDT and a digital crack measuring device. For the deflection, the results by DIC and linear variable differential transformer (LVDT) were quite close to each other, but the sum of the crack widths measured by the device in the range of measurement was relatively smaller than that measured by DIC. It suggests that some minor cracks were not detected by the naked eye when the device was used. The DIC measurement was just applied to the maximum moment zone due to the limitation of measurement range, and the deflection in the shear span was additionally evaluated considering the shear deformation. As a result, the relationship between crack width and deflection in reinforced concrete beams was identified by combining the DIC measurement data in the maximum moment zone and the data in the shear span.

The construction of sustainable and resilient structures and infrastructures that ensure people's safety while minimizing maintenance costs is a crucial goal. One way to achieve this is through the healing of micro-cracks and defects. In real structures that are subjected to service loading, time-dependent behavior is of utmost importance, especially in the presence of cracks. Such cracks can lead to nonlinear creep behavior, which might ultimately cause structural failure. Hence, the new challenge is to investigate and quantify the effect of crack-healing on nonlinear creep behavior.

This study has two objectives. Firstly, it aims to experimentally investigate the effect of healing on specimens that are continuously subjected to sustained load under controlled environmental conditions. The amount of load is determined based on the expected service load, which is calculated as a fraction of the pre-cracking load. Secondly, the study aims to develop a comprehensive numerical framework to interpret and simulate the results observed in the experiments. For this purpose, an experimental investigation was conducted at Politecnico di Milano with reference to an Ultra-High-Performance Concrete developed in the framework of the H2020 ReSHEALience project for exposure to extremely aggressive environments. The numerical framework is based on the recent developments of the multiphysics lattice particle model (M-LDPM). The numerical framework is framed into a coupled hygro-thermo-chemo-mechanical numerical framework, resulting from pairing the mesoscale Lattice Discrete Particle Model (LDPM) and the Hygro-Thermo-Chemical (HTC) model [4-5].

Reliable and computationally efficient models are crucial for various applications, yet simulating granular material mechanics often poses challenges due to high computational cost. This paper addresses the need for trade-offs between accuracy and calculation time in computational models, focusing on concrete simulated at the coarse aggregate level using the lattice discrete particle model (LDPM). A novel discretization approach is proposed, which reduces the number of tessellation facets. Two options are investigated. In the first case, the number of facets is reduced from 12 to 6 per tetrahedron connecting 4 adjacent particles. In the second case all facets shared by a link between two particles are merged into a single facet. The study examines the computational cost and accuracy of predicting concrete fracture behavior via the novel discretization approaches for a number of different loading situations. Results indicate that both models significantly reduce computational cost while maintaining accurate predictions of structural mechanical response compared to the original LDPM and experimental data. The analyses validates the efficiency and promise of these approaches in advancing LDPM utilization for concrete mechanics simulations.

The study presents a numerical model aimed at exploring the intricate behavior of concrete during its early stages of maturation, with a particular focus on thermo-mechanical and hygral phenomena. Drawing inspiration from Gawin's work [1], the model conceptualizes concrete as a multiphase material, comprising a solid phase (cement, gravel, etc.) and fluid and gas phases filling the pores with water and dry air, respectively. Distinguishing itself from previous models, this model based on the Framework of Theory of Porous Media integrates the processes of hydration-dehydration and evaporation-condensation, providing a comprehensive understanding of concrete behavior. To validate the model's efficacy, experimental investigations are conducted to examine the evaporation kinetics in fresh concrete and its impact on concrete’s properties. Employing a multi-field finite-element solver, numerical simulations are performed to assess the model's predictive accuracy in capturing concrete behavior during its early hydration period. Through refinement and expansion upon Gawin's foundational model, including the incorporation of additional phenomena such as evaporation-condensation dynamics, the study enhances the predictive capabilities crucial for concrete mechanics research. Furthermore, the research focuses to deepen insights into the evaporation mechanisms within porous materials, pivotal for concrete's response to internal and environmental stimuli. Leveraging the Dynamic Vapor Sorption method facilitates a accurate investigation into the complex interplay between hydration, evaporation, and external influences, thereby broadening our understanding of concrete structure maturation.

[1] Gawin, D., Pesavento, F., Schrefler, B., Hygro-thermo-chemo-mechanical modelling of concrete at early ages and beyond. Part I: Hydration and hygro-thermal phenomena. International Journal for numerical methods in engineering, Wiley, 2006.

Corrosion-induced cracking is one of the most common deterioration problems of reinforced concrete structures. The embedded rebars corrode under the combined influence of moisture, oxygen, and an electrical field. The oxidation of iron leads to rust non-uniformly distributed around the single rebar, as considered in this work. Since the rust occupies a larger volume than the iron, corrosion results in pressure acting on the concrete surrounding the rebar. When the tensile stresses of concrete reach the tensile strength, the concrete starts cracking. Concrete is a composite material consisting of aggregates, (i) surrounded by interfacial transition zones and (ii) embedded in a mortar matrix. The transport of ions, the electrical conductivity, and crack propagation are influenced by the mesoscopic heterogeneity of concrete. Therefore, an accurate representation of the mesostructure is necessary for the simulation of corrosion-induced cracking. In the present contribution, a Finite Element model for corrosion-induced cracking of reinforced concrete is described. It accounts for the interplay of the mesostructure of concrete and relevant multiphysical mechanisms. The model is used to simulate an accelerated corrosion test [DOI: 10.1007/BF02472805]. The non-uniform penetration of the corrosion front into the rebar and its associated non-uniform expansion are quantified based on the local current densities. The model is validated by comparing the simulated crack mouth opening displacements with corresponding measurements, performed at the surface of the tested specimen.

Carbonation tests of hardened cementitious materials are time-consuming, even in 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 that is able to estimate the carbonation front during accelerated carbonation tests for a given concrete composition. Amongst abundant models in the literature addressing the carbonation process of hardened cementitious materials, kinetic models are promising as they can capture key features of the carbonation process as well as being computationally efficient. In this paper, we firstly provide a critical study of existing kinetic models discussing their theoretical foundations, input parameters, and primary applications. Then, we introduce an implementation in COMSOL of a reactive-transport model for OPC-based materials. Following this methodology, we advance to establish a novel 3-D meso-scale model based on lattice flow elements dual to the Lattice Discrete Particle Model (LDPM) for the mechanical analysis. This model uniquely employs conduit elements to represent CO₂ diffusion pathways. Two CO₂ concentrations (1%, 3%) are applied in both implementations with constant temperature field (20 ℃) and relative humidity field (65%) to simulate accelerated carbonation tests in the environmental chamber. It is shown that the meso-scale model can predict well the average carbonation depth in comparison with continuum case while retaining the heterogeneity of concrete and, thus, spatial variability in 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.