Introduction
Why we need self-healing in concrete materials?
Concrete is probably the most important and commonly used construction materials However, cracking at any stage of the service life of concrete structure has been experienced by more clients, designers, researchers, and contractors than any other impact, and overall by an average of 90 % of the respondents (Gardner et al., 2018) Although the strength and low cost of concrete are the main reason for becoming the most widely used construction material worldwide, low tensile and cracking strength affect its integrity It is well known that cracks are unavoidable in reinforced concrete structures Even when reinforced with rebars, mineral fibers, or polymer, concrete is sensitive to crack formation-one of several damage types Cracking, mostly below the groundwater level, can lead to many problems, such as water leakage and reinforcement corrosion For many years, a full array of crack repair solutions has been developed with deliberate external intervention However, it is difficult to repair the micro-cracks or crack embedded deep in concrete structures (highways, tunnels, or bridges) A smart and automated method to repair cracks is necessary for sustainable concrete infrastructure This concern is calling for the development of intelligent self-healing materials and preventive repair methods
,QPDQ\FDVHVFUDFNVOHVVWKDQȝPLQconcrete can be healed autogenously due to the hydration of residual clinker powder or the carbonation of dissolved calcium hydroxide (Wu et al., 2012; Kim Van Tittelboom and De Belie, 2013; Reinhardt et al., 2013) According to the practical guideline for cracked concrete structures by the Japan Concrete Institute (JCI), the American Concrete Institute (ACI), and other committees, cracks width of less than 0.2 mm (small-crack) does not pose a considerable structural (N Otsuki et al., 2014; Nobuaki Otsuki et al., 2015; Edvardsen, 1999) On the other hand, the appearance of small cracks (less than 0.30 mm) in concrete is almost inevitable, does not necessarily pose a risk of collapse to the structure, but inevitably degrades function and increases speed degradation, reducing life durability of the structure Also, threat, chloride, sulfate, and acid penetration through cracks in long-term durability can lead to the corrosion of reinforcement or expansion of cement paste, resulting in damage and even serious harm to the structure.
Advances and challenges for current self-healing approaches
Generally, humans, animals, or plants can heal their damages themselves within a small range Inspired by natural and biological systems, self-healing concrete has been researched and developed For concrete materials, self-healing can occur as a natural phenomenon (autogenic) or a result of engineering techniques (autonomic) (Gardner et al., 2018; Joseph et al., 2010) The engineering self-healing can be obtained by fiber reinforcement (Gray, 1984; Hannant and Keer, 1983; V C Li et al., 1998; M Koda, H Mihashi, T Nishiwaki, T Kikuta and S.M Kwon, 2011; Mihashi et al., 2011; Y Zhu et al., 2012), using additives with chemical agents (K Van Tittelboom and De Belie, 2010), mineral geomaterials (Ahn and Kishi, 2010), and microbial- induced calcium carbonate precipitation (MICP) (Ramachandran et al., 2001; Jonkers, 2007a, 2007a; Kim Van Tittelboom et al., 2010) Therefore, self-healing concrete using biomineralization by bacteria can be a sustainable solution to extend the service life and durability of concrete structures According to previous studies, limited types of bacteria can be used for MICP, such as Bacillus cohnii (Jonkers, 2007a), Bacillus pasteurii (Ramachandran et al., 2001), Bacillus pseudofirmus (Jonkers and Schlangen, 2008), Bacillus subtilis (Huynh et al., 2017; Matsushita et al., 2010; M S Rao et al., 2013) Each type of bacteria needs proper nutrients for their growth Based on the metabolic pathways involved in MICP, the self-healing
2 mechanism includes the ureolytic and the non-ureolytic process According to many research findings, the most effective way of producing calcium carbonate (CaCO3) is urea hydrolysis Also, non-ureolytic bacteria have been explored (Lee et al., 2017) to prevent the adverse effects on the mechanical properties of concrete from ammonia produced by urea hydrolysis (Dhami et al., 2013; T Zhu and Dittrich, 2016) However, this mechanism can lead to high costs for organic nutrients and other treatments
