Crack Healing Process Research Articles

Analysis of the Current State of Research on Bio-Healing Concrete (Bioconcrete).

The relatively small tensile strength of concrete makes this material particularly vulnerable to cracking. However, the reality is that it is not always possible and practically useful to conduct studies on high-quality sealing cracks due to their inaccessibility or small opening width. Despite the fact that currently there are many technologies for creating self-healing cement composites, one of the most popular is the technology for creating a biologically active self-healing mechanism for concrete. It is based on the process of carbonate ion production by cellular respiration or urease enzymes by bacteria, which results in the precipitation of calcium carbonate in concrete. This technology is environmentally friendly and promising from a scientific and practical point of view. This research focuses on the technology of creating autonomous self-healing concrete using a biological crack-healing mechanism. The research methodology consisted of four main stages, including an analysis of the already conducted global studies, ecological and economic analysis, the prospects and advantages of further studies, as well as a discussion and the conclusions. A total of 257 works from about 10 global databases were analyzed. An overview of the physical, mechanical and operational properties of bioconcrete and their changes is presented, depending on the type of active bacteria and the method of their introduction into the concrete mixture. An analysis of the influence of the automatic addition of various types of bacteria on various properties of self-healing bioconcrete is carried out, and an assessment of the influence of the method of adding bacteria to concrete on the process of crack healing is also given. A comparative analysis of various techniques for creating self-healing bioconcrete was performed from the point of view of technical progress, scientific potential, the methods of application of this technology, and their resulting advantages, considered as the factor impacting on strength and life cycle. The main conditions for a quantitative assessment of the sustainability and the possibility of the industrial implementation of the technology of self-healing bioconcrete are identified and presented. Various techniques aimed at improving the recovery process of such materials are considered. An assessment of the influence of the strength of cement mortar after adding bacteria to it is also given. Images obtained using electron microscopy methods are analyzed in relation to the life cycle of bacteria in mineral deposits of microbiological origin. Current gaps and future research prospects are discussed.

Crack-healing and rheological properties of high content fly ash/slag/silica fume green and sustainable cement-based materials incorporating crystalline admixture and calcium alginate biomass hydrogel

Cracking is an important factor affecting the durability of concrete. Rheological properties are important performance indicators of the workability of fresh concrete. Ion chelator (CA) is one kind of crystalline admixture, which can enhance crack-healing of concrete by promoting the formation of calcium carbonate in wet environment. Calcium alginate hydrogel (CaAlg) can maintain the humidity of cementitious matrix and promote the crystallization of inorganic minerals. Therefore, in this study, CaAlg bead was prepared to further improve the crack-healing of cementitious materials containing CA. Self-healing performance was evaluated by visual crack closure and water permeability test. Rheological property was measured by rotor rheometer. Healing mechanism of cementitious materials with CA and CaAlg was analyzed. Results showed that with the increase of CaAlg dosage, yield stress and plastic viscosity of paste decreased gradually. Meanwhile, fly ash and slag reduced viscosity of pastes, while silica fume increased the viscosity of pastes. CA could evidently improve the permeability and mechanical properties of mortar, especially for slag mortar. Self-healing performance test and characterization showed that CaAlg could further enhance crack-healing process of mortar with CA, especially for pure cement and slag mortar. Microscopic testing indicates that CaAlg could induce the formation of vaterite and calcite on its surface to further improve crack-healing efficiency.

Near-in-situ investigation of surface crack healing and strengthening mechanism of Ti-43.5Al-4Nb-1Mo-0.1B alloy by novel electroshock treatment

