Effect Of Crack Width Research Articles

Study on calcium dissolution of concrete specimens with surface cracks

The effects of crack width, crack depth and water-cement ratio (w/c) on calcium dissolution resistance of cracked concrete were evaluated. Results show that the degradation in physical properties and mechanical properties of concrete after dissolution increase with the increasing crack width, crack depth and w/c. In the case of concrete with w/c of 0.40 and dissolution age of 100 d, the degradation of splitting tensile strength of specimens with crack widths of 0.1, 0.2 and 0.3 mm was 1.27 times, 1.39 times and 1.54 times that of uncracked specimens. Dissolution resistance of cracked concrete is obviously lower than that of uncracked concrete, and the effect of crack width on it is more significant than that of crack depth, and the higher the w/c of concrete, the more significant the effect of crack width. Dissolution damage increasing coefficient of cracked concrete can be used to quantitatively characterise the effect of cracks on the dissolution damage of concrete, and its maximum value is approximately 1.08 corresponding to the crack width of 0.3 mm. The results of this study can be used as a reference for the accurate evaluation of calcium dissolution resistance and service life of the water-related concrete structures.

Oxide growth in high-strain tolerance thermal barrier coating with segmented vertical cracks

Segmented vertical cracks in high-strain-tolerance thermal barrier coating (TBC) systems provide fast diffusion pathways for oxygen, leading to the accelerated growth of thermally grown oxide (TGO) interfaces. This results in a competition between enhanced strain tolerance and accelerated oxidation. Here, the effects of crack width on oxygen diffusion and TGO growth in TBCs with segmented vertical cracks and underlying mechanism were investigated experimentally and numerically. The findings reveal a critical crack width of approximately 4 μm, underscoring the importance of selecting an appropriate segmented vertical crack width to design TBCs with superior strain tolerance and sufficient oxidation resistance.

Shear design of RC members strengthened with steel reinforcing bars embedded through section

The shear strengthening technique investigated in this paper consists of inserting steel reinforcing bars into holes drilled into a shear-deficient existing concrete member and bonding these bars to the concrete with high-strength epoxy adhesive. It is important to realize that current shear design methods are applicable to RC members with conventional stirrups and hence overestimate the shear capacity of members with epoxy-bonded bars. In order to overcome this difficulty, a shear design method for RC members strengthened with epoxy-bonded shear reinforcement is presented. The proposed method was developed considering the development of epoxy-bonded bars as well as the effect of crack width and aggregate interlock on shear capacity. The predicted shear capacities were compared with beam test results and provide accurate predictions.

Modelling the corrosion mechanism of steel bars in chloride-contaminated concrete with transverse cracks

The development of cracks in reinforced concrete structures can accelerate structural deterioration and reduce service life. A numerical model was established to analyse steel bar corrosion in chloride-contaminated concrete with transverse cracks. In the model, the dynamic distinction between anode and cathode regions on the steel surface is considered by introducing an empirical formula for the anodic Tafel slope related to chloride concentration. The time-dependent characteristics of the corroded region were examined using the proposed corrosion prediction model and the corrosion process of steel bars in cracked concrete was revealed. The effects of crack width and crack spacing on steel corrosion were analysed in detail in terms of the corrosion area and corrosion rate. The results showed a variation in the corrosion area adjacent to cracks over time and a positive correlation between corrosion area and the square root of time. According to the micro-cell and macro-cell contributions to the corrosion rate, the process of steel bar corrosion was determined to occur in three stages. The effects of transverse cracks on the corrosion rate were found to vary with exposure time and to depend on the control steps of the micro- or macro-cells.

Self-healing of high-performance engineered cementitious materials with crystalline admixture in the seawater environment

The present paper studies the crack healing effect of high-performance cement-based materials mixed with crystalline admixture (CA) in seawater environments. Specifically, the healing effects of specimens with different initial crack widths in tap water and seawater environments were investigated through the seepage healing test (simulating a structure that a side contact with water and the other side contact with air). The variations of seepage velocity and water flow in the early 24 h of healing were mainly investigated. It was found that crystalline materials delay the healing of cracks in the initial stage of healing and this defect is more obvious under the seawater healing condition. Inductive Coupled Plasma (ICP) test was used to detect the variation of ion concentration in seawater; XRD, FTIR, and TG tests were carried out for characterizing the composition and relative content of healing products in the crack under the seawater and tap water healing conditions. Moreover, the effect of CA on the composition of healing products and the effect of crack width on healing products were quantified. The distribution characteristics of healing products along the crack depth under seawater seepage and seawater immersion healing conditions were then obtained.

