Concrete Failure Research Articles

Efficacy of functionalized sodium-montmorillonite in mitigating alkali-silica reaction

Alkali-silica reaction (ASR) is a fatal deterioration that can cause volume expansion, cracking, and premature failure of concrete. In this study, the efficacy of sodium montmorillonite (NaMt) organically functionalized with two non-ionic surfactants (ONaMts) in mitigating ASR is investigated by determining the expansion and cracking behavior of mortars containing reactive aggregates. The underlying mitigation mechanisms were analyzed through the quantification of reaction products and in-situ characterizations of ASR gels. The results revealed that, compared with raw NaMt, ASR-induced expansion and cracking can be more substantially mitigated in the presence of ONaMts, which is supported by the improved consumption of portlandite and reduced formations of both crystalline and amorphous ASR gels. The functionalized ONaMts appeared to further suppress the formation of Q3 polymerization sites, decrease the [K + Na]/Si atomic ratio and increase the Al/Ca in ASR gels.

Experimental study on infrared thermal response characteristics of water-bearing concrete under drop hammer impact

The dynamic impact damage of concrete will lead to serious safety accidents, and the water environment will aggravate the degree of damage. In this paper, an infrared monitoring experimental system for drop hammer impact damage of water-bearing concrete was designed and established. The mechanical properties, infrared radiation temperature (IRT) and infrared thermography of concrete impact damage with different soak time were tested and analyzed. The influence of water on the infrared generation mechanism of concrete was discussed. The results show that water has an initial weakening effect on concrete, which weakens the cementation between concrete particles and aggregate strength, resulting in a decrease in concrete strength. Compared with dry concrete, the infrared temperature of water-bearing concrete increased more during impact damage. With the increase of soak time, the average infrared temperature (AIRT) and the maximum infrared temperature (MIRT) of water-bearing concrete decreased. When dry concrete was damaged, tensile cracks were mainly produced and accompanied by heat absorption. When water-bearing concrete was damaged, high temperature shear cracks appeared. The high temperature generated at the moment of impact failure of water-bearing concrete may be caused by the cavitation phenomenon of water in the microscopic pores of concrete during the drop hammer impact and the combined effect of concrete microstructure damage. The research results are of great significance for monitoring and evaluating the stability of the dynamic evolution process of concrete structures.

Cracks Classification using Acoustic Emission Technique on a Reinforced Concrete Beam

The usage of non-destructive techniques for structure's state assessment is highly desirable because they offer the possibility to monitor continuously and in a non-invasive manner the sign of failures of any structure. Among the several techniques proposed over the years, Acoustic Emission (AE) seems very promising. Such a technique, which applies to various materials, consents to the evaluation of micro-fractures generated during failure by detecting their acoustic emission through sensors located on the surface of the material itself. Concrete beam failure is suitable for such kind of procedure. It has been widely investigated through AE, but despite the many literature contributes, there still is a scarcity of practical applications on real structures, and no consensus on protocols. In this work, an AE technique has been paired with a four-point bending test to try and find a robust and reliable experimental setup for AE application on concrete beams. Results show a proper classification of the occurring cracks, which change according to different zones of the concrete beam and different load values. Axial crack signals exhibit different features concerning shear crack ones. In such a way, the categorization of damages can be performed and crosschecked with the theoretical expectations. All these results suggest that the proposed setup can be used as a possible protocol for practical AE measurements.

The effect of using steel fibers reinforced concrete layer in compression zone on the flexural behavior of over‐reinforced concrete beams

