Cracking Behavior Of Concrete Research Articles

Prediction of concrete cracking behavior under different strain rates based on the boundary effects model

Predicting the cracking behavior of concrete under different strain rates through fracture parameters has been a longstanding topic of interest. In this study, the effect of concrete strength and strain rate on the fracture toughness and initial fracture energy for three-point bending notched beams is investigated by boundary effect model (BEM). With the help of BEM, only a series of basic parameters (such as tensile strength, maximum aggregate size and specimen size) are used in the process of calculating the fracture toughness and initial fracture energy. The cumbersome concrete fracture experiment is avoided in this model. The initial fracture toughness and unstable fracture toughness, predicted by BEM are agreed with the experimental results in the literature. The results demonstrate that BEM is valid for predicting the fracture toughness of different concrete strengths, even at increased strain rates. As the loading strain rate increases, the initial fracture toughness of different concrete strength shows a slight growth with increasing loading strain rate, which indicates that the concrete needs more energy to reach the cracking condition.

3D FRP Reinforcement Systems for Concrete Beams: Innovation towards High Performance Concrete Structures.

Despite the advantages of using lightweight and non-corrosive carbon fiber reinforced polymer (CFRP) reinforcements in concrete structures, their widespread adoption has been limited due to concerns regarding the brittle failure of CFRP rupture and its relatively softer load-deflection stiffness. This work offers logical solutions to these two crucial problems: using aggregate coating to strengthen the CFRP-concrete bond and ultimately the load-deflection stiffness, and using CFRP-concrete debonding propagation to create pseudo-ductile behavior. Subsequently, the concrete cracking behavior, the apparent CFRP modulus with aggregates, and the post-peak capacity and deflection of three-dimensional (3D) CFRP-reinforced concrete are all described by equations derived from experiments. These formulas will be helpful in the future design of non-prismatic concrete components for low-impact building projects. The potential of this innovative design scheme in terms of increased capacity and deflections with less concrete material is demonstrated through comparisons between non-prismatic CFRP-reinforced concrete and measured steel reinforced equivalency.

Cohesive element-based chemo-thermo-mechanical multi-field coupled cracking simulation of early-age concrete

Due to the intense exothermic hydration process, early-age concrete undergoes restrained shrinkage deformation, which can easily lead to cracks in concrete structures during construction. In order to accurately predict the adverse effects of early-age concrete cracking behavior, a cohesive element-based chemo-thermo-mechanical multi-field coupled cracking model of early-age concrete is proposed in this study. Parametric analysis shows that by selecting appropriate gap conductance, constitutive thickness, mesh size, and viscosity coefficient for the cohesive elements, the multi-field coupled cracking model can successfully simulate the entire cracking process of early-age concrete, and it has the ability to obtain crack development behavior based on the real displacement field jumps, coordinates, and damage of cohesive elements. The validation of the numerical examples reveals the competing mechanisms between thermal expansion and autogenous shrinkage in early-age concrete and accurately predicts the cracking strain, region, time, and width (within an order of magnitude) as reported in the literature.

Cracking and thermal resistance in concrete: Coupled thermo-mechanics and phase-field modeling

Modeling damage and fracture in concrete accurately is crucial for a comprehensive analysis of structures under concurrent thermal and mechanical actions. This paper presents a novel coupled thermo-mechanical phase field model for concrete at high temperatures. Derived from principles of thermodynamics and unified phase field theory, the model integrates temperature-dependent thermal and mechanical properties, accounting for thermal expansion and transient creep. Mechanical damage, represented by the crack phase field, is augmented by a temperature-dependent thermal damage variable for heat-induced degradation. Addressing the impact of cracks on heat conduction and stress redistributions, the model introduces a novel approach to depict thermal resistance, seamlessly integrating mechanics, heat transfer, and crack propagation. Governing equations for damage evolution are derived, and the numerical implementation is detailed. Numerical illustrations showcase the model's ability to simulate diverse thermo-mechanical cracking patterns without explicit fracture path tracking or assumed criteria. Moreover, the model captures the influence of thermal actions on concrete cracking behavior and mechanical performance. This research is significant for predicting multi-field coupling damage in concrete and structures exposed to elevated temperatures.