The Ti-43.5Al-4Nb-1Mo-0.1B (TNM) alloy is prone to emerge surface cracks and other defects during processing and service, which will deteriorate the mechanical properties and fatigue life of the materials. In this work, a novel electroshock treatment (EST) for the surface crack repair and strengthening process has been proposed. Combined with near-in-situ experiments and theoretical analysis, the influence law and healing mechanism of different current densities and EST modes on the healing of surface cracks in the alloy were investigated. The scanning electron microscopy (SEM) near-in-situ observation reveals that the main factors influencing the healing of surface cracks relate to the time of energization, the current density, and the cracking angle. Meanwhile, the crack tip and locally bulging deflected positions are more likely to be healed in a short time under continuous EST mode and medium current density (75 A/mm2). The surface crack width at the calibration position decreases from 0.47 μm and 2.23 μm to 0 μm and 0.03 μm, respectively. The electron back scattered diffraction (EBSD) results show that the dislocation density increases around the surface crack healing area, and the dislocation density at the crack tip and away from the healing region is decreased and uniformly distributed after EST, which can further suppress the generation and propagation of the crack, resulting in a 20.1 % increase in tensile strength and a 40.3 % increase in fracture strain. Considering the coupling influence of the thermal and non-thermal effects of EST, a two-stage progressive atomic diffusion of thermal compressive stresses and crack bonding interfaces has been proposed to describe the evolution process of surface crack healing during EST.

The Effects of Crystalline Admixture on the Self-Healing Performance and Mechanical Properties of Mortar with Internally Added Superabsorbent Polymer.

Crystalline admixture (CA) can be incorporated into concrete to achieve self-healing of concrete cracks. In this study, both CA and superabsorbent polymer (SAP) were used as self-healing agents to investigate the effects of CA on the self-healing performance and mechanical properties of mortar with internally added SAP at different self-healing ages. The healing effect of cracks in mortar is assessed by crack observation and impermeability. The structure and composition of the filler in the cracks were analyzed by microscopic experiment. The experimental results indicate that CA enhances the healing of cracks in mortar specimens. The chemical reactions of CA primarily contribute to significantly improving the early-age crack-healing ability of the specimens, and the water absorption and expansion ability as well as the internal curing effect of SAP also facilitate the crack-healing process. Increasing the CA content leads to an increase in the Ca/Si ratio of C-S-H, causing a transition from a layered structure to a more compact needle-like structure. When 4% CA was added to the mortar, it resulted in an adequate formation of needle-like C-S-H structures, which eventually penetrate and fill the pits formed by SAP, compensating for the strength loss caused by SAP.

Enhancing the Viscoelastic Properties of Asphalt Concrete by Crack Healing Process

Enhancing the Viscoelastic Properties of Asphalt Concrete by Crack Healing Process

Long-term viable SF immobilized bacterial cells as sustainable solution for crack healing in concrete

Utilization of microbially induced calcium carbonate precipitation (MICCP) via biomineralization process has been considered a novel method in self healing of concrete structures. To develop MICCP as ready product for field scale construction, mineral based inoculum of higher shelf life is required. The present study focuses on this aspect of field based application of MICCP. In this study, mineral admixture (silica fume (SF), cement kiln dust (CKD) and rice husk ash (RHA)) based bacterial inoculum were developed to immobilize bacteria for self healing capabilities in concrete. The prepared inoculum was stored at varying temperature (4 °C and 25 °C) and the survival of bacterial cells in carrier based materials were tested on weekly basis until 180 days of storage at both temperature. After 180 days of storage, the most efficient bacterial inoculum based upon viability studies was incorporated in concrete and tested for crack healing performance. For this, crack of approximately 0.5 mm width was generated during the casting and healed using a bacteria-based healing agent (nutrient broth, urea and CaCl2). The healed cracked surface was examined through optical imaging to monitor the crack width reduction. Along with this, Electromechanical Impedance (EMI) technique was used to monitor the crack healing potential until the full healing of cracked surface was achieved. Statistical EMI indicators such as root mean square deviation (RMSD), mean absolute percentage deviation (MAPD) and correlation coefficient deviation (CCD) were employed to quantify crack healing process. RMSD was found to be promising parameter to monitor the crack healing process and reflected an increasing trend from 1 % to 14 % in healed bacterial specimen. At the end of test, the healed specimens were subjected to bending failure to assess the strength regain. Significant regain was noticed in healed bacterial specimen (approximately 33 %) in comparison to the control. The healing mineral precipitated inside the cracks was examined through field emission scanning electron microscopy(FESEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) to evaluate its physicochemical attributes. The results give clear proof that the SF-based carrier material can be effectively used in healing the cracks and the crack healing process can be efficiently monitored by the EMI technique. Results further indicated that RMSD values were very effective in quantifying the progressive crack healing achieved due to MICCP precipitation.

