Self-healing Techniques Research Articles

Biomimetic three-dimensional microchannel non-destructive self-healing flexible strain sensor based on liquid metal-polydimethylsiloxane elastomer

Flexible strain sensors (FSS) have garnered widespread attention due to their immense potential in wearable electronics, motion health monitoring, artificial electronic skin, and soft robotics. However, FSSs are susceptible to mechanical damage such as wear, cracks or breaks during long-term use, which diminish their reliability and service life. Inspired by the self-healing dual-phase structure of human skin and vascular networks, this study proposes a biomimetic three-dimensional microchannel non-destructive self-healing flexible strain sensor (B-TMN-SHFSS) based on the liquid metal-polydimethylsiloxane (LM-PDMS) elastomer. The B-TMN-SHFSS employs a layered design, layer-by-layer fabrication, and interlayer self-healing techniques to construct the microchannel within the self-healing PDMS elastomer (SPE), with the liquid metal (LM) being injected into the microchannel using a negative pressure injection method. Based on the modified protective layer design of the biomimetic three-dimensional microchannel, the high self-healing efficiency of the SPE and the fluidity of the LM, the B-TMN-SHFSS is able to restore the initial sensing performance after self-healing, while maintaining the integrity of the 3D microchannels with an electrical healing efficiency (EHE) of 100 %. Additionally, the B-TMN-SHFSS features high sensitivity (GFmax = 3.464) and a wide measurement range (0 to 216.68 %), making it suitable for human motion detection.

Innovative Strategies for Enhanced Concrete Durability: A Comparative Analysis of Autogenous and Autonomous Self-healing Mechanisms

AbstractThis study explores incorporating self-healing mechanisms into concrete to address cracks compromising structural integrity. Two self-healing techniques, autogenous and autonomous, are compared. Specimens with excessive cement were created to investigate the impact of cement content on autogenous healing. The autonomous technique used Bacillus subtilis bacteria with a constant concentration, using two insertion methods: direct and immobilization. Crumb rubber was used to immobilize bacteria, assessing its effect in preserving them over long periods. Calcium lactate was used as a source of calcium in some of the autonomous mixtures. Healing techniques were evaluated using compression tests, chloride permeability, visible crack inspection, and microscopic investigation. The test results showed a reduction of 32% in compressive strength at 7 days when using calcium lactate with bacteria. However, after 28 days, the strength was enhanced by about 15% compared to the control mix. Despite the strength reduction, the crack healing ability exceeded the control mix in 7- and 28-day cracked specimens. The best results were achieved using bacteria immobilized in rubber without calcium lactate by healing 2mm cracks with a 71% compressive strength increase and 89% strength recovery. The immobilization method outperformed the direct method in preserving bacteria, as confirmed by scanning electron microscope images revealing bacterial presence after 100 days, accompanied by a substantially reduced chloride permeability to very low levels. For the autogenous mixture, adding excess cement enhanced the crack healing efficiency by 67%, healing a 0.5mm crack width. SEM results showed calcite precipitation in both autogenous and autonomous mixtures. However, autonomous mixtures exhibited denser and sharper crystal morphology, confirmed by energy dispersive spectrometer results since the bacterial concrete achieved a calcium weight of 36.52% compared to its control mixture of 8.69%.

Shear strength recovery of sand with self-healing polymeric capsules

Self-healing approaches are increasingly being explored in various fields as a potential method to recover damaged material properties. By self-recovering without external intervention, self-healing techniques emerge as a potential solution to arrest or prevent the development of large strains problems in soils (e.g., landslides) and other ground effects that influence the serviceability of structures (e.g., differential settlement). In this study, a microcapsule-based self-healing sand was developed, and its performance during mixing and compaction, shearing, and recovery of shear strength was demonstrated. The cargo used for sand improvement, a hardening oil, tung oil, was encapsulated in calcium alginate capsules by the ionic gelation method. The surface properties, internal structure, thermal stability and molecular structure of the capsules were evaluated by advanced material characterization techniques. The survivability of capsules during mixing and compaction was assessed by measuring the content of tung oil released into the sand, while their influence on sand shear strength and its recovery was assessed with shear box tests. The results showed that the capsules could rupture due to movement of the sand particles, releasing the tung oil cargo, leading to its hardening and minimizing its strain-softening response and enhancing up to 76% of the sand shear strength (at a normal stress of 10 kPa and capsules content of 4%). This study demonstrates the potential of a capsules-based self-healing system to provide ‘smart’ autonomous soil strength recovery and thus with potential to actively control the large strain behavior of soils.

