Cracking Properties Research Articles

Effect of mendable polymer stitch density on the toughening and healing of delamination cracks in carbon–epoxy laminates

This paper presents an investigation into the effect of stitch density on the delamination toughening and self-healing properties of carbon–epoxy laminates. The stitches provide the laminate with the synergistic combination of high mode I interlaminar fracture toughness to resist delamination cracking and healing properties to repair delamination damage. The results show that the fracture toughness of the laminate increased with stitch density, due to higher traction (crack closure) loads exerted by the stitches bridging the delamination. During the healing process these bridging stitches first melt and then flow into the delamination, leading to self-healing with full restoration of the mode I fracture toughness. Furthermore, the stitches were capable of repairing delamination cracks many times larger than the original size of the stitches. The effect of stitch density on the healing process of delamination cracks and restoration of fracture toughness was found to remain approximately the same under multiple repair operations.

Cracking behavior of reinforced concrete beams: experiment and simulations on the numerical influence of the steel-concrete bond

Experimental and numerical results are provided in this contribution to study the global and cracking behaviors of two reinforced concrete beams subjected to four point bending. Experimentally, the use of image correlation technique enables to obtain precise information concerning the cracking properties (spacing, cumulated, maximum and mean values of the opening). Numerically, two simulations are compared taking into account a bond model between steel and concrete or supposing a perfect relation between the two materials. In both cases, a good agreement is achieved between numerical and experimental results even if the introduction of the bond effects has a direct influence during the development of the cracks (better agreement during the “active” cracking phase).

Cracking and isomerization functionalities of bi-metallic zeolites for naphtha value upgradation

Effect of acid and metal functionalities of several mono- and bi-metallic wide pore zeolites such as BEA and Y on the cracking and isomerization properties of n-heptane as well as two industrial naphtha feedstocks have been studied. Among these, the bi-metallic Pt–Cr–HBEA catalyst exhibited appropriate catalytic properties responsible for high isomerization and octane boosting. Detailed studies envision that the role of Cr is bi-functional, namely, to change the acidity of the zeolite support towards the moderate strength responsible for controlled cracking and to promote the reducibility and dispersion properties of the Pt for the effective isomerization reaction. This has resulted in enhancement in research octane number (ΔRON) of two industrial naphtha feedstocks with 22 and 43 units increase in RON along with negligible amount of aromatics, especially benzene that makes the product suitable for gasoline applications. The catalyst exhibited constant performance in the studied period of 70h.

Conditions for Failure of Normal Section in Flexural Reinforced Concrete Beams of Rectangular Cross-Section

The stress in longitudinal tensile reinforcement is one of the main important parameters while examining the technical state of under- reinforced concrete structures. The most important issue is to determine whether the external loads cause the close to yield stress in the main reinforcement. Yield stress in tensile reinforcement could be treated as the start of incipient failure of the flexural structure. The state of tensile reinforcement of flexural reinforced concrete structures could be examined by observing the properties of the normal cracks. The application of fracture mechanics of solids could be used for determining the actual damage to the structure by knowing only the measured height of the normal crack.

Microstructure and Stress Corrosion Cracking of Spray Forming 7075 Alloy after Retrogression and Re-ageing Treatment

A typical age-strengthening 7075 aluminum alloy with high tensile properties can be spray-formed through T6 treatment,but its stress corrosion cracking(SCC) property appears very poor after this treatment. On the other hand,the SCC property may be improved by T7 treatment but the tensile strength of the alloy then be seriously harmed. Therefore,the effects of four kinds of retrogression and re-ageing(RRA) treatments on the microstructure and mechanical properties of a spray forming 7075 alloy are investigated by using mechanical,electric and transmission electron microscope observation measures in this research. It is obtained that the tensile strength and electric conductivity of the alloy reaches up to 748 MPa and 22.8 MS/m respectively under the condition of retrogressed at 200 ℃ for 10 min,and re-aged at 120 ℃ for 24 h. During retrogression treatment,GP zone and η′ phase are dissolved in matrix,η′ phase is then re-precipitated at 200 ℃ retrogression treatment over 10 min,which leads to the slight increase of tensile strength of the alloy. Because of the precipitation of shaped-η′ phases during retrogression and the corresponding RRA treatment a lots of η′ phases re-precipitate and η phases at grain boundary may improve the SCC resistance of the alloy.

