Concrete Crack Width Research Articles

Short- and long-term performance of the novel additional aluminum alloy ribs anchored CFRP reinforced pretensioned PC beams

The anchorage shortage in FRP (fiber reinforced polymer) reinforced pretensioned prestressed concrete (PPC) elements has frequently led to the uncontrollable slippage. To provide a practical answer to this issue, an innovative additional aluminum alloy ribs (ARs) anchorage was developed. This study mainly investigated the effect of the ARs anchorage on the performance of the CFRP reinforced PPC beams subjected to flexural loading. Two kinds of loading types (i.e. short- and long-term loading) and two sustained loading levels (i.e. 40% and 75% of the short-term capacity) for the tested beams were included. The results indicated that ARs anchorage could shorten the transfer length and improve the short-term diagonal concrete cracking load in PPC beams by as much as about 20%. In addition, the ARs anchorage presence was capable of reducing the long-term slip by more than 2 times after the beams were loaded up to 120 days, and meanwhile delaying the diagonal concrete crack width increase by up to 70.9%-86.4%. Due to such merits, a less long-term prestressing loss was found and the long-term deflection of the beam was decreased by 50.8%–82.9%. More significantly, one of the unanchored PPC beam failed by complete bar slippage after being loaded for 146 days, whereas the ARs anchored beams have successfully sustained the 584-day loading and showed a convergent slip development. Finally, two calculation methods for the FRP reinforced beams were adopted to predict the long-term deflection of the tested beams, and the analytical and experimental results were compared and analyzed.

Optimization of the Structural Performance of Buried Reinforced Concrete Pipelines in Cohesionless Soils.

Pipelines are widely used to transport water, wastewater, and energy products. However, the recently published American Society of Civil Engineers report revealed that the USA drinking water infrastructure is deficient, where 12,000 miles of pipelines have deteriorated. This would require substantial financial investment to rebuild. Furthermore, the current pipeline design practice lacks the guideline to obtain the optimum steel reinforcement and pipeline geometry. Therefore, the current study aimed to fill this gap and help the pipeline designers and practitioners select the most economical reinforced concrete pipelines with optimum steel reinforcement while satisfying the shear stresses demand and serviceability limitations. Experimental testing is considered uneconomical and impractical for measuring the performance of pipelines under a high soil fill depth. Therefore, a parametric study was carried out for reinforced concrete pipes with various diameters buried under soil fill depths using a reliable finite element analysis to execute this investigation. The deflection range of the investigated reinforced concrete pipelines was between 0.5 to 13 mm. This indicates that the finite element analysis carefully selected the pipeline thickness, required flexural steel reinforcement, and concrete crack width while the pipeline does not undergo excessive deformation. This study revealed that the recommended optimum reinforced concrete pipeline diameter-to-thickness ratio, which is highly sensitive to the soil fill depth, is 6.0, 4.6, 4.2, and 3.8 for soil fill depths of 9.1, 12.2, 15.2, and 18.3 m, respectively. Moreover, the parametric study results offered an equation to estimate the optimum pipeline diameter-to-thickness ratio via a design example. The current research outcomes are imperative for decision-makers to accurately evaluate the structural performance of buried reinforced concrete pipelines.

Machine Learning-Based Concrete Crack Depth Prediction Using Thermal Images Taken under Daylight Conditions

Concrete cracks can threaten the usability of structures and degrade the aesthetics of buildings. Furthermore, minor cracks can develop into large-scale cracks that may lead to structural failure when exposed to excessive external loads. In addition, the concrete crack width and depth should be precisely measured to investigate the effects of concrete cracks on the stability of structures. Thus, a nondestructive and noncontact testing method was introduced for detecting concrete crack depth using thermal images and machine learning. The thermal images of the cracked specimens were obtained using a constant test setup for several months under daylight conditions, which provided sufficient heat for measuring the temperature distributions of the specimens, with recording parameters such as air temperature, humidity, and illuminance. From the thermal images, the crack and surface temperatures were obtained depending on the crack widths and depths using the parameters. Four machine-learning algorithms (decision tree, extremely randomized tree, gradient boosting, and AdaBoost) were selected, and the results of crack depth prediction were compared to identify the best algorithm. In addition, data bias analysis using principal component analysis, singular value decomposition, and independent component analysis were conducted to evaluate the efficiency of machine learning.