Figure 1.1 Schematic description of repair mechanism through biomineralization using porous controlled release material immobilized Bacillus subtilis natto
Figure 1.2 Illustration of two approaches of crack repairing using bacteria in concrete and the healing products after long time Outside treatment by spraying or injection (left) and inside treatment by adding bacteria into concrete mix through lightweight aggregate (LWA) (right) (a) The self-healing mechanism by activating Bacillus subtilis natto immobilized in LWA combines with natural carbonation and chemical reactions (b)
3 When the concrete mix is designed by adding certain minerals, crystallization additives, fibers, hydrogels, polymers, or bacteria, which can be added or after packaging, it can be enhanced in the natural self-healing ability Since some self-healing admixtures, such as swell mineral supplements or hydrogels, only improve or stimulate the intrinsic self-healing of concrete, it is only possible to heal cracks completely when the crack is limited to a few hundred micrometers In the case that larger cracks need to be healed, additional healing materials should be provided either by bacterial precipitation mechanism or by encapsulated polymeric agents
In recent years, to create a sustainable and cost-effective alternative, microbially calcium carbonate precipitation (MICP) by microorganisms has been studied for application in concrete crack repairing Some bacteria strains can convert carbonate ions (CO3 2-) through the urea hydrolysis to bind with calcium ions (Ca 2+ ) to form calcium carbonate (CaCO3) (Fig 1.1) There are challenges when adding bacteria in the concrete structure directly due to this harsh environment Firstly, the regular concrete porosity is usually less than 1 %, and the average size RIWKHSRUHVLVVPDOOHUWKDQȝP0HDQZKLOHWKHEDFWHULDODYHUDJHVL]HLVDURXQG-2.0 àm (for spherical bacteria), and 1- ȝm (for rod-like or filamentous bacteria) (Holley, 2017; Khalifa, 2016; Mitchell and Santamarina, 2005) Hence, the bacteria may be squeezed easily during the cement hydration by the volume of capillary pores decrease Secondly, the cement matrix in the concrete structure is a high-alkaline environment, in which the pH is around 12-
13, with limited moisture and oxygen by the cement minerals setting and hardening process These conditions can be a challenge for bacteria to survive, grow, multiply, and activate Also, at that high pH value, the bio-mineralization of bacteria was decreased significantly (Whiffin, 2004) due to the decreasing of urease activity shown by the low rate of urea decomposition As reported in a previous study, only at 28 days and more, the compressive strength increased, while early strength could decrease to lower than the reference without bacteria (Jonkers, 2011) Finally, the bacteria can be destroyed by the shearing force during mixing, or the gradual shrinkage of concrete In 2011, a study using B megaterium showed that bacterial concentration decreased sharply from 10 7 to 10 5 CFU/ml just after three days in the mortar specimens After 28 days, the survival ratio was 0.1 % Similar results were obtained when using S pasteurii in cement paste (Basaran, 2013) In this case, the viable cell concentration remained was decreased by 80 % after one day The viable cells remained after 28 days was just 0.4 % After 28 days from the B megaterium and nutrients were added into the mixture, nearly 0.06 % (from 5x10 7 CFU/ml to 3.2x10 4 CFU/ml) of the bacteria could survive (Achal et al., 2011) For nearly one year, another study showed that 2 % of the initial S Pasteurii cells survived (Bundur et al., 2015) Mixing bacteria with the nutrient-rich medium as glucose, yeast extract, or other organic compounds directly could cause a delay in the setting time of cement
