Crack Healing Performance Research Articles

Crack-healing of cost-effective engineered cementitious composites reinforced by recycled selvage fiber

This paper presents the first experimental investigation of the crack-healing behavior of recycled selvage fiber-reinforced engineered cementitious composites (RSF-ECCs). Fly ash (FA), ground granulated blast-furnace slag (GGBS), and crumb rubber powder were utilized to fabricate greener ECCs. RSF was used as main reinforcement; it contains polyethylene (PE), glass (GS), and PET fibers. For overall mechanical properties, RSF-ECC incorporating GGBS (ECC-S-RSF) obtained a compressive strength of over 80 MPa and a tensile strain capacity of over 10%, values that are unprecedented in other recycled fiber-reinforced ECCs. Furthermore, the ECC-S-RSF showed the best cost efficiency among representative recycled and PE fiber-reinforced high-performance ECCs. In terms of the crack-healing performance, test results indicated that RSF-ECCs had excellent healing capacity in closing crack openings, and GGBS had a greater contribution to crack-healing than FA did. However, the stiffness and tensile restorations of RSF-ECCs were relatively modest compared to those of conventional ECCs. Calcium carbonate and C-S-H gel were dominant healing materials of RSF-ECCs.

Variation of microbial self-healing performance of cementitious composites with their biogranule content

Existing studies on microbial self-healing concrete often employed an arbitrary approach to the initial amount of healing agents, leading to significant performance variations. The amount of bacteria becomes a crucial parameter affecting the overall cost of the material. Therefore, assessing the effect of initial bacteria content on microbial self-healing performances is essential. This study presents the variation of self-healing performances of biomortars with initial bacteria content ranging from 0.05 % to 2.50 % (0.07 %–3.20 % biogranule) w/w cement. All biomortars outperformed the crack healing performance of abiotic control specimens. The net contribution of microbial healing (MH‾net) was determined by analysing autogenous healing and microbial healing periods separately. The variations in initial bacteria content did not significantly affect MH‾net which could reach up to 125 μm in 2-weeks of water immersion. The minimum effective bacteria dosage in the form of biogranules for developing microbial self-healing concrete was determined as 0.05 % bacteria w/w cement with an overall crack healing limit of 300 μm. Microbial healing of cracks up to 300 μm crack width led to 50–80 % higher water tightness regain compared to the autogenously healed specimens. The purity of CaCO3 minerals sealing the cracks decreased with the increasing initial bacteria content of the biomortars. Overall, the initial bacteria content did not significantly affect the microbial self-healing performance in the tested dosage range. At the minimum effective bacteria dosage, consistent self-healing of cracks up to 300 μm became possible at the expense of approximately 20 % increase in the overall cost of the material.

The crack-healing performance of asphalt mixture based on acoustic emission system

The self-healing properties of asphalt pavements reduce the need for frequent maintenance and repair of cracks and promote road sustainability. In this study, multiple healing tests were conducted under different healing conditions using the semicircular bending "crack-heal-crack" test. The beneficial effects of the healing temperatures and times were determined. However, below 60 °C, the healing index of asphalt mixture does not exceed 0.4. The peak healing indices of the 70# asphalt mixture in the fourth healing stage were 86% of the initial healing index. This correspond to the SBS# asphalt mixture parameters of 88%. Using the acoustic emission system, changes in the ring count and energy of the specimens before and after the healing were compared. The healing index of the cumulative ring count proposed in this study sufficiently correlates with that of the peak load. According to the three-dimensional time-difference positioning method, at the initial loading stage of the prehealing specimen, cracks first appeared at the top of the specimen in contact with the load, then concentrated near the prefabricated incision at the bottom, and finally expanded upward. When the specimen was loaded once again after healing, cracks mainly developed from the bottom upward.

Correction to: Development on bio-based concrete crack healing in soil exposures: isolation, identification, and characterization of potential bacteria and evaluation of crack healing performance

Correction to: Development on bio-based concrete crack healing in soil exposures: isolation, identification, and characterization of potential bacteria and evaluation of crack healing performance

Development on bio-based concrete crack healing in soil exposures: isolation, identification, and characterization of potential bacteria and evaluation of crack healing performance

Development on bio-based concrete crack healing in soil exposures: isolation, identification, and characterization of potential bacteria and evaluation of crack healing performance

Performance evaluation concept for crack healing in bacterial concrete structure using electro mechanical impedance technique with PZT patch