Experimental Study of the Concrete Cracking Behavior of an Immersed Tunnel under Fire

This study investigates the impact of fire on the cracking behavior of immersed tunnels. A reduced-scale (1:5) model of an immersed tunnel was constructed to conduct fire tests in both traffic tubes using the HCinc curve as the applied fire. Temperature field changes were carefully monitored during the test by thermocouples and infrared thermography on the outer surface of the tunnel’s ceiling. The continuous temperature field and temperature changes in the concrete cracks were recorded by infrared thermography. By integrating the temperature field distribution in concrete and the behavior of concrete cracking, an analysis of the depth of concrete cracking in the immersed tunnel under fire was conducted. The concrete cracks exceeded 150 mm at 95 min of the fire test. The results indicate that the inner concrete exposed to fire undergoes thermal expansion, leading to tensile cracking of the outer concrete. Additionally, the fire-exposed surface of the tunnel is vulnerable to cracking due to a temperature decrease. Thus, the design of fire resistance of immersed tunnels should take into consideration the potential for concrete cracking caused by thermal strain.

On the choice of a phase field model for describing fracture behavior of concrete

Numerical modeling of concrete fractures is of prime importance in the durability assessment of civil engineering structures. The phase field model has been demonstrated as a promising framework to simulate crack propagation in brittle material while using the many existing techniques. In this paper, we discuss choosing the most appropriate phase field model for describing the fracture behavior of concrete. More specifically, we present a detailed analysis of the existing models, which have been created by combining different spectral decompositions and crack density functions. The numerical simulation predictions are confronted with the experimental observation of a benchmark problem from the literature. The obtained results showed that the extensive/ compressive decomposition and the quadratic crack density function are the most suitable models to study concrete cracking behavior. The investigation’s size effects demonstrated heterogeneities played an important role in concrete’s post-cracking behavior and softening branches, especially for the small concrete structure.

3D RBSM Analysis of Bond Degradation in Corroded Reinforced Concrete as Observed Using Digital Image Correlation.

The buildup of corrosion products over a reinforcing bar and associated reduction in rib height lead to degradation of the bond between reinforcement and concrete. The authors have previously used digital image correlation (DIC) to visualize and quantify load-induced cracking at the interface in specimens with varying degrees of corrosion. The results obtained in that study are used here to simulate the post-corrosion local bond behavior. A bond degradation model is incorporated into the discrete analysis tool, 3D Rigid Body Spring Model (RBSM) for the simulation. This analysis method allows the shape of the reinforcing bar to be directly modeled, and concrete cracking behavior is simulated by using a randomly shaped mesh. The magnitude of opening and sliding over the tips of ribs in the simulation, in which the reduction in rib height could not be modeled, is significantly lower than observed in the experiment. The results demonstrate that reduction in rib height is an important factor in post-corrosion behavior, and needs to be included in simulation models. It is also understood that in order to gain a better understanding of local post-corrosion bond behavior, de-bonding between reinforcement and concrete needs to be modeled in a discrete analysis framework.

Strain localization analysis using digital image correlation for PVA fiber-reinforced concrete-filled FRP tubes under compressive loading

This study presents the outcomes of the first experimental study on the strain localization of polyvinyl alcohol (PVA) fiber-reinforced concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs). 24 CFFT specimens were prepared and tested with various instrumentations, such as linear variable differential transformer (LVDT) and strain gauges (SGs), to record required full-field strains, i.e., axial, lateral and Von Mises strains. The strain evolutions over the surface of the specimens were recorded during axial compression loading. The FRPs were prepared with carbon, S-glass or basalt fiber to examine the influence of the fiber type and confinement stiffness on the behavior and strain localization of CFFTs. The evolution of Von Mises strains was determined and studied under axial compression. The obtained results show that although the general pattern of localization for both CFFTs without and with PVA fiber is nearly similar, the characteristics of the localization are different. The expansion of shear zone for insufficiently basalt FRP (BFRP)-confined concrete is more localized compared to the more homogenized behavior of sufficiently FRP-confined concrete. However, insufficiently BFRP-confined PVA fiber-reinforced concrete exhibits less localized behavior compared to insufficiently BFRP-confined plain concrete, which is due to the influence of the internal fibers on the concrete cracking behavior. At FRP rupture, hoop strains vary along the height and around the perimeter of the specimens, which results in the inability of SGs to consistently capture the actual hoop rupture strain.