Plasma-electrified repair of damaged polymer composites for surface crack healing and insulation recovery

Polymer composites, widely used in aerospace and electrical power systems, are inevitably aged by environmental stress causing cracks on the material’s surface, which weakens their mechanical and electrical properties. Addressing the issue requires significant effort and the use of hazardous chemicals. In this study, a novel plasma-electrified repair method based on the Ar/H2O/alkoxysilane (PMDMS) low temperature plasma is developed for the surface crack healing and insulation recovery of silicone rubber (SIR) composites. It is demonstrated that the plasma-enabled polymerization effectively repairs the cracked SIR, with a new fin-like insulating layer deposited on the crack surface. The mechanical and electrical properties of the cracked SIR are improved after the plasma repair, with the result clearly better than using the conventional coating method. Hydrolysis-condensation of PMDMS by plasma-enabled dissociation and re-assembly, surface activation of the crack by plasma modification and grafting-crosslinking in the crack account for the multiphase chemical reactions induced within the crack. Further analysis based on quantum chemistry calculations reveals that the plasma treatment both promotes the chemical reactivity of the SIR surface and reconstructs a dense repair phase in the crack with a wide forbidden gap and shallow taps, further confirming this effective crack healing process which improves the mechanical and electrical performances of the damaged SIR. Overall, this newly-developed plasma-electrified repair method for damaged SIR eliminates the environmental pollution caused by large scale and overused chemical coatings, and offers new possibilities for sustainable and low-carbon-emission material engineering for processing and restoration of composite materials.

Crack evolution during the film drying process of fuel cell microporous layer ink

Study on the film crack formation process of microporous layer (MPL) in fuel cells is necessary as the size of cracks substantially affects fuel cell durability. In-situ characterization of crack evolution in the full MPL ink drying process is essential to understand the crack formation mechanism. In this work, quasi in-situ crack evolution in the full MPL ink drying process under different stages is comprehensively investigated using ESEM, PLM, and regular SEM. A crack formation with subsequent crack healing mechanisms is discovered. Physiochemical characterizations indicated that the crack formation process is related to the evaporation of isopropanol, whereas the crack healing process is related to the subsequent evaporation of water. Experiments on solvent composition further indicate that the final crack size depends on the ink dispersion during the drying process. Furthermore, the optimal 1/2 IPA/water weight ratio formulation is proposed for the resulting MPL with fewer cracks.

Study on Mechanical Properties of crack Healing of low carbon Steel based on cyclic Phase Transformation Heat treatment

With the rapid development of materials, metal materials are used less and less, but at this stage, metal materials are still widely used, and iron and steel materials are the most widely used. Cracks often appear in the process of metal material processing and use, and these cracks will have a certain impact on the use of metal materials. The existence of microcracks will affect the mechanical properties of materials to some extent, but in most cases, the mechanical properties of materials will be greatly reduced, and in serious cases, metal materials will break directly in the process of use or processing. The crack healing process needed after the emergence of cracks can effectively change this situation, but so far, the research on metal crack healing is still not perfect. In this paper, taking the internal crack of low carbon steel as the object, the recovery of mechanical properties of low carbon steel by cyclic phase transformation heat treatment was studied. The results show that with the increase of the healing area, the microhardness of the area after crack healing also increases, and the tensile strength of the specimen also increases after the healing. When the healing area is similar, increasing the healing time and temperature will result in grain coarsening, resulting in the decrease of microhardness and tensile strength in the crack healing zone.

Microcrack healing in zirconia ceramics under a DC electric field/current

Flash event caused by a DC electric field/current was applied to the crack healing in 8 mol % Y2O3 stabilized cubic ZrO2 polycrystals (8Y-CSZ). The flash event, which occurred by applying the DC power higher than a critical value of 100 mW/mm3, successfully healed the microcrack within several minutes without any healing agents at a furnace temperature of 800 °C. As compared to the healing treatment under static annealing, the healing phenomena were accelerated about 2 times under the flash treatment even at the same temperatures, suggesting that the enhanced healing phenomena cannot be explained only by the temperature effect. Since the rate of grain growth was accelerated under the flash treatment, the flash healing would be accelerated through the current-enhanced diffusional processes. This study shows for the first time that the flash event has a potential to apply to the crack healing process in the ceramic materials and composites.