Beginning and development of cracks reduce the structural performance and durability, thus a novel strategy is required to prevent such kind of occurrence. The incorporation of bacteria in the concrete system is likewise a technique to prevent the growth of the cracks by the microbial induced calcite precipitation. The Electro mechanical impedance (EMI) technique is the smart sensor-based technology that is an efficacious technique to examine the health of structures, whereas the prediction of frequency band and corresponding healing damage indicator for real-life application is the governing factor. The examination of crack healing performance in bacterial concrete by EMI technique with PZT sensors was not reported by previous studies to date. This research is motivated by the quality evaluation of crack healing in bacterial reinforced concrete beam specimens using the EMI technique with surface-bonded PZT patch and embedded concrete vibration sensor (CVS), respectively. For the fabrication of bacterial reinforced concrete beam specimen, the Gram-positive Bacillus subtilis bacteria have been used. To induce the structural damage, the three point loading was applied to the prepared reinforced concrete beam specimen. The optimal frequency band was determined which resulted in the structural condition for that the four statistical indices were investigated with various crack severities in several sub-frequency bands. The optimal frequency band was determined as 161–215 kHz. Further, the crack healing performance was investigated with a pre-evaluated optimal frequency band using the statistical damage indices. The damage indicators RMSD, MAPD, and CC were appropriate for the evaluation of damage severity; however Cov was appropriate for damage severity evaluation in lesser amounts in a sub-frequency band. The evaluated damage indicators RMSD, MAPD, Cov, and CC successfully signified the crack healing by the bacterial incorporation in concrete structures. The SEM and XRD tests were performed for the confirmation of calcite deposition at the cracks. The developed concept is resulted in significantly evaluating the healing quality of the cracks by bacterial incorporation over time.

The effect of oxygen and water on the provision of crack closure in bacteria-based self-healing cementitious composites

This study determined the impact of oxygen and water on the crack healing performance of bacteria-based self-healing cementitious composites (BBSHCCs). Oxygen and water are considered essential to BBSHCCs using non-ureolytic bacteria, but in practice, the availability of either, for even short periods of time, cannot be guaranteed in the immediate aftermath of a crack forming. In this study, four healing regimes, (i) daily wet-dry cycle, (ii) weekly wet-dry cycle, (iii) semi-submerged and (iv) a deposition medium, were utilised to compare the impact of oxygen and water on the performance of BBSHCCs. Furthermore, an oxygen-releasing coating (ORC) containing calcium peroxide was evaluated and used in this study to further understand the function of oxygen in bacteria-based self-healing. Results showed that bacteria-based self-healing was only effective in wet conditions that also permit oxygen to penetrate the crack. Where there was a possibility for the composite to dry, after cracking, despite being wet some of the time the self-healing was far less efficient. It was observed that an overdose of nutrients and calcium in the healing environment resulted in early rapid healing, followed at a later stage by the dissolution of the initially formed precipitates. Moreover, it was found that the ORC contributed significantly to the recovery of both crack width and water tightness of samples. These findings will aid the development of appropriate test standards for self-healing cementitious composites and for the design and implementation of such cementitious composites in practice.

Study on crack healing performance of Al2O3/SiCw/TiSi2 new ceramic tool material

In consideration of the crack sensitivity in ceramics, a new alumina-based ceramic material with excellent crack healing ability was successfully fabricated by adding SiC whiskers and TiSi2 particles. Different sizes of cracks were prefabricated on the surface of the material with the diamond indenter, and corresponding crack healing behavior was studied by high temperature oxidation experiments in a muffle furnace under air. The influences of healing temperature, healing time, and crack size on the surface morphology and flexural strength of the material were investigated in detail. When the crack width was 0.68 μm, the appropriate temperature and duration time for crack healing and full-strength recovery were 800 °C for 60 min or 1000 °C for 30 min, respectively. The maximum crack size capable for self-healing of the ceramic material was 2c = 250–300 μm and w = 0.68 μm, and the corresponding healing condition was of 800 °C/60 min. The crack healing of Al2O3/SiCw/TiSi2 ceramics was primarily driven by the high temperature oxidation reactions of Ti5Si3 and SiCw. Ti5Si3 was a new phase formed during sintering, and its formation could be described by thermodynamically feasible reactions. The new crack healing mechanism was revealed deeply, including both the local crack bridging generated by the in-situ development of TiO2 and the liquid phase filling of SiO2 intermediate oxides (Si2O3 and SiO). This research conclusion has great significance for the repairing and remanufacturing of ceramic materials with crack defects.

