Self-healing Agent Research Articles

Strength retrieval and microstructural characterization of Bacillus subtilis and Bacillus megaterium incorporated plain and reinforced concrete

This study aims to develop a self-healing concrete by using Bacillus subtilis and Bacillus megaterium as self-healing agents and subsequently extend the application to structural elements. Bacillus subtilis and Bacillus megaterium were directly incorporated in concrete at 0.5%, 1.0%, and 1.5% by weight of cement. Compression test, flexural strength test, and split tensile test were performed to analyse the strength properties of self-healing concrete. The self-healing efficiency of plain concrete was determined in terms of regain in compressive strength by testing standard pre-cracked concrete cube specimens, while as for reinforced concrete beams, self-healing efficiency was determined by means of repeated four-point load test (4PLT) and non-destructive testing (NDT). In addition to regain in compressive strength of plain concrete specimens, a significant recovery in flexural strength and crack depth was observed in both the Bacillus subtilis incorporated reinforced concrete (BSRC) beam and Bacillus subtilis incorporated reinforced concrete (BMRC) beams after 56-days of curing. The effect of Bacillus subtilis and Bacillus megaterium on water absorption capacity of concrete was studied and a significant reduction in water absorption capacity was observed. Microstructural analysis in the form of X-Ray Diffraction and Field Emission-Scanning Electron Microscopy analysis was also conducted on concrete samples. The microstructural analysis confirms the calcite precipitation by bacteria in cracks which attributes to the strength retrieval of cracked concrete specimens.

An alkali-responsive mineral self-healing agent with mechanical property enhancement for cementitious composites

Self-healing cementitious materials are regarded as an effective choice to increase the sustainability of the resource and environment. In this study, an alkali-responsive mineral self-healing agent (AMS) was prepared inspired by bone repair. The healing component, phosphate, was loaded into the halloysite nanotubes (HNTs) and encapsulated by the layer-by-layer (LbL) self-assembly method. The structure and alkali-responsive behavior of AMS, the effect of AMS on the mechanical properties of cement pastes, the stability of AMS before cement cracking, and its effect on the self-healing efficiency of the cement pastes were investigated with a range of analytical techniques. Results showed that AMS was successfully encapsulated and endowed with excellent alkali responsiveness. The incorporation of AMS was effective in reinforcing the mechanical performances of cement pastes. XRD analysis showed that the phosphate encapsulated in AMS can be mostly retained until cracks appear. When cracks occurred, the B-type carbonated calcium-deficient hydroxyapatite was found as the main product in the crack environment. The surface crack around 130 μm in the damaged specimens containing 5% AMS was fully sealed and healed, and its damaged compressive strength was almost completely recovered after curing for 28 days. The synergistic effect of autonomous healing triggered by AMS and autogenous healing behavior promotes the self-healing process and improves the self-healing efficiency of the hardened cement pastes.

Multilayered LDH/Microcapsule Smart Epoxy Coating for Corrosion Protection.

A multilayered smart epoxy coating for corrosion prevention of carbon steel was developed and characterized. Toward this direction, as a first step, zinc-aluminum nitrate-layered double hydroxide (Zn/Al LDH) was synthesized using the hydrothermal crystallization technique and then loaded with dodecylamine (DOD), which was used as an inhibitor (pH-sensitive). Similarly, the synthesis of the urea-formaldehyde microcapsules (UFMCs) has been carried out using the in-situ polymerization method, and then the microcapsules (LAUFCs) were encapsulated with linalyl acetate (LA) as a self-healing agent. Finally, the loaded Zn/Al LDH (3 wt %) and modified LAUFCs (5 wt %) were reinforced into an epoxy matrix to develop a double-layer coating (DL-EP). For an exact comparison, pre-layer epoxy coatings comprising 3 wt % of the loaded Zn/Al LDH (referred to as LDH-EP), top-layer epoxy coatings comprising 5 wt % linalyl acetate urea-formaldehyde microcapsules (referred to as UFMLA COAT), and a blank epoxy coating (reference coating) were also developed. The developed epoxy coatings were characterized using various techniques such as XRD, XPS, BET, TGA, FTIR, EIS, etc. Electrochemical tests performed on the synthesized coatings indicate that the DL-EP demonstrates improved self-healing properties compared to LDH-EP and UFMLA COAT.

