Crack Repair Research Articles

Robust alkali-resistance of cover glass's UV-shielding and strengthening sol-gel coatings by tailoring the coupling between SiO2 and 2,2′,4,4′-tetrahydroxybenzophenone

Cover glass with UV-shielding function is important to mobile displays such as mobile phones and tablet PCs, as well as flexible photovoltaic cells. UV-shielding over 90 % while visible light transmittance over 90 % is a rather difficult technical challenge for cover glass. In this report, robust alkali-resistance of display cover glass's UV-shielding and strengthening sol-gel coatings have been successfully prepared, using 2,2′,4,4′-tetrahydroxybenzophenone (BP-2), γ-(2,3-epoxypropoxy) propyltrimethoxysilane (KH560) and tetraethyl orthosilicate (TEOS) as raw materials. The coupling between SiO2 and BP-2 was tailored by using a condensation reflux method for the mixture of BP-2 and KH560. Compared to blank glass (0.7 mm thickness), UV-shielding (UV-A and UV-B) of the coated glass (coated on one side, 3 μm thickness of coating) increases significantly from 13.43 % to 99.93 %, while the visible light transmittance (380–780 nm) changes only slightly from 91.87 % to 90.16 %. Moreover, the bending strength of the coated glass improves by 52 MPa, and the drop ball impact resistance increases by 16 %. After alkali corrosion, glass's UV-shielding with the BP-2/SiO2 coupling or uncoupling coatings is 90.03 % or 80.03 %, respectively. The BP-2/SiO2 coupling coatings significantly improve alkaline corrosion resistance. Fourier transform infrared spectroscopy analysis confirms that BP-2 is chemically grafted into the SiO2 grid of the coating, which contributes to the robust alkali-resistance. Demonstrated by the finite element simulation, the strengthening effect originates from the repair of cracks on the surface of glass by the coating. The coating presents its application possibility on cover glass.

Hydration properties of magnesium phosphate cement paste mixed with metakaolin and silica fume

AbstractMagnesium phosphate cement (MPC) exhibits a faster setting time and higher early strength, making it suitable for crack repair. However, its application in civil engineering is hindered by its fast initial hydration rate and poor water resistance. To address these limitations, metakaolin (MK) and silica fume (SF) were utilized to enhance the properties of MPC. The effects of MK and SF on the setting time, compressive strength, water resistance, hydration process, and microstructure of MPC were investigated. The results demonstrate that both MK and SF significantly prolong the setting time of MPC and improve its water resistance. The main hydration products of MPC, after incorporating MK and SF, are k‐struvite (MgKPO4·6H2O) and unreacted MgO. The presence of MgSiO3 and AlPO4 also contributes to the enhancement of compressive strength and water resistance. The incorporation of MK and SF actively participates in the hydration reaction of the MPC system. Furthermore, MgSiO3 and AlPO4 intertwine with MKP, resulting in a denser internal structure of the cured MPC, thereby improving its water resistance.

Molecular Engineering Enables Hydrogel Electrolyte with Ionic Hopping Migration and Self-Healability toward Dendrite-Free Zinc-Metal Anodes.

Hydrogel electrolytes (HEs), characterized by intrinsic safety, mechanical stability, and biocompatibility, can promote the development of flexible aqueous zinc-ion batteries (FAZIBs). However, current FAZIB technology is severely restricted by the uncontrollable dendrite growth arising from undesirable reactions between the HEs with sluggish ionic conductivity and Zn metal. To overcome this challenge, this work proposes a molecular engineering strategy, which involves the introduction of oxygen-rich poly(urea-urethane) (OR-PUU) into polyacrylamide (PAM)-based HEs. The OR-PUU/PAM HEs facilitate rapid ion transfer through their ionic hopping migration mechanism, resulting in uniform and orderly Zn2+ deposition. The abundant polar groups on the OR-PUU molecules in OR-PUU/PAM HEs break the inherent H-bond network, tune the solvation structure of hydrated Zn2+, and inhibit the occurrence of side reactions. Moreover, the interaction of hierarchical H-bonds in the OR-PUU/PAM HEs endows them with self-healability, enabling in situ repair of cracks induced by plating/stripping. Consequently, Zn symmetric cells incorporating the novel OR-PUU/PAM HEs exhibit a long cycling life of 2000h. The resulting Zn-MnO2 battery displays a low capacity decay rate of 0.009% over 2000 cycles at 2000mA g-1. Overall, this work provides valuable insights to facilitate the realization of dendrite-free Zn-metal anodes through the molecular engineering of HEs.