Development of a functionally graded bacteria capsule for self-healing concrete

This paper reported the development of a novel functionally graded reactive magnesia cement-based bacteria spores (RMC-B) capsule for self-healing concrete. The capsule had a gradient structure with a dense shell and a porous and low alkaline core to better protect and to enhance the viability of the bacteria spores. With the addition of the capsule, the strength of the matrix can be maintained while engaging self-healing of cracks. Results showed that the inclusion of the RMC-B capsules did not negatively impact the hydration and the fresh properties of the PC paste and enhanced the 28-day compressive strength of the hardened PC paste by 18%. Specimens with the RMC-B capsules exhibited strong crack healing performance as evidenced by the closure of cracks of few hundred microns and reduction of transport properties due to the dense formation of layered rhombohedral calcite along the entire crack from the surface to the interior.

Graphene/nickel/carbon fiber composite conductive asphalt: Optimization, electrical properties and heating performance

The preparation of composite conductive asphalt with excellent electrical properties and thermal performance is an important way to enhance the ability of conductive asphalt mixture to melt ice and snow. Nine groups of graphene/nickel/carbon fiber composite conductive asphalt were prepared based on the orthogonal test scheme, and Gr-Ni-CF-1 with Gr, Ni and CF contents of 5.9 %, 19.1 % and 0.4 % respectively was optimized based on electrical resistivity and heating rate. The effects of the electrode material, current type, voltage, temperature and lateral pressure on its electrical properties were researched, and its thermal properties were tested, including the thermal conductivity, heat distribution, ice melting performance and crack healing performance. Scanning electron microscopy (SEM) was used to observe the distribution of Gr, Ni and CF in the sample, which was helpful to speculate its conductive mechanism. The results show that the average heating rate of Gr-Ni-CF-1 at 12 V is about 2.76 ℃/min, and its maximum increase in temperature within 9 min is about 64 ℃ at 16 V. The volt ampere characteristics of Gr-Ni-CF-1 show a nonlinear relationship, and the average electrical current value and standard deviation of Gr-Ni-CF-1 samples at 20 V DC are 0.319 A and 0.087 A, respectively, 74.7 % and 83.3 % lower than that at 20 V AC. There are simultaneous PTC effects and NTC effects and the PTCα and NTCα are 0.072 kΩ/℃ and 0.106 kΩ/℃, respectively. The electrical resistance of Gr-Ni-CF-1 decreases with the increase of lateral pressure, and it tends to be stable when the lateral pressure is above 80 N. When electric energy is applied, the heat in the sample is evenly distributed in layers, and 2 g ice can be melted in 16 min. The 2 cm× cm×2 cm Gr-Ni-CF-1 sample formed at least seven conductive paths through conductive material contact or electronic transition.

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.

A Study on the Healing Performance of Solid Capsules for Crack Self-Healing of Cementitious Composites

The purpose of this study is to investigate the healing performance of solid capsules made of cement as a basis for manufacturing self-healing capsules that can heal cracks in cementitious composites. The solid capsules were mixed with 5%, 10%, and 15% concentrations on the cement. The self-healing performance of cementitious composites with solid capsules was investigated through three evaluations. First, the mechanical strength-healing performance was evaluated through a re-loading test. Second, the durability-healing performance was evaluated through a permeability test. Finally, the crack-healing performance was examined by observing the crack widths. Through evaluation of the healing performance of the solid capsules, the healing performance of the compressive strength was found to be high when the capsule proportion was 10% and its size was within the range of 300 μm to 850 μm. Furthermore, the splitting tensile strength showed a high healing performance when the capsule proportion mixed was 15% and its size was 850 μm. In the case of the permeability test, a capsule size of 850 μm showed a healing effect greater than 95%. Cracks with a width of up to 200 μm tended to heal using capsules with a size of 600 μm to 850 μm.