Solvent effect of microcapsules endows self-lubricating polymer composites with wear in-situ self-healing function

The integration of solvent-based self-healing mechanism into self-lubricating materials becomes a novel and effective method to improve the friction and wear behaviors of motion pairs, which promises to enhance the stability, reliability and durability of machinery equipment during service. Herein, a self-lubricating polymer composite incorporated with the microcapsules including different self-healing agents was designed and prepared in this work. These microcapsules were synthesized by the in-situ polymerization to package different polarity solvents, and then were dispersively embedded into a polyester resin containing the solid lubricating material of polytetrafluoroethylene (PTFE). Multiple characterization methods such as UMT-5 tribometer and 3-D white light interference surface profiler were adopted to investigate the healing property and mechanism of materials. The composite presented a comprehensively exceptional performance of wear reduction, damage repair and low friction by combining the swelling effect of solvent with the lubricating action of transfer film. In comparison with the pure polyester resin, the scratch self-healing efficiency at the composite surface was higher than 69 % by volume in an hour at 50 °C. Meanwhile, the bifunctional composite exhibited a visibly lower coefficient of friction (0.069) and excellent wear resistance (1.19 × 10−7 mm3/(N m)), which is highly expected for engineering applications.

Structural integrity and healing efficiency study of micro-capsule based composite materials via 1H NMR relaxometry

In this work we present a novel approach utilizing nuclear magnetic resonance (NMR) relaxometry to assess the structural stability of microcapsules employed as self-healing agents in advanced aerospace composites both in ambient and harsh environmental conditions. We successfully correlate the amount of the encapsulated self-healing agent with the signal intensity and confirm non-destructively the quantity of the encapsulated self-healing agent mass for the first time in the literature using 1H NMR spin–spin relaxation techniques on urea–formaldehyde (UF) microcapsules of different diameters containing an epoxy healing agent. The amount of self-healing agent is shown to increase by reducing the capsule diameter; however, the reduced shell mass renders the capsules more fragile and prone to failure. Most notably, via NMR experiments conducted during thermal cycling simulating flight conditions, we demonstrate that the microcapsule integrity under thermal fatigue varies according to their size. Especially we experimentally verify that the microcapsules with the most sensitive shells are the 147 nm and 133 nm diameter microcapsules, which are the most commonly used in self-healing systems. Finally, we were able to retrieve the same results using a portable NMR spectrometer developed in-house for in situ microcapsule testing, thus demonstrating the potential of NMR relaxometry as a powerful non-destructive evaluation tool for the microcapsule production line.

Oxidation resistance, ablation resistance and in situ ceramization mechanism of Al-coated carbon fiber/boron phenolic resin ceramizable composites modified with Ti3SiC2

Inherent defect of easy oxidation limited further application of carbon fiber/phenolic resin composites in hostile environments. Herein, a combined strategy of matrix modification and fiber coating was proposed to fabricate a novel ceramizable composite containing Al-coated carbon fibers and Ti3SiC2 toward thermal protection materials (TPM), which offered a promising solution to challenge facing long-term thermal protection and load-bearing subject to severe oxidation corrosion and ablation in hypersonic vehicle applications. Oxidation resistance, mechanical strength evolution, phase evolution, microstructure evolution and mechanical strength failure mechanism at elevated temperatures were studied based on thermogravimetric analysis, static ablation test, mechanical test, X-ray diffraction analysis, and scanning electron microscopy coupled with energy dispersive X-ray analysis. The resulting composites exhibited outstanding oxidation resistance, with residue yield at 1600 °C and flexural strength at 1400 °C as high as 87.7% and 31.7 MPa, respectively. It was found that dense multiphase ceramics formed by reactions between Ti3SiC2, O2, pyrolytic carbon (PyC) and N2, acted as oxygen barriers and self-healing agents during static ablation. Besides, the resulting composites exhibited satisfactory ablation resistance and the linear ablation rate was as low as 0.00853 mm/s. Furthermore, ablation mechanisms were revealed based on phase identification, microstructure characterization and thermodynamic calculation analysis. It was revealed that multiphase ceramics composed of PyC, Al coatings, Ti3SiC2, TiC, Al2OC and AlB2 contributed great to the ablation resistance during oxyacetylene ablation.