Methods for segmenting cracks in 3d images of concrete: A comparison based on semi-synthetic images

Concrete is the standard construction material for buildings, bridges, and roads. As safety plays a central role in the design, monitoring, and maintenance of such constructions, it is important to understand the cracking behavior of concrete. Computed tomography captures the microstructure of building materials and allows to study crack initiation and propagation. Manual segmentation of crack surfaces in large 3d images is not feasible. In this paper, automatic crack segmentation methods for 3d images are reviewed and compared. Classical image processing methods (edge detection filters, template matching, minimal path and region growing algorithms) and learning methods (convolutional neural networks, random forests) are considered and tested on semi-synthetic 3d images. Their performance strongly depends on parameter selection which should be adapted to the grayvalue distribution of the images and the geometric properties of the concrete. In general, the learning methods perform best, in particular for thin cracks and low grayvalue contrast.

Monitoring Reinforced Concrete Cracking Behavior under Uniaxial Tension Using Distributed Fiber-Optic Sensing Technology

AbstractFiber-optic sensing (FOS) provides distributed strain measurement that can enhance both structural health monitoring (SHM) and laboratory testing capabilities. In particular, optical freque...

The impact of water to cement ratio on the fracture behavior of rubberized concrete

In the failure mechanism of concrete, its cracking behavior is an essential issue. Application of light and recycled materials such as crumb rubber can change the cracking behavior of concrete. The fracture behavior of rubberized concrete beams with varying water to cement ratios (WCR) of 0.35 to 0.55 was assessed in this investigation. Fracture parameters were achieved through WFM (work of fracture method) and SEM (size effect method). The findings revealed that with the reduction of the WCR, effective crack tip opening displacement at the peak load and the length of the fracture process zone in SEM and characteristic length in WFM decreased, while brittleness number, initial fracture energy and fracture toughness in SEM and the total fracture energy in WFM increased. Furthermore, for rubberized concrete containing different WCRs, the GF/Gf ratio was approximately 2.44.

Influence of ultrafine diatomite on cracking behavior of concrete: an acoustic emission analysis

The chief objective of this study is to investigate the cracking behavior of concrete with variable loadings of diatomite. Acoustic emission parameters during the compression testing such as the crack growth, the failure process, the crack pattern recognition, and the fracture modes are used to analyze the cracking behavior of concrete. The results demonstrate that the specimens containing diatomite can withstand higher crack initiation and crack damage, which is a stress threshold for the crack to change from stable to unstable. Moreover, the cumulative energy of the concrete specimens conforms to the Weibull distribution, which has important implications for developing a relation between the physical properties of concrete and the acoustic emission parameters. In addition, the variation of the b value shows that the formation of the main failure surface of the diatomite-treated concrete is delayed, which, through the pattern recognition, is attributed to the enhancement of the internal structure of the modified concrete. An attempt was also made to compare the fracture mode of the control specimen with that of the specimens containing diatomite through the analysis of the ratio of the rise time to the maximum amplitude and the average frequency. Finally, the density of the cracks was further investigated using the Gaussian mixture modeling.

Effects of carrier on the performance of bacteria-based self-healing concrete

To prolong the survival time of microorganisms in concrete, a new type of core-shell carrier was designed and prepared. Then, the mechanical properties, porosity, protection performance, and distribution in the concrete of the carrier were tested. After the healing agents were mixed into concrete, the influences of the carrier on the self-repairing performance, workability, mechanical properties, durability, and repair products in cracks of the concrete were studied. Finally, the mechanism of carrier protection and crack self-healing was inspected and analyzed. The results show that the batch prepared carrier has good quality stability, can achieve secondary strength growth, has low porosity and small pore size, and can greatly extend the survival time of microorganisms. The self-repairing capability of the later cracks was greatly improved, and there was no obvious negative impact on the basic performance of concrete. The resistance to chloride ions and carbonization can be improved to a certain extent. The invading alkaline substances would be consumed by fly ash, and the pores of the carrier would be filled by the produced gelled products, which is the trigger mechanism of the protective and secondary strength increase. The carrier provides a stable physical and chemical environment for the spores, ensuring that it can effectively play a role in the later cracking behavior of concrete. This research provides a technical choice for the low-cost preparation of the carrier and is expected to promote microbial self-healing concrete into engineering applications.