Effect of crack width and wet-dry cycles on the chloride penetration resistance of engineered cementitious composite (ECC)

• Influence of crack width and wet-dry cycles on the chloride ingress in cracked ECC was investigated. • Chloride penetration profile as well as the change of total and water-soluble chloride ion content was measured. • The “maximum phenomenon” is observed for both water-soluble and bound chloride ions profiles under wet-dry cycles. • The change of the mineral phases and porosity is related with the chloride binding behaviour. The resistance of cracked ECC against chloride ingress is mainly governed by the accumulated crack width of all the cracks rather than the maximum width of multiple cracks. However, most studies focus on the influence of a single fine crack (<100 μm), which is far smaller than the accumulated crack width. To this end, this study focuses on a relatively large crack width scale. Cracks with widths of 0.1, 0.2 and 0.3 mm were notched on an ECC specimen. Both NaCl solution immersion and wet-dry cycles conditions were applied. Chloride penetration profile as well as the change of total and water-soluble chloride ion content was measured. Relationship between the bound chloride and water-soluble chloride was studied. X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) tests were carried out to show the influence of crack width and wet-dry cycles on the changes of the mineral phases, porosity and pore size distribution in the vicinity of the crack.

Effect of crack width on electromagnetic interference shielding effectiveness of high-performance cementitious composites containing steel and carbon fibers

In this study, the effects of carbon fibers and crack widths on the electromagnetic interference (EMI) shielding effectiveness of high-performance fiber-reinforced cementitious composites (HPFRCCs) with 2 vol.% straight steel fibers were evaluated. To this end, 0.2 vol.% carbon fibers were added and four penetrated pre-crack widths ranging from 0.02 to 0.2 mm were applied under tension. The tensile strength and electrical resistance of the composites were also investigated. The test results indicated that adding 0.2% carbon fibers effectively enhanced the tensile strength, electrical conductivity, and shielding effectiveness of the HPFRCC. Furthermore, the electrical conductivity was improved by 224%, and a 27% higher shielding effectiveness was achieved. A shielding effectiveness of 48.5 dB at 1 GHz was achieved with a specimen thickness of 25 mm. Tiny cracks with a width of 20 μm significantly reduced the EMI shielding effectiveness of the HPFRCC by approximately 40%. For the plain HPFRCC, the shielding effectiveness was not significantly affected by the crack width, as it was thoroughly cracked. The benefits of adding carbon fibers for improving the shielding effectiveness disappeared at crack widths greater than 0.1 mm. Thus, the addition of carbon fibers was effective only for HPFRCCs without cracks or with very tiny cracks of less than 40 μm.

Effects of Crack Width and Healing Time on Healing Performance of Microcapsule-Based Self-Healing Concrete

Abstract Self-healing concrete is one of the effective methods for solving concrete deterioration and improving durability. However, the effects of crack width and healing time on healing performance are still part of an open problem. In this paper, the effects of crack width and healing time on healing performance of microcapsule-based self-healing concrete are studied. First, the chloride ion permeability tests were conducted to evaluate the effects of crack width and healing time on chloride ion permeability of the self-healing concrete. Then, three-point bending tests were conducted to study the effects of crack width and healing time on flexural behavior of the self-healing concrete system. The results show that the chloride ion penetration healing rate decreases significantly with the increase of crack width. The increasing trend of the healing rate of the specimens healing for 7 days and 14 days is faster, while the increasing trend of the healing rate of the specimens healed for 56 days is slower. When the crack width is less than 0.05 mm, the self-healing can restore or even exceed the initial performance of concrete specimens. When the crack width exceeds 0.15 mm, the damage degree has exceeded the healing capacity of the healing system, and it is difficult to restore the initial performance of concrete. This work provides a valuable reference for the design and preparation of self-healing concrete structures.

Theoretical and numerical fracture analysis of bovine cortical bone under tensile loading in mode I and mixed-mode fracture

Elastic and elastic–plastic theoretical and numerical analyses are performed to evaluate the bone containing initial crack. The mode I + II of fracture is applied to identify the most critical incline crack and the analytical results are compared with experimental evaluation. The loading capacity in bones with smaller thickness decreases more significantly in the elastic–plastic analysis. Both plastic zone and the elastic–plastic stress are higher in smaller initial crack length. Simultaneous initiation of non-close multiple cracks has no significant influence on the ultimate tensile load and the effect of crack width on fracture decreases in higher crack width and longer length.

