Changes In Crack Width Research Articles

Cracks monitoring in reinforced concrete structure with optical fibers patch

In the context of the necessity to monitor civil engineering structures in order to prevent incidents, this paper presents the performance of an innovative optical fibers patch sensor. The patch comprises a tissue containing an optical fiber network. The sensor is attached to the concrete surface and capable of detecting opening cracks in the order of 0.01 mm with good precision, thus satisfying the regulatory limits. The sensor is capable of precisely following the evolution of the crack, including cyclic changes in crack width. The procedure presented in this paper includes a preliminary investigation into the influence of the fibers’ diameter and the density of fibers in the patch, as well as the method of attachment to the concrete’s surface with the objective of identifying an optimal sensor configuration. Subsequently, a series of laboratory tests were conducted on reinforced concrete samples of varying dimensions. Comparisons and verifications of measurements of optical fiber patch sensors are conducted via Digital Image Correlation process. The conclusions of this paper permit the consideration of the use of this novel sensor on and within real reinforced concrete structures.

Multi-scale characterization of SAP impact on self-healing behavior in UHPC under varied crack widths and environments

This paper studies the effects of the content and particle size of superabsorbent polymer (SAP) on the self-healing behavior of precracked Ultra-high-performance concrete (UHPC) under different crack widths. In this experiment, bending and compression-resistant internal damage to UHPC was first created with different amounts and particle sizes of SAP added, and then the damaged specimens were placed in a water environment, a dry environment, and a water-dry cycle environment for self-healing. Finally, the self-healing effect of pre-cracked UHPC was evaluated from the changes in crack width, recovery of mechanical properties, and changes in ultrasonic speed. In addition, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to conduct microscopic analysis of the products of the self-healing reaction. The experimental results show that SAP itself does not participate in self-healing chemical reactions. It mainly seals cracks by absorbing water and expands and promotes the continued hydration of the internal gelling materials of UHPC through water storage to improve the self-healing performance. Therefore, in a dry environment, SAP has almost no effect on the self-healing performance of UHPC. In moisture-rich environments, SAP can significantly improve the healing of macroscopic cracks with a width greater than 50 μm. In addition, the experimental results also show that under the same environment, changes in SAP content and particle size have a consistent effect on the recovery of UHPC's mechanical properties and the recovery of ultrasonic speed. The results of this study can promote the application of internal curing in the self-healing of UHPC cracks and further reduce the maintenance cost of UHPC throughout its life cycle.

Changes in crack width on the surface of heavy soils during drought, determined by precise measurement and calculation

Abstract In heavy soils, changes in humidity incur soil volume changes. In the horizontal plane, these are manifested by cracks formation and in the vertical plane by the movement of the soil surface. Cracks have a significant impact on hydrodynamics of the soil profile. The work is based on the hypothesis that soil volume changes depend on both the content of clay particles in soil and soil volumetric moisture. The aim of the work is to measure and analyze the changes in the width of the cracks and their reaction to the changes in volumetric soil moisture. One of the objectives of the work was to design a simple tool for accurate measurement and calculation of the crack width on the soil surface. For the study of crack width, a soil profile in an area on the East Slovakia Lowland was selected. The profile was examined under conditions of extreme drought, at the turn of July and August 2022. Crack width varied between 1.0 cm and 3.3 cm. The calculation procedure was evaluated as satisfactory for estimating the change in crack width on the soil surface.

Effect of NaCl and Na2SO4 on Low Temperature Corrosion of Vapour- and Pack-Aluminide Coated Single Crystal Turbine Blade Alloys CMSX-4 and RR3010

The current work presents a systematic study of two alloy compositions (RR3010 and CMSX-4) and two types of coatings: inward grown (pack) and outward grown (vapour) deposited aluminides, exposed to 98Na2SO4–2NaCl mixture. Grit blasting was used on some of the samples, prior to coating, to mimic in-service procedures and remove oxides from the surface prior to coating. Two-point bend tests were then performed on the coated samples, with and without applied salt at 550 °C for 100 hours. Samples were pre-strained at 0.6 pct strain to deliberately pre-crack the coating and then strained at 0.3 pct for the heat treatment. Exposure to 98Na2SO4–2NaCl under applied stress of vapour-aluminide coated samples of both alloys, revealed significant coating damage in the form of secondary cracks in the intermetallic-rich inter-diffusion zone, although only CMSX-4 exhibited cracks propagating further into the bulk alloy while RR3010 proved more resistant. The pack-aluminide coating proved more protective for both alloys, with cracks propagating only into the coating and never into the underlying alloy. In addition, grit blasting proved beneficial in reducing spallation and cracking for both types of coating. The findings were used to propose a mechanism based on thermodynamic reactions, to explain the crack width changes through the formation of volatile AlCl3 in the cracks.