Experimental study on crushing of concrete columns by high voltage pulse discharge

High voltage pulse discharge (HVPD) crushing tests were carried out on 30 concrete columns with section sizes of 400 mm × 400 mm, 500 mm × 500 mm, 600 mm × 600 mm and 700 mm × 700 mm respectively. Based on the comparative analysis of the electrohydraulic effect and the copper wire explosion on the fracture test of a concrete beam, the latter is determined as the optimal method. The parameters in the test of crushing concrete columns by HVPD include strength grade of concrete, column borehole aperture, hole spacing, discharge voltage and number of copper wires. Columns with sectional dimensions of 400 mm × 400 mm and 500 mm × 500 mm are arranged in single row boreholes, and columns with sectional dimensions of 600 mm × 600 mm and 700 mm × 700 mm are arranged in double rows of boreholes. The results show that the crushing effect of concrete columns increases obviously with the increase of discharging voltage and the number of copper wires, and slightly increases with the decrease of concrete strength. When other parameters are the same, the crushing effect of the concrete columns with hole diameter of 40 mm is better than that of the ones with hole diameter of 50 mm. The crack connectivity of concrete columns with hole spacing of 300 mm is similar to that of the ones with hole spacing of 400 mm. According to the test results, the mathematical expressions of the damage degree of concrete columns with single and double rows of holes (i.e., the width of concrete cracks around boreholes) and the output voltage, the number of copper wires and the strength grade of concrete are established respectively. In order to meet the needs of the project, the suggestion of further crushing construction combined with mechanical method was put forward

Development of Concrete Damage Classification in Beam-Column Joint based on Ultrasonic Pulse Velocity

The concreted conditions assessment of the systems is an essential aspect of security assessment programs. In situ measurements of Ultrasonic Pulse Velocity (UPV) may be indicative of the level of damage in the original concrete. UPV influenced by the specific characteristics of the mixture. In situ UPV measurements can be indicative of the level of damage in the original concrete. The research purpose is the damage classification, UPV test interpretation (strength, density, elasticity modulus, Concrete Quality Designation (CQD)), and determines the level of structural damage visually so that more accurate inspection results. The research result showed that the plastic hinge was more damaged than other parts of the beam-column joints. The UPV test obtained density 0.84-1.03 g/cm3, CQD 10% -20%, static elastic modulus 7.68-8.39 Gpa according to [3],[4] including very poor and visually is included in category IV spalling off of covering concrete (crack width > 2mm). The use of UPV as supporting assessment for classification, repair, and maintenance of structures. If density, CQD, and elastic modulus of defining very poor classification, the structure that needs immediate repair. The use of UPV is faster, without damaging parts of the structure, and also induces damage to the core specimens as a result of the coring process, making it faster and more economical.

Durability Evaluation of Concrete Bridges Based on the Theory of Matter Element Extension—Entropy Weight Method—Unascertained Measure

To accurately evaluate the durability of reinforced concrete girder bridges, a durability evaluation model was developed based on the matter element extension theory, entropy weight method, and unascertained measure theory. A total of seven indicators were selected for durability evaluation: the concrete presumed strength uniformity coefficient, reinforcement corrosion potential level, chloride ion content, average value of concrete relative carbonation depth, crack width, resistivity, and characteristic value of the reinforcement protective layer thickness. The weights of the durability evaluation indices were assigned using matter element extension combined with the entropy weight method, and the multi-indicator comprehensive evaluation vector was obtained by combining the single-indicator measurement matrix. The evaluation results were analyzed by applying the confidence criterion. The results showed that the evaluation results of this model matched with the actual conditions of the girder bridges, which indicates that this durability evaluation model has good applicability and is reasonable. Finally, a comparative study proved that the model could accurately evaluate the bridge durability.

