Autogenous Healing Research Articles

Long-term autogenous healing and re-healing performance in concrete: Evaluation using air-coupled surface-wave method

This study aimed at investigating two original topics on self-healing concrete, 1) the prediction of long-term healing progress and 2) the evaluation of re-healing performance for a previously healed but reopened crack, using the air-coupled surface-wave method. Small-scale plate concrete specimens were fabricated with a self-healing binder incorporating ground granulated blast furnace slag, Na2SO4, anhydrite, and graded clinkers. A single flexural crack of 0.25–0.30 mm width was generated near the mid-span of each specimen. Then, the specimens were kept immersed in water, and the healing progress of the cracks was monitored for approximately one year. As a result, the residual surface crack area was reduced to 15.1% of the fully-cracked condition, and the surface wave transmission ratio recovered up to 82.9% of the uncracked condition. A prediction model for the ultimate healing rate and initial healing rate was proposed based on surface-wave results. After the first self-healing process, the specimens were loaded again, and a similar crack was produced at the previously healed zone in each specimen. Then, the re-healing performance was evaluated for about two months. From the second self-healing process, one specimen with a narrow reopened crack showed a satisfactory recovery in surface wave transmission, comparable to that in the first healing.

Application of Superabsorbent Polymer as Self-Healing Agent in Self-Consolidating Concrete for Mitigating Precracking Phenomenon at the Rebar–Concrete Interface

Improved autogenous healing capacity of concrete using superabsorbent polymers (SAPs) was used as an efficient approach for mitigating damage between steel rebar and self-consolidating concrete (SCC). The results for normal concrete (NC) and those for SCC mixtures were compared. Two SAPs with different particle sizes and chemical compositions were used in the experimental program. Results showed that despite the greater reduction effect of SAP with a smaller particle size on compressive strength, SCC containing this type of SAP had the highest bond strength in uncracked specimens, compared with SAP with larger particle sizes, for SAP-modified NC and SCC mixtures. Moreover, results showed that SCC and NC containing SAP had considerably greater healing improvement factors for large crack widths (w≥0.30 mm) compared with mixtures without polymers; almost 46%, 30%, and 24% healing improvement factors were obtained for average bond stress, bond strength, and residual bond stress of SAP-containing concrete mixtures, respectively. Furthermore, complete strength recovery (100% healing improvement factor) was obtained for SCC mixture with w=0.10 mm after a 28-day healing period.

Bioactive strontium ions/ginsenoside Rg1-incorporated biodegradable silk fibroin-gelatin scaffold promoted challenging osteoporotic bone regeneration.

Autogenous healing of osteoporotic fractures is challenging, as the regenerative capacity of bone tissues is impaired by estrogen reduction and existed pro-inflammatory cytokines. In this study, a biofunctional ginsenoside Rg1 and strontium-containing mineral (SrHPO4, SrP)-incorporated biodegradable silk fibroin-gelatin (SG) scaffold (Rg1/SrP/SG) was developed to stimulate the osteoporotic bone repair. The incorporation of 15 wt% SrP significantly enhanced the mechanical strength, stimulated the osteogenic differentiation of mouse bone marrow mesenchymal stem cells, and suppressed the osteoclastogenesis of RAW264.7 in a concentration-related manner. The loading of Rg1 in SG and 15SrP/SG scaffolds obviously promoted the angiogenesis of human umbilical vein endothelial cells via activating the expression of vascular endothelial growth factor and basic fibroblast growth factor genes and proteins. The bioactive strontium ions (Sr2+) and Rg1 released from the scaffolds together mediated lipopolysaccharide-treated macrophages polarizing into M2 type. They downregulated the expression of inflammatory-related genes (interleukin (IL)-1β, tumor necrosis factor α, and IL-6) and stimulated the expression of genes related to anti-inflammation (Arginase and IL-10) as well as bone repair (BMP-2 and PDGF-BB) in the macrophages. The in vivo results also displayed that SrP and Rg1 significantly promoted the bone repair effect of SG scaffolds in osteoporotic critical-sized calvarial defects. Besides, the degradation rate of the scaffolds was close to the bone regeneration rate. Therefore, the simultaneous addition of SrP and Rg1 is a promising way for facilitating the osteoporotic bone repair activity of SG scaffolds via promoting the osteogenesis and angiogenesis, as well as inhibiting the osteoclastogenesis and inflammation.