ADDITION OF BACTERIOLOGICAL ADDITIVES IN THE PRODUCTION OF SELFHEALING CONCRETE

Self-repairing concrete is a product in which microorganisms will be used to produce limestone to fill cracks appearing on the surface of concrete structures. It is presented by the author that specially selected types of bacteria of the genus Bacillus, a calcium-based nutrient known as calcium lactate, and nitrogen and phosphorus are added to the ingredients of concrete when it is mixed. These self-healing agents can remain dormant within concrete for up to 200 years. Self-repairing materials are a special type of materials that regenerate their strength properties after minor damage caused to the material during its service life. Self-repair technology is particularly useful in the case of composite materials because composites have low damage detection capability and are susceptible to sudden and brittle failure. Modern man-made materials have excellent mechanical properties. However, they lack the ability to self-repair. Therefore, in the event of damage, there is the possibility of loss of mechanical strength and, over time, a gradual loss of functional strength in the absence of human intervention.Different bacterial species along with abiotic factors such as salinity, ambient pH value, temperature, nutrient availability and habitat composition play a significant role in the calcium carbonate precipitation process in a wide range of different environments. There are four key factors that determine the MICP process: (I) calcium concentration, (II) dissolved inorganic carbon concentration, (III) pH value and (IV) presence of nucleation centres.

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.

Investigation of particle size effect on the performance of micro/nano capsules and composite coatings

In this paper, a series of micro/nano capsules encapsulating linseed oil (self-healing agent) with different particle sizes (500 nm, 1.0 µm, 5.0 µm and 10.0 µm) were prepared by emulsion template method combined with photopolymerization and solvent volatilization. The sizes of micro/nano capsules were facilely and efficiently tuned by adjusting emulsifying method, emulsification time and emulsifier concentration. And the effects of the capsule size on the morphology, loading property, dispersibility and solvent resistance of capsule were investigated. The results showed that the larger capsules exhibited higher yield, loading rate and loading efficiency. In addition, the solvent resistance increased gradually with the increase of capsule size. The composite coating was prepared by dispersing the micro/nano capsules in coating matrix. The effect of the capsule sizes on the coating properties was systematically investigated. The nanocapsules were easily aggregated owing to its nano-size effect and thus showed a relatively poorer dispersibility in coating matrix. Whereas better dispersibility was observed for the larger capsules, and the coating with larger capsules showed better self-healing performance and corrosion resistance.

Enhancing self-healing efficiency of concrete using multifunctional granules and PVA fibers

Self-healing concrete can prolong the lifespan of structures by sealing cracks. This study assessed the self-healing efficiency of combined multifunctional self-healing granules (SHGs) and PVA fibers under different curing conditions in self-healing concrete. Microstructure analysis of self-healing specimens and products was conducted to reveal the self-healing mechanism. Compared to using SHGs or PVA fibers alone, the synergistic effect of SHGs and PVA fibers improved the compressive strength recovery rate, permeability coefficient recovery, and surface crack closure effect. PVA fiber inhibited crack propagation and provided attachment points for self-healing product deposition, while SHGs released self-healing agents and produced hydrated calcium silicate, calcium carbonate, and magnesium hydroxide to repair cracks. The addition of SHGs also increased the utilization of carbon dioxide and ions in seawater, thereby decarbonizing the environment and reducing the erosive effect of seawater ions.