Influence of Hydrogreen Bioasphalt on Viscoelastic Properties of Reclaimed Asphalt Mixtures

The incorporation of reclaimed asphalt pavement (RAP) into asphalt mixtures exposes some challenges from the design perspective because of the aged asphalt binder in RAP. Steps are being taken to offset the addition of stiff materials, often with the use of rejuvenating additives. This paper summarizes the laboratory evaluation of one of the available bio-rejuvenating agents called BituTech RAP. High RAP content mixtures used in Manitoba, Canada, were evaluated to study the impact of BituTech RAP on the viscoelastic properties of asphalt mixtures to overcome any possible moisture damage or thermal cracking problems that might arise in such a wet–freeze environment. The laboratory experiment consisted of the production and test of mixtures that contained 15% and 50% RAP, with and without BituTech RAP. The 2S2P1D analogical model was used to generate the complex modulus (E*) of the various evaluated mixtures and to assess the influence of BituTech RAP on the storage and loss moduli. The addition of BituTech RAP improved the moisture resistance of the mixtures that contained RAP, as observed after three freeze–thaw cycles. The addition of BituTech RAP restored the thermal cracking properties of the mixtures revealed by the thermal stress restrained specimen test. The use of BituTech RAP could result in cost savings without the need to use a softer binder, as long as the high-temperature properties of the mixtures were not jeopardized.

Forensic Study on the Cracking of New Jersey's Long-Term Pavement Performance Specific Pavement Study Sections

In 2010, New Jersey's long-term pavement performance (LTPP) Specific Pavement Study (SPS-5) sections closed out. Before the rehabilitation of these pavement sections, an extensive coring and forensic study was conducted to characterize the material properties of the virgin and the 30% reclaimed asphalt pavement (RAP) asphalt mixtures used on the project. Along with field cores, raw materials (i.e., aggregates, binder, loose mix) were procured from FHWA-LTPP Materials Reference Library. Visual distress surveys from the LTPP database were collected and used to compare the mixture performance with the general field performance. Overall, the field performance indicated that the virgin and the 30% RAP sections initiated cracking within 1 to 3 years of each other, given the section evaluated. Once cracking began, however, the 30% RAP sections cracked at a faster rate than the virgin sections; this behavior resulted in higher crack counts even though the 30% RAP section had a softer binder (i.e., AC-10 versus AC-20). The overlay tester (OT), disk-shaped compact tension [DC(T)], and low-temperature indirect tension and creep compliance were used to characterize intermediate and low-temperature cracking properties of the mixtures. Asphalt binder characterization included performance grading, master stiffness curves, and linear amplitude sweep (LAS) testing to characterize the stiffness and fatigue properties of the asphalt binders. The material testing program showed that the mixture test results matched the observed field cracking performance better than the asphalt binder testing conducted on the extracted and recovered asphalt binders. The OT and DC(T) tests appeared to be the most sensitive to the cracking performance differences between the virgin and 30% RAP mixtures, while the LAS test appeared to rank the fatigue performance of the 30% RAP mixture better than that of the virgin mixture, which contradicted the observed field performance.