Coupling Behavior of Autogenous and Autonomous Self-Healing Techniques for Durable Concrete

Coupling Behavior of Autogenous and Autonomous Self-Healing Techniques for Durable Concrete

Water-Triggered Self-Healing of Ti3C2Tx MXene Standalone Electrodes: Systematic Examination of Factors Affecting the Healing Process.

MXenes, with their remarkable attributes, stand at the forefront of diverse applications. However, the challenge remains in sustaining their performance, especially concerning Ti3C2Tx MXene electrodes. Current self-healing techniques, although promising, often rely heavily on adjacent organic materials. This study illuminates a pioneering water-initiated self-healing mechanism tailored specifically for standalone MXene electrodes. Here, both water and select organic solvents seamlessly mend impaired regions. Comprehensive evaluations around solvent types, thermal conditions, and substrate nuances underline water's unmatched healing efficacy, attributed to its innate ability to forge enduring hydrogen bonds with MXenes. Optimal healing environments range from ambient conditions to a modest 50°C. Notably, on substrates rich in hydroxyl groups, the healing efficiency remains consistently high. The proposed healing mechanism encompasses hydrogen bonding formation, capillary action-induced expansion of interlayer spacing, solvent lubrication, Gibbs free energy minimizing MXene nanosheet rearrangement, and solvent evaporation-triggered MXene layer recombination. MXenes' resilience is further showcased by their electrical revival from profound damages, culminating in the crafting of Joule-heated circuits and heaters.

Effect of self-healing behavior and self-healing technologies on the structural characteristics of cracked RC/ECC composite beams

The improving potential of self-healing behavior and self-healing technology to degradation of structural characteristics of cracked reinforced concrete structures was explored at the member level. Reinforced concrete/engineered cementitious composite (RC/ECC) composite beams were prepared by three self-healing technologies, including crystalline additives (CA), two types of superabsorbent polymers (SAP), and beam without self-healing technology was used as reference specimens. The self-healing properties of structural characteristics of beams were studied by four-point bending tests, including bear capacity, stiffness, ductility index, energy absorption capacity (EAC), and failure mode. The self-healing behavior of damage was evaluated by ultrasonic wave test and damage identification test based on natural frequency. Self-healing behavior of four types of RC/ECC composite beams improved the structural characteristics after cracking to varying degrees. The stiffness of CB-0, CB-S, CB-C, and CB-SH after self-healing increased by 10.80%, 22.88%, 36.71%, and 28.80% compared to that without self-healing, respectively. Recovery ability of structural characteristics of RC/ECC composite beam is enhanced by self-healing technologies. Moreover, CA exhibits a superior improvement in the recovery ability of the structural characteristics compared with two types of SAP. Moreover, the natural frequency and ultrasonic velocity of pre-cracked beams after self-healing were higher than those without self-healing, especially when self-healing technologies were applied. There is a positive correlation between the recovery ability of ultrasonic velocity and self-healing behavior of the structural characteristics of RC/ECC composite beams. This also explains why the structural characteristics of pre-cracked beams have been improved to varying degrees due to different self-healing techniques.

Preparation and properties of dynamic crosslinked styrene butadiene rubber

Abstract As the second largest synthetic rubber after styrene butadiene rubber, cis-butadiene rubber (BR) is one of the important raw materials for automobile tires and cold-resistant products. Herein, a traditional rubber preparation process was used to introduce dynamic reversible bonds into BR based on an “imitative” click reaction. Compared with traditional complex self-healing techniques, this method is undoubtedly simpler and more efficient. Dynamic reversible bonds are able to break and recombine under the stimulation of external conditions, which endow rubber with self-healing properties. We use the small biological molecule lipoic acid (LA) as a cross-linking agent and cross-link LA and BR through mechanical compounding and hot press vulcanization to obtain self-healing butadiene rubber (BLA). In addition, BLA-(Zn2+) was further prepared by introducing Zn2+ to form metal-oxygen coordination bonds with carboxyl groups. And systematically studied the effect of Zn2+ on the mechanical properties and self-healing properties of cross-linked BR. Through the combined action of disulfide bonds, hydrogen bonds and Zn2+-O coordination bonds, BLA-(Zn2+) has better properties than BLA, the tensile strength can reach 3.76 MPa, and the repair efficiency is about 82 %. This simple preparation process is certainly more cost effective.