Effect of Crack Width, Density, and Depth on Strength and Durability of Concrete-Equivalent Mortar

Effect of Crack Width, Density, and Depth on Strength and Durability of Concrete-Equivalent Mortar

Tensile properties of cracked reactive powder concrete in corrosive environment - effects of crack width and exposure duration

The combined effect of the pre-crack width and exposure duration in a corrosion environment on the tensile properties of reactive powder concrete (RPC) was investigated. For this purpose, singly cracked RPC was exposed to a standard 3.5% sodium chloride (NaCl) solution. The tensile performance of pre-cracked RPC was deteriorated by severely corroded steel fibers when a wide crack width and long exposure duration were applied. No performance deterioration was observed in the pre-cracked RPC at a width of 0.02 mm (20 μm) up to an exposure duration of 20 weeks, and the surface oxidation degree of steel fibers was also minor. However, the tensile strength decreased after 20 weeks of exposure when the crack width was 0.05 mm (50 μm) or greater. The wider crack width generally accelerated the performance deterioration when exposed to the corrosion environment. Some of the samples with crack widths of 0.3 and 0.15 mm exhibited an increase in tensile strength after exposure to the NaCl solution for 4 or 10 weeks owing to the moderately corroded steel fibers but showed a decrease in strength with a longer exposure duration.

Influence of Crack Width on Chloride Penetration in Concrete Subjected to Alternating Wetting-Drying Cycles.

To investigate the durability of reinforced concrete (RC) beams under the combined actions of transverse cracks and corrosion, corrosion tests were conducted on a total of eight RC beams with different water–cement ratios and cracking states. The effects of the transverse crack width, water–cement ratio, and the length of the wetting–drying cycle on the distribution of the free chloride concentration, the cross-sectional loss of the tensile steel bars, and the chloride diffusion coefficient are analyzed. The results show that the widths of the transverse crack and the water–cement ratio of concrete greatly affected the chloride profile and content of the RC beam specimens. Specifically, the chloride contents in all the cracked RC beams at the depth of the steel bar exceeded the threshold value of 0.15%. As the width of the cracks increased, the chloride concentration and penetration of the cracked concrete beam increased. However, the chloride concentration at the reinforcement position did not seem to be obviously affected by increasing the wetting–drying cycles from 182 days to 364 days. Moreover, the decrease of the water–cement ratio effectively inhibited the penetration of chloride ions in the RC beam specimens. In terms of the cross-sectional loss of the steel bars, the average loss of the steel bar increases with increasing crack width for the beams with 182-day cycles, while the effect of crack width on the average loss is not as noticeable for the beams with 364-day cycles. Finally, a model is proposed to predict the relationship between the crack width influence coefficient, μ, and the crack width, w, and this model shows good agreement with the experimental results.

Study on the Durability of the T-Beam Based on Chloride Ion Erosion.

Based on analyzing the bearing capacity of existing T-beam bridges in service, the factors that affect the T-beams cracked by chloride ions mainly include the width and the depth of cracks. Combined with practical engineering examples, a single-piece T-beam model is established to explore the influence of factors such as crack width and crack depth on the T-beams affected by chloride ion erosion through numerical simulation in this paper. In addition, the attenuation models of bending capacity and shear capacity of the T-beam are obtained to analyze the possible failure modes of T-beams with cracks. All of which provides a reference for exploring the effect of crack width and depth on the durability of reinforced concrete members under chloride ion field.

The effect of crack width on chloride threshold reaching time in reinforced concrete members

In this study, the effects of changes in the surface chloride concentration and crack width have been simultaneously investigated. To estimate the corrosion occurrence in cracked reinforced concrete members, various samples with different crack widths were modelled and the finite element method was used to model chloride ingress into the concrete. The results of modelling showed that the effect of crack on the corrosion initiation (time that chloride content reach to threshold values) is dependent on surface chloride concentration, chloride threshold, and distance from the crack. In cases of cracks with higher thickness and higher surface chloride concentration, the effect of concrete cover thickness is the most important factor on increases durability of the cracked RC members.

The infrared thermal wave imaging detection of micro-crack defects in Ti-Al alloy plate

The Ti-Al alloy has good physical, chemical and mechanical properties, and it is the preferred material in aerospace and other special fields. The laser spots array is used for thermal excitation of the Ti-Al alloy specimen. Based on the fractional differential equation and Fourier heat conduction equation, the fractional heat transfer model of Ti-Al alloy plate specimen ex-cited by short pulse laser spots array is established, and the infrared thermal imaging simulation analysis is carried out by finite element method. The effects of crack width, crack depth and the distance between the crack and its nearest laser spot center on temperature abrupt jump is analyzed. With the increase of crack width and depth, the temperature abrupt jump increases, but the trend gradually slows down. The distance between the crack and its nearest laser spot center has a significant effect on the temperature abrupt jump. With the increase of the distance, the temperature abrupt jump first increases and then decreases. When the distance equals the laser spot radius, that is, the crack is tangent to the spot, the temperature abrupt jump reaches its maximum.

Applicability of Diffuse Ultrasound to Evaluation of the Water Permeability and Chloride Ion Penetrability of Cracked Concrete.

