Concrete Fracture Research Articles

Numerical analysis of bonded and unbonded prestressed RC beams using cohesive and non-compatible rod elements

This research presents a numerical approach to simulate prestressed RC beams. It combines state-of-the-art finite element models to simulate the concrete (including fracture), tendons, passive reinforcements, and the rebar–concrete interaction. This provides more realistic simulations and rich details on deformability, crack patterns, and axial and contact stress distributions in passive reinforcements and tendons. Concrete fracture is simulated using cohesive elements with a constitutive model based on the plasticity theory and fracture mechanics, enabling crack development and propagation prediction. Reinforcements are simulated using rod elements with incompatible nodes. Special contact elements link rod to bulk elements and are placed along the reinforcements and at tips. These contact elements also predict relative displacements between rebars and concrete. Prestressing is simulated by setting initial stresses in tendons and applying forces to its nodes simultaneously. The approach also includes two numerical techniques to improve the convergence of the highly nonlinear problem. Five experimental beams are simulated. In all cases, the numerical load–deflection curves agree with the experiments. Fracture patterns also match rupture modes. Finally, contact stress discontinuities in tendons due to crack development are examined in more detail.

Effect of maximum coarse aggregate size upon shear strengthening of RC beams using NSM-CFRP strips

Reinforced concrete (RC) is widely used because of its many desirable characteristics, such as high strength, fire resistance, and durability. However, structures that are made of concrete may need strengthening or repairing due to concrete deterioration, the harshness of the environment, steel corrosion, errors in design, and damage caused by earthquake load. The use of composite materials has recently become more popular for strengthening and repairing damaged concrete structures. It is also known that properties of the aggregates, such as shape, size, and surface texture, have important influences on the behavior of concrete. In fact, many studies have shown that changes in coarse aggregate will affect the concrete's strength and fracture properties. Towards this end, very little research has been carried out on the effect of maximum aggregate size (MAS) on the shear behavior of reinforced concrete beams. The impact of maximum coarse aggregate size on shear strengthening using the methods proposed in this study was not studied. This research is driven by both environmental and economic aspects where the use of large-size coarse aggregates provides a large volume and less void space compared to small-size aggregates. From an environmental perspective, such an approach will reduce the need for cement in concrete unit volume, hence reducing the pollution. The main purpose of this study is to examine the behavior of reinforced concrete beams under general loading and how this is affected by using different coarse aggregate sizes. This work’s main objective is to investigate the effect of maximum coarse aggregate size on the shear behavior of reinforced concrete beams and study the effectiveness of using the Near Surface Mounted (NSM) – Carbon Fiber Reinforced Polymer (CFRP) strips technique on the shear strengthening of the RC beams. The experimental variables of the study consist of different maximum coarse aggregate sizes (9.5 mm, 12.5 mm, 19 mm, and 25 mm), Carbon Fiber Reinforced Polymer (CFRP) strips spacing (75 mm and 150 mm), and concrete compressive strength (25 MPa and 40 MPa). Fourteen RC beams (150 mm × 200 mm × 1150 mm) were cast using six mixes of concrete to be prepared and tested. The experimental results showed that using maximum coarse aggregate size has a positive effect on ultimate shear strength, maximum deflections, toughness, and stiffness of strengthened RC beams. Using NSM-CFRP strips change the failure mode from pure shear for the control beams to shear-flexural failure for the strengthened beams, which is an ideal enhancement.

Experimental investigation on Hybrid Fibre-Reinforced Concrete (HFRC) fracture toughness and impact resistance with partial replacement of nano-silica

This paper focuses on the compressive strength, fracture toughness and impact resistance of hybrid fibre-reinforced concrete. A total of 78 numbers of compressive strength test cubes, 24 numbers fracture Edge Notched Disc Bend (ENDB) specimens, and 20 numbers of impact disc specimens were constructed and tested. The replacement of Nano-silica was kept constant at 2% based on literature. Glass and steel fibres of 50 mm length were used with 1–4% by weight of cement content. Based on the obtained results, Steel Fibre (SF), Glass Fibre (GS) and Nano-Silica (NS) combinations gave better strength and performance in concrete. The observation made herein is that NS reduces the porosity of concrete as verified with the ultrasonic pulse velocity (UPV) test and microstructural studies including Scanning Electron Microscope (SEM) analysis. The results indicate that fibre combinations achieved better fracture toughness and high-impact resistance while maximum compressive strength was attained for 2% NS + 0.5% SF and 0.5% GF combinations.