The effect of temperature expansion on cracking behavior of slabs

The current design standards refer to the necessity for expansion joint, there are no clear limitations as to the location and spacing of expansion joint. To find the effect of the rebar ratio, structural tests were performed on Samples with adjustments of the rebar ratio. As the rebar ratio increases, the average crack width decreas-es. The number of crack increase but the concrete crack width decrease. Also, comparing results of experiment with those of analysis, it is necessary to apply the concrete tensile strength, which reflects the contribution of the reinforcement ratio.

Mechanical Properties of Engineered Cementitious Composite Materials Using Different Types of Fibers

An Engineered Cementitious composite is an ultra ductile cementitious composite which is highly crack resistant, with a tensile strain capacity over that of normal concrete. In this study, three different types of PP. fibers are added to cement mortars with the aim to determine how they can be used to develop ECC materials. Fibers are used in different (aspect ratio, tensile strength and different proportions in volume fraction (1.0, 2.0, 3.0 and 4%)) in concrete mixture design. Hardened concrete properties, 28-days splitting tensile strength, flexural strength, cracking width were evaluated. Statistically significant effects were observed for polypropylene fibers on the splitting tensile and flexural strength, toughness indexes, and durability parameters showed an increase in the presence of polypropylene fibers. Increased fiber availability (fiber aspect ratio) in the concrete matrix, in addition to the ability of longer polypropylene fibers to bridge on the micro cracks, are suggested as the reasons for the enhancement in mechanical properties. Finally, crack width in fiber-reinforced concrete is calculated analytically with fiber property variables (fiber type, length, diameter and proportion). Results are compared with experimental values and concluded that with an increase in fiber length and/or decrease in fiber diameter crack width, decrease significantly

Effect of shrinkage on rapid hardening plain and recycled steel fibre concrete overlays

The durability and functionality of concrete overlay repairs are highly dependent on the extent of cracking and crack widths, which are difficult to predict. This article presents an experimental and analytical investigation on restrained shrinkage of overlays made with rapid hardening mortar mixes reinforced with recycled fibres. The investigated parameters include cement type (calcium sulfoaluminate cement-CSA and calcium aluminate cement-RSC), overlay depth, bond condition and fibre dosage. Sixteen composite prisms were tested to determine shrinkage strains and cracking development over time. Both plain (RSC) and fibre reinforced (FRSC) overlaid prisms made of calcium aluminate cement developed multiple cracks in less than 16 h due to their high shrinkage values, but 60% lower crack widths developed in FRSC. An effective analytical model is derived to estimate the crack spacing of concrete overlays. As concrete crack width predictive models are shown to be deficient in predicting the crack width of materials with flexural hardening properties, a semi-empirical approach is adopted to quantify the effect of fibres in such matrices. The predicted crack widths are in a good agreement with the experimentally measured values. The suggested model is expected to make a contribution towards safer and more sustainable solutions for concrete repairs.

Early age bond stress-slip behaviour of macro-synthetic fibre reinforced concrete

The magnitude of bond stress that exists between concrete and steel reinforcement heavily influences the width and spacing of cracks. An understanding of the bond stress available is important when estimating deformations and crack widths in structural concrete. Experimental studies and modelling have shown that the inclusion of fibres improves bond characteristics in structural concrete. These studies have focused on the strength criterion in mature aged concretes containing steel fibres. No early age bond test results currently exist for macro-synthetic fibre reinforced concrete (FRC). In this paper, the results of an experimental campaign are presented on the bond-slip behaviour of macro-synthetic fibre reinforced concrete (containing either 0, 4 or 8 kg/m3 of fibres) tested at 1, 3, 7, 14, 28 and 90 days using standard pull-out tests. The tests are complimented with a suite of material characterisation tests. Furthermore, a simple model founded on previous approaches is presented to describe the ascending portion of the bond stress – slip relationship for FRC. It is concluded that the early age bond strength is slightly improved through the addition of macro-synthetic fibre reinforcement. On the other hand, the early age bond stiffness of reinforced concrete is substantially improved through the addition of macro-synthetic fibre reinforcement.