Shear Behavior of High-Performance Reinforced Concrete Beams

High-performance concrete (HPC) is one of such new material that has a major improvement over conventional concrete; however, its behavior has to be fully understood. This paper presents experimental and numerical investigations in order to study the shear behavior of high-performance reinforced concrete beams. Four RC-HPC beams were tested experimentally in order to study the effect of the existence of web reinforcement and bar diameter of the web reinforcement as well as the amount of the tensile longitudinal steel bars on the shear behavior. Test results showed higher values of shear strength, stiffness, ductility and controlled the concrete cracking behavior due to the presence of stirrups. The ultimate load for beam having shear reinforcement of 6 mm diameter increased by about 16% compared to that of control beam BI-1 without shear reinforcement, while, that increase reached up to 34% for beam having 8 mm diameter web reinforcement. Besides, the numerical modeling enabled to capture satisfactory the behavior of HPC beam so that it can be used to study the effect of more parameters on the behavior of HPC beams.

A Practical Finite Element Modeling Strategy to Capture Cracking and Crushing Behavior of Reinforced Concrete Structures.

Nonlinear finite element (FE) analysis of reinforced concrete (RC) structures is characterized by numerous modeling options and input parameters. To accurately model the nonlinear RC behavior involving concrete cracking in tension and crushing in compression, practitioners make different choices regarding the critical modeling issues, e.g., defining the concrete constitutive relations, assigning the bond between the concrete and the steel reinforcement, and solving problems related to convergence difficulties and mesh sensitivities. Thus, it is imperative to review the common modeling choices critically and develop a robust modeling strategy with consistency, reliability, and comparability. This paper proposes a modeling strategy and practical recommendations for the nonlinear FE analysis of RC structures based on parametric studies of critical modeling choices. The proposed modeling strategy aims at providing reliable predictions of flexural responses of RC members with a focus on concrete cracking behavior and crushing failure, which serve as the foundation for more complex modeling cases, e.g., RC beams bonded with fiber reinforced polymer (FRP) laminates. Additionally, herein, the implementation procedure for the proposed modeling strategy is comprehensively described with a focus on the critical modeling issues for RC structures. The proposed strategy is demonstrated through FE analyses of RC beams tested in four-point bending—one RC beam as reference and one beam externally bonded with a carbon-FRP (CFRP) laminate in its soffit. The simulated results agree well with experimental measurements regarding load-deformation relationship, cracking, flexural failure due to concrete crushing, and CFRP debonding initiated by intermediate cracks. The modeling strategy and recommendations presented herein are applicable to the nonlinear FE analysis of RC structures in general.

Cyclic Performance of Steel–Concrete–Steel Sandwich Beams with Rubcrete and LECA Concrete Core

Due to the structural and economic features of steel–concrete–steel (SCS) structural systems compared with conventional reinforced concrete ones, they are now used for a range of structural applications. Rubcrete, in which crumbed rubber from scrap tires partially replaces mineral aggregates in concrete, can be used instead of conventional concrete. Utilizing rubber waste in concrete potentially results in a more ductile lightweight concrete that can introduce additional features to the SCS structural members. This study aimed to explore different concrete core materials in SCS beams and the appropriate shear connectors required. In this study, four SCS sandwich beams were tested experimentally under incrementally increasing flexure cyclic loading. Each beam had a length of 1000 mm, and upper and lower steel plates with 3 mm thickness sandwiched the concrete core, which had a cross-section of 150 mm × 150 mm. Two of the beams were constructed out of Rubcrete core with welded and bolted shear connectors, while the other two beams were constructed with welded shear connectors and either conventional concrete or lightweight expanded clay aggregate (LECA) concrete cores. The performance of the SCS sandwich beams including damage pattern, failure mode, load-displacement response, and energy dissipation behavior was compared. The results showed that, while Rubcrete was able to provide similar concrete cracking behavior and strength to that of conventional concrete, LECA concrete degraded the strength properties of SCS. Using bolted shear connectors instead of welded ones caused a high number of cracks that resulted in a reduced ductility and deflection capacity of the beam before failure. The rubberized concrete specimen presented an improved ductility and deflection capacity compared with its conventional concrete counterpart.