AbstractDuctility is one of the most important requirements of RC design besides other requirements such as strength and stiffness. In recent years, concrete beams with a large amount of tensile reinforcement ratio (ρ) have been required in large projects, such as high‐rise buildings and bridges. Using high (ρ) increases the strength and stiffness of the beams and leads to a decrease the ductility. This paper aimed to investigate the effect of using steel fibers reinforced concrete (SFRC) layer in compression zone on the flexural behavior of over‐reinforced concrete beams. Partial replacement of concrete with SFRC layer in compression zone was used to avoid the brittle compression failure of concrete. For this purpose, 12 over‐reinforced concrete beams with a span of 1300 mm and a cross‐section of 120 mm × 180 mm were cast and tested under a three‐point loading. The first beam was used as a reference beam and others as strengthened beams using SFRC layer. The effects of thickness and length of strengthening layer, (ρ), volume fractions of steel fibers, and strengthening methods on flexural performance of tested beams were investigated. The flexural capacity, failure modes, crack patterns, load–deflection relationships, load–strain relationships, ductility index, and toughness were evaluated. The results showed that the suggested technique (SFRC layer in the compression zone) is an effective technique to increase ultimate load, ductility, and toughness by up to 35.72%, 121.01%, and 349.16%, respectively, compared to the reference beam. Furthermore, the failure mode changed from brittle to ductile failure. Also, one of the main advantages of this technique is allows to increase of (ρ) up to 8.55% (4.15ρb) without needing the compressive reinforcement. The results of this study indicate that the using SFRC layer in the compression zone is an appropriate and economical method to provide high flexural capacity and ductility over‐reinforced concrete beams.

Study on stage characteristics of hydraulic concrete fracture under uniaxial compression using acoustic emission

ABSTRACT Acoustic emission (AE) can monitor and evaluate the cracking situations of hydraulic structures for it is real-time and non-destructive. However, a current challenge of this approach is to accurately identify the various stages during the cracking process. The innovation of this paper lies in the application of AE data in analyzing the stage characteristics during the whole process of hydraulic concrete fracture. First, the slope changing of the cumulative ringing count curve was used to determine the cracking stages of hydraulic concrete. Second, the function of inter-event times (denoted as F-function) was used to further investigate the AE characteristics proximity to the final fracture. Last, the spatial-temporal-energy evolution of cracks was studied. The results show that: (1) The whole process of hydraulic concrete failure shows an obvious stage characteristic from the perspective of AE feature and it can be distinguished to five stages by the slope change of the cumulative ringing count curve; (2) The F-function can be used to identify the last two cracking stages, and it is capable of early warning the macroscopic cracking in ahead of b-value; (3) The spatial-temporal-energy distribution of cracks helps to better understanding the generation and evolution for cracks inside hydraulic concrete.

Study on failure characteristics of basalt fiber reactive powder concrete under uniaxial loading

The uniaxial compression experiments of basalt fiber reactive powder concrete (BFRPC) were carried out by acoustic emission (AE) and DIC techniques, focusing on the AE characteristics in the process of BFRPC failure. The cracking modes of internal and surface cracks of BFRPC are judged by clustering analysis of average frequency (AF) and rise angle (RA) based on Gaussian mixture model (GMM) and displacement on both sides of cracks measured by DIC. Research investigates that the peak frequencies of BFRPC are mainly distributed in 5 ∼ 35 kHz, 60 ∼ 100 kHz, 185 ∼ 215 kHz and 230 ∼ 280 kHz. With the increase of stress level, the absolute energy in the peak frequency range increases gradually. The volume content of 0.5% and 1.0% basalt fiber increased the absolute energy in each peak frequency range. Basalt fiber can improve the compressive strength and the strength and density of AE energy of RPC to some extent. The shear failure of BFRPC mainly occurs in the later stage of loading. Basalt fiber can change the failure mode of BFRPC from tensile failure to tensile shear failure. Meanwhile, basalt fiber can effectively increase the stress level during cracking and reduce the damage degree of BFRPC. Judging the AE characteristics and crack types of concrete failure is of great consequence to predict the precursory failure of BFRPC.