Efficient approaches to autogenous and autonomous self-healing concrete: a review

Concrete and cementitious composites have far been the main and most widely used construction materials throughout the world due to their outstanding features, such as high structural properties, accessibility and relatively low production costs. However, these materials are prone to degradation caused either by automatic cracking or external excitations, which leads to structural degradation. The increasing concern for maintaining safety and enhancing durability of cement composite structures has led to the development of several smart self-healing techniques by researchers. Regarding the diversity of these methods, this study aims to provide a comprehensive review of state-of-the-art technologies in self-healing concrete. For this purpose, the methods are divided into two general categories: autogenous and autonomous self-healing, each of which are subdivided into different methods. The basic principles and influencing factors as well as the main advantages and challenges of these techniques are discussed. Finally, general conclusions are drawn and some suggestions for future advances are presented.

Exploring the potential of bacterial concrete: An analysis of self-healing capabilities and compressive strength

Cracks in concrete structures can result in rapid degradation and strength loss due to ingression of chemical substances. Regular maintenance or repair of concrete-based structures can be costly. This circumstance motivates scientists to explore the development of self-healing concrete. This cement-based composite has the ability to repair itself after experiencing degradation, preventing the entry of water and chemicals, and thereby providing strength and durability and making self-healing concrete an attractive solution to save those maintenance costs. Microbial self-healing techniques, also called bacterial concrete offer a long-lasting, fast, and ecologically friendly approach to repairing cracks in concrete materials. The potential sustainability of using bacterial concrete demands more experimental investigations. In this research paper, the focus is on B. Megaterium bacteria, which were incorporated into concrete through three different methods i.e., directly incorporating the bacterial solution, using lightweight aggregates as a carrier, and utilizing exfoliated graphite nano-platelets as a carrier. The research work aimed to analyze the self-healing capabilities and compressive strength of bacterial concrete. It also provides a comparison between the effectiveness different methods of bacteria incorporation into the concrete. The bacterial self-healing technique outperforms other treatment methods due to its excellent bonding capability and affinity with concrete mixtures. The results of this study could potentially contribute to the development of more sustainable and efficient solutions for maintaining our built environment. The findings could pave the way for the wider use of bacterial concrete as a more sustainable and efficient alternative to traditional concrete in the construction industry.

A 3D Coupled Finite-Element Model for Simulating Mechanical Regain in Self-Healing Cementitious Materials

Interest in self-healing techniques that can enhance the performance of cementitious materials has been ever increasing over the past two decades. Alongside the experimental developments, a great deal of progress has been made on the development of numerical models for simulating the self-healing behavior. In spite of this, many models do not consider the coupled physical processes that govern the healing response. In addition, few are developed in a 3D setting that is necessary for many self-healing systems. This study aims to address this through the development of a new 3D coupled model for simulating self-healing cementitious materials. Key features of the model are a new embedded strong discontinuity hexahedral element that employs a damage-healing cohesive zone model to describe the mechanical behavior, a new approach for describing the dependence of the mechanical regain on healing agent transport based on a local crack filling function, and a generalized healing front model that is applicable to different healing agents. The performance of the model is demonstrated with a healing front study and experimental tests on self-healing cementitious specimens. The examples consider a vascular self-healing cementitious specimen that uses a sodium silicate solution as the healing agent and the autogenous healing of a cementitious specimen with and without crystalline admixtures. The results of the validations show that the model is able to reproduce the experimentally observed behavior with good accuracy.

