Healing Of Cracks In Concrete Research Articles

Healing of cracks in concrete by using bacterial spores immobilized in metakaolin

Microbial-induced self-healing of micro cracks is an economical and effective biotechnological approach in concrete structures. The current study explores metakaolin as a suitable carrier material for immobilizing bacterial spores using adsorption technique. The developed biomaterial was stored at 4 °C and 25 °C for 180 days and showed sustainable shelf life of the bacterial spores. The biomaterial stored at 4 °C added as supplementary material during the casting of concrete significantly improved the compressive and flexural strength of concrete at 7 and 28 days. The sorptivity coefficient was 0.006 and 0.002 at 7 and 28 days, respectively, which was comparatively lower than the control. Further, the self-healing capabilities of biomaterial were investigated for approximately 0.5 mm crack in 400 × 100 × 100 mm prismatic specimens. During the crack healing period, the ultrasonic pulse velocity (UPV) was observed to improve by 21.7 % compared to the cracked specimens. The crack was completely healed with 98.2 % healing efficiency. During the healing of crack, the water tightness of the repaired surface was 92.8% efficient verifying reduction in water flow upon complete healing. At the end of testing, the precipitated mineral was assessed by field emission scanning electron microscopy and X-ray diffraction. The developed metakaolin based biomaterial can be used as self-healing supplementary cementitious material.

A critical review on the effectiveness of microbial concentrations for enhancing self-healing in cement concrete and mortar

A significant consideration in the design of any structure is the choice of materials. Construction relies heavily on concrete due to its exceptional characteristics and is the primary material used to construct infrastructure across the globe. Moreover, these materials caused micro-cracks under cyclic loading due to tension, significantly reducing their life expectancy. Nowadays, structures have a decreased service life because of the degradation of their durability, strength, and many other attributes. In concrete or mortar structures, cracks are a significant concern as they cause deterioration and allow unwelcome chemicals to enter the system. Sealants and surface treatments have become increasingly popular in enhancing structural appearance in recent years. Despite their limitations, these products are unstable, costly, and contribute to higher pollution levels. When micro-cracks extend and end up inside reinforcement, not only will the concrete be destroyed, but its support will also be corroded by oxygen, water, and harmful gases. Access to the cracked zones may be difficult aside from these operations requiring capital and labour. Crack healing in concrete may be of assistance in reducing the growth and propagation of cracks in concrete. The application of such a concept has led to the development of concrete known as Bacterial Concrete, in which bacteria play the role of carrier and perform bio mineralization by decomposing urea and calcium to produce calcium carbonate (CaCO3), which is capable of filling cracks. Bacteria-induced carbonate precipitation is an environmentally friendly mechanism for autonomously sealing cracks. Many researchers around the world have recently been exploring this mechanism in depth. This paper aims to review the assessment of strength and other properties both in concrete and mortar in relation to specific microbial cell concentrations and to analyse its effectiveness in promoting crack healing and microstructural properties.

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.

Crack healing in concrete by microbially induced calcium carbonate precipitation as assessed through electromechanical impedance technique

In the present study, Electromechanical Impedance (EMI) technique is utilized to assess the application of the microbially induced calcium carbonate precipitation (MICCP) to restore the integrity of cracked concrete. The artificial crack width of approximately 0.5 mm is healed autonomously using a bacteria-based healing agent, using flyash (FA) as a carrier material. Lead Zirconate Titanate sensors were bonded on the cracked specimen to monitor the continuous healing process. The EMI signatures were captured over the healing period using an impedance analyser in the frequency range of 100 to 250 kHz. Statistical crack healing indicator, root mean square deviation (RMSD) was employed for evaluating crack efficiency based on extracted signatures. Results revealed that the RMSD values were effective in quantifying the progressive healing achieved due to MICCP precipitation. This is the first study with a successful implementation of the EMI technique to monitor the crack sealing in concrete through MICCP. Healing capacity was also correlated with the crack width reduction that was evaluated by optical imaging of repaired cracked surface. Also, the bacterial mineralization products were analyzed by FESEM, EDX, XRD and TGA. The results give clear proof that the FA-based carrier material can be effectively used in healing the cracks.