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

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

Use of buffer treatment to utilize local non-alkali tolerant bacteria in microbial induced calcium carbonate sedimentation in concrete crack repair

Concrete often suffers cracks due to its low tensile strength. The repair process can vary ranging from surface coating, grouting, and strengthening. Microbial induced calcium carbonate sedimentation process (MICP) is a process of utilizing non-pathogenic bacteria to produce calcium carbonate through its urease activity in crack repair (filling). It is known as an alternative crack repair method that does not utilize Portland cement. In general, the bacteria used in MICP are alkali tolerant bacteria that have a higher chance of surviving the high alkalinity environment in concrete. However, in some regions, alkali tolerant bacteria are difficult to acquire and unavailable locally. This study introduced a technique to utilize non-alkali tolerant bacteria in MICP using buffer treatment. Instead of injecting bacteria directly onto the crack surface, the buffer solution was applied onto the crack surface prior to the bacteria injection. Results from the laboratory indicated a higher bacteria survival rate when the buffer treatment was applied to the medium. For the crack filling, with the buffer treatment, the crack was completely filled within 21–28 days. The microstructure results also showed that the crystal deposits from both laboratory and crack surface were similar in both physical appearance and phase composition.

Development and performance of a novel hybrid toughened unsaturated polyester resin (UPR) composite for crack repair of asphalt pavement

In order to effectively seal the cracks, a novel hybrid toughened unsaturated polyester resin (RMUP) crack repair material using liquid nitrile rubber (LNR) and nano-montmorillonite (nano-MMT) is developed in this study. The optimum RMUP formula is determined through mechanical performance tests, viscosity test, fluorescence microscopy, etc. The mechanical properties of the RMUP composite are compared individually with those of toughened UPR by LNR or nano-MMT, while the workability, mechanical performance, durability and cost are compared to other commonly used crack repair materials such as epoxy resin (EP), polyurethane (PU), silicone (SI) and SBS-modified emulsified asphalt (SEA) sealants. The hybrid toughening effect and potential of RMUP as a crack repair material is validated. Furthermore, the hybrid toughening mechanisms are analyzed using Fourier transform infrared spectroscopy (FT-IR). The test results show that the hybrid combination of LNR and nano-MMT effectively toughens UPR, not only improving its ductility but also maintaining its high mechanical strength. Additionally, as a repair material, RMUP exhibits excellent workability, being less temperature-dependent, with a moderate operating time and rapid strength increase following repair, and possesses high mechanical strength (the tensile strength up to 19 MPa) and favorable durability with only a 2%− 4% performance degradation exposing to water immersion environments and no weight loss in extremely hot weather, as well as cost-effectiveness, featuring similar properties to EP sealant but at half the cost of EP. The mechanism analysis reveals that the LNR chemically interacts with the UPR matrix, cross-linking to the UPR’s polymer chains. Simultaneously, the nano-MMT galleries are intercalated by the UPR polymer chains, resulting in an intercalated nanocomposite formation. Both interactions contribute to RMUP's improved toughness.

Fatigue Life Estimation Model of Repaired Components with the Expanded Stop-Hole Technique

Fatigue crack growth tests are conducted to assess the efficacy of the stop-hole crack repair method. This straightforward and widely adopted technique involves drilling a hole at the crack tip and subsequently enlarging it using a pin inserted into the hole. A fracture mechanics-based model is proposed to estimate the extension of fatigue life achieved through the implementation of the stop-hole technique. The model’s predictions are validated using data obtained from fatigue crack growth tests conducted on both unrepaired and repaired M(T) specimens, following the guidelines outlined in the ASTM E647 standard. The error of the fracture mechanics-based model was 1.4% in comparison with the fatigue tests.

Monitoring of crack repair in concrete using spherical smart aggregates based on electromechanical impedance (EMI) technique

Cracks will inevitably occur in concrete structures or members during the construction process and service life due to aging, environmental factors, external loads, etc. To improve the strength and stability of the cracked concrete structures, many methods have been proposed to repair the cracks. However, the monitoring of the repairing process and repair quality has not been fully studied. The previous studies have proved that the spherical smart aggregates (SSAs) based on the electromechanical impedance (EMI) technique have outperformed the traditional smart aggregates (SAs) based on the EMI technique in structural health monitoring of civil structures, however, SSAs have not been applied to the monitoring of the concrete crack repair. In this work, the monitoring of the concrete crack repair using the SSAs based on the EMI technique was explored. A total of eight concrete specimens were prepared, and cracks in the concrete specimens were simulated by manually cutting under laboratory conditions. According to the principle of grouting method, two repair agents including cement paste and cement mortar were used to repair the cracks. The impedance signals of 28 d were measured, and three quantitative indicators, namely root mean square deviation, mean absolute percentage deviation, and correlation coefficient deviation were used to evaluate the quality of the concrete repair effect. The results indicate that the SSAs show excellent sensitivity and stability over the traditional SAs. In addition, the normalized values of the quantitative indicators were analyzed to distinguish the types of repair agents. A mathematical expression of exponential function was also proposed by fitting the experimental data to quantitatively evaluate and predict the repair effect of concrete cracks. Further, the influences of temperature, humidity, crack depth and width on the experimental results were analyzed and discussed. The numerical simulation was also presented to validate the reasonability of the experimental results.