Selecting bacteria for in-depth self-healing of concrete at both room and low temperature

The large-scale application of microbial self-healing techniques of concrete faces serious challenges from low temperature in high-cold regions and oxygen availability in the cracks. In this study, we focus on the temperature sensitivity and oxygen dependence of microbial self-healing techniques of concrete and select bacteria from the cold-resistant facultative anaerobes through microbial growth, mineralization and healing tests with the most frequently used Sporosarcina pasteurii as control group. The results show the cold-resistant bacteria, Brevibacterium frigoritolerans A779 and A793 have the capability of growing at low temperature compared with S. pasteurii fwzy14. S. pasteurii fwzy14 has the best capability of inducing calcite precipitation at room temperature but its precipitation rate decreases dramatically at low temperature; B. frigoritolerans A779 has the approximate capability with S. pasteurii fwzy14 at low temperature with urea and calcium nitrate as calcium carbonate precursor, which makes it a potential candidate for the in-depth self-healing of concrete in a broad temperature range. Consistent with the results of bacterial growth and mineralization tests, bacterial healing tests show that cold-resistant B. frigoritolerans A779 can not only heal the outer part of the cracks but also heal the inner part better than S. pasteurii fwzy14 at low temperature. Therefore, a plan containing both S. pasteurii fwzy14 and B. frigoritolerans A779 is proposed for in-depth self-healing of concrete at both room and low temperature.

A comparative study of strength and durability characteristics of concrete and mortar admixture by bacterial calcite precipitation: A review

Frequently used concrete is the second most used material after water worldwide, but it is vulnerable to cracks, leading to decreased durability and service life. Self-healing techniques, including natural processes, polymers, carbonated steel slag, S.C.M.s, biological/chemical, bacteria direct/liquid, and immobilization/encapsulation, have been studied. The most recent technique is Microbially Induced Calcium Carbonate Precipitation (MICCP), which uses ureolytic bacteria of the bacillus family to heal or fill cavities, fissures, and cracks by precipitating CaCO3. Researchers aim to enhance self-healing efficiency in mortar and concrete by non-pathogenic bacteria, such as B. Megaterium, Subtilis, Aerius, Sphericus, Cereus, Pseudoforms, Shewanella, and Sporosarcina pasteurii. Previous studies found that 105 cells/ml was the most effective concentration for concrete, while mortar specimens interacted better with bacteria at various cell concentrations. Bacterial concrete at 105 cells/ml exhibited improved microstructure interaction and densification due to the formation of “C.S.H.” gel and a depletion in C.H. bond with confined pore space. Consolidated bacteria produced a copious volume of minerals that could fill the cracks in the concrete, as observed in SEM and EDS studies. XRD analysis confirmed the increase in calcite composition at the bacteria's concentration level of 105 cells/ml in cement concrete specimens. Bacterial concrete at this concentration level has the potential for sustained and strong concrete properties.

A case of 32 Years old female patient with chronic anal fissures healed successfully by Yoga Prana Vidya healing protocols

Introduction: Anal fissures accompanied by pain and discomfort, are common occurrence in 1 out of 5 people. There are several remedial treatment modalities available. This paper presents a case study of a 32-year-old female patient with chronic anal fissures healed successfully using Yoga Prana Vidya (YPV) Protocols which are non-drug and non-invasive modalities, as she had developed the fissures after the delivery of her child and could not find relief with any other modality. Method: This paper uses case study method by going through patient medical records, healer’s records and patient feedback. Results: After 4 days of YPV healings given by the healer, the pain and symptoms had reduced substantially. Further use of consistent healings given by the healer and self-healing of the patient produced sustained results with negligible recurrence of this condition. Eventually YPV distal treatment delivered a cure and resettled the patient with normal life. The psychological and emotional issues the patient had were counselled and treated by YPV techniques simultaneously. Conclusions: Consistent use of Yoga Prana Vidya (YPV) healing protocols have treated the condition of anal fissures successfully without any medicine and without any surgery. YPV integrated therapies are very versatile and holistic in nature whereby a patient is healed psychologically also besides physically through self-healing techniques, in addition to receiving healing sessions from an external healer. Frontline health workers will be benefitted by learning YPV healing protocols to apply complementarily in their respective work areas to treat patients. Further research with appropriate methodology and sample size is recommended.

