Surface Crack Width Research Articles

Investigation on crack propagation of concrete cover induced by non-uniform corrosion of multiple rebars

A 2D diffusion-mechanical model was proposed to predict the reinforcement corrosion and concrete cover cracking. This work was focused on the time-dependent non-uniform corrosion of multiple reinforcing bars, and took into account the influence of adjacent rebars on crack propagation. Based on concrete damaged plasticity model, the non-uniform radial displacement generated by the corrosion expansion was applied on the steel/concrete interface, to simulate the failure behavior of concrete cover. Moreover, some necessary verifications of numerical results have been carried out. Parametric studies were conducted to investigate the effects of some key factors on cracking pattern, crack initiation and through time, as well as surface crack width. Finally, the influence of different reinforcement arrangements in a RC beam on cover cracking was discussed.

Dynamic analysis of an immersed tunnel in Izmir

The original design of the planned Izmir Bay Immersed Tube Tunnel, considered it to be a continuous subsea tunnel for the whole length of about 7.6 km. But this was later changed into having 2 shorter tubes of 2.7 km long each connected thru’ a 2.2 km long artificial island created in the middle of the bay from the excess dredged material, a concept which also reduces costs and increases efficiency. This island will serve as a venue for the 2025 Expo Exhibition, which Izmir city will apply to organize in the future. Reason for the research study was to provide a preliminary design, using a dynamic analysis, during the current pre-feasibility stage, of the immersed tunnel to show whether it can be built across the Izmir Bay. This paper takes into account the new alignment and presents the results of a 2-D dynamic analysis conducted of the prefabricated 100m long tunnel elements, sitting within a backfilled dredged ditch, dug after the recommended ground improvement was carried out. Analyses considered staged construction and the results showed that: Tunnel units and its surrounding soils inside the dredged ditch act together to provide a better earthquake response with a damping effect of the earthquake force; Tunnel units do not float to the sea surface, but continued to stay inside the dredged ditch and applied positive stresses to the foundations during the design earthquakes. As there was no floating, there was no need for anchoring the tunnel to ditch bottom; Tunnel units and immersion joints (made of specified strong elastomer material) continued to stay in compression longitudinally and provided a superb water-tightness level; There were no risky (un-tolerable) ground deformations during, after striking of the design earthquakes. Total vertical and differential displacements of the tunnel units and in the surrounding soils were all at acceptable levels; Concrete surface crack widths occurring in the tunnel units, during striking of the design earthquakes were also found to be allowable. Study results show that the tunnel elements can withstand Mw=7 short duration ( 10 sec) earthquakes without major damages to their structure

Application of GGBFS and Bentonite to Auto-Healing Cracks of Cement Paste

Cracks are caused by many factors. Shrinkage and external loading are the most common reason. It becomes a problem when the ingression of aggressive and harmful substance penetrates to the concrete gap. This problem reduces the durability of the structures. It is well known that self – healing of cracks significantly improves the durability of the concrete structure. This paper presents self-healing cracks of cement paste containing bentonite associated with ground granulated blast furnace slag. The self-healing properties were evaluated with four parameters: crack width on the surface, crack depth, tensile strength recovery, and flexural recovery. In combination with microscopic observation, a healing process over time is also performed. The results show that bentonite improves the healing properties, in terms of surface crack width and crack depth. On the other hand, GGBFS could also improve the healing process, in terms of crack depth, direst tensile recovery, and flexural stiffness recovery. Carbonation reaction is believed as the main mechanism, which contributes the self-healing process as well as the continuous hydration progress.

Observations on crack branching of zirconia coating manufactured by plasma spray technology

Observations on fracture and crack bifurcation phenomenon of plasma spray Zr coating is studied in current paper with new understanding based on new recognized information.A new model is developed for Zr coating layers and cracks. Analytical fundamental characterization is carried out regarding mechanism under high thermal stresses on outer face with cooling back side of the substrate. Results are new such as crack branches at 120°, layered cracks, stepped crack surface and variable crack width. The zirconia coating has hexahedral shape as a honeycomb microstructure. Due to effect of heating-cooling, the first coating layer and near layers to substrate surface of zirconia coating will be contracted or do not be expanded while outside coating layers will be extended producing bi-interfacial de-bonding between particles and propagation to other crystals producing cracks and branching. Depth and width of the crack will be extended and increased in the coating layers producing stepped and layered cracks with branches. Propagation angles of branches are always 60°. Cracking load will be maximum at main crack orientation angle of β = 45° for equal stresses in both X and Y directions while for β<30, β>60 cracking load will be minimized meaning that crack will carry high stresses at 30>β > 60.