Enhanced UV-protection and antibacterial properties of natural rubber/rutile-TiO2 nanocomposites

Natural rubber/rutile-TiO2 nanocomposites (NR/n-TiO2(R) composites) with different n-TiO2(R) contents were prepared. The n-TiO2(R) with median particle size (d50) of 73 nm was successfully prepared from commercial micron-TiO2(R) by ultrasonication. NR incorporated with n-TiO2(R) shows the good performance in mechanical properties as well as UV-protection and antibacterial properties. The mechanical performance of NR/n-TiO2(R) composites was enhanced with an increase of n-TiO2(R) content up to the optimum content at 5 phr (parts per hundred parts of rubber) and then declined. In addition, the prepared NR/n-TiO2(R) composites possess the UV-protection material. The UV-protection property of NR nanocomposites was evaluated by measuring the evolution of carbonyl absorption band from ATR-FTIR spectra, surface cracking, and mechanical properties after UV irradiation. The presence of n-TiO2(R) exhibits significant improvement in photo-degradation by UV irradiation compared to the unfilled NR. More importantly, the obtained NR/n-TiO2(R) composites demonstrate effective antibacterial property against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), the strong antibacterial property of the prepared NR nanocomposites was obtained at the only loading level of 1 phr of n-TiO2(R). The prepared NR/n-TiO2(R) composites could be used as a novel antibacterial material.

Crack Behavior of Si-Doped GaAs Crystals Grown by Pulling-Down Method

The crack behavior of Si-doped GaAs crystals produced by a novel pulling-down method was investigated. Some cracks were observed in the crystal tail part and no twins or polycrystals were observed. The cracking mechanism was discussed considering the growth parameters, such as the pulling-down rate, annealing time and cooling speed of the furnace. The crystal was easily broken if the cooling rate was too fast. To avoid cracking, the temperature profile and the growth parameters had been optimized. The cleavage property of the GaAs crystal was strongly related to its atomic arrangement and corresponding electron density map. Ultrasonic vibration or mechanical machine would make the crystal cleaved along (110) plane. GaAs crystal displayed a strong anisotropic crack property under the force of microindentation test.

Constructing the convex quadratic function for the evaluation of crack density of HTI media using P- and converted waves

In future years, cracked reservoirs will be an important target for oil and gas exploration. Cracks play an essential role in the evaluation and prediction of cracked reservoirs. The amplitude variation with azimuth (AVA) method of studying crack properties is becoming an important means of evaluating cracks and now the P-wave AVA method can be used in the inversion of crack density. In order to improve the precision of inversion, we constructed a convex objective function on the basis of the combination of P- and converted-wave data. We then used conjugate gradient methods for the inversion of crack density. Numerical calculations in both fluid-filled and dry crack models and stability analysis of this method proved its viability and stability.

Use of a warm mix asphalt additive to reduce the production temperatures and to improve the performance of asphalt rubber mixtures

Asphalt rubber mixtures are often described as environmentally friendly mixtures due to the incorporation of recycled rubber from used tires and due to their improved service life. In fact, their fatigue cracking and rut resistance properties are better than those of conventional asphalt concrete mixtures. However, asphalt rubber mixtures demand higher production temperatures than conventional mixtures due to the higher viscosity of the asphalt rubber binder. The objective of this paper is to assess the efficiency of using a surfactant based additive in the production of warm mix asphalts, by lowering the mixing temperatures of asphalt rubber and asphalt concrete mixtures without changing their performance. Several laboratory tests were carried out on asphalt rubber and asphalt concrete mixtures, with and without the additive, in order to evaluate and compare the performance of the mixtures. It was concluded that the incorporation of small amounts of a surfactant based additive allowed reducing the production temperatures of both types of mixture by 30 °C without compromising their performance, and this can be seen as a great step forward towards the production of cleaner asphalt rubber mixtures.