Microbiologically induced concrete corrosion in the cracked sewer pipe under sustained load

Microbiologically induced concrete corrosion (MICC) and stress crack are the most common structural defects in concrete sewer pipes. To investigate the microbial corrosion behavior of cracked concrete pipes under sustained loading, coupons with no load, 100% D-Load, and 120% D-Load were pre-adjusted to a suitable environment for acidophilic sulfur oxidizing bacteria (ASOB) colonization, and then placed together in a microbial chamber for 90-day accelerated corrosion. The corrosion variances of these coupons were compared in terms of surface morphology, crystalline violet staining, pH evolutions, crack width changes, as well as characterization results including Scanning Electron Microscope- Energy Dispersive Spectrometer (SEM-EDS) and X-ray Diffraction (XRD). It was found that the stress level slightly accelerates the pH drop on the coupon surface, positively correlates with the corrosion product content of the semi-corrosive layer, and causes stress-corrosion cracking of the semi-corrosive layer, but has little effect on corrosion loss. Stress-corrosion effects were only found in the semi-deteriorated layer of the stressed coupon, but no significant acceleration effect on corrosion rate was observed. This is explained by the fact that MICC is a non-diffusive corrosion where the semi-deteriorated layer is rather thin. Thus, cracking or not of the semi-deteriorated layer does not affect the corrosion rate. This study improves understanding of the service deterioration of sewage pipes.

Quantifying Crack Self-Healing in Concrete with Superabsorbent Polymers under Varying Temperature and Relative Humidity

During their service life, concrete structures are subjected to combined fluctuations of temperature and relative humidity, which can influence their durability and service life performance. Self-healing has in recent years attracted great interest to mitigate the effects of such environmental exposure on concrete structures. Several studies have explored the autogenous crack self-healing in concrete incorporating superabsorbent polymers (SAPs) and exposed to different environments. However, none of the published studies to date has investigated the self-healing in concrete incorporating SAPs under a combined change in temperature and relative humidity. In the present study, the crack width changes due to self-healing of cement mortars incorporating SAPs under a combined change of temperature and relative humidity were investigated and quantified using micro-computed tomography and three-dimensional image analysis. A varying dosage of SAPs expressed as a percentage (0.5%, 1% and 2%) of the cement mass was incorporated in the mortar mixtures. In addition, the influence of other environments such as continuous water submersion and cyclic wetting and drying was studied and quantified. The results of segmentation and quantification analysis of X-ray µCT scans showed that mortar specimens incorporating 1% SAPs and exposed to environments with a combined change in temperature and relative humidity exhibited less self-healing (around 6.58% of healing efficiency). Conversely, when specimens were subjected to cyclic wetting and drying or water submersion, the healing efficiency increased to 19.11% and 26.32%, respectively. It appears that to achieve sustained self-healing of cracks, novel engineered systems that can assure an internal supply of moisture are needed.

Structural Health Monitoring of Underground Structures in Reclamation Area Using Fiber Bragg Grating Sensors.

The long-term structural performance of underground structures in reclamation areas is very sensitive to the vibrations caused by vehicles passing above the structures and environmental factors (e.g., tide levels, rainfall and temperature). In the present study, an integrated remote real-time structural health monitoring system using fiber Bragg grating sensors was developed to assess the structural performance of underground structures. Using a composite road box-type structure project in a reclamation area in Southern China as a case study, the developed real-time system was implemented to investigate the effects of changes in tide levels, rainfall, temperature and vehicle induced vibrations on crack propagation in the structure. The results show that the change in tide levels has little influence on the change in crack width in the structure, whereas variations in temperature could significantly influence the crack width with an average Pearson correlation of around 0.8. In addition, the crack width generally decreases with an increase in rainfall. Furthermore, a relatively low frequency (<25 Hz) induced by the traffic could result in a relatively larger crack width.