Influence of concrete and unbonded ratio on RC beams

Hybrid aggregates, comprising normal-weight and lightweight aggregates, offer an effective means to enhance the physical and mechanical properties of concrete. However, the comprehensive effect of hybrid aggregate concrete on the flexural performance of reinforced concrete (RC) beams remains largely unexplored. In this study, utilizing LC30 lightweight concrete, LC40 gravel lightweight concrete, hybrid aggregate lightweight concrete, and hybrid aggregate concrete with reduced ceramsite content as matrix materials, RC ordinary beams and RC bond-slip beams with dimensions of 150 mm × 300 mm × 2400 mm were meticulously designed and fabricated. Employing a four-point bending test, the effects of the concrete matrix, the unbonded ratio, and the reinforcement ratio of the bottom longitudinal rebar on the flexural behavior of the two types of beams were scrutinized. Furthermore, the load–deflection and load–slip responses were subjected to numerical simulation using the finite element method. The findings demonstrate that hybrid aggregates exert a substantial influence on adjusting the dry apparent density, strength, and elastic modulus of concrete to align with design specifications. While the physical and mechanical characteristics of both beam types are primarily governed by the reinforcement ratio and unbonded ratio, the concrete matrix, despite its distinct properties, exhibits minimal effect on these attributes. Nevertheless, it significantly affects beam stiffness and the relative slip between the rebar and the concrete matrix. Both beam categories adhere to the plane section assumption and reveal that optimal collaborative performance between the rebar and concrete matrix occurs at a bottom longitudinal reinforcement ratio of 1%, albeit diminishing with escalating unbonded ratios. The failure progression of both beam types can be categorized into three stages: elastic phase, crack propagation phase, and compressive failure phase. The process of crack advancement, the load–deflection profile, and the load–slip behavior of the beams manifest similarities, albeit subject to variations attributable to the concrete matrix, bottom longitudinal reinforcement ratio, and unbonded ratio. The Menetrey–Willam constitutive model effectively replicates the load–deflection and load–slip characteristics of both beam types. However, its simulation precision is influenced by the friction coefficient existing between the rebar and the concrete matrix. Notably, this friction coefficient undergoes alteration in consonance with the concrete failure process, thereby reflecting the gradual degradation of bonding performance between the rebar and the concrete matrix.

Characteristics of energy evolution and acoustic emission response of concrete under the action of acidic drying-saturation processes cycle

The continuous fluctuation in the acidic mine water level of the underground reservoir will affect the artificial dam's strength and stability. The uniaxial compression test of C25 concrete under different drying-saturation processes cycle (DSPC) numbers and pH solutions were performed. The degradation mechanism of mechanical properties of concrete under acidic DSPC was investigated; the calculation formula for the elastic strain energy at peak stress has been corrected and the energy evolution law has been obtained; besides, the evolution characteristics of acoustic emission (AE) parameters were studied using multi-fractal theory and the precursor characteristics of concrete failure were obtained. The results revealed that increasing the DSPC times or decreasing the pH caused an increase in the saturation moisture content of the concrete, the strain and elastic strain energy of the concrete at peak stress increased, a drop in the ultrasonic velocity, the uniaxial compressive strength (UCS), the elastic modulus (EM) and the overall input energy. The accumulated ringing count and accumulated energy of AE dramatically increased before the concrete was close to failure, and numerous low-frequency and high-amplitude signals started to appear. The information mentioned above might be considered a short-impending warning of concrete failure. During the plastic deformation, the large increase of the multi-fractal parameter Δα and the significant drop of Δf might be viewed as early warning for concrete failure. This research will offer some theoretical direction for artificial dam design and long-term stability monitoring in underground reservoirs.

Classification and prediction of deformed steel and concrete bond-slip failure modes based on SSA-ELM model

Bond-slip failure modes between reinforcement and concrete can seriously affect the load-bearing performance and safety of reinforced concrete (RC) structures. The pull-out test is widely used to analyze RC bond-slip and failure modes because of its simplicity. Therefore, a prediction model based on Sparrow Search Algorithm (SSA) Optimized Extreme Learning Machine (SSA-ELM) is proposed in this study to quickly and effectively evaluate the failure forms of RC structures. The bond-slip test samples containing 399 sets of deformed bar and concrete deformation pull-out tests were first collected as a database, and the various characteristic parameters were preprocessed. Then, the features significantly influencing the failure pattern were screened out using random forest, and the plausibility tests were performed using the Pearson correlation coefficient and mutual information. Subsequently, a classification prediction model of the pull-out failure pattern was developed based on standard machine learning (ML) algorithms. In addition, nine well-known ML algorithms (LR, K-NN, DT, SVC, BPNN, NB, RF, AdaBoost, and XGBoost) are considered. This model's accuracy and generalization ability are compared based on the Precision and Recall confusion matrix. Finally, the optimized ELM was trained by SSA using the training set data with optimized ELM weights and thresholds. The results showed that the concrete protective layer thickness ratio to reinforcement diameter had the highest sensitivity to the failure pattern of RC-drawn specimens. The accuracy of the prediction results of the SSA-ELM model was better than other ML algorithms (Accuracy = 95.8%), such as BP Neural Network. In addition, SSA has better stability and higher accuracy than Gray Wolf Optimization (GWO) Algorithm, Particle Swarm Optimization (PSO) Algorithm, Genetic Algorithm (GA), Ant Colony Optimization (ACO), and other ML classification algorithms.