Effect of concrete cracks on the corrosion of headed studs in steel and concrete composite structures

Corrosion of headed studs leads to the degradation of mechanical properties of shear connectors and thus decreases the durability of steel and concrete composite structures. The effect of concrete cracks on stud corrosion was investigated in this study. Accelerated corrosion tests on headed stud shear connectors and numerical simulation on chloride migration were presented. 3D corrosion morphologies of headed studs in concrete slabs with different concrete cover thicknesses and crack widths and depths were precisely measured by using an optical surface measurement technique. The results show that there was highly localized corrosion in the stud head, and cracks had significant effect on the corrosion distribution. Then, after finite element models for chloride migration were verified by experimental results, a parametric study was carried out. It was found that in concrete slab with higher crack depth, chloride concentration around the headed stud increased more rapidly, while the crack width had slight effect on the distribution of chloride concentration. Moreover, the length of the chloride transport path was found to be a significant parameter that affect the stud corrosion.

Study of the Residual Bond Strength between Corroded Steel Bars and Concrete—A Comparison with the Recommendations of Fib Model Code 2010

As is well known, corrosion of steel reinforcement deteriorates the steel–concrete interface and causes concrete cracking, degrading significantly the bond strength. Several experimental studies have investigated the magnitude of residual bond strength due to corrosion, which affects either the function of corrosion-damaged steel bars or the surface crack width in concrete. As a result, linear and exponential correlation relationships have been proposed in order to predict the bond loss due to corrosion. Based on the results of an ongoing experimental campaign on the degradation of bond strength of RC specimens, combined with comparable outcomes from existing literature, this manuscript summarizes a database, comparing with the recommendations of Model Code 2010, to analyze and interpret the corrosion effect on the bond loss and highlights some points that need improvement in the current regulations. As indicated, the density of transverse reinforcement (stirrups spacing) has intense impact on the resulting bond loss due to corrosion. Hence, in order to quantify this aspect, the present manuscript introduces a discretization of confinement levels of RC elements, depending on the stirrups spacing. Based on this, regression analyses of data were conducted to extract fitting curves of bond loss, taking into account the amount of transverse reinforcement and predictive zones of residual bond strength in relationship to either corrosion penetration or surface crack width. Furthermore, the outcomes demonstrate that the corrosion penetration depth is an appropriate assessment tool to correlate the residual bond strength with the corrosion level, whereas the surface crack width on concrete is not yet an effective index, since there is a plethora of factors affecting the crack width. Due to this, more research is needed to improve the current level of knowledge on the surface crack width and link it with the corrosion damage of the steel bar and the residual bond strength due to corrosion.

Enhancement of self-healing to mechanical properties of concrete

Concrete is the main construction material of many structures. Exposing to loads creates cracks in concrete, which reduce the performance and durability. The decrease of concrete cracks becomes a necessity demand to ensure more durability and structural integrity of the concrete structure. Autogenous healing concrete is a kind of new smart concretes, which has the ability to reclose its cracks by means of itself. Concrete self-healing is a type of free repairs processes, which is reduce direct and indirect cost of maintenance and repairing. This work targets to inspect the mechanical properties of concrete after using two combinations of two materials (20 kg/m3 calcium hydroxide Ca(OH)2 and 2 kg/m3 sodium carbonate Na2CO3 and 30 kg/m3 calcium hydroxide and 3 kg/m3 sodium carbonate) as a partial replacement of cement to work as self-healing agents. The paper reports and study the compressive, flexural and splitting tensile strengths and ultrasonic pulse velocity tests’ results at 7, 28 and 90 days of concrete age. Use of two combinations of calcium hydroxide and sodium carbonate, as healing agents, enhanced the mechanical properties of concrete and reduced the width of concrete cracks with time. The concrete compressive strength was increased after curing for 90 days by 9.3 and 11.1 %, respectively. The flexural strength was improved by 14.3 and 15.9 %, respectively. Also, the splitting tensile strength was enhanced by 6.9 and 9.3 %, respectively.