Formation mechanism of bubbles in the crack healing process of fused silica using a CO2 laser.

The machining-induced cracks and other defects on the surface of fused silica would incur damage when irradiated by intense lasers, which greatly shortens the service life of the fused silica optical components. The high absorption coefficient of fused silica for far-infrared lasers makes it possible to use low-energy CO2 lasers to melt and heal micro defects on the surface, and hence improve its damage threshold under the service conditions of extremely intense laser. However, the air in the cracks may evolve into bubbles during the laser healing process, but the law of crack morphology evolution and the bubble formation mechanism have not been clearly revealed. In this work, a simulation model of the healing process of fused silica surface cracks under the effect of low-energy CO2 laser is established. Three bubble formation mechanisms (i.e., the uneven fluidity caused by temperature gradient, the collapse effect caused by inclined cracks, and the internal cracks) are identified based on the simulation results of cracks with various original morphologies and characteristic structural parameters. The simulated fused silica morphology is consistent with the results of the laser healing experiment. This work can provide theoretical guidance for the optimization of optical manufacturing parameters of fused silica, as well as the CO2 laser healing and polishing strategies.

Experimentally Investigation of Nano Clay Effects on Leaching and Self-healing Process of Cracked Clayey Soils

Compacted clay layers are known as one of the common low impermeable layers used in geotechnical structures. Due to geotechnical properties, these layers damaged through cracks in their lifespan. This research has attempted to improve the workability by using self-healing features of clays. By conducting numerous experimental tests, it has been shown that, by increasing the plasticity index of clays, the pace of crack healing process will be enhanced. Experiments have shown that percentages of Montmorillonite Nano Clay (MNC) are quite effective and reduce the flow rate in the samples, which is a sign of self-healing of the cracks by an NC additive. On this basis, NC can be perfectly used to repairing cracks in clayey soils. The results of this study show that in the sample with 1 mm crack, about 500 milliliters of water pass through the crack in 60 minutes under no pressuring conditions. While, if the sample contains 2 and 5 percent NC, the amount of water passing through the cracks within 60 minutes, will be 40 and 5 ml, respectively. This dramatic reduction for passing water reflects the positive effect of Nano sized grains on the closure of the created cracks. Therefore, it can be concluded that the self-healing process occurs earlier in smaller cracks, because the NC and soil particles can easily touch each other after swelling. Five percent of MNC can insure the cracks closure at 100% density. I

Crack-Healing Investigation in Asphalt Mixture with Modified Thermoplastic-Bitumen Composite

This study aims to investigate the crack-healing of asphalt mixture by induction heating of bitumen-thermoplastic binder. This system employs a heterogeneous mixture, in which different percentages (2, 4, 6, and 8% by weigh) of thermoplastic healing agent (polyethylene (PE) and polypropylene (PP)) dissolve with the bitumen, respectively. Healing was achieved by heating the fractured asphalt composite to a specific temperature; in which heterogeneous blend has undergone random molecule diffusion and volumetric thermal expansion of healing agent within the matrix. The thermal properties in the bitumen-thermoplastic were characterized by means of dynamic mechanical thermal analysis (DMTA); in which the glass transition temperature (Tg ) has been used as a reference for the healing process. The FTIR shows no chemical reaction between bitumen and thermoplastic. Three-point bending test was conducted to demonstrate details crack-healing capability in asphalt composite. The results show that 6% of PE and PP to the mixture of bitumenthermoplastic has the highest tensile strength. The percentage of recovery was also measured through the healing cycle process using a three-point bending test. Overall, within the third healing cycle, asphalt composite with modified bitumen (with PP or PE) shows 98-55% of healing recovery. The best percentage recovery is using bitumen-PP mixture with a ratio of 94:6. The crack-healing process was also proven through the surface and cross-section asphalt morphology analyses using optical microscopy and scanning electron microscope (SEM).