The Utilization of Milk as a Catalyst Material in Enzyme-Mediated Calcite Precipitation (EMCP) for Crack-Healing in Concrete

This study discussed the applicability of the calcite precipitation method to repair the concrete's crack. The grouting solution of Enzyme-Mediated Calcite Precipitation (EMCP) was modified by adding milk as a catalyst in calcite formation. Cracks in concrete samples were made when the concrete was 28 days with a width of 0.1-0.3 mm. The EMCP solution composed of urease, urea, CaCl2, and milk was injected into the cracked concrete sample, and its effect on permeability and compressive strength tests were evaluated. The result shows that the optimum composition of milk used in the formation of calcite had a concentration of 5 g/L with an initial preparation temperature of 70oC, which produced 26% higher than the initial EMCP solution. The mechanical test results show that the reduction of coefficient of permeability of 92.23% compared to the cracked sample and the improve strength up to 98.75% of the non-cracked sample were obtained by three circles injection. This study elucidated that milk utilization as a catalyst material in repairing cracks with the EMCP method is a potential method for crack-healing concrete.

The Effect of Crystalline Waterproofing Admixtures on the Self-Healing and Permeability of Concrete.

This paper investigates the effectiveness of a specific crystalline waterproofing admixture (CWA) in concrete as a function of a water–binder ratio. Four concrete mixes with and without CWA were prepared; two of them with a water–binder ratio of 0.45 and two of them with a water–binder ratio of 0.55. Water permeability and compressive strength were tested on hardened concrete specimens and self-healing of cracks over time was observed. Cement paste and CWA paste were prepared to clarify the results obtained on the concrete specimens. SEM and EDS and XRD and FTIR were performed on the hardened pastes to explain the mechanism of CWA working. The results show that the addition of CWA had no significant effect on the compressive strength of the concrete, but reduced the water penetration depth in the concrete, and the reduction was more effective for mixes with lower water–binder ratio. Regarding the self-healing effect, it can be concluded that the addition of CWA improves the crack healing in concrete, but the efficiency of self-healing is highly dependent on the initial crack width. The mechanisms involved in the reduction of water penetration depth and crack healing in concrete can be explained by different mechanisms; one is creation of the CSH gel from unreacted clinker grains, then formation carbonate, and additional mechanism is gel formation (highly expansive Mg-rich hydro-carbonate) from magnesium based additives. The presence of sodium silicate, which would transform into carbonate/bicarbonate, also cannot be excluded.