Development of simulation method of concrete cracking behavior and corrosion products movement due to rebar corrosion

In this paper, both experimental and numerical studies were carried out to evaluate the concrete cracking behavior and the corrosion products movement during rebar corrosion process. The electric corrosion tests with an applied current density of 900 μA/cm2 were conducted, in which the development of surface and internal cracks and the distribution of corrosion products within the concrete were investigated. The test results showed that the corrosion products movement through cracks affects the crack propagation. Therefore, a numerical model based on three-dimensional Rigid Body Spring Method combined with Truss Network model was developed, which treated the corrosion products movement as a diffusion problem. The model was validated against the test results, showing that it can reasonably reproduce the effect of corrosion products movement on the crack propagation.

SHEAR BEHAVIOR OF FIBER REINFORCED CONCRETE BEAMS

Shear strength of fiber reinforced concrete (FRC) has prime importance in structural design. Concrete members like brackets, corbels and ledger beams may fail in shear. Such failure can be sudden and brittle. The presence of fibers positively affects the behavior of concrete, as it increases the residual shear transfer and reduces the formation and extension of cracks. As many parameters affect it, shear strength of FRC could not be precisely detected. Experimental investigation was carried out to study the shear transfer of un-cracked fibrous concrete. The study investigates the shear strength of FRC beams. The experimental parameters were the type and the percentage of fibers volume fraction and the presence of stirrups in reinforced concrete beams. Test results showed that the presence of fibers resulted in higher values of shear strength, stiffness, ductility and controlled the concrete cracking behavior. Instead of glass fibers, the use of steel fibers improved overall shear behavior of concrete.

Investigation on the cracking behavior of concrete cover induced by corner located rebar corrosion

Non-uniform corrosion of reinforcement causes concrete cracking in chloride contaminated RC structures. Due to the special boundary conditions, the concrete cover with corner located rebar is often subjected to the attack of chloride ions in a marine environment from two directions, and thus the corresponding non-uniform corrosion distribution should be different from the one for side-located rebar. The aim of the work is to explore the effect of corner located rebar corrosion on the cracking of cover concrete. For corner located rebar, an improved non-uniform corrosion distribution model was established based on the analysis results of two-dimensional chloride diffusion in concrete. Considering the heterogeneities of concrete, a meso-scale mechanical model and method for the study on the failure behavior of concrete cover was built. In the analysis model and method, the non-uniform radial displacement distribution was adopted to simulate the corrosion expansion behavior of the rebar. The cracking of concrete cover with corner located rebar was simulated and studied. The present approach was verified by the available experimental observations. The influences of concrete heterogeneity, corrosion distribution types, rebar diameter and concrete cover thickness on the failure patterns of concrete cover and the expansive pressure were investigated. The simulation results indicate that the developed approach can well describe the cracking behavior of cover concrete and the corrosion-expansion behavior of steel rebar.

Influence of accelerated corrosion on the reinforced cover concrete cracking behavior: experimental and numerical study

This article aims to present both experimental and numerical studies of the corrosion induced cracking pattern evolution of a reinforced concrete sample subjected to accelerated corrosion. The beam was not mechanically loaded. Rebars were intentiostatically corroded using a current density of 100μA/cm² of steel, in a chloride pond and for a 30 day period. Electrochemical tests and visual inspections were carried out in order to characterise the rebar state. Width evolution of the main longitudinal cover crack was measured thanks to ball-extensometer. A numerical modeling of the corroded RC beam has also been realised. The experimental and numerical results are in good agreement confirming the efficiency of the proposed modelling Cet article présente les principaux résultats d’une étude combinant approches expérimentale et numérique appliquées à un essai de corrosion accélérée sur un corps d’épreuve en béton armé. Ces résultats portent sur le suivi et la prédiction de l’évolution de la fissuration du béton sous l’effet de l’expansion des produits de corrosion. L’éprouvette n’a pas été chargée mécaniquement. Les armatures ont été corrodées en imposant un courant de densité de 100μA/cm² d’acier dans une solution saline pendant 30 jours. Des essais de caractérisation électrochimique ont été réalisés puis complétés par des inspections visuelles en vue de décrire l’état de dégradation de l’interface acier/béton. Les résultats de la simulation numérique conduisent à une évaluation satisfaisante de l’évolution de la fissure principale démontrant ainsi la pertinence de la modélisation proposée