Autogenous Healing of Cracked Mortar Using Modified Steady-State Migration Test against Chloride Penetration

Concrete is a popular building material all over the world, but because of different physiochemical processes, it is susceptible to crack development. One of the primary deterioration processes of reinforced concrete buildings is corrosion of steel bars within the concrete through these cracks. In this regard, a self-healing technique for crack repair would be the best solution to reduce the penetration of chloride ions inside concrete mass. In this study, a rapid chloride migration (RCM) test was conducted to determine the self-healing capacity of cracked mortar. With the help of the RCM test, the steady-state migration coefficient of cracked and uncracked specimens incorporating expansive and crystalline admixtures was calculated. Based on the rate of change of the chloride ion concentrations in the steady-state condition, the migration coefficient was calculated. Furthermore, bulk electrical conductivity tests were also conducted before and after the migration test to understand the self-healing behavior. It was evident from the test results that the self-healing of cracks was helpful to reduce the penetration of chloride ions and that it enhanced the ability of cracked mortar to restrict the chloride ingress. Using this test method, the self-healing capacity of the new self-healing technologies can be evaluated. The RCM test can be an acceptable technique to assess the self-healing ability of cement-based materials in a very short period, and the self-healing capacity can be characterized in terms of the decrease of chloride migration coefficients.

Crack repairing of high strength engineered cementitious composites using bacteria-free waste medium

High strength engineered cementitious composites (ECC) that fracture under tensile stress present cracks with the width over 100 μm, which may not be easily repaired by autogenous healing. Herein, this study investigated the healing efficiency of high strength ECC after being immersed in bacteria-free medium which is waste medium during spore cultivation. During incubation of bacteria, concentration of carbonate ions in the medium could rise to 0.30 mol/L approximately. These carbonate ions can be leveraged in calcium carbonate precipitation process for crack healing, which contributed to greater reduction of crack width of ECC specimens in waste medium than that in water. The superior crack closure led to the recovery of water tightness by lowering down the water absorption of cracked specimens and the restoration of tensile properties including both tensile strength and ultimate strain even after final failure of specimens. Therefore, it can be concluded that bacteria-free waste medium is promising to promote healing of concrete cracks.

Prediction of Healing Performance of Autogenous Healing Concrete Using Machine Learning.

Cracks typically develop in concrete due to shrinkage, loading actions, and weather conditions; and may occur anytime in its life span. Autogenous healing concrete is a type of self-healing concrete that can automatically heal cracks based on physical or chemical reactions in concrete matrix. It is imperative to investigate the healing performance that autogenous healing concrete possesses, to assess the extent of the cracking and to predict the extent of healing. In the research of self-healing concrete, testing the healing performance of concrete in a laboratory is costly, and a mass of instances may be needed to explore reliable concrete design. This study is thus the world’s first to establish six types of machine learning algorithms, which are capable of predicting the healing performance (HP) of self-healing concrete. These algorithms involve an artificial neural network (ANN), a k-nearest neighbours (kNN), a gradient boosting regression (GBR), a decision tree regression (DTR), a support vector regression (SVR) and a random forest (RF). Parameters of these algorithms are tuned utilising grid search algorithm (GSA) and genetic algorithm (GA). The prediction performance indicated by coefficient of determination (R2) and root mean square error (RMSE) measures of these algorithms are evaluated on the basis of 1417 data sets from the open literature. The results show that GSA-GBR performs higher prediction performance (R2GSA-GBR = 0.958) and stronger robustness (RMSEGSA-GBR = 0.202) than the other five types of algorithms employed to predict the healing performance of autogenous healing concrete. Therefore, reliable prediction accuracy of the healing performance and efficient assistance on the design of autogenous healing concrete can be achieved.