Evaluation of the crack-healing performance and durability of bacteria integrated alkali-activated fly ash composites

This study aims to introduce Bacillus Cohnii endospores into an alkali-activated fly ash-based composite (AAFC) to improve the crack-healing properties and durability while maintaining an environment-friendly strategy. Few important parameters such as water absorption capacity, sulfate resistivity, rapid chloride ions penetration, and its migration through bacteria impregnated AAFC (Bio-AAFC) are considered for the assessment of the healed structure's activities. The cracks up to 0.59 mm width dimension are completely plugged up and 12% of mechanical strength of healed-AAFC is regained within 28 days, determined in the microscopic study, strength gains calculation, and velocity of ultrasonic pulse waves assessment. Bio-mineral precipitation into Bio-AAFC produces durable concrete, particularly in chloride and sulfate-laden environments. Due to calcium/sodium carbonate precipitation in pores and voids, the microstructure of the biosystem became compact and dense, resulting in excellent performances. It is the microbial activity for the biomineralization process that causes mainly calcium carbonate deposition to reduce pore size (35% average 510 nm pore diameter) in Bio-AAFC samples, thereby verifying the bacterial endospores can persist for a long time inside AAFC. Specifically, Bio-AAFC, having magnificent durability and crack-healing abilities explores the recycling of industrial dry wastes in a promising way.

An Experimental Study on the Strength and Crack Healing Performance of E. coli Bacteria‐Induced Microbial Concrete

The most commonly used building material in the construction industry is concrete. However, the weak features of concrete are its low ductility and limited tension capacity and hence crack development with the increase in load. These cracks get more worsened by the intrusion of water and salt present in the composition and hence causing deterioration and reducing the longevity of the material. This study focuses on an innovative approach to mitigate concrete’s fractures and flaws by utilizing microbiologically induced calcite (CaCO3) precipitation (MICP) excited by Escherichia coli (E. coli) bacteria to improve the performance of cementitious building materials. The study investigated the development of microbiological concrete in plain water using only one culture density (OD600 0.5 ± 0.1). In this study, two water‐to‐bacterial mix ratios (75 : 25 and 50 : 50) were used and compared to the conventional concrete (100 : 0). 100‐mm cube‐sized specimens cured for a period of 7, 28, 90, and 365 days were tested for compressive strength, water absorption capacity, ultrasonic pulse velocity (UPV), and SEM analysis, which were performed on the samples at regular intervals. According to the results of these experiments, microbial concrete with the 50 : 50 ratio exhibited the highest strength for all curing times. From the water absorption test of samples, it is found that the absorption of the materials got reduced due to the infusion of microorganisms in concrete. On the other hand, the UPV test showed high velocity than the control samples for specimens with an OD600 0.5 ± 0.1. Scanning electron microscope (SEM) analysis performed on distinct concrete groups at the age of 28 days showed fewer voids in the concrete lumps due to the increase in water substitution rate caused by microbial culture.

Self-healing cementitious materials containing encapsulated epoxy-montmorillonite-calcium nitrate: evaluating crack-healing performance, mechanical and thermal properties

Propagating micro-cracks in a structure decrease its load bearing capacity and would lead to collapse the entire structure. By the aim of enhancing the microencapsulated self-healing cementitious materials performance, montmorillonite (MMT) is used as a component of ternary healing agent. Microcapsules were synthesized by in-situ polymerization of urea-formaldehyde as shell around the core materials inclusive epoxy resin, calcium nitrate and montmorillonite. Physicochemical characterization of microcapsules was conducted by Fourier transformation infrared spectroscopy, field emission scanning electron microscopy, particles size analyzer, atomic force microscopy, and thermal gravimetric analysis. The mechanical assessment of cementitious specimens with different dosages of microcapsules (0%, 1%, 3%, and 6%) was performed by three-point bending, and compressive tests. The addition of MMT (0.5 wt.% by epoxy) led to enhance thermal stability up to 472 °C, and showed a significant performance at flexural and compressive recovery rates up to 170.21%, and 152.02%, respectively.

Crack healing performance of bacteria-based mortar under sustained tensile loading in marine environment

Healing performance of bacteria-based mortar was evaluated under sustained axial tensile loading at 90% of the cracking load in submerged freshwater, submerged marine and tidal conditions. The bacteria-based mortar contained Halobacillus Halophilus bacteria, calcium lactate and expanded perlite aggregates. Loaded bacterial specimens showed 20%–30% less healing compared to unloaded ones. Crack widening due to creep under sustained loading decreased healing. Healing increased by 5% in bacterial specimens under tidal conditions when the loading level was reduced from 90% to 60%. Compared to control specimens, bacterial specimens enhanced healing by 14% under sustained loading in submerged marine conditions. However, bacteria had no noticeable impact on healing for specimens under sustained load in tidal conditions. Specimens in tidal conditions displayed 14%–25% less healing compared to those under submerged marine conditions. The reduced healing in tidal conditions was the result of deterioration of healing products under wet-dry cycles.