Approximate Relationship for the Bond-Slip Using a Concrete Damage-Plastic Model

This paper presents an approximate multicontact model to study dynamic bond stress-slip based on the concrete damage-plastic model. To establish the bond stress-slip between rebar and concrete, an elastic-plastic steel cylinder contact element was used as the tube (ring contact element), and then, by reducing the bond strength, the amount of slip between rebar and concrete and its effect on concrete damage-plastic parameters were considered. When concrete cracks, the parameters of concrete cracking, the plasticity of rebar and concrete fracture, and the pull-out of rebar from concrete are used to consider the bond-slip relationship between rebar and concrete. Meanwhile, an external constraint in the cylinder model is taken into account. The bond strength calculated by the presented model is compared with the pull-out test specimen results, and the errors are generally within 15%. Finally, using the results obtained from the amount of slip in models, an approximate mathematical relationship between the slip of the rebar inside the concrete can be obtained in terms of the resistance of the ring contact element (instead of the concrete surrounding). This formula can be used to calculate the bond-slip rate of all the rebars of a structure. The results of the mentioned model using the ABAQUS software demonstrated that by reducing the strength of the ring contact element by 20%, slip increased by 4.2%. Also, with an 80% reduction in ring strength, the bond-slip rate increases by 45%. The proposed approximate relationship has reasonable accuracy and lower computational cost.

Volume stability study of new low-clinker high performance concrete

The use of cement clinker in concrete results in the production of greenhouse gases. Rubber powder and polypropylene fiber were chosen in this study to replace part of the cement in the creation of a unique type of low-clinker, high-performance concrete in order to reduce the amount of cement clinker used in concrete and therefore its impact on the environment. The volumetric stability of concrete was studied using flat plate and circular trials under the impact of various conditions. The study's findings revealed that the addition of rubber powder and fibers could successfully prevent the creation of fractures in concrete. The optimum crack development prevention is achieved when the water-cement ratio is 0.25 and the sand rate is 36%, however the amount of cement has a negative influence on the concrete's early fracture resistance.

A three-dimensional meso-scale approach to the fracture analysis of ultrahigh performance concrete based on micropolar peridynamics

A three-dimensional (3D) meso-scale approach is proposed to simulate the fracture of ultrahigh performance concrete (UHPC) within the framework of peridynamics (PD). Micropolar PD, as an improved form of bond-based PD, is adopted to model the cementitious matrix. A PD constitutive model considering strain-hardening and strain-softening is introduced to simulate the mechanical behavior of UHPC. To improve the computational efficiency, a semi-discrete technique is employed to simulate the fibers. Meanwhile, to compensate for the drawbacks of the semi-discrete technique in analyzing fiber deformation, the effects of fiber inclination and end deformation on the fiber–matrix interface are incorporated into the fiber pullout model. In the analysis of cracking in UHPC, uniaxial tensile and uniaxial compressive tests were simulated to calibrate the proposed 3D PD model. Then, mode Ⅰ fracture and mixed-mode fracture of UHPC beams under three-point bending were simulated. Satisfactory agreement is achieved between PD analysis and experimental observations in terms of crack paths and load–displacement curves. Additionally, the numerical results show that the random distribution of fibers has a stronger impact on the 3D fracture surface for mixed-mode fracture compared to mode Ⅰ fracture.

Experimental and analytical investigation on shear mechanism of steel-UHPC composite T-Perfobond shear connectors

This paper proposed a T-Perfobond shear connectors to increase the end bearing area of the intermittently arranged PBL shear connectors. The failure modes, load-slip curves, and strains of perforating rebar of T-Perfobond shear connectors were discussed. Following that, a finite element analysis (FEA) model was established to investigate the influences of design parameters on the behavior of T-Perfobond shear connectors. A theoretical shear bearing capacity prediction method on T-Perfobond shear connectors was proposed, which can consider the effect of end concrete bearing pressure and the reduction coefficient of welding effect. The results showed that the specimens failed in three stages with bond damage, concrete dowel fracture and end concrete crushing. The shear bearing capacity of T-Perfobond shear connectors increased with the increase of web plate thickness and decreased with the increase of flange plate thickness. The hole diameter weakened the web plate strength and reduced the stability of T-Perfobond shear connectors. The theoretical predictions agreed well with the experimental and numerical calculation results. This study can be used to guide the design and application of shear connectors of steel–concrete composite beams.