Correlation between surface crack width and steel corrosion in reinforced concrete

Reinforced concrete structures are subjected to weather conditions, chemical attack and other sources of deterioration that can affect their performance. In particular, corrosion of the internal steel reinforcement is considered to be one of the main causes of structural deterioration. A possible consequence of corrosion is cracking of the surrounding concrete. Visual inspections are often used to inform asset management strategies. Finding a relationship between cracks that are visible on the outer surface of a structure and corrosion of the internal reinforcement can be helpful when making assessment decisions. To this end, unconfined cylindrical concrete specimens with an embedded steel bar have been subjected to accelerated corrosion using an impressed current density of 200µA/cm2, leading to steel mass losses between 5-24%. This paper discusses the measured correlation between corrosion-induced surface crack widths and degree of reinforcement corrosion. The tests highlighted some limitations of a set-up that is commonly adopted for accelerated corrosion and concentric pull-out bond testing. The findings of this study represent a first step towards the standardisation of accelerated corrosion testing procedures using an impressed current.

Quantification of Geometrical and Morphological Characteristics of Desiccation Crack and Shrinkage Behavior of Composite Clay Liner

Clay soil and their related irregular behavior such as shrinkage, swelling, desiccation cracks etc. are the main concern for the construction of composite clay liner (CCL) in waste landfill site. In this study, an investigation was conducted on a scaled model of prototype landfill liner to quantify both the geometrical and morphological characteristics of desiccation crack of CCL. For evaluating its cracking behavior cement, Khoa Brick and fiber were used as additives for two phases of investigation. In this study, for the quantification of geometrical and morphological characteristics of desiccation crack of CCL, both the image-based algorithms on MATLAB and Image J software was performed. To evaluate additives significance on soil, surface crack ratio, average length and width of cracks, number of crack segments, crack density and others related parameters were determined. Results showed significant impact on clayed soil due to presence of various types and percentages of additives. Experiential results depicted that surface crack ratio increases with reducing water content on prototype sample and finally stabilized its propagation. For preparing CCL with clay from selected landfill site of Khulna the optimum content of additives were found 5, 5 and 1.5% for Khoa Brick, cement and polymer fiber, respectively.

Crack Detection of Reinforced Concrete Structures Based on BOFDA and FBG Sensors

Reinforced concrete structural elements, as an important component of buildings and structures, require inspection for the purposes of crack detection which is an important part of structural health monitoring. Now existing crack detection methods usually use a single technology and can only detect internal or external cracks. In this paper, the authors propose a new sensing system combining BOFDA (Brillouin optical frequency‐domain analysis) and FBG (fiber Bragg grating) technology, which are used to detect internal and surface cracks and their development in reinforced concrete structures, and an attempt is made to estimate the width of surface cracks. In these experiments, a special reinforced concrete beam structure was designed by the author for crack detection under load. Four continuous distributed optical fibers are fixed on the steel skeleton, which is located within the reinforced concrete beam. Three FBG sensors are fixed on the lower surface of the beam, near its centre. By analysing the sensor data, it can be found that the BOFDA‐distributed fiber can be used to detect internal cracking before surface cracking, and the difference between scans can be used to judge the time of onset of internal cracking, but the relative error in position is about 5%, while the FBG sensor can detect the cracking time of microcracks on the lower surface in near‐real‐time and can be used to calculate the crack width. Through the experiment, it is found that if the combination of BOFDA and FBG technology is adopted, we can initially use the strain data obtained by multiple groups of BOFDA monitoring to predict the general location of the internal cracks, then to monitor the exact location of the surface cracks by FBG in the medium term, and to estimate the width of the final expansion of the cracks finally.