Self Healing of Cracks in Concrete with Bacteria

During the service life of concrete structures, internal and external effects and micro-cracks occur in the structure. These cracks cause leakage of harmful substances into the concrete, deterioration of the strength and durability properties of the concrete, structural damages and crashes, and the high cost of maintenance and repair of the concrete structure. It is known that water-dissolved CO2 reacts with Ca+2 ions in the concrete and can repair the concrete by forming CaCO3 (limestone) crystals with very little water solubility. However, for this type of self-repair to occur, there must be water in the environment and this repair can only be made if the cracks are too small. Recently, bacterial concrete methods which has ability to self-healing are used to overcome maintenance and repair costs. In 1994, the first study on the ability to self-healing with the extra materials that were added to the concrete during the production of concrete was published by Carolyn Dry of Illinois University. Eric Schlagen and Henk Jonkers who have been researching about self-healing concrete by adding bacterial spores and calcium lactate foods to the mixture while producing concrete have made a remarkable study in this field since 2006. Bacterial concrete, Bacillus bacterial spores in the medium of the water-activated nutrients and calcium sources in the range of appropriate pH values in the concrete due to the formation of a fibrous structure is caused by precipitation of calcite. Thus, with the precipitation of calcite, the bacteria are embedded in concrete and the concrete is provided to improve itself. In previous studies, it has been shown that the cracks and voids in the concrete are filled with the ethrengeite and C-S-H structure when the control and bio-based concrete samples examined by SEM and XRD are compared. In previous studies, it was observed that mechanical strength and durability of the concrete is increased. It should be noted that the concentration of bacteria used in the solution and the ambient pH value is specified. Although conventional maintenance and repair methods are fast reacting, and short-term efficient, bacterial concrete method is sustainable, slow and long-term efficient. In addition, it is an environmentally friendly method compared to chemical repair methods and is expected to be among the remarkable materials of the future. The high initial cost leads to a reduction in producer demand, and the development process must continue to achieve the desired results and cost. As a result, it will be possible to obtain more durable structures by not wasting time, saving money and reducing the costs of high maintenance and repair. In other respects, it is a great advantage for sustainable development. Technical studies are continuing due to the high cost and laboratory test results of the bacterial family, as well as the impacts on the survival of the bacterial family. In this study, previous studies were evaluated, and some suggestions were made based on these studies.

Probabilistic analysis models to determine capsule dosage for healing of cracks in concrete

In order to analyze the optimal dosage of capsule pre-embedded in concrete materials, this article simplified the irregular cracks generated in concrete materials into linear regular hexagonal cracks in two-dimensional plane and planar cracks in three-dimensional space. Then, the probability model describing the interaction between the cracks and capsules was established using the probability theory of integral geometry. The theoretical solutions for the required capsule dosage for the two- and three-dimensional cases were derived. Finally, the calculated results for the theoretical model were compared with those provided by the computer simulation software. The results indicated that the model is suitable for analyzing and optimizing the capsule dosage required to repair cracks in concrete materials. It can provide a theoretical basis for the design of self-healing materials.

Optimization of culture parameters of Pseudomonas alcaligenes for crack healing in concrete

Crack formation is a commonly observed phenomenon in concrete. It effects the durability of concrete due to increased permeability and consequent ingress of harmful chemicals through these cracks. The introduction of certain microorganisms in concrete can remediate these cracks through calcium carbonate precipitation. The present study aims at evaluating the potential of Pseudomonas alcaligenes in crack healing of concrete by optimizing the growth parameters of the culture for concrete environment. The internal pH of cementitious concrete system is around 13 and the temperature is around 37 °C. It is essential to identify the survival and sustenance of the bacterial colonies under these conditions. Culture parameters like temperature and inoculum volume have been studied for P. alcaligenes. Conventional methods like single parameter optimization keeping the other variables constant have been employed to find optimum growth conditions of the bacteria to be studied for crack healing in concrete. The optimum operating conditions were obtained based on the optical density of bacterial cells at 600 nm in the culture broth in the form of colony forming units (CFU) varying the inoculum volume from 0.5%, 1%, 1.5% to 2% and temperature from 35 °C, 37 °C, 40 °C to 42 °C. Based on the findings of this study, recommendations will be provided for the practical application of Pseudomonas alcaligenes in the construction industry.

Light induced self-healing in concrete using novel cementitious capsules containing UV curable adhesive

Cracking related deterioration is one of the most important sources of risk that seriously influences the integrity and durability of concrete structures. In this study, a novel type of light induced self-healing mechanism was designed and prepared for automatic healing of cracks in concrete. The self-healing mechanism consists of waterproofing cementitious capsules filled with UV adhesive and a UV light radiator. The shell of capsule is made of three separated but organically bonded functional layers. UV adhesive was first time employed as healing agent for concrete self-healing. The survival of the prepared capsules in the cementitious materials and the ability of capsules to break upon crack were testified. The self-healing efficiency in concrete was evaluated in terms of mechanical recovery, water absorption and water permeability. The test results implied that the proposed self-healing mechanism can be used as an ideal option in revitalizing the performance of cracked concrete.