Bio-Concrete and Beyond: Advancements in Self-Healing Techniques for Durable Infrastructure

Concrete is widely used in construction due to its durability and strength. However, structures made of concrete may weaken over time due to a variety of reasons, such as cracks, chemical attack, and environmental factors. This necessitates the development of new techniques to improve the lifespan and sustainability of concrete structures. Bio-concrete and self-healing techniques have emerged as viable approaches to address the challenges of concrete degradation. This literature review aims to provide a comprehensive overview of the advancements made in bio-concrete and self-healing technologies for concrete. The review begins by discussing the fundamental principles of bio-concrete, which is defined as the incorporation of bacteria or other microorganisms into the concrete matrix. These bacteria are capable of producing calcite precipitation, thereby sealing cracks and enhancing the concrete’s self-healing properties. Moreover, the review explores the mechanical and chemical characterization techniques used to assess the performance of bio-concrete as a self-healing concrete. It analyzes the results of various experimental studies and field applications that offer insights into the performance and effectiveness of these technologies under diverse environmental conditions. Overall, this literature review aims to consolidate the current knowledge and advancements in bio-concrete and self-healing technologies. The findings from this review can serve as a valuable resource for researchers, engineers, and practitioners involved in the design, construction, and maintenance of concrete infrastructure. This contribution ultimately promotes the development of more sustainable and durable concrete materials.

Self-healing concrete techniques and performance, A review

Modern society faces the duality of rapidly expanding structure, making concrete one of the world's most traded materials. However, cement manufacturing can pollute the environment by releasing approximately one tonne of CO2 for every tonne of cement produced. Concrete cracks can provide superior access for aggressive substances such as chlorides and sulfates, resulting in structural deterioration. So, to fix concrete cracks, different traditional methods were used, which use cement and some chemical agents that are hazardous to the environment. Because of the environmental issues and sustainability challenges associated with cement and concrete, it is preferable to reduce the amount of cement used by developing promising and unique solutions to enable quick crack healing in concrete and extend the structure's lifetime. Therefore, incorporating self-healing mechanisms into construction materials has been proposed to improve their performance and durability while reducing the need for maintenance and repair. This review assesses the performance and causes of autogenous and autonomous self-healing techniques. The autogenous technique occurs naturally due to inherent material properties, while the autonomous technique uses various healing agents, such as chemical or biological substances. Both techniques rely on forming calcium carbonate (CaCO3) crystals as the principal agent for concrete healing. Previous findings showed that the autogenous technique has limited efficacy in repairing larger cracks with a width exceeding 0.3mm. In contrast, autonomous techniques have shown successful repai of cracks exceeding 2mm in width. The application of an autonomous methodology in the field of concrete has resulted in significant results, such as effectively repairing large cracks, enhancing structural integrity, and substantially decreasing permeability levels from high to exceedingly low levels

A Comprehensive Review of Self-Healing Polymer, Metal, and Ceramic Matrix Composites and Their Modeling Aspects for Aerospace Applications.

Composites can be divided into three groups based on their matrix materials, namely polymer, metal and ceramic. Composite materials fail due to micro cracks. Repairing is complex and almost impossible if cracks appear on the surface and interior, which minimizes reliability and material life. In order to save the material from failure and prolong its lifetime without compromising mechanical properties, self-healing is one of the emerging and best techniques. The studies to address the advantages and challenges of self-healing properties of different matrix materials are very limited; however, this review addresses all three different groups of composites. Self-healing composites are fabricated to heal cracks, prevent any obstructed failure, and improve the lifetime of structures. They can self-diagnose their structure after being affected by external forces and repair damages and cracks to a certain degree. This review aims to provide information on the recent developments and prospects of self-healing composites and their applications in various fields such as aerospace, automobiles etc. Fabrication and characterization techniques as well as intrinsic and extrinsic self-healing techniques are discussed based on the latest achievements, including microcapsule embedment, fibers embedment, and vascular networks self-healing.

Effects of Capsule Type on the Characteristics of Cement Mortars Containing Powder Compacted Capsules.