Review study towards corrosion mechanism and its impact on the durability of concrete structures

This paper imparts a review study on the causes and factors responsible for corrosion, its initiation and propagation mechanism inside the structures, leading to a better discernment of the problem associated with the durability of the existing structures. This study employs all necessary information related to the corrosion activity, fostering the researchers towards explicating some productive outcome to enhance the durability characteristics as well as the service life of reinforced concrete structures. Different techniques like, Impressed current technique (normally in a range of 1 mA/cm2 to 4 mA/cm2) has been adopted by several authors to induce corrosion artificially to better correlate the result with the natural form of corrosion in the structures. This paper particularly emphasizes on residual flexure and shear capacity of reinforced concrete sections undergoing corrosion mechanism, the effect of which leads to a reduction in strength of up to 50%–60%. Several empirical relationships for the prediction of residual load capacity (flexure and shear) of a reinforced-concrete members and relationships for the surface crack width (lying in a range of 0.05 mm to 15 mm) and weight/mass loss (average loss of 15%–30%) were established based on the data obtained by various experimental observations.

Bond strength evaluation of corroded steel bars via the surface crack width induced by reinforcement corrosion

The corrosion of steel bars in reinforced concrete structures induces concrete cover cracking and leads to reduction in steel–concrete bond strength. In the present study, a series of pull-out tests were carried out to investigate the potential correlations between corrosion level, surface crack width, and bond strength. The main variables are corrosion level, concrete cover depth, and spacing of stirrups. The test results indicate that the surface crack width is closely linked to the corrosion level of the tensile steel bar, and the crack propagation can be divided into three stages. It is further revealed that the bond strength decreases exponentially with the surface crack width. Based on the test results, an empirical model for estimating the bond strength using the surface crack width is formulated, which considers the pronounced limiting effect of stirrups on the bond degradation. The model is further improved by incorporating the adverse effect of the corrosion of stirrups according to the previous investigations. Comparison with existing experimental database in the literature proves that the proposed models are able to realistically predict the bond strength of corroded steel bars.

Time to surface cracking and crack width of reinforced concrete structures under corrosion of multiple rebars

Concrete cover cracking caused by corrosion of reinforcement is one of major deterioration mechanisms for reinforced concrete structures. In practice, time to surface cracking and crack width evolution are of significance in regards to the assessment of serviceability of reinforced concrete structures. Literature review suggests that, although considerable research has been undertaken on corrosion-induced concrete cracking, little has been focused on corrosion of multiple reinforcing bars, especially by considering the non-uniform corrosion process. In this paper, a time-dependent non-uniform corrosion model is established. A cohesive crack model is then formulated to simulate arbitrary cracking in the whole cover of concrete structures. Two typical cover failure modes (i.e., “delamination” and “combined delamination and corner spalling”) have been simulated under the non-uniform corrosion of multiple reinforcing bars and found dependent on spacing of reinforcement and fracture energy of concrete. The effects of corrosion, geometric and mechanical parameters on the time to surface cracking after corrosion initiation and the crack width evolution are also investigated and discussed. The developed model is partially verified by comparing the results with those from experimental tests on uniform corrosion of multiple reinforcing bars.

Numerical determination of concrete crack width for corrosion-affected concrete structures

Corrosion-induced deterioration of reinforced concrete (RC) structures results in premature failure of the RC structures. In practice concrete crack width is one of the most important criteria for the assessment of the serviceability of RC structures. It is therefore desirable to predict the growth of the crack width over time so that better informed decisions can be made concerning the repairs due to concrete cracking. Literature review shows that little research has been undertaken on numerical prediction of concrete crack width. The intention of this study was to develop a numerical method to predict concrete crack width for corrosion-affected concrete structures. A cohesive crack model for concrete is implemented in the numerical formulation to simulate crack initiation and propagation in concrete. Choices for evaluating the parameters of cohesive elements are extensively discussed which is a key for developing a plausible model employing cohesive elements. The surface crack width is obtained as a function of service time. Accurate prediction of crack width can allow timely maintenance which prolongs the service life of the reinforced concrete structures.

Principles and Applications of Ultrasonic-Based Nondestructive Methods for Self-Healing in Cementitious Materials.

Recently, self-healing technologies have emerged as a promising approach to extend the service life of social infrastructure in the field of concrete construction. However, current evaluations of the self-healing technologies developed for cementitious materials are mostly limited to lab-scale experiments to inspect changes in surface crack width (by optical microscopy) and permeability. Furthermore, there is a universal lack of unified test methods to assess the effectiveness of self-healing technologies. Particularly, with respect to the self-healing of concrete applied in actual construction, nondestructive test methods are required to avoid interrupting the use of the structures under evaluation. This paper presents a review of all existing research on the principles of ultrasonic test methods and case studies pertaining to self-healing concrete. The main objective of the study is to examine the applicability and limitation of various ultrasonic test methods in assessing the self-healing performance. Finally, future directions on the development of reliable assessment methods for self-healing cementitious materials are suggested.