Effects of Cracks on the Electrical Conductivity of a Fissured Laterite: A Combined Experimental and Statistical Study

Abstract This paper presents an experimental study of the effects of cracks on the electrical conductivity (EC) of a fissured laterite in Hunan Province, People’s Republic of China, followed by multi-variant statistical analyses of the sensitivity of the EC dependence on different crack parameters (e.g., depth, length, width, orientation, and crack density). The results show that the soil EC is highly dependent on the crack properties. In general, the EC decreases linearly as the crack depth, length, width, orientation angle, or density increases. However, the EC decreases non-linearly, and the rate of reduction increases more dramatically, as the depth of cracks exceeds 1/4 of the thickness of the soil sample. When the width of the crack increases to 2.8 cm, the EC decreases less obviously and tends to remain at a constant value. Moreover, the EC decreases more dramatically with the orientation angle when it is less than 45° (otherwise the EC decreases more slowly with the orientation angle). With an increase in crack density (or the number of cracks), the EC exhibits much higher dependence on crack depth, length, and width. Finally, of all these crack parameters, the depth and orientation are the two primary factors influencing the soil EC, and the crack length, width, and density are secondary ones. As such, the degree of effect of different crack parameters on the soil EC follows the order of depth > orientation angle > density > length > width.

순환굵은골재 흡수율에 따른 철근콘크리트 보의 구조 성능 평가

This study estimates the flexural behavior of reinforced recycled aggregate concrete beams. Three specimens with different types and water absorption of coarse aggregates were constructed and tested. Not only all specimens were designed to be subjected to 4-point concentrated loads, but also the shear span-to-depth ratio of 2.5 was adjusted to all specimens to increase the effect of shear. A nonlinear flexural analysis considering the tension stiffening effect of concrete was performed to predict the moment versus curvature relationships of the specimens. Furthermore, a nonlinear finite element analysis considering the effect of shear was carried out to estimate the behavior of the specimens. It can be found from experimental results that the flexural strength and the crack properties of the specimens with recycled coarse aggregate having a water absorption of 6% were similar to those of the specimen with natural aggregates. The comparison between the experimental and analytical results showed that existing analytical methods can be successfully used to predict the behavior of reinforced recycled aggregate concrete beams.

Artificial Intelligence Helps Bring Objectivity to Bridge Health Evaluations

Researchers at Kansas State University are developing an artificial intelligence program that can objectively determine the health of a bridge on the basis of crack properties and beam stiffnesses.

A comparison of engineered cementitious composites versus normal concrete in beam-column joints under reversed cyclic loading

Engineered cementitious composites (ECC) are a class of high-performance fiber reinforced cementitious composite with strain hardening and multiple cracking properties. For a reinforced concrete member, substitution of conventional concrete with ECC can significantly improve the deformation characteristics in terms of reinforced composite tensile or shear strength and energy dissipation ability. In this paper, a number of RC/ECC composite beam-column joints have been tested under reversed cyclic loading to study the effect of substitution of concrete with ECC in the joint zone on the seismic behaviors of composite members. The experimental parameters include shear reinforcement ratio in the joint zone, axial load level on the column and substitution of concrete with ECC or not. According to the test results, for the specimens without shear reinforcement in the joint zone, substitution of concrete with ECC in the joint zone cannot change the brittle shear failure in the joint zone, but can significantly increase the load capacity and ductility of the beam-column joint specimens, as well as the energy dissipation ability due to high ductility and shear strength of ECC material. For the specimens with insufficient or proper shear reinforcement ratio, substitution of concrete with ECC in the joint zone can lead to failure mode change from brittle shear failure in the joint zone to a more ductile failure mode, i.e. flexural failure at the base of the beam, with increased load capacity, ductility and energy dissipation ability. Increase of axial load on column and shear reinforcement in the joint zone have little effect on seismic behaviors of the members when they failed by flexural failure at the base of beam. In a word, the substitution of concrete with ECC in the joint zone was experimentally proved to be an effective method to increase the seismic resistance of beam-column joint specimens.