Exogenous healing in concrete with pH-sustained internal carbonation

In this study, experimental investigations were conducted on enhancing the crack-healing potential of concrete using the internal carbonation process. The objective is to overcome one major limitation of autogenous healing (limited carbonation) by using Sodium Carbonate (Na2CO3) solution as a healing agent. To replicate the different types of damages and internal cracking that could arise during the service life of concrete structures, the effects of drying shrinkage and mechanical stresses on the crack-healing proclivity of cement-based materials were explored. A novel technique to measure crack-healing under constantly applied stress is also introduced for better assessment of healing in real-world situations. Results show a significant improvement in healing by using 0.95 M Na2CO3 solution over plain water. Moreover, permeability observations under stress revealed that the potential for healing by the proposed mechanism is strongly dependant on the stress level in samples. In the later part of the paper, Service Life Predictions were also undertaken by utilizing chloride ion diffusion coefficients extracted from the measured permeability coefficients and service life models available in the literature. Results from comparison of predicted service life indicate that at least in qualitative terms, healing with internal carbonation using the Na2CO3 solution led to an increase in the service life of concrete composites.

Pre- and peri-operative factors influence autogenous tooth transplantation healing in insufficient bone sites

BackgroundThe amount of bone remaining at the transplant site for autogenous tooth transplantation can facilitate successful healing. Therefore, this retrospective study evaluated the factors influencing the healing of 50 successful autogenous tooth transplantations with insufficient bone support at the transplanted site without a bone graft.MethodsThe factors were classified as pre- and peri-operative factors, and the healing outcomes were clinical and radiographic observations. The factors were statistically analyzed using the chi-square test to identify correlations between the pre- and peri-operative factors and the clinical and radiographic outcomes. The T-test or one-way analysis of variance was used to compare the percent bone change in each factor.ResultsThe results indicated that gingival healing was delayed in the intra-arch transplantations, and pulp obliteration was seen earlier when transplanted in the maxilla. Patients under 18-years-old demonstrated a greater percent bone change than the over 18-year-old patients, while the peri-operative variables did not have a relationship with clinical healing and the amount of bone change over 12 months. Furthermore, the percent bone change significantly increased during the first three months.ConclusionsIn conclusion, pre-operative factors, age and transplant site, influenced the healing rate of autogenous transplanted teeth. In contrast, the peri-operative factors were not related with the clinical and radiographic outcomes. Generating the least trauma to the periodontal ligament cells is the most important concern.

Effects of Curing Conditions and Supplementary Cementitious Materials on Autogenous Self-Healing of Early Age Cracks in Cement Mortar

The autogenous healing potential of cement-based materials is affected by multiple factors, such as mix composition, crack width, pre-cracking age and external environmental conditions. In this study, the effects of curing conditions and supplementary cementitious materials (SCMs) on autogenous self-healing of early age cracks in cement mortar were investigated. Three curing conditions, i.e., standard curing, wet–dry cycles and incubated in water, and two SCMs, i.e., fly ash (FA) and blast furnace slag (BFS) with various contents (cement replacement ratio at 0%, 20%, and 40%) were examined. A single early age crack (pre-cracking age of 3 days) with a width of 200~300 μm was generated in cylindrical mortar specimens. Autogenous crack self-healing efficiency of mortar specimens was evaluated by performing a visual observation and a water permeability test. Moreover, microstructure analysis (XRD, SEM and TG/DTG) was utilized to characterize the healing products. The results indicated that the presence of water was essential for the autogenous self-healing of early age cracks in cement mortar. The efficiency of self-healing cracks was highest in specimens incubated in water. However, no significant self-healing occurred in specimens exposed to standard curing. For wet–dry cycles, a longer healing time was needed to obtain good self-healing compared to samples incubated in water. SCMs type and content significantly affected the autogenous self-healing ability of early age cracks. The self-healing efficiency of early age cracks decreased with increases in FA and BFS content. BFS mortars exhibited greater recovery in relation to water penetration resistance compared to the reference and FA mortars. Almost the same regain of water tightness and a lower crack-healing ratio after healing of 28 days in FA mortars were observed compared to the reference. The major healing product in the surface cracks of specimens with and without SCMs was micron-sized calcite crystals with a typical rhombohedral morphology.