A fully coupled meso-scale electro-chemo-mechanical phase field method for corrosion-induced fracture in concrete

A fully coupled meso-scale electro-chemo-mechanical phase field method for corrosion-induced fracture in concrete

Behavior of Reinforced Concrete Beams without Stirrups and Strengthened with Basalt Fiber–Reinforced Polymer Sheets

This paper reports on a series of four-point bending experiments to investigate the shear capacity of reinforced concrete (RC) beams strengthened with externally bonded basalt fiber–reinforced polymer (BFRP) sheets. The experimental results show that BFRP sheets can significantly increase RC beams’ shear capacity and ductility. To analyze the fracture and mechanical behaviors of BFRP sheet–strengthened RC beams, a three-dimensional (3D) finite-element model (FEM) based on the application of cohesive elements was developed. Mixed-mode constitutive models of the BFRP–concrete interface, the concrete potential fracture surface, and the reinforcement–concrete interface were proposed. The proposed constitutive models were able to characterize the interface’s normal separation, tangential slip, and friction. A comparison of the simulation and experimental results indicates that the proposed numerical model can appropriately simulate the mechanical response, crack propagation, and crack distribution of BFRP sheet–strengthened RC beams. Finally, based on the proposed 3D FEM, a series of numerical tests were conducted to investigate the influence of key parameters (i.e., sheet elastic modulus, sheet bonding area, and sheet bonding angle) on the shear capacity of BFRP sheet–strengthened RC beams.

Fracture behaviour of concrete with different replacement rates of iron tailings sand based on double-K criterion

The article conducts a study on the iron tailings sand concrete's fracture behaviour based on the double-K criterion. Five sets of standard three-point bending beam specimens of concrete with 0%, 25%, 50%, 75% and 100% iron tailings sand replacement river sand respectively were fracture tested, and the P-CMOD and P- ε curves of each set of specimens were measured to determine the pertinent fracture parameters. The specimens were also microscopically tested using scanning electron microscopy and mercury intrusion porosimetry. The results demonstrate that the fracture processes and damage patterns of iron tailings sand concrete and river sand concrete are comparable; the addition of iron tailings sand improves initial cracking load and initial cracking toughness more significantly than unstable cracking load and unstable cracking toughness; the ductility of iron tailings sand concrete is marginally inferior; and the results of microscopic tests demonstrate that the addition of iron tailings sand can improve the morphology and pore structure of the interface transition zone. Therefore, from the assessment of fracture mechanics, iron tailings sand can totally replace river sand in equivalent quantities for concrete preparation, which will provide great potential for the secondary use of iron tailings sand.

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.

Evaluating fracture parameters of basalt fiber reinforced and pozzolana slurry modified recycled concrete produced from waste

Recycling of construction and demolition waste provides one of the most effective paths for sustainable development, valorising recycled concrete, and environment protection. Unfortunately, due to substandard concrete matrix quality, lower strength and fracture parameters the practical applications of recycled concrete still remain the foremost concerns. To overcome these issues, a new effective strength enhancing approach was investigated in this study. More explicitly, two types of recycled concrete consisting of 20% and 100% of pozzolana slurry encrusted recycled aggregate and strengthened with various dosages of basalt fiber (BF) were evaluated in terms of fracture properties, namely compressive strength, fracture energy, fracture toughness, flexural strength, and elastic modulus. In addition, a digital image correlation (DIC) analysis was established to evaluate the strain contour variation while the microstructure study was conducted to inspect the concrete matrix quality. Experimental result revealed improvement in the ultimate load capacity as well as the overall load-CMOD response of BF modified formulations. For 20TRAC-1BF and 100TRAC-1BF, the fracture energy was improved by 91% and 56% and the fracture toughness was enhanced by 69% and 43%, respectively. Furthermore, the added dosages of BF were found useful in improving the flexural strength, elastic modulus, and toughness indices of both types of recycled concretes. From the DIC analysis, it was found that the BF modified concrete contained continuous spread of strain contours throughout the beam depth and revealed higher strain values than the reference sample. Lastly, the microstructure observation demonstrated better concrete matrix quality and BF-cement matrix interaction which thereby confirms the usefulness of the applied strength enhancing technique for the application of high strength fiber reinforced recycled concrete.