Several studies have been reported on self-healing concrete using bacteria, admixtures, and microcapsules. Among these self-healing techniques, encapsulating cement-based materials is advantageous in that large amounts of self-healing material can be contained in a capsule and released at the cracked site for a targeted reaction. This study produced a powder compacted capsule (PCC) using the droplet and blended manufacturing methods to encapsulate cementitious materials. This study refers to the PCCs as droplet-PCC (D-PCC) and blended-PCC (B-PCC) according to the manufacturing method used. The fluidity, compressive strength, carbonation, drying shrinkage, and water permeability of cement mortar with PCCs were evaluated. The test results show that the flow of the mortar sample using D-PCC was slightly higher than that of the mortar using B-PCC. The compressive strength of the mortar sample with B-PCC was generally higher than that of the mortar sample with D-PCC. The compressive strength of the B-PCC2 sample (with 0.2% of B-PCC) was the highest at all curing ages. This may be because the B-PCC fracture load was higher than that of the D-PCC. In addition, more hydrates were observed in the B-PCC sample than in the D-PCC sample. A crack healing effect was observed in the samples with PCC, regardless of the PCC type. The effect was the greatest in the B-PCC6 sample (with 0.6% of B-PCC). The results of this study provide a reference for the PCC type and mix ratio that would yield the best mechanical properties and crack healing effect.

New Self-Repairing System for Brittle Matrix Composites Using Corrosion-Induced Intelligent Fiber.

Brittle matrix composites such as concrete are susceptible to damage in the form of cracks. Most of the current self-repair and self-healing techniques have repair limits on crack widths or high costs of an external stimulator, or have an unfavorable effect on the composite’s strength. This paper proposes a new concept of corrosion-induced intelligent fiber (CIF) and a new self-repairing system that uses the CIFs to close cracks in brittle matrix composites within a corrosive environment without external help, and without compromising the strength. The CIF comprises an inner core fiber and an outer corrodible coating that are in equilibrium, with the core fiber in tension and the corrodible coating in compression. The preparation steps and shape recovery mechanism of the CIF and the self-repair mechanism of the CIF composites are explained. Based on these concepts, this paper also describes several mechanical models built to predict the magnitude of pre-stress stored in the core fiber, and the maximum pre-stress released to the matrix composites, and the minimum length of the reliable anchor ends of CIF. The sample calculation results show that the recovery strain was 0.5% for the CIF with the steel core fiber and 12.7% for the CIF with the nylon core fiber; the maximum crack closing force provided by the CIF to concrete can be increased by increasing the amount of the CIFs in concrete and the initial tensile stress of the core fiber. This paper provides some suggestions for enhancing the self-repair capability of brittle composites in complex working environments.

Effects of independently designed and prepared self-healing granules on self-healing efficiency for cement cracks

Cement-based materials are prone to cracks, especially in marine environments where aggressive ions accelerate structural damage through cracks. Thus, self-healing techniques are essential to increase the service life of concrete structures. In this study, three types of self-healing granules were designed and prepared, and their characteristics were analyzed. The self-healing efficiency under different conditions was evaluated, and the self-healing mechanism was elucidated. The results indicated that self-healing granules had acceptable waterproofness and were compatible with cement mortar. Additionally, self-healing granules ruptured through their cracks and showed acceptable dispersion. Repair products were produced at cracks after curing. The cracks below 300 μm were effectively sealed. The area repair rate reached a range of 70 %–90 %, and the relative permeability coefficient decreased to a range of 0.2–0.4 in the presence of self-healing granules. High carbonate source contents in the self-healing granules afforded better self-healing efficiencies. The self-healing efficiency was not significantly different for 7 and 56 d cracks, indicating long-term effectiveness. When cured in seawater, the self-healing rate and efficiency was improved, especially within 3 d. The repair products mainly consist of calcium carbonate and hydrated calcium silicate, as well as magnesium hydroxide in seawater.

The Improvement of Durability of Reinforced Concretes for Sustainable Structures: A Review on Different Approaches.

The topic of sustainability of reinforced concrete structures is strictly related with their durability in aggressive environments. In particular, at equal environmental impact, the higher the durability of construction materials, the higher the sustainability. The present review deals with the possible strategies aimed at producing sustainable and durable reinforced concrete structures in different environments. It focuses on the design methodologies as well as the use of unconventional corrosion-resistant reinforcements, alternative binders to Portland cement, and innovative or traditional solutions for reinforced concrete protection and prevention against rebars corrosion such as corrosion inhibitors, coatings, self-healing techniques, and waterproofing aggregates. Analysis of the scientific literature highlights that there is no preferential way for the production of “green” concrete but that the sustainability of the building materials can only be achieved by implementing simultaneous multiple strategies aimed at reducing environmental impact and improving both durability and performances.