Characterisation of bending cracks in R/FRC using image analysis

In this study, experiments were conducted to induce bending cracks of specific surface crack width to reinforced concrete beams made of plain concrete (RC) and reinforced concrete beams made of fibre reinforced concrete (R/FRC). After injecting and impregnating the cracks with dyed epoxy resin, image processing and analysis were employed to investigate the internal crack morphology. Several crack features including crack width (accumulated, effective and maximum), branching and tortuosity were defined and quantified. The results showed that in addition to arrested crack development, the presence of fibres yielded a distinctive change in the internal crack pattern, including increased branching and tortuosity, both of which have positive implications regarding concrete permeation. Likewise, specimens with fibres exhibited reduced maximum individual crack widths near the rebar, potentially increasing the ability of autogenous crack healing and reducing the risk of corrosion initiation.

Sensitivity of chloride-induced corrosion rate of steel in concrete to cover depth, crack width and concrete quality

This paper presents the results of analyses carried out to assess the sensitivity of chloride-induced corrosion rate to change(s) in cover depth, concrete quality and crack width. An empirical chloride-induced corrosion rate prediction model is used to carry out the sensitivity analyses. The main model input parameters for the model are surface crack width (w cr), cover (c) and concrete quality (characterized by a long-term diffusion coefficient, D 90). A two tier sensitivity analysis is carried out to establish (i) which individual input parameter (D 90, c or w cr) corrosion rate is most sensitive to, and (ii) which combination of two input parameters out of the possible three (D 90, c and w cr) corrosion rate is most sensitive to. The sensitivity analyses results show that in cracked concrete change in corrosion rate is greater if concrete quality is varied than if either crack width or cover depth is varied i.e. concrete quality has a dominating role on the effect of either crack width or cover depth on corrosion rate. Generally, in cracked concrete corrosion rate is more sensitive to change in concrete quality than change in either crack width or cover depth. Even though cover cracking increases corrosion rate, and that it should be minimized, a holistic approach considering the effect of cover depth, crack width, and more importantly, concrete quality on corrosion rate should be adopted.

Mechanical performance of deep beams damaged by corrosion in a chloride environment

Two full-scale beams with dimensions 3000 × 280 × 150 mm were exposed in a chloride chamber for 27 and 36 months. Corrosion of the reinforcement in the beams was accelerated by wetting and drying cycles. Two deep beams were taken from each full-scale beam. Loading tests were carried out on the four deep beams and loading–deflection curves and slip of tensile bars were recorded during the tests. Then, the cross-sectional loss in the tensile bars and diameter loss in the stirrups were examined. The results showed that corrosion distribution was not uniform along the tensile bars. The correlation between cross-sectional loss of steel bar and surface crack width was weak. Serious pitting corrosion on the tensile bars changed the failure mode of deep beams from shear to flexure. The failure mode of corroded deep beams depends not only on span to effective depth ratio and the degree of corrosion of the tensile bars but also on the corrosion degree of the stirrups.

Char Trace Analysis of Composite Wood Floor under Different Heating Conditions

Under different heating conditions, the composite wood floor and pine carbonization samples were prepared, and the charring surface morphology, crack width, carbonization depth and average charring rate were compared and analyzed. The results show that under the thermal radiation condition, the carbonization of composite wood floor is the most serious, and cracks distributed radially; under the arc condition, the compound wood floor is difficult to ignite, and the carbonization layer is shallow; small amount spilled gasoline combustion has little effect on carbonization degree, but the char is obvious at the corner; at the same heating condition, the carbonization degree of pine was more serious than the composite wood floor, and the carbonized surface morphology had significant differences.