Parthenocissus-inspired, strongly adhesive, efficiently self-healing polymers for energetic adhesive applications

Strong interaction force improves the mechanical properties of energetic composites, and plentiful dynamic H-bonds endue excellent crack-healing performance.

Effect of Clinker Binder and Aggregates on Autogenous Healing in Post-Crack Flexural Behavior of Concrete Members.

Crack healing has been studied extensively to protect reinforced concrete structures from the ingress of harmful ions. Research examining the regain in the mechanical properties of self-healing composites has focused mostly on the computation of the healing ratio based on the measurement of the tensile and compressive strengths but with poor regard for the flexural performance. However, the regain in the flexural performance should also be investigated for design purposes. The present study performs flexural testing on reinforced concrete members using crushed clinker binder and aggregates as well as crystalline admixtures as healing agents. Healing ratios of 100% for crack widths smaller than 200 μm and 85% to 90% for crack widths of 250 μm were observed according to the admixing of clinker binder and aggregates. Water flow test showed that the members replacing binder by 100% of clinker achieved the best crack healing performance. The crack healing property of concrete improved to some extent the rebar yield load, the members’ ultimate load and energy absorption capacity and ductility index. The crack distribution density from the observed crack patterns confirmed the crack healing effect provided by clinker powder. The fine grain size of clinker made it possible to replace fine aggregates and longer healing time increased the crack healing effect.

Bacteria-based self-healing concrete: evaluation of full scale demonstrator projects

Bacteria-based self-healing concrete is an innovative concrete that contains a self-healing agent that provides the material with enhanced autonomous crack-sealing performance. A specific type of this concrete, based on a healing agent composed of bacterial spores and lactate as carbon source, has been developed and applied by the Delft University of Technology for over ten years. Under laboratory conditions it was proven that, depending on the dosage of healing agent, self-healing of cracks up to 0.8 mm widths occurs. As such the material potentially allows reduction of steel reinforcement used for crack width limitation in watertight constructions. Application of self-healing concrete would therefore not only result in a reduction of costs but also in improvement of environmental performance (lower CO2 footprint) and ease of in situ casting due to reduction of use of steel in waterproof applications. However, according to the EN 1990 Eurocode (Basis of structural design), customary application of a novel type of concrete must be preceded by full scale demonstrators proving evidence for safe and functional performance. In this contribution we portray full scale application of bacteria-based self-healing agent as developed by the Delft research group in two repair mortar- and in two concrete construction demonstrator projects. These demonstrator projects show that addition of the bacteria-based self-healing agent to the concrete mix is safe as no negative side effects on construction performance was observed. However, it also proved difficult to find evidence for increased crack-healing performance as cracking in the demonstrator constructions hardly occurred. In further full scale demonstrators we therefore plan to drastically reduce amount of crack width-restraining reinforcement to show crack-healing capacity and potential to save on use of reinforcement steel in watertight concrete constructions.

Crack-healing performance and oxidation behavior of SiC dispersed yttrium silicate composites

ABSTRACT Yttrium silicate-based composites dispersed with silicon carbide particles have been proposed as a novel material concept of self-healing environmental barrier coatings applied for Si-based ceramics and their composites. Crack-healing effectiveness as well as high-temperature oxidation behavior of the yttrium silicate composites was investigated as functions of oxidation time and temperatures. Dense samples of the composites dispersed with 5 vol% SiC particles were fabricated by using the pulsed electric current sintering technique. Thermal oxidation for self-healing was conducted at temperatures ranging from 1000°C to 1300°C for from 1 to 24 h in air. High-temperature oxidation experiments were carried out at temperatures ranging from 1200°C to 1400°C for from 1 to 60 h in air. As a result, the surface cracks with approximately 200 µm in length introduced on the sample surface were disappeared completely after heat treatment at 1300°C for 1 h in air. Crack-healing performance of SiC/Y2SiO5 is better than that of SiC/Y2Si2O7. The crack-healing performance of SiC/Y2SiO5-Y2Si2O7 is in the middle of that of SiC/Y2SiO5 and SiC/Y2Si2O7. The mechanism of crack healing was identified as the consequence of SiC oxidation into SiO2, which accompanies a volume expansion, and outward diffusion of Y3+ cations caused the formation of Y2Si2O7 outer layer. Oxidation of SiC particles within the matrix developed an oxidized zone. Growth of the oxidized zone obeyed the parabolic law, which meant diffusion process in the oxidized zone is the rate-controlling process.