Two‐dimensional meso‐structural simulation of concrete fracture by the implementation of zero‐thickness cohesive interface elements

AbstractConcrete is considered as a non‐homogeneous material and from a mesoscopic point of view is constituted of three main phases, namely aggregates, mortar matrix and interfacial transition zone (ITZ). To investigate the damage process of concrete materials at the mesoscale due to mechanical loading, an explicit numerical model with full representation of the three mesoscopic phases is required. To this end, in this work, a Python code is developed to generate zero‐thickness cohesive interface elements in two‐dimensions (2D). The generated code is capable of generating two‐dimensional quadratic cohesive interface elements (i) within the mortar elements, (ii) within the aggregates elements and (iii) at interfaces between mortar and aggregates. To simulate the crack propagation, the generated zero thickness‐cohesive elements are preinserted at the interface of solid elements and different traction‐separation laws are assigned to them to simulate all potential crack paths. The implemented algorithms to generate the cohesive elements are discussed in detail and numerical examples of crack propagation in concrete is presented using Abaqus/CAE. The numerical results are compared with those in the literature qualitatively to validate the performance of the model. The developed method provides the possibility to investigate the damage processes in meso‐and micro‐scales underlying the macroscopic behavior of the semi‐brittle materials.

Synergistic performance of steel-brass hybrid fibres on the concrete fracture properties

Synergistic performance of steel-brass hybrid fibres on the concrete fracture properties

Non-fitting theoretical models for the fracture properties of concretes subjected to high temperature

The fracture properties of concretes, which are often characterized by the tensile fracture strength, compressive fracture strength, fracture energy and characteristic length are closely related to temperature. However, there are still few systematic theoretical models of temperature-dependent fracture properties of concretes. In this work, a series of novel temperature-dependent theoretical models are developed to determine the fracture properties of concretes based on the force-heat equivalence energy density principle and classical concrete fracture theories. The models establish the quantitative relationship between the high-temperature tensile fracture strength, compressive fracture strength and characteristic length, and the basic material parameters including the Young's modulus and melting point. It is worth noting that this work quantitatively characterizes the fracture properties of concretes subjected to high temperatures using the simple material parameters, without the need to carry out any data fitting. The fracture properties of concretes with different aggregate types, different fiber-reinforced concretes, and ordinary Portland cement-based concretes are predicted and systematically analyzed using the proposed models. The model-predicted tensile fracture strength, compressive fracture strength and characteristic length of materials up to 800 °C agree well with the experimental measurements without using any fitting parameters. The coincidence rate at many temperature points could reach up to and above 90%, even approaching about 100%. The fracture properties of concretes and their main mechanisms at various temperatures thus can be depicted by using the developed models. Additionally, this work offers a new and simple testing method to determine the characteristic length of concretes and its change with temperature.

Multigene Genetic Programming Based Prediction of Concrete Fracture Parameters of Unnotched Specimens

This study explores the fracture energy of notched and unnotched concrete specimens subjected to the classical three-point bend test, instantiating a gradational step in the continued development of concrete fracture mechanics. An experimental campaign involving 18 notched test specimens and nine unnotched specimens of three different grades of concrete, an examination of the existing literature models for unnotched specimens, and a novel Multigene Genetic programming (MGGP) based concrete fracture energy model for unnotched specimens are integral to this study. As a salient result, the multiple approaches to quasi-brittle materials adopted in the study, highlighted the criticality of the determination of fracture energy, tensile strength and characteristic length for the crack width study. The failure modes of notched and unnotched specimens were found to be similar. The reported literature has mainly focused on a limited number of fracture energy influencing parameters. Therefore, six impact parameters have been chosen and incorporated into the present study to provide a more acceptable explanation of concrete fracture behaviour. A sensitivity analysis of the parameters and an error analysis of the model undertaken have established the accuracy and robustness of the developed MGGP model. Doi: 10.28991/CEJ-2023-09-02-011 Full Text: PDF

Using beam and ENDB specimens to evaluate fracture characteristics of wavy steel fiber‐reinforced self‐compacting concrete containing different coarse aggregate volumes

AbstractThis research has addressed the effects of coarse aggregate (CA) and wavy steel fiber (WSF) volumes on the self‐compacting concrete (SCC) fracture parameters in beam and edge notched disk bend (ENDB) specimens using size effect and work fracture methods (SEM and WFM). Mix designs were based on 30%–60% CA volumes and 0.15%–0.45% WSF volumes, and 144 different‐size notched beam specimens underwent 3‐point bending tests. Results showed that increasing the CA volume and percent WSFs increased the SCC ductility in both SEM and WFM; increasing the WSF volume affected the fracture energy‐compressive strength relationship negatively at 30% and 40% CA volumes, and increasing the WSF affected the mentioned relationship positively at 50 and 60% CA volumes. Finally, we predicted the relationship between the fracture parameters calculated with ENDB specimens and those of beam specimens calculated with SEM and WFM.