Numerical investigation of the carrying capacity of single polyurethane foam pile in clay and sand soils

The definition of soil stabilization is a method to enhance the engineering properties. Polyurethane grout is one of the least expensive methods and can be used in construction. Polyurethane injection resin systems for crack injection, slab lifting, soil stabilization, leak sealing, and structural crack repair have been used for the last two decades. Polyurethane foam hasn't been used or understood as a loaded structural element in soils like as embedded piles. In this piece of work, a trial was made to numerically study the behavior of polyurethane foam when used as piles embedded in the clay and sand soils. Plaxis 3D software was adopted to carry out this study. Polyurethane piles of varying diameters and lengths were modelled as embedments in the clay and sand soil, and then incremental loads were applied. Moreover, the study involved the behavior of polyurethane piles when the clay strength was increased. The results indicated that embedded pile resistance to loading increased with the increase in length and pile diameter. When the loading results of polyurethane foam embedded in loose sand are compared with the loading results of piles in soft clay, the ultimate capacity of piles in loose sand, was much higher than that in soft clay. The results also indicated that the polyurethane pile load-carrying capacity increased when L/D ratio decreased for both soft and stiff clay. In this study concrete piles in clay and sand soil were modelled to examine the percentage of loading capacity of concrete piles to that of polyurethane piles for clay and sand soil.

Reverse-seepage and saturation action anti-corrosion tech (RS-AAT) for corrosion resistance and self-healing of cracked concrete in seawater immersion

Reverse-seepage and Saturation based Action Anti-corrosion Tech (RS-AAT) is a cutting-edge technology that saturates concrete materials and provides anti-hydraulic pressure to offer robust protection against chloride salt-induced corrosion. This study examined the crack repair capability and anti-chloride invasion effect of RS-AAT-treated concrete by experimental and numerical analyses. The results indicated that, under the effect of RS-AAT, the crack healing rate achieved the highest value of 12 % and the total chloride concentration dropped by the largest amount of 51.41 % after 120 days. Under 0.4 MPa water pressure, the surface chloride concentration decreased by the most of 69.42 % and the depth concentration curves of different crack widths approached a variance of 1. Moreover, the crack repair coefficients were introduced to improve the accuracy of numerically simulating the chloride ion migration process in cracked concrete. The findings unequivocally demonstrate that the use of RS-AAT could significantly inhibit chloride ion intrusion into the concrete's protective layer, of which effect was intensified with the increase of reverse osmosis water pressure. Such results provided invaluable insights into enhancing the durability and chloride ion resistance of marine-immersed concrete structures.

Predicting the crack repair rate of self-healing concrete using soft-computing tools

To tackle the challenges of cracking and insufficient durability in traditional concrete, researchers are exploring self-healing concrete (SHC) as a potential alternative material. Nevertheless, doing laboratory studies can incur significant expenses and consume considerable time. Therefore, utilizing machine learning (ML) algorithms can contribute to advancing improved predictions for self-healing concrete. This study aimed to create ML models, specifically adaptive boosting (AB), artificial neural network (ANN), and gradient boosting (GB), to forecast and evaluate the repair rate of the cracked region in SHC that incorporates fibers and bacteria in their compositions. To further evaluate the importance of inputs, RReliefF analysis was performed. The findings indicated that the AB algorithm outperformed GB and ANN algorithms by achieving a coefficient of determination (R2) value of 0.987, a mean absolute error (MAE) value of 0.001 mm, and a root mean square error (RMSE) value of 0.026 mm. The GB approach yielded an R2 value of 0.962, an MAE value of 0.035 mm, and an RMSE value of 0.044 mm. Similarly, the ANN approach yielded an R2 value of 0.943, an MAE value of 0.040 mm, and an RMSE value of 0.054 mm. These results demonstrate that all AB, GB, and ANN algorithms outperformed in terms of prediction accuracy and model fit. Hence, the application of these models can be employed to construct and verify advanced SHC compositions that rely on polymeric fibers and bacteria, aiming to achieve superior performance. However, comparing the outcomes of developed models revealed that the AB model accuracy is higher than the GB and ANN models for predicting the area repair rate of cracks.