Full paper: Image based retrieval of concrete crack properties

Full paper: Image based retrieval of concrete crack properties

Image based retrieval of concrete crack properties

Purpose This paper presents a new method to retrieve concrete crack properties based on image processing techniques. Method Detection and quantification of cracks in concrete bridges pose various challenges. Cracks have fewer pixels compared to their background. For effective visualization, the objects need to be captured from near field. But it is not always possible to capture the complete cracked surface in a single frame while taking the image from near field. Hence image stitching is required before pre-processing of images for further analysis. Usually retrieved images have low contrast due to environmental and equipment limitations which add another difficulty in image visualization. State-ofthe-art image pre-processing as suggested in the literature may not be suitable for images captured in different environmental conditions. This paper discusses various techniques for image enhancement using point processing, histogram equalization and mask processing. Furthermore, a binary image is required to obtain a skeleton of an object. However, the pre-processing techniques cause discontinuity in crack alignment. Morphological techniques (e.g. dilation) are used in this work through successive iteration to ensure connectivity. Then the object skeleton which is unaffected by expanded boundaries is obtained by using skeleton algorithm to retrieve concrete crack properties such as length, bounding rectangle, and major and minor principal axes lengths. Results & Discussion The preliminary results obtained using this methodology is capable of retrieving length, orientation and bounding box of the identified cracks. This method is aimed at assisting in obtaining automated prediction of condition state (CS) rating of cracks in bridges. It can be also used as a tool for post-earthquake damage evaluation purposes.

Effects of polymeric matrix on accelerated UV weathering properties of wood-plastic composites

Abstract The purpose of this work is to compare the weathering properties of different types of wood-plastic composites (WPCs) based on high-density polyethylene (HDPE), recycled high-density polyethylene (rHDPE-I and rHDPE-II), low-density polyethylene (LDPE), polypropylene (PP), recycled polypropylene (rPP), polystyrene (PS), and recycled polystyrene (rPS). The modulus of rupture (MOR) and modulus of elasticity (MOE) of all WPCs decreased with increasing exposure time of weathering. Of these, the rHDPE-II-based composite exhibited the highest MOR and MOE retention ratios after 2000 h of accelerated ultraviolet (UV) weathering, while the PS-based WPC had the lowest values. In addition, the carbonyl index difference (CID) of various WPCs increased significantly as a function of exposure time. Among them, the PS-based WPCs exhibited the most severe degradation due to photo-oxidation on the surface, while the degradation of PE-based WPCs was the mildest. These results are consistent with the change in the surface cracking and flexural properties of the composites. The PS-based WPCs also exhibited higher moisture diffusion coefficients. The mechanical behavior of WPCs after weathering is influenced by a combination of factors, such as surface oxidation, morphology changes, and moisture absorption.

Dumbbell Test Method for Evaluation of the Early Age Cracking Property of Concrete Material by Stress Risers

This article develops one new test technology, dumbbell test method, for evaluation of the early age cracking property of Concrete Material under constraint conditions. Its exercise of stress risers could lead concrete to crack quickly, providing a quick method to evaluate the early age crack performance of concrete material and to perform simulated test at job site conveniently. By this method, the anti-cracking performance of different concrete material can be evaluated quickly in the construction site.

Nonconventional Vacuum Residue Upgrading Blended with Coal Tar by Solvent Deasphalting and Fluid Catalytic Cracking

To optimize the ratio of vacuum residua/coal tar (VR/CT) in VR solvent deasphalting processing and catalytic cracking processing, their compatibility and properties are investigated in the present work. The investigation reveals two competitive processes of dissolution and adsorption during the blend process. At low CT blending ratio, the molecule interactions in the VR colloidal system are unchanged. The dissolution is nearly balanced with flocculation, and VR is almost compatible with CT. At high CT blending ratio, the flocculation predominates over dissolution and VR is incompatible with CT. Solvent deasphalting experiments revealed that the supercritical fluid extraction and fractionation process of VR has been improved by blending with CT. Fluid catalytic cracking (FCC) results of this deasphalted oil (DAO) indicated that more light oil can be produced with no obvious increase in the diesel/gasoline ratio. The VR can be upgraded by blending with an appropriate amount of CT (<20%) in the solvent deasphalting–fluid catalytic cracking processes.