Experimental investigation of strength characteristics of concrete reinforcement with neem powders

Collapsibility is the major problem faced by every structural element in buildings. Several innovations are happening every year to prevent concrete failure for better stability of these structures. This study is focused on analysing the strength aspects by using Neem powders on the concrete reinforcement and strength performance of the Neem mixed concrete at various percentages such as 0%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% with that of cement. Beam elements have been casted and tested using a Universal Tensile Testing machine. It was found that the Neem powder contained sample showed positive strength enhancement, and it showed excellent performance towards the strength of the concrete in terms of compressive and split tensile strength. The input process parameters are analysed using L18 orthogonal array for validating the impact of response outputs considered in this study. The findings show that the compressive strength of the concrete mixture keeps on increasing with the increase in neem powder percentage but the split tensile strength shows a maximum strength value of 3.536 MPa at 0.2% replacement of neem powder, 28 days curing in comparison with conventional concrete. ANOVA results show that the percentage contribution of factors is 77.19 % and 14.9 %, for curing days and percentage replacement of neem powder respectively. Thus, this type of neem powder mixed concrete structure can be used as a strength-enhancing agent in RC beam elements.

The seismic behaviors of steel-concrete-steel composite walls with dumbbell-shaped connectors

In this study, quasi-static tests were conducted on six steel-concrete-steel composite wall (SCSCW) specimens with novel dumbbell-shaped connectors (DSCs) to investigate their seismic performance. The research parameters included the connector arrangement scheme and the axial load. The failure mode, load-displacement curve, and strain data were analyzed in detail. All the specimens exhibited flexural failure, and the experimental phenomena included the local buckling of external steel plates and compressive failure of internal concrete. The local buckling located between the foundation and first row of connectors, had a limited effect on the bearing capacity of the specimens. The connectors effectively controlled the buckling range of the external steel plates. With increasing axial load, the deformation capacity of the specimens decreased significantly. Under the same displacement, the greater the axial load, the greater the secant stiffness, and the higher the accumulated energy dissipation value. When the load reached its peak value, the yield range of the bottom front steel plates of specimen with large axial load was less than that of the specimen with small axial load. The theoretical formula accurately calculated the flexural bearing capacity of SCSCWs, and the maximum error and the average ratio which was defined as experimental value to calculated value were 9% and 1.02, respectively. The horizontal load-displacement relationship of the specimens was calculated using the OpenSees software, and the maximum error of the bearing capacity was 4%. The parametric analysis showed that increasing the steel plate thickness can effectively improve the bearing capacity of SCSCWs.

Application of Fractal Theory to the Analysis of Failure Characteristics of Low-Velocity-Impact Concrete Slabs

The fractal characteristics of low-velocity-impact concrete slabs were studied using fractal theory, and the fractal dimension value of cracks of each concrete specimen plate was calculated using box dimension as the basic principle and digital image analysis technology in conjunction with MATLAB software (R2021b) calculation functions. The energy dissipation of concrete slabs during low-velocity impact is calculated using the elastic sheet theory. The calculation results are realistic, and the energy conversion of concrete slabs during low-velocity impact is analyzed based on these results. The research findings indicate that concrete slab cracks exhibit good fractal characteristics during low-velocity impact, and their values can be utilized as a parameter to determine the extent of concrete slab failure. Moreover, the study found that the fractal dimension value of concrete slab cracks and the associated plastic deformation energy display good exponential function characteristics in the energy dissipation mechanism of low-velocity concrete slabs.

Concrete failure based on a localizing gradient‐enhanced damage formulation coupled with plasticity

AbstractInvestigations of the mechanical behavior of concrete, including plastic deformability and failure mechanisms, have always been of vital importance. In this work, a modified yield criterion with three surfaces is proposed to capture the plastic yielding behavior under different loading conditions. The failure, that is, the gradual degradation and the final loss of material integrity, can be described through a damage concept. For the purpose of robust finite element (FE) implementations as well as the failure description at an appropriate scale, a localizing gradient‐enhanced damage model has been adopted. As such, one obtains mesh‐insensitive material responses, while ruling out the unphysical damage broadening observed in conventional gradient‐enhanced damage models with a constant regularization length. Following a consistent derivation, the plasticity‐damage coupled model is implemented into an in‐house FE framework, based on which an experiment‐inspired example is simulated to illustrate the capability of the proposed description in concrete modeling, especially the mixed‐mode failure. Lastly, the conclusion provides some final insights.