This study aims to explore the applicability of diffuse ultrasound to the evaluation of water permeability and chloride ion penetrability of cracked concrete. Lab-scale experiments were conducted on disk-shaped concrete specimens, each having a different width of a penetrating crack that was generated by splitting tension along the centerline. The average crack width of each specimen was determined using an image binarization technique. The diffuse ultrasound test employed signals in the frequency range of 200 to 440 kHz. The water flow rate was measured using a constant water-head permeability method, and the chloride diffusion coefficient was determined using a modified steady-state migration method. Then, the effects of crack width on the diffusion characteristics of ultrasound (i.e., diffusivity, dissipation), water flow rate, and chloride diffusion coefficient are investigated. The correlations between the water flow rate and diffuse ultrasound parameters, and between the chloride diffusion coefficient and diffuse ultrasound parameters, are examined. The results suggest that diffuse ultrasound is a promising method for assessing the water permeability and chloride ion penetrability of cracked concrete.

Study on water and chloride transport in cracked mortar using X-ray CT, gravimetric method and natural immersion method

Concrete structures are frequently suffered to physical and chemical damage in the service period and then cracking is unavoidable. Cracks provide rapid access to aggressive agents and have a significant effect on the durability and service life of concrete structures. In this work, water and chloride transport in cracked mortars were investigated systematically. Firstly, the dynamic process of water transport in cracked mortars was visually monitored by X-ray CT and water absorption of cracked mortar was also quantitatively investigated by the gravimetric method. Later, chloride transport in saturated and unsaturated cracked mortars was studied by natural immersion method. What’s more, the effect of gravity on chloride transport in cracked mortar was considered in this study. The results show that the threshold crack width for water absorption of cracked mortar is 0.1 mm. The effect of crack width on chloride transport in saturated and unsaturated mortars is different. The gravity effect improves the rate of chloride transport in cracked mortars.

The effect of crack width on the service life of reinforced concrete structures

Reinforced concrete has become a widely used construction material around the world. Nowadays, the assessment of deterioration and life expectancy of reinforced concrete structure is very important and necessary as concrete is a complex material with brittle failure. Under the effect of load and over time, cracks occur in the structure, significantly reducing its performance and durability. Therefore, a number of models for predicting the penetration of chloride ions into the concrete were proposed to assess the durability of the structure. In the study performed by T B Viet (2016) [1], the author proposed a new theoretical model, especially considering the effects of macro and micro cracking on the diffusion coefficient of chloride ion in the cracked concrete. The following experimental results, in term of electrical indication of concrete’s ability to resist chloride ion penetration, are used to calculate the lifespan of a reinforced concrete structure according to Dura Crete approach [8] with different crack widths to evaluate the accuracy and reliability of the above model in the range of concrete compressive strength of 30-70MPa.

Numerical investigation of chloride diffusivity in cracked concrete

Cracks within concrete accelerate the ingress of chloride ions, causing acceleration of the degradation of the mechanical performance of reinforced-concrete (RC) structures. The effects of cracks should therefore be considered in the durability design of RC structures. However, the available test observations show large discrepancies regarding the quantitative effect of cracks on chloride diffusivity in concrete, and the corresponding developed empirical formulas have some limitations. In the present study, a unified quantitative relation between the chloride diffusion coefficient in cracks and crack width was developed. The parameters in the proposed formula have their own physical meanings, and the corresponding curve of the formula is smooth without an inflection point. The rationality and accuracy of the developed simplified formula were verified through comparisons with test data. Furthermore, chloride diffusivity in cracked concrete was studied and simulated based on the developed simplified formula, and the effects of crack width and crack depth were examined. The simulation results indicate that chloride diffusivity in cracked concrete is significantly affected by both crack width and crack depth. Moreover, the chloride diffusion behaviour in higher strength concrete with lower porosity is much more sensitive to cracks than normal- and lower strength concretes.

Effects of crack width on chloride penetration and performance deterioration of RC columns with sustained eccentric compressive load

In a marine environment, the mechanical performance of Reinforced Concrete (RC) structures deteriorates mainly due to the coupling action of service load and/or the corrosion of steel bars. Here, the working conditions of RC columns in a marine environment were simulated in the laboratory. The chloride penetration and performance deterioration of RC columns with different widths for the maximum initial crack of 0, 50, 100 and 200 microns, induced by different levels of external sustained eccentric compressive load and environments of chloride corrosion, were simulated by seawater wet-dry cycles. The results showed that the yielding load and ultimate load of the RC column specimens were significantly decreased as the width of the initial cracks increased. Tensile strain and crack width were both parameters contributing to chloride penetration in the tensile area of the RC column specimens. During the seawater wet-dry cycles, the initial cracks on the column specimens changed. The initial cracks tended to vanish due to the self-healing capacity of concrete when the width of the initial crack was smaller than 50 microns. The initial cracks remained relatively constant when the crack widths were between 50 and 100 microns, and the crack widths increased when the initial crack width was larger than 100 microns.