Visualization and quantification of crack self-healing in cement-based materials incorporating different minerals

Self-healing efficiency of cement-based materials has so far been evaluated mostly through the healing of surface cracks, without adequately capturing the dominant effects of environmental exposure or accurately quantifying the volume of cracks healed. In addition, the effects of diverse additions such as silica-based materials, swelling agents, and carbonating minerals on self-healing performance under different environmental exposure, remain largely unexplored. In this study, multiple test methods were used to investigate self-healing of cracks in cement mortar incorporating metakaolin, bentonite, and calcium carbonate microfiller in different environmental exposure. Change in crack width was monitored using optical microscopy. Backscattered electron microscopy coupled with energy disperse X-ray analysis was used to identify healing compounds. Mercury intrusion porosimetry and water absorption were employed to assess porosity. X-ray computed micro-tomography (X-ray μCT) with 3-dimensional image processing was used to segment and quantify cracks before and after healing. After one year of exposure, no significant self-healing occurred in all specimens exposed to cyclic T and RH. Conversely, all specimens submerged in water exhibited variable levels of self-healing, which depended on the type of mineral added. The healing efficiency was 32.26%, 27.27%, 25.6%, and 24.1% for specimens incorporating limestone microfiller, portland cement alone, bentonite, and metakaolin, respectively. The formation of calcium carbonate was found to be the main contributor to self-healing of surface cracks.

Effect of environmental exposure on autogenous self-healing of cracked cement-based materials

Despite abundant literature on self-healing of cement-based materials, there is dearth of information on how environmental exposure affects self-healing. In this study, self-healing of cracks in cement mortar under different environmental exposure was investigated. Pre-cracked mortar specimens were submerged in water, while identical specimens were exposed to cyclic temperature and relative humidity. Change in crack width was examined using optical microscopy. SEM coupled with energy dispersive X-ray analysis was used to identify healing compounds. Mercury Intrusion Porosimetry, water absorption and permeability were employed to assess porosity. X-ray computed tomography was deployed to explore healing of internal cracks. No significant self-healing occurred in specimens exposed to cyclic T and RH. Although crack self-healing was identified in submerged specimens, X-ray μCT demonstrated that it was limited to exposed surface of specimens. This warrants further research to bridge the gap between laboratory findings on self-healing and actual field performance of ageing civil infrastructure.

The computational analysis of the crack width of beams reinforced with CFRP and steel bars

The aim of the paper is to explain the particular problems related to the use of FRP reinforcement in bending beams. The paper compares the aspect of Serviceability Limit State (SLS) of simply supported concrete beams reinforced with Carbon Fiber Reinforced Polymer (CFRP) bars and three various types of steel bars (the steel grades are 35G2Y, 20G2VY-b and B500SP). The computational analysis of change in crack width under the influence of various level of service live load was investigated. The calculations of beam reinforced with FRP bars was based on Italian design guideline (CNR-DT 203/2006) and the conventional reinforced concrete beams (RC) were analysed in accordance with the European standard Eurocode 2 (EN 1992-1-1:2004).

Field Qualification of Inexpensive Wireless Systems to Monitor Micrometer Crack Response for Structural Health Monitoring

This paper describes the details of installation and operation of a commercially available wireless system to measure response of interior cosmetic cracks in a residential structure over a period of a year. Wireless data loggers managed the response of low-power-draw potentiometers that measured micrometer changes in crack width. Systems like those studied herein are useful to describe the performance of any component of a constructed facility that involves existing cracks such as bridges, building facades, or other structures. Four wireless nodes were deployed within and around a test home of frame construction to qualify the system for further field use. Considerations for qualification included: fidelity of the measured crack response, ease of installation, resolution of structural health measurement, length of operation under a variety of conditions without intervention, and ease of display and interpretation of data. The article first describes the components of the system and the measurement plan. It then closes with an evaluation of the considerations for field qualification.

비내진상세를 가지는 철근콘크리트 부재의 균열발생특성

지진발생시 건축물의 긴급 위험도 평가를 통한 여진에 따른 2차 인명피해 방지를 위해서는 건축물의 구조형식에 따른 정량적 손상도 평가 기준이 필요하다. 본 논문은 비내진상세를 가지는 철근콘크리트조 건축물을 대상으로 정량적 손상도 평가 기준을 제시하기 위한 기초 연구로 부재 표면에 발생하는 손상 중 균열을 대상으로 비내진상세를 가지는 철근콘크리트 1층 1경간 실험체의 정적실험결과를 바탕으로 지진응답에 따른 균열폭 변화양상에 대하여 평가하였다. 그 결과, 실험체의 접합부 및 기둥 상 하부 위험단면에서부터 기둥 중앙부로 2.0D(D:기둥 높이)까지의 구간을 중심으로 휨균열 및 휨전단균열이 발생하였다. 이 중 기둥 상부 위험단면위치 휨균열과 휨전단균열만이 층간변형각 증가에 따라 크게 벌어지는 것으로 나타났으며, 기둥 주근 항복에 따라 잔류 균열폭이 점차적으로 발생하기 시작하였다. 한편, 잔류 최대 균열폭은 기둥 주근이 항복하기 전에는 피크시 최대 균열폭의 1/2배 미만인 반면에, 기둥 주근이 항복한 후에는 피크시 최대 균열폭의 1/6~1배인 것으로 나타났다. 또한, 피크시 최대 균열폭은 경험 최대 층간변형각에 상관없이 균열폭 합의 1/2정도인 것으로 나타났다. The quantitative damage index considering structural types are essential for the effective post-earuthquake safety evaluation. This paper is the fundamental research in order to present the quantitative damage index for reinforced concrete members with non-seismic details. The crack width changes related with seismic response were studied based on the static test results of one-span and -story specimen with non-seismic details. According to the test result, cracks mostly occurred on the beam-column joints and the upper- and lower- part of columns. The flexural crack width on the column end section and shear crack width on the upper column were widely opened by loading. The residual crack widths were also getting larger since yielding of reinforcements. Meanwhile, the maximum residual crack width was lower than the 1/2-fold of the maximum crack width before yielding, and got the 1/6- and 1-fold of the maximum crack width after yielding.