The use Immobilized Bacteria-Alginate-Chitin for crack remediation

Cracks in concrete allow water and chemicals to enter, a process that may lead eventually to the unwanted damage of the concrete structure. However, this material is that it easily cracks due to its low tensile strength. The potential of self-healing of calcium carbonate precipitating bacteria. The possible application of bacteria to extend the lifetime of concrete is studied. The goal of this project is to incorporate dormant but viable bacteria in the concrete matrix. The research is the healing of cracks in concrete by bacteria immobilization using alginate-chitin. Bacteria were mixed into the gel and both were a concrete mixture. However, as the bacteria-gel matrix showed capable of producing calcium carbonate at pH 7-11, and could precipitate calcium carbonate 0.054 g. Concrete that mixed with bacteria-alginate-chitin 6.3%, showed compressive strength 18.75 Mpa and water absorption 1.6%, after immersion in water for 28 days.

Microbial network of the carbonate precipitation process induced by microbial consortia and the potential application to crack healing in concrete

Current studies have employed various pure-cultures for improving concrete durability based on microbially induced carbonate precipitation (MICP). However, there have been very few reports concerned with microbial consortia, which could perform more complex tasks and be more robust in their resistance to environmental fluctuations. In this study, we constructed three microbial consortia that are capable of MICP under aerobic (AE), anaerobic (AN) and facultative anaerobic (FA) conditions. The results showed that AE consortia showed more positive effects on inorganic carbon conversion than AN and FA consortia. Pyrosequencing analysis showed that clear distinctions appeared in the community structure between different microbial consortia systems. Further investigation on microbial community networks revealed that the species in the three microbial consortia built thorough energetic and metabolic interaction networks regarding MICP, nitrate-reduction, bacterial endospores and fermentation communities. Crack-healing experiments showed that the selected cracks of the three consortia-based concrete specimens were almost completely healed in 28 days, which was consistent with the studies using pure cultures. Although the economic advantage might not be clear yet, this study highlights the potential implementation of microbial consortia on crack healing in concrete.

Crack healing in concrete using various bio influenced self-healing techniques

Crack formation and progression under tensile stress is a major weakness of concrete. These cracks also make concrete vulnerable to deleterious environment due to ingress of harmful compounds. Crack healing in concrete can be helpful in mitigation of development and propagation of cracks in concrete. This paper presents the process of crack healing phenomenon in concrete by microbial activity of bacteria, Bacillus subtilis. Bacteria were introduced in concrete by direct incorporation, and thorough various carrier compounds namely light weight aggregate and graphite nano platelets. In all the techniques, calcium lactate was used as an organic precursor. Specimens were made for each mix to quantify crack healing and to compare changes in compressive strength of concrete. Results showed that bacteria immobilized in graphite nano platelets gave better results in specimens pre-cracked at 3 and 7days while bacteria immobilized in light weight aggregates were more effective in samples pre-cracked at 14 and 28days. In addition, concrete incorporated with bacteria immobilized in light weight aggregate, also exhibited significant enhancement in compressive strength of concrete.

Detecting the Activation of a Self‐Healing Mechanism in Concrete by Acoustic Emission and Digital Image Correlation

Autonomous crack healing in concrete is obtained when encapsulated healing agent is embedded into the material. Cracking damage in concrete elements ruptures the capsules and activates the healing process by healing agent release. Previously, the strength and stiffness recovery as well as the sealing efficiency after autonomous crack repair was well established. However, the mechanisms that trigger capsule breakage remain unknown. In parallel, the conditions under which the crack interacts with embedded capsules stay black-box. In this research, an experimental approach implementing an advanced optical and acoustic method sets up scopes to monitor and justify the crack formation and capsule breakage of concrete samples tested under three-point bending. Digital Image Correlation was used to visualize the crack opening. The optical information was the basis for an extensive and analytical study of the damage by Acoustic Emission analysis. The influence of embedding capsules on the concrete fracture process, the location of capsule damage, and the differentiation between emissions due to capsule rupture and crack formation are presented in this research. A profound observation of the capsules performance provides a clear view of the healing activation process.