Implication of Nondestructive Test NDT for Evaluation of Crack Healing in Asphalt Concret

Asphalt concrete practices heavy loading and environmental impacts through the service life of the pavement. Micro cracks usually initiate and accumulate to form various types of distresses. However, asphalt concrete has the ability of self-healing under rest period and environment conditioning. Asphalt concrete is a composite material consisting of aggregates, bitumen, and air voids. Its mechanical behavior is complex due to its dependency of temperature, loading frequency, and strain level. In this investigation, asphalt concrete specimens of wearing course have been prepared in the laboratory and subjected to repeated indirect tensile stresses to initiate the micro-cracks. The test was stopped after 1200 load repetitions, and the specimens were stored in an oven at 60°C for 120 minutes to allow the crack healing process by external heating to start. Specimens were returned to the testing chamber and were subjected to another round of load repetitions. Specimens were tested before and after load repetitions and crack healing with the aid of ultrasonic pulse velocity traversing the specimen using pundit instrument. The healing indicator was the change in pulse velocity before and after the repeated load test and before and after healing process. It was concluded that the velocity decreases as the loading cycles proceeds indicating the start of damage, while the ultrasonic pulse velocity increases after the micro-crack healing process.

Characterisation of pectin and optimization of pectinase enzyme from novel Streptomyces fumigatiscleroticus VIT-SP4 for drug delivery and concrete crack-healing applications: An eco-friendly approach

Pectinases are enzymes which are widely distributed in microbes that are present in pectin enriched sites. The agro-industrial residues can be utilized in the industrial scale for low-cost and efficient pectinase production in an eco-friendly approach. This study employs low-cost substrates (i.e. culinary fruit peels) for maximum pectinase production from novel Streptomyces fumigatiscleroticus VIT-SP4. The extraction and characterization of pectin from different fruit peels were investigated and pectinase activity was analyzed. The orange pectin gave maximum pectinase activity of about 45.93 (U/mL). Further, statistical optimization of process parameters was studied by using Taguchi method showed optimum values of pH-6, temperature −35 °C, orange pectin% − 2.5, incubation time- 48 h and RPM- 200 rpm and pectinase activity was found to be 98.65 (U/mL). The response surface methodology (RSM) was used for the optimization of media components which revealed that starch −1.17%, yeast extract-2%, and orange pectin% − 0.75% produces maximum pectinase of about 170.05 (U/mL). The drug-delivery study showed drug release was not observed at initial pH 3 after 4 h. The immediate drug release was noted at pH 6 caused due to disintegration of pectin by the pectinase activity. The self-healing of cracks by spray culture technique was investigated. The crack healing was observed up to 0.50 mm wide after 12 days. This confirms the ability of actinomycete spores to survive and they react to form calcite complex directly helps in crack healing process. This low-cost microbial pectinase can be used in drug delivery and concrete crack-healing applications sectors in future.

Properties of fly ash concrete containing tropical soil bacteria

The autonomous crack healing process using microbiologically induced calcium carbonate precipitation (MICP) is a sustainable alternative to overcome propagation of micro-cracks and restore the durability of concrete. This paper presents the potential use of tropical soil bacteria as a self-healing agent for fly ash concrete. A solution of 107 cells/mL Lysinibacillus sphaericus (L. sphaericus), was selected to be the self-healing agent by replacing partially the amount of water. Concrete cube specimens with 30% fly ash, were cured under two conditions, which are water and air curing. The potential effects of the self-healing agent was evaluated in terms of the ultrasonic pulse velocity (UPV), initial surface absorption test (ISAT) and compressive strength. The initial results show an improvement of UPV and between 12% and 54% improvement on the compressive strength for the bacterial concrete compared to the control specimen. It was probably due to the presence of the microbial calcium carbonate that fills the concrete pores through the inclusion of bacteria in the concrete. However, based on the ISAT value, the direct addition of bacterial solution increased the concrete’s permeability. Thus, further investigation is suggested to assess the self-healing effect towards permeability and compressive strength of bacterial concrete.