The inspection of magnetic flux leakage from metal surface cracks by magneto-optical sensors

We investigated the feasibility of using magneto-optical sensors for measuring the magnetic leakage fields in non-destructive evaluation. We used magneto-optical garnet thin films as a sensor and the effect of crack dimension on the sensor's response were investigated via a simple Faraday rotation technique. Our results show that the sensor signal displays a linear increase as the length and depth of the cracks increase however; the change in crack width does not have a significant effect on the magnetic leakage field and the sensor's signal. This technique is capable of high resolution magnetic imaging of small surface cracks and thus has great potential for application in the magnetic flux leakage test industry.

Long-Term Wireless Structural Health Monitoring of the Ferriby Road Bridge

As part of an effective bridge management system, sensor networks can provide data to support both inspection and assessment. Wireless sensor networks (WSNs) have the potential to offer significant advantages over traditional wired monitoring systems in terms of sensor, cabling, and installation costs as well as expandability. However, there are drawbacks with WSNs relating to power, data bandwidth, and robustness. To evaluate the potential of WSNs for use in bridge management, a network of seven sensor nodes was installed on the Ferriby Road Bridge, a three-span reinforced concrete bridge. Three displacement transducer nodes were placed across cracks on the soffit of the bridge to measure the change in crack width. Three inclinometer sensor nodes were mounted on two of the elastomeric bearing pads to measure the change in inclination of the bearing pads while a final node monitored temperature in the box that contained the gateway. The installation of the WSN is discussed and data from this network is analyzed. Finally, the use of sensor networks to support inspection and assessment is discussed.

The 8th International Symposium on Rock Fragmentation by Blasting, Fragblast 8, 7 – 11th of May 2006 in Santiago, Chile

This paper describes qualification of devices to measure sub micro-meter changes in crack width, which is the basis of autonomous crack monitoring for control of blasting vibrations. Performance of LVDT, eddy current and potentiometer sensors to monitor long-term and transient displacements will be described. Potentiometers are attractive for wireless measurement, which is important as future autonomous crack displacement measurement almost certainly will be wireless. Long-term performance in the laboratory and the field is described in terms of drift, hysteresis, and noise upon exposure to cyclic changes in displacement and temperature. Transient performance is described in terms of relative response of the three systems to impact induced displacements with eddy current and LVDT serving as the benchmark.

Response of Test House to Vibroseis Vibrations and Environmental Forces

In response to public concerns about the damage potential of vibroseis vibrations from seismic exploration, Fina Oil and Chemical Company (now Total E&P USA, Inc.) sponsored full-scale testing of a typical residence. The test house was vibrated by four vibroseis trucks on both soil and asphalt surfaces at declining separation distances. Ultimately, the vibrators were 13 feet (4.0 m) from the front porch and 10 feet (3 m) from the front sidewalk. Peak particle velocities of the ground motions were about 1 in./second (0.4 cm/second) at the house foundation. As expected, the responses of the superstructure were strongly dependent on the frequencies of the ground motions. No damage to the house of any kind was produced by these vibrations, even though the vibrators were operating at 90% maximum output. Tests were also conducted away from the house to explore the vibration intensities and attenuation characteristics of the ground motions generated. The resulting vibrations were compared to previous work and found to be consistent with those results. Changes in crack width and associated weather-induced changes in temperature, humidity, and other environmental factors were recorded every 2 hours for 1 year. Environmental effects are known to produce larger crack responses than vibrations that conform to common standards and regulated limits, a fact demonstrated again in this case. Response motions in the house were also recorded during common household activities, including hammering nails, slamming doors, and use of the fireplace. In the vicinity of the input forces, some of these activities generated greater response than did the vibroseis excitation.