Acoustic emission analysis for the quantification of autonomous crack healing in concrete

As half of the annual construction budget is spent on remediation of existing structures, self-healing of concrete, which is very sensitive to cracking, would be highly desirable. In this research, encapsulated healing agents were embedded in the concrete matrix in order to obtain self-healing properties. Upon cracking, the capsules break and the healing agent is released, resulting in crack repair. The efficiency of this crack healing technique was evaluated by means of mechanical tests and by using acoustic emission analysis. It was shown that due to autonomous crack repair, more than 80% of the original strength and stiffness can be regained. Events with an energy higher than the energy related to concrete cracking indicated breakage of the capsules. Upon reloading of beams with untreated cracks, the released energy was lower compared to beams with healed cracks. From this study it was shown that AE is a suitable technique to evaluate self-healing of cracks in concrete.

Application of bacteria as self-healing agent for the development of sustainable concrete

The application of concrete is rapidly increasing worldwide and therefore the development of sustainable concrete is urgently needed for environmental reasons. As presently about 7% of the total anthropogenic atmospheric CO 2 emission is due to cement production, mechanisms that would contribute to a longer service life of concrete structures would make the material not only more durable but also more sustainable. One such mechanism that receives increasing attention in recent years is the ability for self-repair, i.e. the autonomous healing of cracks in concrete. In this study we investigated the potential of bacteria to act as self-healing agent in concrete, i.e. their ability to repair occurring cracks. A specific group of alkali-resistant spore-forming bacteria related to the genus Bacillus was selected for this purpose. Bacterial spores directly added to the cement paste mixture remained viable for a period up to 4 months. A continuous decrease in pore size diameter during cement stone setting probably limited life span of spores as pore widths decreased below 1 μm, the typical size of Bacillus spores. However, as bacterial cement stone specimens appeared to produce substantially more crack-plugging minerals than control specimens, the potential application of bacterial spores as self-healing agent appears promising.

Auto-cicatrisation des fissures dans un BUHP

ABSTRACT Self healing of cracks in concrete is investigated through different experimental techniques. An experimental program, based on the ageing of pre-cracked specimens and the characterization of their mechanical behaviour, is thus performed. The research work is mainly carried out on a model material (an UHPC). The mechanical results, a fast recovery of initial stiffness and a slow improvement of flexural resistance, are correlated with investigations carried out on the newly formed crystals in the crack. Acoustic emission permits to characterize the micro-cracking processes of these crystals in the crack, and microscopic investigations establish a link between the products and the mechanical tests.

Water Permeability and Autogenous Healing of Cracks in Concrete

The well-known practical phenomenon of autogenous healing in cracks plays a significant role in relation to the functional reliability of structures subjected to water-pressure loads. Because of the autogenous healing, the water flow through the cracks gradually reduces with time, and in extreme cases, the cracks seal completely. In the past, there has been no deliberate technical exploitation of self-healing, because too little is known about the phenomenon itself and about the chemical/physical processes involved. Based on theoretical and experimental research, the effect of crack healing was investigated on a larger scale for the first time. The experimental studies showed the formation of calcite in the crack to be almost the sole cause for the autogenous healing. A comprehensive theoretical discussion of the laws, which govern the calcite nucleation and the subsequent crystal growth of water-bearing cracks in concrete, revealed that the crystal growth responds to two different crystal growth processes that are determined by the changes in the chemical and physical conditions in the crack. Further, the crystal growth rate is dependent on the crack width and water pressure, whereas concrete composition and water hardness have no influence on autogenous healing. On the basis of the experimental studies, an algorithm that can be used to estimate the reduction in water over time as a result of autogenous healing was developed.