Relationship Study and Primary Application between Gas Permeability and Crack State on Bridge Joint Concrete

For evaluating the crack state on solid bridge joint on site, the relationship between gas permeability and crack width of joint concrete is studied both on material and structural levels in this article. In laboratory tests, gas permeability tests on concrete samples with macrocrack are performed, the relationship between the relative gas permeability rate k/k0 and the relative variation of crack width ac is established combining with regression analysis, the fitting curve equation is . when ac increases by 1.125×10-2 mm, the gas permeability increases about 10 times compared with the initial state. In field tests, “pulse tests” are performed on bridge joint based on 3 embedded pulse probes to measure the evolution of gas permeability during bridge operation. The results show, firstly, the gas permeability of joint concrete are in the order of 10-16~10-19 m2, which indicates a good compaction performance; Secondly, an order of magnitude increase of gas permeability of one probe in different ages, or the fact that the gas permeability at one position in solid joint is obviously larger than the other positions, these phenomena indicate the existence of original defects, or the possibility of macrocrack appearance from microcracks, and the crack width increases by about 0.01 mm.

Experimental study on the post-cracking behavior of preflex beams under cyclic loading

Preflex beam composite girders are widely used in the bridge industry. Understanding the post-cracking behavior of preflex beam girders under cyclic loading is essential to improve monitoring and maintenance. The aim of this study was to evaluate the relationship of the deterioration of the lower flange concrete under cyclic loading to the resulting changes in stiffness, neutral axis location, reinforcement bar stress, and steel-lower-flange stresses of the preflex beam. The study also compared the preflex beam behavior with a conventional girder without prestress under cyclic loading. The experimental study included two specimens of the same details, of which one was preflexed and the other was a conventional non-preflexed specimen. The cracking and post-cracking behavior of the specimens were investigated under multiple cyclic loading stages. The study concluded that changes in the concrete crack width can be used to fairly estimate changes occurring in the neutral axis location, rebar stress, and steel-lower-flange stress of the preflex beam under cyclic loading. The smaller width and shorter length of concrete cracks, implying smaller changes in the preflex beam girder, improved its behavior remarkably compared with the non-preflexed girder with wider and longer concrete cracks under cyclic loading. Furthermore, the study concluded that a closer spacing of the shear ribs reduces the crack width. However, the number of cracks would be larger.

Feasibility and flexural behavior of RC beams prestressed with straight unbonded aluminum alloy tendons

This paper investigates the feasibility and flexural behavior of reinforced concrete beams internally prestressed with straight unbonded aluminum alloy tendons by testing five partially prestressed beams and one reference beam. For each beam specimen, load-deflection curves, failure modes and cracking behavior, the relationship between load and strains in steel and prestressing aluminum alloy tendons were examined and analyzed. In particular, the effects of effective prestress, combined reinforcement index (CRI), and partial prestressing ratio (PPR) on flexure of concrete beams were discussed. The test results indicated that the spacing and width of concrete cracks of prestressed beams containing the same amount of bonded longitudinal steel reinforcement decreased with the increase of effective prestress, and the combined reinforcement index governs flexural behavior of the prestressed beams. The flexural crack width and displacement ductility exhibited a reduction with the increase of CRI. In addition, an analytical model was established to calculate the flexural strength and corresponding deflection at midspan of the concrete beams internally prestressed with unbonded aluminum alloy tendons by suggesting a new simplified curvature distribution, which is more accordant with the original curvature distribution. The proposed model provides a relatively good estimation of the flexural capacity and midspan deflection of the prestressed beams.

Acoustic method for measurement of crack width in concrete

The article presents the results of research and experimental studies aimed at measurement of crack width in concrete under the impact of mechanical loading. During the research, the author simultaneously measured load, deformation, crack width, acoustic emission gross counting by tensiometric and acoustic methods and obtained full diagrams of concrete deformation. The experiments resulted in regression equations and their combined diagrams showing relation between acoustic emission gross counting and mechanical loading level. The author identified the parameters of macro-crack initiation and their width in lightweight concrete depending on the value of the applied load. The conducted experiments and statistic processing of the data produced the correlation between the crack width and acoustic emission gross counting.