Restoration of tensile properties in cracked aluminum specimens via composite patching

This study investigates the tensile behavior and crack repair of aluminum using fiberglass-reinforced composite patches. Tensile testing compared uncracked, pre-cracked, and repaired aluminum specimens. Pre-cracking by hole drilling decreased strength and ductility from stress concentrations. Composite patching recovered strength, with 4-ply laminates optimal. Uncracked samples failed by necking, pre-cracked by crack growth, and repaired by adhesive detachment. Results demonstrate composite patching effectively restores strength to cracked aluminum by mitigating stress concentrations when appropriately designed. Finite element modeling simulated stress reduction after patching. This work provides experimental data on composite patch performance for metal crack repair and confirms the approach as an effective strengthening technique, although further optimization is needed.

Application of adhesively bonded CFRP for reinforcement and rehabilitation of fatigue damaged steel structure - only a nice idea?

As an alternative to classic repair measures of fatigue-damaged steel structures, adhesively bonded CFRP lamellas are ideal. In this way, disadvantages of the established methods can be circumvented Compared to bolted reinforcing measures, cross-sectional weakening by the bolt is avoided. Heat-induced residual stresses and distortions, as they usually occur during repair welding, can also be excluded. These disadvantages represent a weak point during cyclic loading due to the notch effect. To characterize the materials, tests are carried out on small scale specimens. With the help of tests on CT-samples a comparison with established methods such as drilling the crack tip and repair welding is realized. Based on the crack propagation, the great potential of bonded CFRP reinforcements can be deduced. By prestressing the lamellas, the remaining lifetime can generally be further increased. It should be noted, however, that with single-sided prestressing, a precamber of the specimen and, during loading, a secondary bending moment may occur. The combination of bonded CFRP with established methods can be described as particularly effective. With a reinforcement on both sides with pre-stressed plates, up to 7.9 times the remaining service life can be determined in comparison to unreinforced specimens. The effectiveness of adhesively bonded CFRP lamellas is examined in a German research project. Selected results are presented in this paper.

The comparative study of epoxy and bacterial injections for cracked concrete beam flexural strength

Cracks in concrete beams can significantly affect the performance of reinforced structures. To repair cracks in concrete, Traditional crack repair methods typically involve epoxy injection, but studies have suggested that epoxy may not fully restore the original strength. Therefore, concrete structure repair requires the development of new and more efficient materials. This study focuses on investigating the potential of Bacillus megaterium, a bacterium known for its self-healing properties in concrete. This bacterium has the capability to precipitate minerals like calcium carbonate, which can fill the cracks and increase the strength of concrete. Testing is carried out on reinforced concrete beams with existing cracks, sized at 100 mm x 100 mm x 500 mm. The specimens are divided into two groups, one repaired with epoxy injection and the other with bacterial injection, with varying additions of 10% and 15%. The research results show that the injection process with the addition of 15% bacteria is able to restore approximately 99.72% of the initial strength of the concrete beams. The results of this research contribute to the development of improved repair techniques that can restore the flexural strength of cracked concrete beams and extend the service life of concrete structures.

Development and Characterization of Self-Healing Glass Fiber Composites for Applications Requiring Autonomous Crack Repair

Development and Characterization of Self-Healing Glass Fiber Composites for Applications Requiring Autonomous Crack Repair

A polymer latex modified superfine cement grouting material for cement-stabilized macadam – Experimental and simulation study

Cement-stabilized macadam (CSM) has been prevalently employed in transportation infrastructure owing to its superior bearing capacity and stability. However, with inherent dry shrinkage, temperature shrinkage, and inadequate tensile capacity, cracks will inevitably occur. These cracks can reflect on the asphalt layer and cause diseases such as transverse cracks, dynamic water scouring, voids, etc. A predominant remediation method involves utilizing grouting material for trenchless repair. In this research, a vinyl acetate-ethylene (VAE) latex modified superfine cement (VMSC) for grouting material is proposed to improve the flexibility of the grouting material and enhance crack repair dimensions. The interaction mechanism was investigated through mechanical experiments, microscopic tests, and molecular simulation. The results show that VMSC30 exhibits the highest fluidity. VAE latex addition extends the initial and final setting times of the grouting material, alongside an escalation in yield stress and plastic viscosity. VAE latex reduces the compressive strength of the grouting material, while 10% can increase the flexural strength, and the overall toughness can be improved. Characteristic spectral peaks of VAE latex are identified at 1740 cm−1 and 1240 cm−1, respectively, and it can form a film to cover the surface of cement, inhibit hydration diminish the CH peak value. VAE can form the 2.95 Å ionic bond and the 3.05 Å hydrogen bond on the Ca atom and water molecules, respectively. The peak value of the ionic bond is higher. The ionic bond and hydrogen bond formed by bridging can improve the strength of VAE and cement interfaces.