Aerobic non-ureolytic bacteria-based self-healing cementitious composites: a novel approach without added calcium precursor

Self-healing concrete has been widely researched to reduce the cost of repairing and maintaining concrete infrastructure. Microbially induced calcite precipitation (MICP) is a promising solution that uses bacteria to produce calcite within cracks and seal them, preventing further deterioration. However, protecting the self-healing agents, including calcium precursors, bacteria, and growth nutrients, from the concrete matrix can be challenging, and encapsulation methods can lead to strength loss, slowed cement hydration, and complicated manufacturing. Therefore, in this study, to reduce the need for protective shells and their negative impact, we investigated the role of aerobic non-ureolytic bacteria in the healing process and determine the feasibility of inducing calcite precipitation without extra added calcium precursor in the concrete matrix. This study investigated the self-healing efficiency of this novel bacteria-based self-healing cementitious composites (BBSHCC) via crack observation, permeability test and compositions’ analysis. Samples at different curing ages were prepared as well to clearly indicate the impact of minerals of cementitious composites on the microbial activities. The novel BBSHCC samples, consisting solely of bacteria and nutrients, demonstrated exceptional self-healing ratios in terms of crack closure and water tightness regain. These ratios exceeded 95% and 80%, respectively, after 28 days of healing, irrespective of the curing ages. This demonstrates the high potential of using calcium minerals naturally present in the cement matrix as a calcium source for aerobic non-ureolytic bacteria Bacillus cohnii to activate biomineralization and achieve healing. Notably, with increasing curing age of the novel BBSHCC, the rate of crack closure decreased, which was likely due to decreased accessibility of calcium for biomineralization. Additionally, healing products generated by biomineralization tended to initially form locally around cementitious composites, especially in mature samples. Further analysis of the cementitious composites near the healed crack revealed a large presence of portlandite, which was suggested to be a result of biomineralization.

Optimization of spore production and activation conditions of concrete crack healing bacteria and research on crack repair effect

Currently, research on the spore production rate and spore activation rate of microorganisms is mostly used in the pharmaceutical and food industries, with little research on their application in repairing concrete cracks. The spore production ability of mineralized microorganisms and the spore activation ability in the concrete environment are key influencing factors in ensuring the repair effect of concrete cracks. The effects of various factors on the spore production rate and spore activation rate of Bacillus alcalophilus (Bacillus cohnii) were studied using a single factor controlled variable method in this paper, and the optimal spore production culture conditions and activation conditions were determined. Furthermore, the mineralization reaction after microbial spore activation and the repair effect of concrete cracks were investigated. The results showed that under optimal spore production culture conditions, the spore production rate reached 93.9 %. The spore activation rate of microorganisms was as high as 94.5 % under optimal spore activation conditions. The rate of microbial spore activation was 78.6 % at room temperature (20 ℃) without heat shock treatment. Calcite calcium carbonate produced by the mineralization reaction after microbial spore activation could be used to repair subsequent concrete cracks. The optimal concentration of calcium acetate required for microbially induced carbonate deposition was 100 g/L. The concrete crack with a width of 1.12 mm could be repaired after 28 days of repair age, and the concrete strength recovery rate was 70.81 % when the microbial self-healing agent prepared by Bacillus alkalophilus (Bacillus cohnii) was incorporated into concrete.

Fabrication and characterizations of glass fiber-reinforced functional leaf spring composites with or without microcapsule-based dicyclopentadiene as self-healing agent for automobile industrial applications: comparative analysis

This study described a critical review of the biological system of self-curing agents and catalysts in which damage triggers an automatic healing response. In the first phase, a glass fiber-reinforced composite (GFRC) mono-leaf spring was prepared, which is made of glass fiber with a cement-based metal matrix. GFRC was further embedded with a microcapsule-based self-healing agent dicyclopentadiene (DCPD) that prevents sudden breakdown/failure of automobile suspension components resulting in micro-cracks produced in the material due to constant load application. In this paper, GFRC mono leaf spring samples were prepared with and without a healing agent under three different categories of varying thicknesses 20, 30, and 40 mm. In the second phase, the load-carrying capacity of all the samples was investigated and found a continuous increase in load-carrying capacity. Percentage increase in load carrying capacity before the time break was 1.09%, 1.42%, and 1.08% followed by time break of 05 min was 24.24%, 17.67%, and 21.67% respectively. It was clearly identified from the results that the addition of microcapsule-based healing substituents increases the load-carrying capacity of GFRC mono-leaf spring and avoids sudden fracture.

Toward Self-Healing Concrete Infrastructure: Review of Experiments and Simulations across Scales.