Investigation of pull-out characteristics of connections for post-installed rebar utilizing mortar-based binders and chemical adhesives

ABSTRACT In this study, various types of adhesives were tested for their ability to adhere steel reinforcement bars to old concrete during a pull-out test when they were used in connection to a post-installed re-bar. The cylinder samples were 150 mm in diameter and had anchors made of rebar that varied in diameter (8 mm, 10 mm, 12 mm, 16 mm, and 20 mm) and embedded depth (10, 12.5, 15, and 20 times the rebar diameter). In contrast to the control group of (60 Nos.) cast-in-situ rebar concrete specimens, the other samples (240 samples) were post-installed-rebar concrete specimens with various bonding agents, epoxy-based chemical adhesive, vinyl-ester-based chemical adhesive, and cement-based binders (geopolymer mortar, conventional mortar). The results showed that while they all performed better than cement-based mortar-bonded specimens, the use of the epoxy-based chemical adhesive and vinyl-ester-based chemical adhesive pull-out load values were closely related. The anchorage depth and rebar diameter both improve the bond strength which reflects in terms of pull-out load. The anchorage depth and the region of contact with the adhesives or binder determine the failure mechanism of post-installed rebar connections. Due to the higher strength at the interface between the binder and the rebar in comparison to the binder-concrete, larger rebar diameters favour splitting or failure of concrete.

Research on the Bonding Performance of BFRP Bars with Reactive Powder Concrete

In recent years, replacing steel bars with basalt fiber-reinforced polymer (BFRP) bars and replacing ordinary concrete with reactive powder concrete (RPC) are considered effective solutions to the corrosion problem of steel bars in ordinary reinforced concrete structures. In order to study the bonding performance between BFRP bars and RPC, a total of 27 bonding specimens were tested by pull-out test. The effects of steel fiber volume content (0%, 1.5%, 2%), protective layer thickness (25 mm, 40 mm, 55 mm, 69 mm), and bond anchorage length of bars (3 d, 4 d, 5 d; d is the diameter of the bars) on the bond performance were studied. The experimental results indicated that the BFRP bar and reactive powder (RPC) concrete interface exhibited better bonding performance, and the steel fibers mixed in RPC can play the role of crack-blocking enhancement in the specimen, which improves the shear and tensile properties of the concrete, thus improving the bond strength between BFRP bar and RPC. Three failure modes were observed in the pull-out tests: BFRP bar shear failure, splitting failure, and concrete shear failure. The bond strengths of BFRP bars and RPC with 0%, 1.5%, and 2% steel fiber content were 24.2 MPa, 32.1 MPa, and 34.5 MPa, respectively. With the increase in bond anchorage length, the ultimate bond strength tended to increase first and then decrease. There may be an optimal bonding length between BFRP bar and reactive powder concrete, and when the optimal bonding length is exceeded, the bond strength decreases with the increase in bonding length. With the increase in the protective layer thickness, the improvement in the bond strength of the BFRP bar and RPC was not very significant.

Push-out behavior of GFRP bolts shear connectors in FRP-concrete hybrid beam

GFRP bolt has emerged as a promising shear connector in FRP-concrete hybrid beams due to flexible arrangement and ease of installation. Shear connectors are critical to maintaining the composite action and are key to the design of hybrid beams. 30 push-out tests were conducted to investigate failure mode, ultimate strength, and shear load-slip (P-S) relationship of GFRP bolts. Test parameters included bolt types, layout of bolts, longitudinal row spacing of bolts (Sl), bolt diameter (d), and bolt embedment depth (he). Results revealed that specimens with GFRP bolts exhibited bolt shank shear failure, pry-out failure of bolts, and splitting failure of concrete. In contrast, specimens with stainless-steel bolts suffered bearing failure of bolt holes in the FRP flange. Typical P-S curves of GFRP bolt specimens consisted of micro-slipping and significant-slipping phases, showing non-linear response, while P-S curves of stainless-steel bolts exhibited a linear response till failure. The effect of layout of bolts was found negligible if the longitudinal row spacing and horizontal spacing was not less than 6d and 4d, respectively. Specimens with a larger d and he demonstrated greater shear capacity. Based on the test results, prediction equations associated with failure modes were introduced to predict the capacity of GFRP bolt, which yielded results in accordance with experiments. Additionally, a refined description of P-S relationship was proposed by curving fitting, and the results correlated well with the experiments.