Classification and quantification of cracks in concrete structures using deep learning image-based techniques

Visual inspection has been the most widely used technique for monitoring concrete structures in service. Inspectors visually evaluate defects based on experience, skill, and engineering judgment. However, this process is subjective, laborious, time-consuming, and hampered by demanding access to numerous parts of complex structures. Accordingly, the present study proposes a nearly automated inspection model based on image processing and deep learning for detecting defects in typically inaccessible areas of concrete structures. Results indicate that using the Keras classifier combined with Otsu image processing can achieve superior classification accuracy of 97.63%, 96.5%, and 96.17% for training, validation, and testing data, respectively, along with low quantification error of 1.5%, 5% and 2% for the crack length, width, and angle of orientation, respectively. The type of structural damage and its severity are identified based on the allowed range of concrete crack width for different structures, including buildings and bridges based on different international standards and codes. The proposed method can deploy unmanned aerial vehicle image acquisition to offer a nearly automated inspection platform for the colossal backlog of aging concrete structures.

Structural damage assessment of mountain tunnels in fault fracture zone subjected to multiple strike-slip fault movement

Fault fracture zones are adverse geological conditions often encountered in the constructions of mountain tunnels. Extensive structural damage to the mountain tunnels in adjacent to the fault fracture zones has been documented in the past earthquakes. In current work, three-dimensional numerical model of a water conveyance tunnel crossing multiple active strike-slip faults was established to assess the structural damage with consideration of four primary influence factors: the magnitude of fault movement, the distance between adjacent fault planes, the tunnel-fault intersection angle and the mechanical properties of the rock mass in the fault fracture zone. Two quantitative damage indices, namely, the overall structural damage index and the concrete lining crack width, are proposed in this study to investigate the structural integraty and the serviceability of the water conveyance tunnel subjected to fault movements. The numerical results indicate that the cross-sectional damage of the tunnels primarily concentrated in the vicinities of the fault planes, and the boundaries between the fault and the competent rock. With the increase of the distance between adjacent fault planes, the structural damage of the tunnel in the region near the center of the fault fracture zone rapidly decreases. The tunnel-fault intersection angle also significantly affects the performance of the tunnel under fault movement. Moreover, the increase of surrounding rock mass stiffness in the fault fracture zone reduces the extension but increases the severity of damage to the tunnel lining. Overall, the numerical results of this study provide a better understanding of the response of mountain tunnels under multiple strike-slip fault movement.

Experimental evaluation of the tensile bonding strength of the basalt fiber-reinforced polymer–concrete interface

The bonding performance of basalt fiber-reinforced polymer and concrete substrate has a significant effect on the reliability of externally strengthened existing concrete structure, due to being the most vulnerable element to failure in this fiber-reinforced polymer–concrete strengthening system. Its failure can result in the failure of the whole structure. Although many previous researchers have been interested in the tensile bonding strength of carbon fiber-reinforced polymer and glass fiber-reinforced polymer–concrete interface, that of basalt fiber-reinforced polymer–concrete interface has been very limited. Thus, the objective of this study is to experimentally assess the tensile bonding strength of the basalt fiber-reinforced polymer–concrete interface. The effects of high temperature, freezing–thawing cycles, type of resin, and concrete crack widths on the tensile bonding strength are also investigated. The pull-off experiment is conducted according to ASTM D7522/D7522M-15. A total of 205 core specimens of 50 mm diameter and 10 mm depth were taken from 41 concrete beams. The experimental results illustrate that both freezing–thawing and high-temperature condition have a substantial effect on the bonding strength of the basalt fiber-reinforced polymer–concrete interface. Bonding strength was decreased within the range of about 9%–30% when the number of freezing–thawing cycles increases from 100 to 300; likewise, it was decreased up to 30% when the exposure temperature rises to 200°C. Also, the specimens which were repaired to close their cracks by epoxy resin had no significant effect on the bonding strength of basalt fiber-reinforced polymer–concrete interface, when the specimens had crack width of less than 1.5 mm.