Evaluation of Autogenous Healing in Flexural Mortar Members by Chloride Ion Penetration Resistance.

In this study, we investigated the effects of mineral admixtures on the autogenous healing of flexural mortar members through a chloride ion penetration test. The mineral admixtures used were ground granulated blast-furnace slag (GGBS), fly ash, silica fume (SF), clinker binder, and clinker sand. Through a four-point bending test, a crack of approximately 100 μm was induced at the bottom of the flexural mortar member, and the chloride ion penetration depth through the crack was measured to evaluate the self-healing performance. Additionally, we analyzed the correlation between the self-healing performances, which was measured through water flow and water absorption tests. The experimental results showed that the chloride ion penetration depth decreased due to crack healing, and the self-healing performance of the GGBS and SF was the highest. It was found that the subtle change in the self-healing performance was more accurately evaluated by the chloride ion penetration test.

Experimental Investigation of Microbial Precipitation of Concrete with Bacillus Halodurans

This study is about the potential for bacteria to fill the micro pores in the concrete the experimental investigation was to find the ability of the concrete with and without bacteria. The micro pores are filled by calcite precipitation created by the bacteria that will create autogenous healing to the concrete. The bacillus family bacteria was create the alkali-resistant spore this formation make as self-healing of the concrete. The active viable period of the bacteria was 4 months in water before adding to the concrete. The continuous decrease of the spore size diameter in concrete its helps to increase the compressive strength of the concrete. The life span and the concrete that is the durability of the concrete was increased we have a sustainable concrete. The present investigation is aimed to answer the following queries: Growth and culture of bacteria, effect of different cell concentration of bacteria embedded on the strength and durability characteristics of concrete.

Self-healing concrete-What Is it Good For?

Self-healing of concrete is the process in which the material regenerates itself repairing inner cracks. This process can be produced by autogenous or autonomous healing. Autogenous healing is a natural process, produced by carbonation and/or continuing hydration. Autonomous healing is based on the use of specific agents to produce self-healing, which can be added directly to the concrete matrix, embedded in capsules or introduced through vascular networks. Some examples are superabsorbent polymers, crystalline admixtures, microencapsulated sodium silicate, and bacteria. This review is structured into two parts. The first part is an overview of self-healing concrete that summarises the basic concepts and the main advances produced in the last years. The second part is a critical discussion on the feasibility of self-healing concrete, its possibilities, current weaknesses, and challenges that need to be addressed in the coming years.

Review: Microbial induced mineralization of calcium carbonate for self-healing concrete

Abstract. Elkhateeb WA, Elnahas MO, Daba GM. 2021. Review: Microbial induced mineralization of calcium carbonate for self-Healing concrete. Asian J Nat Prod Biochem 19: 1-9. Low-cost solutions achieving concrete self-healing are attracting researchers attention. Generally, concrete self-healing mechanism has been so far accomplished by three approaches: autogenous healing, encapsulation of polymeric material, and microbial induced mineralization of calcium carbonate. Microbial approach seems like an attractive potent, relatively cheap way to achieve concrete self-healing. Hence, this review elucidates the microbial concrete self-healing mechanisms, and compare the roles of fungal and bacterial mediated self-healing concrete.