Investigation on Self-Healing Concrete Using Bacillus Subtilis Bacteria

Cracking is a common occurrence in concrete, primarily attributed to its relatively low tensile strength due to External loads which induce high tensile stresses. Immediate and proper treatment is essential to prevent the expansion of cracks, as their unchecked growth may lead to higher repair costs. Bacterially induced calcium carbonate precipitation emerges as an eco-friendly alternative for crack repair. This technique involves the metabolic activities of specific bacteria in concrete, resulting in microbial mineral precipitation. In this study an attempt has been made to define bacterial concrete and its behavior such as self-healing by minor cracks induced in the samples. Concrete cubes of M20, M25 and M30 have been casted with three dosages of bacterial solution (Bascillus Subtilis) as 60 ml, 75 ml & 90 ml per cube (150 mm size). It has been observed that the compressive strength of bacterial concrete has increased slightly as compared to conventional concrete for each dose. The best performance in compressive strength enhancement has been observed for 75 ml dose and best self-healing has been observed for 90 ml dose of bacterial solution (per cube) in bacterial concrete. Ultrasonic pulse velocity test shows excellent quality for all samples of bacterial concrete.

Innovative Biomaterials in Green Construction: Economic Benefits and Challenges

The integration of biotechnology in green building represents a cutting-edge approach that harnesses biological processes to enhance sustainability and efficiency in construction practices. This abstract explores modern strategies and provides examples of how biotechnology is revolutionizing green building. Biotechnology offers innovative solutions to traditional challenges in green building, leveraging biological systems to optimize resource utilization, energy efficiency, and waste reduction. By integrating living organisms, biomaterials, and biological processes into building design and construction, biotechnology enables the development of structures that are not only environmentally friendly but also adaptive and resilient.One modern approach involves incorporating living organisms such as algae, bacteria, and fungi into building materials to enhance their performance. For example, algae can be used in bio-facades to capture carbon dioxide and produce oxygen, contributing to improved indoor air quality and reducing the building's carbon footprint. Similarly, bacteria can be embedded in concrete to repair cracks autonomously, increasing the durability and lifespan of structures while minimizing maintenance needs.

Experimental analysis of biocementation technique for sealing cracks in concrete water storage tanks

Water supply systems are vital infrastructures that provide an indispensable public service to society. An important percentage of water losses is caused by the development of cracks in water storage tanks, so efficient crack sealing repair works must be investigated. Biocementation has been used with good results for sealing cracks in many construction concrete infrastructures (e.g., buildings), as an alternative to standard materials, such as polymeric resins and cement mortars. This research aims at the experimental evaluation of biocimentation effectiveness in terms of watertightness for sealing cracks structures in contact with pressurized water, to be further applied to repair cracks in water storage tanks. Biocementation treatment is applied in cracks artificially created in small rectangular concrete plates 4 cm thick, with three crack widths (i.e., 0.1, 1 and 10 mm) to cover different real cases in which the repair with this technique is viable. The 10 mm width cracks were filled with sand before the treatment. Different rounds of bacteria Sporosarcina pasteurii are applied, being the efficiency of the treatment investigated by performing watertightness tests through variable water head tests starting at 10 kPa (1 m of water). Dissolution is discarded through measurements of ultrasonic pulse velocities before and after the watertightness tests and the results are explained by images of thermographic camera. The presence of biocement is confirmed by mineralogical analysis of the precipitate extracted from the cracks after breaking the plates through bending tests. Obtained results are very promising since the biocement precipitated can completely stop water flow in the 0.1 mm cracks and, for the cracks with 1 mm and 10 mm widths, the treatment can reduce the initial flow rate, on average, by 95% and 98%, respectively. The performance of the 10 mm width cracks previously filled with sand was similar to that of the 1 mm cracks, where no sand was used. The material strength recovered after the treatment is not as good as desirable: although a maximum recovery of 95.5% of the initial strength (average values) is found for the smallest crack width and it was almost null for the other two crack widths. These results demonstrate that the technique is effective when watertightness is required, but not when material strength must also be recovered. Further research is required to investigate the maximum water pressures that can be applied to each case, eventual effects of biocimentation on water quality and the durability of the treatment.

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.