Tensile Fracture Property of Concrete Affected by Interfacial Transition Zone

As a weak link between aggregate and mortar in concrete, interfacial transition zone (ITZ) usually plays a key role in concrete fracture. To investigate the tensile fracture property of concrete affected by the mechanical properties of ITZ numerically, the geometrical models of heterogeneous concrete were established with the parameterization modeling. They include three phases, namely, mortar, ITZ, and randomly distributed aggregates with distinct sizes and orientations. The cracking behaviors of mortar and ITZ were characterized by the bilinear cohesive zone constitutive model. Based on the experiments, the mechanical properties of ITZ were mediated by changing the water–cement ratio of mortar, the aggregate surface roughness and the content of silica fume in interfacial agent. A series of numerical simulations were conducted on the concrete models in tension after the numerical modeling method was validated. The macroscopic tensile fracture properties of concrete were quantitatively connected with some microscopic variables, including the water–cement ratio of mortar, the aggregate surface roughness and the silica fume content in interfacial agent. It was found that the tensile fracture properties of concrete have negative linear correlations with the water–cement ratio of mortar, while the effects of the aggregate surface roughness and the silica fume content in interfacial agent are very complex. The tensile fracture mechanical properties of concrete have a bilinear relationship with the aggregate surface roughness and an approximate quadratic parabola relationship with the content of silica fume in the interfacial agent. This study is beneficial to improve the fracture resistance of concrete by some interface handling measures.

A dynamic FEM-DEM multiscale modeling approach for concrete structures

The dynamic behavior of concrete is strain-rate-dependent, which affects the failure modes of structures. In this study, a multiscale modeling approach is developed for concrete structures under dynamic loading, which couples the macroscale finite element method (FEM) and the mesoscale discrete element method (DEM). The dynamic response of structures is analyzed using the macroscale FEM, and a representative volume element (RVE), composed of aggregate, mortar, and interface, is simulated using the mesoscale DEM to capture the strain rate effects of concrete. By fully taking the advantages of macroscale and mesoscale simulations, it is no longer essential to use complex constitutive laws or input rate-dependent parameters for the macroscale FEM modeling because the concrete fracture can be explicitly illustrated through the breaking process of the mesoscale RVE. This approach is applied to concrete beams and the Koyna dam to verify its applicability. These practical comparisons demonstrate that the seismic tensile strength increases with the strain rates under seismic loading and that the actual repeated crack-closure process of concrete is adequately simulated by the proposed method.

Appraisal of Asphalt Mixtures’ Cracking Resistance Modified with Waste Aluminum Scrap Powder (WASP) at Intermediate Temperatures

Considering that most asphalt concrete pavement distresses are fracture-related, evaluating and quantifying mix fracture properties is essential to improved pavement design. Therefore, the first step of the study, a pre-development phase, determines the optimal value for adding waste aluminum scrap powder (WASP) with a fraction size of 2.36-0.075 mm to mixes. Based on previous digital image analysis (DIA), AlDoz and AlNibaa’e aggregates were selected from seven central, northern, and southern Iraq sources. The second post-development phase studies the testing factors of a reliable and practical semi-circular bending (SCB) test for assessing asphalt concrete mixture fracture properties at intermediate service temperatures. The development and calibration of the Marshall System into the SCB-Tester, which switched from analog to digital and computerized control, accurately predicted reference and modified mix fracture characteristics at 50.8 mm/min. Three notch lengths (25, 32, and 38) mm were selected to be studied. Five percentages of WASP (0.5, 1.0, 1.5, 2.0, and 2.5) percent were added by weight to the entire mix and compared to the reference mixture. Results indicate that 1.5% WASP decreases fracture severity and stiffen AlNibaa’e and AlDoz mixes. Increased fracture strength and toughness of modified mixes relative to the reference may dramatically increase asphalt concrete fracture resistance. Even though a higher evaluation for AlNibaa’e mixes than AlDoz with an expected difference, the impact of modifying appears to be an effective influence for AlDoz mixes with determination factors (R2) of 0.9788 and 0.9889 than that of AlNibaa’e modified coarse and fine mixes, which have R2 of 0.8535 and 0.8461, respectively.