In the case of using an optimum bacteria with a nutrient-rich medium, although adding directly inside the concrete mixture may prevent the micro-cracks appears by modifying the setting time and the water removal, there was adverse in the concrete mix reported in a study on using Bacillus subtilis JC3 (MV Seshagiri Rao et al., 2017) The compressive strength reduction of mortar specimens with bacterial concentrations of more than 10 5 CFU/ml of mixing water (Rao et al., 2017) may be caused by the disruption of the integrity of the hydrated cement matrix, which was the result of organic matter exceeding the permissible limit (according to IS 456:2000) Also, a high concentration of bacteria could create new voids inside the concrete structure due to the by-product urease reaction, decreasing concrete strength Nutrients, such as lactose, glucose, corn starch, tapioca, and soybean meal, could be used for bacterial bio-mineralization, while the optimum concentration should be from 2 to 20 g/L in the bacterial solution with the range of the bacterial spore from 4.28x10 8 to 8.05x10 9 spores/mL Yeast extract has the highest impact on decreasing compressive strength when the addition is more than 0.85 % of the cement weight (J Wang, 2013; J Y Wang et al., 2014) mainly because of the delay on cement hydration Urea has a moderate effect on cement hydration (J Y Wang et al., 2014), while calcium sources such as CaCl2 can increase the strength due to accelerating the cement hydration (Wang et al., 2014) A combination of nutrients with proper dosage can
4 adversely compensate To avoid that impacts, as surface treatments, injections were preferred to adding to the concrete mixture, as the repairing liquid-based systems with bio-grout can easily transport to cracks (Putri et al., 2019; Ujike et al., 2014) However, for many cases, the bonding between the healing agent and concrete substrate may decrease over time, resulting in re-crack or sometimes even more severe (Fig 1.2a) In contrast, adding bacteria into the concrete mixture can become "smart-living" material with the adaption immediately without human actions when cracks appear As reported in a study using Diatomaceous Earth to immobilize Bacillus subtilis HU58 (Huynh et al., 2017), there was a small reduction of 2.7x10 8 CFU/g from the initial concentration after five months in concrete As described in Fig
1.2b, the incorporation of immobilized bacteria in the lightweight aggregate (LWA) in concrete can enhance crack healing by generating CaCO3 due to their metabolic activity and subsequent chemical reactions with other hydrated cement minerals and metabolic by-products
Figure 1.3 Range of crack width for sufficient healing capacity through different self-healing approaches (De Rooij et al., 2013; Souradeep and Kua, 2016; Fernandez et al., 2020).
What bacteria can do and how to shorten the way from the laboratory to real self-healing applications?
In this study, Bacillus subtilis natto, a native Japanese microorganism, will be used with a suitable proportion of nutrients to form CaCO3 and prevent any adverse effects on concrete durability Bacillus subtilis natto, the main factor for fermented soybean, was reclassified as Bacillus subtilis EDVHG RQ EDFWHULRORJLFDO FKDUDFWHUL]DWLRQ LQ %HUJH\ảV 0DQXDO RI Determinative Bacteriology (Balows, 1975) As a gram-positive bacteria, Bacillus subtilis natto can survive in the high-alkaline environment of concrete by its ability to form spores (Samanya and Yamauchi, 2002; Kawaai et al., 2017) As mentioned before, Fig 1.1 demonstrates that the biomineralization mechanism of Bacillus subtilis natto is relatively similar to Bacillus subtilis HU58 (Huynh et al., 2017) and other members of the subtilis family Based on urea hydrolysis, bacterial cells become negatively charged, leading to the rapid attraction of surrounding calcium ions Also, bacteria can degrade organic compounds included lactose (sugar), as a carbon source for growth and activation Therefore, these processes controlled the adverse effects of nutrients on the properties of fresh and hardened concrete
Note that bacteria can naturally produce CaCO3 in environments (Boquet et al., 1973) with a high concentration of Ca 2+ by changing the precipitation factors, separately or in combinations (Krajewska, 2018; Dhami et al., 2013; Hammes and Verstraete, 2002) Their primary role is often recorded in increasing the pH value After the first stage of nucleation sites forming, the amount of CaCO3 crystals begins to increase When CaCO3 crystals cover all of the cell wall surfaces, new crystals may not form Instead, the crystals start to grow larger and become compact Also, Bacillus subtilis natto does not cause disease (Brenner and Miller, 2014) This strain is almost safe and easy to work within the laboratory