Enhancement of self-healing to mechanical properties of concrete

Concrete is the main construction material of many structures. Exposing to loads creates cracks in concrete, which reduce the performance and durability. The decrease of concrete cracks becomes a necessity demand to ensure more durability and structural integrity of the concrete structure. Autogenous healing concrete is a kind of new smart concretes, which has the ability to reclose its cracks by means of itself. Concrete self-healing is a type of free repairs processes, which is reduce direct and indirect cost of maintenance and repairing. This work targets to inspect the mechanical properties of concrete after using two combinations of two materials (20 kg/m3 calcium hydroxide Ca(OH)2 and 2 kg/m3 sodium carbonate Na2CO3 and 30 kg/m3 calcium hydroxide and 3 kg/m3 sodium carbonate) as a partial replacement of cement to work as self-healing agents. The paper reports and study the compressive, flexural and splitting tensile strengths and ultrasonic pulse velocity tests’ results at 7, 28 and 90 days of concrete age. Use of two combinations of calcium hydroxide and sodium carbonate, as healing agents, enhanced the mechanical properties of concrete and reduced the width of concrete cracks with time. The concrete compressive strength was increased after curing for 90 days by 9.3 and 11.1 %, respectively. The flexural strength was improved by 14.3 and 15.9 %, respectively. Also, the splitting tensile strength was enhanced by 6.9 and 9.3 %, respectively.

Stimulated autogenous-healing capacity of fiber-reinforced mortar incorporating healing agents for recovery against fracture and mechanical properties

Abstract This study aimed to investigate the effect of autogenous healing capacity with the addition of expansive and crystalline agents on mechanical and fracture behaviors of fiber-reinforced (FR) mortar specimens with crack mouth opening displacement (CMOD) controlled test set-up. The experimental results of a self-healing approach of FR mortar were analyzed in terms of first cracking peak load (FCPL) increase, index of fracture toughness recovery (IFTR), and index of fracture energy recovery (IFER). Initially, the specimens were pre-cracked at different crack widths ranging from 30 μm to 200 μm after 28-days of curing. After pre-cracking, the specimens were kept in water for 56- and 120-day healing. A controlled three-point bending test (PBT) was applied on prism specimen having a central notch of 40 mm depth for pre-cracking as well as the post-conditioning stage for determining the FCPL. However, the crack surfaces were monitored by a high-range digital microscope and scanning electron microscope (SEM) to examine the nature of healed products near the damaged area. Test results revealed that a significant recovery of small cracks (≤50 μm) could be achieved for self-healing specimens by using healing agents (HA), while for large cracks (≥100 μm) partial recovery could be achieved after the 120-day healing period.

Self-healing potential of supplementary cementitious materials in cement mortars: Sorptivity and pore structure

This paper presents the autogenic self-healing potential of Portland cement (PC) blends made with conventional supplementary cementitious materials (SCMs), to improve the water-tightness by reducing the overall pore size. Mortar samples were prepared by mixing PC, sand and water, and partially replacing PC by either silica fume (SF), pulverised fuel ash (PFA), or ground granulated blast-furnace slag (GGBS). Damaged samples were subjected to a water bath to heal microcracks and recover the water-tightness, by further hydration of the starting minerals. Water absorption and density measurements in undamaged, damaged and healed conditions were used to determine the autogenous healing potential of SCMs mixes, showing a post-healing absorption recovery of up to 68% compared to the mix with PC only. Thermal analysis, XRD and MIP measurements confirmed the capability of SCMs to promote the formation of hydrated phases, and reduce the overall pore size by more than 88% compared to PC mixes.

Pull-out behaviour of steel fibres in cracked concrete under wet–dry cycles – deterioration phenomena

This paper presents an experimental investigation into the mechanisms altering the pull-out behaviour of partially pulled hooked-end steel fibres inside an artificial crack exposed to wet–dry cycles of chlorides and carbon dioxide for 6 months. Mechanical and corrosion damage at the surface of the steel fibre was investigated using three-dimensional optical interferometric profiling, and petrographic analyses were used to describe damage and healing processes at the matrix surrounding the fibre. Mechanical damage observed in the cementitious matrix and at the fibre's surface confirmed that the pull-out process was governed by yielding of the fibre, fracture of the adjacent matrix, and friction between the hook and the matrix. Increases in the pull-out force of partially pulled-out fibres after exposure were connected to accumulation of corrosion products from the steel fibre and to alteration of the cement matrix surrounding the fibre. This study concluded that autogenous healing and carbonation of the damaged cement matrix around the fibre are the main mechanisms responsible for the increase in the fibre–matrix bond strength of hooked-end steel fibres bridging cracks in concrete exposed to wet–dry cycles.