Facile healing of cracks in organic–inorganic halide perovskite thin films

Organic–inorganic halide perovskite (OIHP) thin films at the heart of the burgeoning thin-film perovskite solar cells (PSCs) technology possess poor mechanical properties, which is likely to limit the long-term reliability of PSCs as they are poised for commercialization. In an effort to address this issue, here we demonstrate that through-thickness cracks induced by bending-tension in thin films of the two prototypical OIHPs, methylammonium lead triiodide (MAPbI3) and formamidinium lead triiodide (FAPbI3), can be healed easily. This is through the application of either a moderate compressive stress (bending-compression) at room temperature or a simple heat-treatment at modest temperatures. The crack-healing process is found to be time-dependent, which indicates that facile mass-transport in OIHPs plays a key role in this phenomenon. An explanation for this phenomenon is provided, one based on the fundamentals of brittle fracture. This discovery has broad implications for the prevention and/or restoration of the overall performance, environmental stability, and mechanical reliability of PSCs, and other devices.

A novel crack healing technique in a low carbon steel by cyclic phase transformation heat treatment: The process and mechanism

Crack is one of the most important factors resulting in the failure of metallic material which may lead to huge engineering losses and even severe accidents. Not only in economically, but also in environmental protection, it is highly meaningful to heal cracks in metallic materials. However, the currently common healing techniques are subject to various disadvantage. Therefor we developed a novel crack healing technique by means of cyclic phase transformation heat treatment. The results show that cyclic phase heat treatment technique can heal internal crack. The process of internal crack healing can be divided into three stages, atomic diffusion or recrystallization is the mechanisms of crack healing. In the first stage of the healing process, crack healing depends on atomic diffusion and recrystallization. However, in other stages of the healing process, atomic diffusion controls the crack healing. Compared to isothermal heat treatment technique, this novel technique can avoid coarsening grains of the matrix effectively, and improve the healing efficiency and healing degree by accelerating atomic diffusion.

Durability of self-healing concrete

Application of self-healing concrete reduces the need for expensive maintenance and repair actions. However, the durability of self-healing concrete has only been scarcely investigated. Here, recent results are presented regarding the resistance of self-healing concrete to chloride ingress. For self-healing concrete with macro-encapsulated polyurethane, chloride profiles and electron probe microanalysis indicated that this mechanism was efficient to reduce the chloride penetration into the crack and from the crack into the concrete matrix [1]. Furthermore, the corrosion behaviour of reinforced concrete specimens subjected to cyclic exposure with a NaCl solution was studied [2]. The electrochemical measurements indicated that autonomous crack healing could significantly reduce the corrosion in the propagation stage. No visual damage could be detected on the rebars after 44 weeks of exposure. On the contrary, cracked specimens without integrated self-healing mechanism, reached a state of active corrosion after 10 weeks of exposure and after 26 weeks clear pitting damage was observed on the rebars. While self-healing by encapsulated polyurethane is complete after one day, bacteria-based products take several weeks to heal a 300 µm crack. Bacterial granules containing denitrifying cultures released nitrite as an intermediate metabolic product which protected the reinforcement during the crack healing process [3].

Evolution Behaviors and Mechanisms of Internal Crack Healing in Steels at Elevated Temperatures

The evolution behaviors and mechanisms of internal crack healing in three different kinds of steels, including 20 high-quality carbon structural steel, 30Cr2Ni4MoV steel, and SUS304 stainless steel, at elevated temperatures were systematically investigated. The morphology of the crack healing zone was observed using an optical microscope (OM) and a scanning electron microscope (SEM). The grain boundary character distribution evolution of the crack healing zone was investigated using electron backscatter diffraction (EBSD). The results show that the existence of two crack healing mechanisms is confirmed in all three experimental steels. Crack healing is controlled by atomic diffusion at lower temperatures 1173 K (≤ 900 °C) and depends mainly on recrystallization and grain growth mechanisms at higher temperatures 1273 K (≥ 1000 °C). Atomic diffusion provides materials for recrystallization and grain growth in the crack healing zone. Recrystallization leads to rapid crack healing, and grain growth facilitates microstructural homogenization and elimination of the crack healing zone. The process of internal crack healing can be divided into five stages.