The role of rock fragments in crack and soil structure development: a laboratory experiment with a Vertisol

SummaryA large number of factors that influence soil surface cracking behaviour in swell‐shrink soils have been studied, but there are few studies on the influence of rock fragments on crack development. Effects of rock fragments have been investigated with reference to the soil pore system but they have mainly been studied indirectly through measurements of water flow and/or bulk density changes. A laboratory experiment was carried out with repacked soil samples that were prepared by adding rock fragments of three different sizes (2–4, 4–8 and 12–16 mm) to a Vertisol at two different rates (10 and 25% by volume). Soil image analysis procedures were applied in order to describe quantitatively the network of surface cracks and the pore system to a depth of 8 cm below the surface, which developed after wetting‐drying cycles. Mean values and standard deviations of surface crack or pore widths decreased with the increase in rock fragment content and the decrease in rock fragment size, while the density of the ‘skeleton’ of the crack and pore networks increased. Rock fragments also induced vertical homogenization of the soil structure. The number of rock fragments was a key factor in determining some crack network characteristics, inducing inverse variations in mean width and skeleton density of the crack or pore network. Overall results suggested that rock fragments acted as triggering points for crack and pore development in Vertisols. The findings of this work provide a contribution to the understanding of the mechanisms of crack network and soil structure development that are induced by stones in swell‐shrink soils.

X-ray computed microtomography of three-dimensional microcracks and self-healing in engineered cementitious composites

Concrete cracking and deterioration can potentially be addressed by innovative self-healing cementitious materials, which can autogenously regain transport properties and mechanical characteristics after the damage self-healing process. For the development of such materials, it is crucial, but challenging, to precisely characterize the extent and quality of self-healing due to a variety of factors. This study adopted x-ray computed microtomography (μCT) to derive three-dimensional morphological data on microcracks before and after healing in engineered cementitious composite (ECC). Scanning electron microscope and energy dispersive x-ray spectroscopy were also used to morphologically and chemically analyze the healing products. This work showed that the evolution of the microcrack 3D structure due to self-healing in cementitious materials can be directly and quantitatively characterized by μCT. A detailed description of the μCT image analysis method applied to ECC self-healing was presented. The results revealed that the self-healing extent and rate strongly depended on initial surface crack width, with smaller crack width favoring fast and robust self-healing. We also found that the self-healing mechanism in cementitious materials is dependent on crack depth. The region of a crack close to the surface (from 0 to around 50–150 μm below the surface) can be sealed quickly with crystalline precipitates. However, at greater depths the healing process inside the crack takes a significantly longer time to occur, with healing products more likely resulting from continued hydration and pozzolanic reactions. Finally, the μCT method was compared with other self-healing characterization methods, with discussions on its importance in generating new scientific knowledge for the development of robust self-healing cementitious materials.

Experimental investigation of the relation between damage at the concrete-steel interface and initiation of reinforcement corrosion in plain and fibre reinforced concrete

Cracks in covering concrete are known to hasten initiation of steel corrosion in reinforced concrete structures. To minimise the impact of cracks on the deterioration of reinforced concrete structures, current approaches in (inter)national design codes often limit the concrete surface crack width. Recent investigations however, indicate that the concrete-reinforcement interfacial condition is a more fundamental criterion related to reinforcement corrosion. This work investigates the relation between macroscopic damage at the concrete-steel interface and corrosion initiation of reinforcement embedded in plain and fibre reinforced concrete. Comparisons of experimental and numerical results indicate a strong correlation between corrosion initiation and interfacial condition.

Study of ultrasonic assisted cryogenically cooled EDM process using sintered (Cu–TiC) tooltip

In most EDM operations, the maximum contribution in the total operation cost is the tool cost. Electrode wear is a major problem in EDM process. Therefore, in this paper, the process performance of sintered copper (Cu)–titanium carbide (TiC) electrode tip in ultrasonic assisted cryogenically cooled electrical discharge machining (UACEDM) has been studied. The performance parameters studied in this paper are electrode wear ratio (EWR), material removal rate (MRR), surface roughness (SR), out of roundness and surface integrity. The process parameters considered in this study are discharge current, pulse on time, duty cycle and gap voltage. Cermet was fabricated, having copper content of 75% and titanium carbide content of 25%, by mixing, pressing, and sintering. The performance of the newly formed cermet electrode tip is compared with conventional copper electrode tip for UACEDM process and analyzed. It has been observed that EWR and out of roundness decreases when cermet electrode tip is used as compared to conventional tooltip. It has also been observed that MRR and SR increase when cermet tooltip is used. The surface cracks density and crack width on workpiece machined by cermet tooltip have been found to be lesser as compared to the specimen machined by conventional tooltip.