Cement and concrete are vital materials used to construct durable habitats and infrastructure that withstand natural and human-caused disasters. Still, concrete cracking imposes enormous repair costs on societies, and excessive cement consumption for repairs contributes to climate change. Therefore, the need for more durable cementitious materials, such as those with self-healing capabilities, has become more urgent. In this review, we present the functioning mechanisms of five different strategies for implementing self-healing capability into cement based materials: (1) autogenous self-healing from ordinary portland cement and supplementary cementitious materials and geopolymers in which defects and cracks are repaired through intrinsic carbonation and crystallization; (2) autonomous self-healing by (a) biomineralization wherein bacteria within the cement produce carbonates, silicates, or phosphates to heal damage, (b) polymer-cement composites in which autonomous self-healing occurs both within the polymer and at the polymer-cement interface, and (c) fibers that inhibit crack propagation, thus allowing autogenous healing mechanisms to be more effective. In all cases, we discuss the self-healing agent and synthesize the state of knowledge on the self-healing mechanism(s). In this review article, the state of computational modeling across nano- to macroscales developed based on experimental data is presented for each self-healing approach. We conclude the review by noting that, although autogenous reactions help repair small cracks, the most fruitful opportunities lay within design strategies for additional components that can migrate into cracks and initiate chemistries that retard crack propagation and generate repair of the cement matrix.

On crack healing in fiber-reinforced cementitious composites incorporating mineral-based healing agent and superabsorbent polymer: Evaluation using modified permeability test method

In this study, the crack healing properties of fiber-reinforced engineered cementitious composites (ECCs) under incremental strains, various fiber contents, and incorporation of a mineral-based self-healing agent (SHA) and a superabsorbent polymer (SAP) were evaluated. A permeability test setup applicable to plain mortar samples was modified to evaluate the fiber-reinforced ECC samples under several strains and crack widths. Supplementary self-healing tests—resonant frequency (RF) recovery, stiffness recovery, and crack image inspection—were also conducted. Changes in the permeability, RF, stiffness, and crack images were monitored for 28 days after sample cracking, to evaluate self-healing. The findings showed that the permeability reduction of the ECCs was significantly influenced by the fiber content instead of by the addition of the SHA and the SAP. In addition, the SAP particles were observed to improve the self-healing properties of the ECC samples.

Carriers of Healing Agents in Biological Self-Healing Concrete

Concrete is the most widely used material in civil engineering, but due to its inherent brittleness, the generation of cracks easily occurs. Crack healing is an effective method for restoring the mechanical properties of concrete and improving its durability. Of all the current concrete crack healing methods, microbial-induced calcium carbonate precipitation technology is an incredibly promising crack self-healing strategy that has received widespread attention in the field of concrete crack repair. As the biological self-healing agent has difficulty resisting the high alkali and high calcium environment in concrete, protection is required when it is used in concrete cracks.

High linoleic waste sunflower oil: A distinctive recycled source of self-healing agent for smart metal coatings

High Linoleic Waste Sunflower Oil (HLWSO) is a new self-healing agent viable to be encapsulated. Meanwhile, the unique mechanism behind the synthesis of microcapsules is deeply illustrated; the emulsification process of HLWSO by anionic surfactant and microencapsulation of HLWSO. In addition, the application of microencapsulated HLWSO in the coating matrix by the layering method is presented followed by a detailed explanation of the self-healing mechanism of a smart coating incorporating the polymerization mechanism of HLWSO developed by the diene structure. Microencapsulation of high linoleic waste sunflower oil (HLWSO) is a wall formation process in which urea-formaldehyde (UF) is attached with emulsified HLWSO to form a microcapsule. In this study, the HLWSO from recycled cooking oil is uniquely bonded with a diene structure, thus possessing the ability to dry fast and be encapsulated via the in-situ polymerization method. The microencapsulated HLWSO was characterized using Field Emission Scanning Electron Microscopy (FESEM) and Fourier Transformation Infra-Red Spectroscopy (FTIR). The optimum microcapsules synthesized from HLWSO resulted in a smooth shell structure with 2.88 μm diameter microcapsules at 0.31 μm shell thickness and 66% core content. It was demonstrated that increased stirring speed decreases the size, shell thickness, and core content of the microcapsules. The FTIR results indicated that HLWSO as a core, while urea-formaldehyde acted as a shell of microcapsules. The scratch on the coating matrix embedded with HLWSO was healed after five days. The corrosion rate of optimum sample was 0.0574 mm/year, with an optimum reduction of 58% from the reference sample. This study revealed that the HLWSO from recycled sources is a viable self-healing agent to be microencapsulated. The smart coating embedded with HLWSO also displayed self-healing performance, reduced corrosion rate and beneficial for the advancement of corrosion control technology.