Study on the static and fatigue performance of MCL-shaped shear connectors

Seven specimens were prefabricated and conducted in the static and fatigue tests to investigate the static mechanical properties and fatigue performance of the MCL (modified clothoid) shape composite dowels. The failure mode, ultimate carrying capacity, shear stiffness, relative slippage, stiffness degradation and residual load-bearing capacity were studied. Additionally, a theoretical model for calculating the residual load-bearing capacity was proposed. Results showed that the failure mode of the specimens under static and fatigue loads is the concrete shear failure. The failure process included the following stages: the bonding failure, yielding of penetrated bar and concrete shear failure. During fatigue test, the static stiffness of the MCL-shaped composite dowel increased initially, then decreased linearly, and dropped abruptly in the final stage. The results obtained from the theoretical model agreed well with the experimental findings.

Comprehensive investigations on the relationship between the 3D concrete printing failure criterion and properties of fresh-state cementitious materials

Comprehensive investigations on the relationship between the 3D concrete printing failure criterion and properties of fresh-state cementitious materials

Structural behavior of stainless steel anchor channels embedded in concrete under perpendicular and longitudinal shear

Stainless steel anchor channels with channel bolts (SSAC-CBs) have been chosen as alternatives to conventional carbon steel anchor channels to enhance corrosion resistance, ductility, and load-bearing capacity. This study evaluated the shear performance of SSAC-CBs embedded in concrete members under perpendicular and longitudinal shear loads using static monotonic tests. The failure modes and shear capacities of the specimens were compared with those obtained by finite element analysis (FEA) models established using ABAQUS. Concrete edge breakout failure accompanying the channel flexural yielding and channel bolt fracture dominated in the SSAC-CBs under perpendicular shear. The load–displacement curves for perpendicular shear exhibited four salient stages: initial linear elasticity, slippage, strain hardening, and damage and failure. Under longitudinal shear, the SSAC-CB specimens exhibited a failure of the serrations in the contact area between the serrated channel bolt head and channel lips and slip failure between the hook-type channel bolt and channel lips. In addition, the numerical analysis results indicated that the load-bearing capacities, initial elastic stiffnesses, and failure modes obtained through the FEA models were consistent with the test results. Furthermore, theoretical formulas were proposed for the shear capacity for SSAC-CBs under perpendicular and longitudinal shear. The research outcomes provide valuable guidance for the design and application of SSAC-CBs in engineering.

Concrete Repair Using Fiber from Surgical Mask

In this new Norma, surgical mask was a thing that important to wear in public. Because of the frequent use of surgical mask, the huge of waste of surgical mask were disposed per day. The surgical mask was made from a polypropylene fiber that widely used in construction in the term of concrete fiber. Polypropylene fiber had their own credibility to provide the ductile strength for concrete to reduce the cracking of concrete that was a brittle material. To study the effectiveness of the fiber from surgical mask, this fiber was used as concrete repaired materials The material of concrete repair was the important things to provide or improved the deteriorated concrete. Therefore, this study will determine that fiber from surgical mask can be used as a concrete repaired material through the comparison of flexural strength between the controlled concrete and repaired concrete. Three methods of concrete repaired was tested in this study, single layer polypropylene fiber, single layer surgical mask fiber, and double layer surgical mask fiber. Those method was applied to deteriorated concrete prism. The result for flexural strength of concrete after repaired for all method was decreasing from the strength before repaired but the result of second method was higher than the first method and the third method was higher than the second method. The concrete failure condition, showed the failure happened on the same location failure before repaired that meant the failure happened on the concrete repaired material. However, the used of surgical mask fiber was changed failure condition of the concrete prism from sudden failure to periodic failures. Therefore, the surgical mask was effective to repair the damage concrete due to crack failure because the fiber of the surgical mask can controlled that crack.