Bacillus subtilis natto would be an economical solution because of the low cost of bacteria spores, compared to the other microorganisms As mentioned, urea hydrolysis is one of the most efficient ways of CaCO3 forming However, previous researches have studied the biomineralization with adequate organic carbon sources for bacterial growth and activation This study tested urease activity and bacterial CaCO3 precipitation with limited organic nutrients (yeast extract and peptone) to prevent rapid activation during the early stage of concrete hardening This test condition also simulated the harsh conditions of lacking nutrients after a long time Note that yeast extract and other organic carbon sources have a considerable impact on decreasing the compressive strength of concrete due to hydration delays
Although spores were shown to have slower CaCO3 precipitation than vegetative cells (J Wang et al., 2017; De Belie et al., 2018), since spores first need to germinate before their precipitation activities can start, spores have a significantly higher possibility to survive in harsh conditions for years than activated cells Consequently, Bacillus subtilis natto spores and lactose need to be immobilized inside the capsules to minimize the negative impacts on hydration and compressive strength Then, the release of the bacterial healing agent was activated by crack formation, which results in the breakage of the embedded brittle capsules However, at first, the capsules also need to have enough strength to protect themselves from the concrete mixing process Therefore, expanded lightweight aggregate (LWA) can be a promising material to carry, protect, and control release Although aggregates are the principal constituent of any concrete type and are expected to be widely used to host self-healing agents, this potential has not been extensively researched Using LWA immobilized bacterial spores reduces the change in concrete mix and prevents negative effects on concrete properties, compared to other complicated encapsulation techniques Using this strategy to force the bacteria to use nutrient-low and be protected strongly in LWA, we suggested having a solution for the question that at later ages of the concrete, under sustained stresses, repeated cracking is possible to repeat the self-healing cycles Moreover, expanded clay LWA was proposed as the bacterial containers and can replace regular aggregates with equivalent or higher strength than regular lightweight concrete
Figure 1.4 The illustrated scenario develops a self-healing system using Bacillus subtilis natto immobilized in LWA for concrete structures
The survival rate was figured out by measuring the bacterial concentration remaining in LWA after multi cracking-healing cycles As reported by various researchers, alkaline bacteria were expected with the ability to lie dormant in the concrete structure for up to 200 years (Schlegel, 1995; Jonkers, 2007b; Jonkers and Schlangen, 2008; Jonkers, 2011; Holley, 2017) before activating to form CaCO3 Previous studies showed that spores are viable as they can
6 withstand mechanical and chemical stresses and remain their lives in a dry state for periods over 50 years (Todar, 2005; Chamali et al., 2019) In this work, the bacterial survival rate was taken for a long-time using concrete for up to 9 months to confirm the survival of Bacillus subtilis natto immobilized in LWA After long-time in concrete, we also aimed to know that the self-healing ability could occur or not in the case of inadequate carbon source when the initial limited-amount of lactose was used end Besides, to clarify one of the significant challenges into the self-healing mechanism (Mahmoodi and Sadeghian, 2019; Mihashi and Nishiwaki, 2012; W Li et al., 2018), we evaluated the repeatability of self-healing concrete specimens with the bacteria immobilized in LWA through the compressive strength restoration experiment of the four cracking-healing cycles with the help of ultrasonic pulse velocity tracking and microstructure analysis methods Also, water pearmeability under the capillary absorption test and a series of water flow tests (Huynh et al., 2020a, 2020b) were carried out The general strategy of research and experiment designs is summarily described in the scenario
Figure 1.5 The general strategy of research and experiment designs