Prolonged creep lifetime of ferritic self-healing steels achieved by offline healing treatment

For the ferritic self-healing (FSH) steel, it remains challenging to solve the low healing efficiency problem, due to the mismatch between the formation kinetics of creep cavities and the precipitation kinetics of healing agents. In this research, an offline healing treatment has been proposed to stimulate the formation of the Laves phase precipitates as self-healing agents to retard creep cavity growth at elevated temperatures. The corresponding treatment parameters were determined by the precipitation behaviors of Laves phases on the external free surfaces and internal cavity surfaces of FSH steels. Results have shown that the creep lifetime of the offline healing treated samples can be extended more than 30% compared to that of non-healed sample, while the creep rates can be reduced by one order of magnitude. The formation kinetics of Laves phases and creep cavities have been quantitatively analyzed. It was found that after the offline healing treatments, the average cavity sizes of the samples decreased significantly, while the growth rates of creep cavities rather than the nucleation kinetics are compensated by the healing phenomena of Laves phase formation. The relationship between the extended lifetime and filling ratios of creep cavities by the healing agents was established as well. The demonstrated potential of offline healing treatments provides a new strategy to cultivate the self-healing capabilities of heat resistant steels.

Self-healing soil mix cut-off wall materials incorporating reactive magnesium oxide pellets

Recent decades have witnessed the increasing use of soil mixing technology to construct cut-off walls for groundwater control or underground pollutant containment. The strength and permeability of soil mix columns deteriorate considerably when subjected to chemical, mechanical and environmental stresses, leading to the need for repair of crack-originated damage. The development of self-healing grouts could provide more resilient and sustainable soil mix cut-off walls. In this study, for the first time, self-healing soil mix columns incorporating reactive magnesium oxide pellets were developed. The magnesium oxide-based cementitious grout was mixed with a sand soil using a laboratory-scale auger, and the embedded magnesium oxide pellets were ruptured upon cracking, producing expansive healing products due to hydration and carbonation, which can significantly fill the crack volume. The effects of magnesium oxide on the grout and soil mix samples were investigated in terms of both fresh and hardened properties. In addition, the self-healing performance was evaluated by examining permeability recovery and crack closure, and the microstructure and morphology of the magnesium oxide pellets and healing products were analysed. The results demonstrate the great potential of reactive magnesium oxide pellets as a self-healing agent for soil mix cut-off wall materials.

Poly(methyl methacrylate) as Healing Agent for Carbon Fibre Reinforced Epoxy Composites.

Self-healing materials offer a potential solution to the problem of damage to fibre-reinforced plastics (FRPs) by allowing for the in-service repair of composite materials at a lower cost, in less time, and with improved mechanical properties compared to traditional repair methods. This study investigates for the first time the use of poly(methyl methacrylate) (PMMA) as a self-healing agent in FRPs and evaluates its effectiveness both when blended with the matrix and when applied as a coating to carbon fibres. The self-healing properties of the material are evaluated using double cantilever beam (DCB) tests for up to three healing cycles. The blending strategy does not impart a healing capacity to the FRP due to its discrete and confined morphology; meanwhile, coating the fibres with the PMMA results in healing efficiencies of up to 53% in terms of fracture toughness recovery. This efficiency remains constant, with a slight decrease over three subsequent healing cycles. It has been demonstrated that spray coating is a simple and scalable method of incorporating a thermoplastic agent into an FRP. This study also compares the healing efficiency of specimens with and without a transesterification catalyst and finds that the catalyst does not increase the healing efficiency, but it does improve the interlaminar properties of the material.