Epitaxial growth of Y Ba2Cu3O7−δ thin films on silicon-on-insulator substrates by pulsed laser deposition

High quality superconducting Y Ba2Cu3O7−δ (YBCO) thin films have been successfully deposited on silicon-on-insulator(SOI) substrates buffered by an yttria-stabilized zirconia (YSZ) layer usingthe in situ pulsed laser deposition (PLD) method. X-ray diffraction (XRD)θ–2θ-scanand φ-scan, and reflection high energy electron diffraction (RHEED), indicate that both theYSZ and YBCO thin films are of high crystallinity and good lattice orientation.Atomic force microscopy (AFM) shows that the root mean square roughnessRq of YSZ thin films is less than 0.9 nm in an area of1 µm × 1 µm, and that of YBCO thin films is about 3 nm in an area of2 µm × 2 µm. The zero-resistancetemperature TC0 of the YBCO/YSZ/SOI multilayers is up to 88 K, measured by a four-probe method.However, scanning electron microscopy (SEM) demonstrates many clear cracks in YBCOthin films due to the lattice constant and thermal expansion coefficient mismatch betweenSOI and YBCO. The crack width changes with the thickness of YBCO thin films.

APPLICATION OF FRACTURE MECHANICS TO CRACKING OF SALINE SOILS

Salt-affected cracking clay soils are common to many irrigated, relatively and regions of the world. The structural changes of these soils having changing water contents lead to a pattern of macro-porosity of concern to water management and groundwater contamination. Herein, we briefly describe the different morphologic observations and attempts at quantifying aspects of the soil-cracking phenomena. After a brief review of fracture mechanics theory, we outline the equations appropriate for its application to soils. Results of the theoretical analysis are compared with field observations of crack morphology in Tulare basin soils irrigated with Na2SO4 waters having Total Dissolved Solids (TDS) concentrations of approximately 400, 4500, and 9000 mg/L The theoretical analysis indicates that widely opened shallow cracks require high tensile stresses for propagation and that sodium-affected soils require yet greater energy to extend crack depth. Combining the theory with field observations indicated that changes in crack width and depth in the high salinity treatment soils required roughly twice the energy as that in the low salinity soils. In addition, we found that the change in water content necessary to induce crack growth increases as the soil dries and that at any given water content, the stress associated with crack growth was less in the high salinity soils. Overall, fracture mechanics, coupled with measurements of soil physical properties can be used to determine quantitatively the propensity of soils to crack and the extent to which cracking will occur. However, additional laboratory and field studies are necessary to verify estimates of strain energy release rates from the fracture mechanics theory

A laboratory evaluation of test apparatus and techniques for investigating spray deposit and drift in crack and crevice treatments.

A crack's width and depth have very little effect on the amount of insecticide deposited on the outside of the crack. Factors such as rate of application, concentration of insecticide, tank pressure and air turbulence would have a more direct effect on the amount of deposit. While other factors such as humidity and temperature were not considered in this study, other researchers have shown their importance in spray deposition. The amount of insecticide deposited along the interior of a crack is strongly influenced by the width of the crack. The wider the crack opening, the more insecticide deposited. Data collected using the test apparatus has shown that the apparatus is able to provide a great deal of information about the factors influencing the amount of insecticide in crack and crevice treatments. The apparatus and techniques utilized during this study have proved to be accurate and sensitive to changes in crack width and depths. This method also gives valuable information as to the efficiency of the application equipment that was used in this study. The next step is to test the apparatus using pressures. Concentrations, and methods presently being using by pest control operators.

VERTICAL MOVEMENTS AND CRACK-WIDTH CHANGES ON HIGHWAY PAVEMENT SURFACES

The results of periodic pavement elevation and crack-width measurements taken over a period of three to four years are presented. Both surface elevation and crack-width changes are shown to follow a similar seasonal cycle. Results show that the sub-grades studied were frozen as closed systems. It is shown that with closed system subgrade freezing the resulting vertical displacement of the pavement may be either positive or negative depending on the moisture content of the subgrade. The negative case, corresponding to vertical freezing shrinkage, occurred with dry clay subgrades. For a given observation section, seasonal surface movements in a vertical direction are shown to vary from the traffic lanes to the shoulders. The difference is explained in terms of corresponding differences in the subgrade moisture conditions.Results are presented which indicate that seasonal changes in the width of transverse pavement cracks cannot be fully explained in terms of simple thermal expansion and contraction in the asphaltic concrete pavement. Indirect evidence is presented which suggests that horizontal freezing shrinkage in a subgrade contributes to the seasonal cycle of crack-width changes.