Characterisation of autogenous healing in cracked mortars under marine water exposure

In this study, autogenous crack healing was quantified in mortar specimens under various exposure conditions. Specimens were cracked at 28 days and then exposed to a single type of environment: submersion in freshwater, submersion in marine water or cyclic submersion in marine water followed by drying daily (tidal conditions). Instead of taking measurements at a few selected points along the crack length, crack widths were innovatively determined through periodic measurements monitoring the entire crack surface profile. This enabled the identification of significant variations in the healing profile and evidence of widening mostly due to spalling. Specimens exposed to submerged marine conditions displayed maximum overall healing and were able to completely heal a higher percentage of cracks as wide as 0.72 mm as compared to the 0.6 mm reported in previous studies. Evidence of crack widening due to spalling was found in the crack profiles, and the phenomenon was shown to be dependent on the initial width, with wider cracks showing less absolute widening. Specimens exposed to tidal conditions showed the least crack widening among all exposure conditions.

Textile Reinforced Concrete in Combination with Improved Self-Healing Ability Caused by Crystalline Admixture.

The main aim of this study was to investigate the improved autogenous healing of concrete caused by a crystalline admixture in combination with textile reinforced concrete (TRC). This phenomenon (improved healing) has not yet been described by any independent study, and not at all in relation to TRC. The results of the study confirmed that the interaction between TRC and the crystalline admixture’s self-healing ability is advantageous and usable. The application of crystalline admixture could ensure the long-term entirety of the TCR element, where microcracks could occur. This allows for the creation of advantageous, thin (achieved by TRC) and waterproof (achieved by the crystalline admixtures) concrete structures. Moreover, this does not depend on temperature in the range of 4–30 °C (lower temperatures are of course problematic, as for most other cementitious materials). However, the interaction of both materials has its limits; the cracks must not be too wide (max. 0.1 mm), otherwise they will not heal. On the other hand, the advantage is that it does not matter what type of cement is used (CEM I and CEM II showed the same results), and the composition of the newly formed crystals in the cracks corresponds to the composition of the C-S-H gel, so it can be assumed that secondary hydration of the Portland cement occurred in the crack area.

Effect of nano-SiO2 and nano-CaO in autogenous Self-healing efficiency

Cracks remain the number one problem of concrete even today. However, with the technological progress and the self-healing materials, this problem seems to have a chance to be reduced drastically. This study investigated the properties of self-healing to cement paste compositions containing nano-SiO2 (NS) and nano-CaO (NL) at dosages of 1.5% w/w, and a combination of them, with 1% NS and 0.5% NL. Due to the filler effect and the pozzolanic reaction of nanoparticles, the microstructure became less porous and more homogeneous. The mechanical properties were determined by compression and flexural tests. For the self-healing observation, pre-cracked specimens, by three-point bending test and pre-damaged specimens, by compressive test up to 90% of the initial strength, were prepared. Tests of the sorptivity properties and dynamic modulus of elasticity through ultrasounds verified the beneficial effects of nanomaterials. Also, the width closure of the pre-crack specimens was observed by a microscope. It revealed the quick autogenous healing of the specimens containing nanomaterials, where after 28 days of hydration, the crack was almost filled. The microstructure of the samples was investigated through scanning electron microscopy (SEM) in each composition after 28 days of healing. The mixtures containing NS exhibit increased compressive strength and denser structure. Also, the addition of nano-CaO has reduced water penetration through the crack and increases self-healing efficiency. The composition with the combination of the nanomaterials revealed interesting results. It seems that even a low percentage of NS improves the mechanical properties, and also, the NL particles assist towards the high healing capacity.