A system using Bacillus subtilis natto immobilized in expanded clay LWA for concrete structures was investigated with the target of long-time using and possibly repeatable of healing effect, leading to sustainable development Furthermore, experimental results and theoretical hypotheses in this work were expected to contribute to shortening the way from laboratory to real-scale application of self-healing concrete such as water retaining structures, low-cost and durable roads, or underwater tunnels
Achal, V., Pan, X., and ệzyurt, N (2011) Improved strength and durability of fly ash-amended concrete by microbial calcite precipitation Ecological Engineering, 37(4), 554±559
Ahn, T.-H., and Kishi, T (2010) Crack self-healing behavior of cementitious composites incorporating various mineral admixtures Journal of Advanced Concrete Technology, 8(2), 171±186
%DORZV $ %HUJH\ảV 0DQXDO RI 'HWHUPLQDWLYH %DFWHULRORJ\ (LJKWK (GLWLRQAmerican
Basaran, Z (2013) Biomineralization in cement based materials: Inoculation of vegetative cells
Boquet, E., Boronat, A., and Ramos-Cormenzana, A (1973) Production of calcite (calcium carbonate) crystals by soil bacteria is a general phenomenon Nature, 246(5434), 527±529 Brenner, S., and Miller, J H (2014) %UHQQHUảVHQF\FORSHGLDRIJHQHWLFV Elsevier Science
Bundur, Z B., Kirisits, M J., and Ferron, R D (2015) Biomineralized cement-based materials:
Impact of inoculating vegetative bacterial cells on hydration and strength Cement and Concrete Research, 67, 237±245
Chamali, B., Al-Nasra, M., and Abu-Lebdeh, T (2019) Sustainable Study of Self-Healing Concrete in Hot Desert Climate 12, 166±172 https://doi.org/10.3844/AJEASSP.2019.166.172
De Belie, N., Wang, J., Bundur, Z B., and Paine, K (2018) Bacteria-based concrete In Eco-efficient repair and rehabilitation of concrete infrastructures (pp 531±567) Elsevier
De Rooij, M., Van Tittelboom, K., De Belie, N., and Schlangen, E (2013) Self-healing phenomena in cement-Based materials: State-of-the-art report of RILEM technical committee 221-SHC: self-Healing phenomena in cement-Based materials (Vol 11) Springer
Dhami, N K., Reddy, M S., and Mukherjee, A (2013) Biomineralization of calcium carbonates and their engineered applications: A review Front Microbiol 4: 314
Edvardsen, C (1999) Water permeability and autogenous healing of cracks in concrete In Innovation in Concrete Structures: Design and Construction (pp 473±487) Thomas Telford Publishing
Fernandez, C A., Correa, M., Nguyen, M.-T., Rod, K A., Dai, G L., Cosimbescu, L., Rousseau, R., and Glezakou, V.-A (2020) Progress and challenges in self-healing cementitious materials
Gardner, D., Lark, R., Jefferson, T., and Davies, R (2018) A survey on problems encountered in current concrete construction and the potential benefits of self-healing cementitious materials
Case Studies in Construction Materials, 8, 238±247
Gray, R J (1984) Autogenous healing of fibre/matrix interfacial bond in fibre-reinforced mortar
Hammes, F., and Verstraete, W (2002) Key roles of pH and calcium metabolism in microbial carbonate precipitation Reviews in Environmental Science and Biotechnology, 1(1), 3±7
Hannant, D J., and Keer, J G (1983) Autogenous healing of thin cement based sheets Cement and
Holley, D (2017) General Biology II: Organisms and Ecology Dog Ear Publishing
Huynh, N N T., Imamoto, K., and Kiyohara, C (2020a) Compressive Strength Improvement and
Water Permeability of Self-Healing Concrete Using Bacillus Subtilis Natto Current Topics and Trends on Durability of Building Materials and Components, 113±120
8 Huynh, N N T., Imamoto, K., and Kiyohara, C (2020b) Eco-friendly technique on nutrient sources and capsulation for bacteria-based self-healing concrete Proceedings of the Japan Concrete
Huynh, N N T., Phuong, N M., Toan, N P A., and Son, N K (2017) Bacillus subtilis HU58
Immobilized in micropores of diatomite for using in self-healing concrete Procedia Engineering, 171, 598±605
Jonkers, H M (2007a) Self healing concrete: A biological approach In Self healing materials (pp
Jonkers, H M (2007b) Self healing concrete: A biological approach In Self healing materials (pp
Jonkers, H M (2011) Bacteria-based self-healing concrete Heron, 56 (1/2)
Jonkers, H M., and Schlangen, E (2008) Development of a bacteria-based self healing concrete
Joseph, C., Gardner, D., Jefferson, T., Isaacs, B., and Lark, B (2010) Self-healing cementitious materials: A review of recent work Proceedings of the Institution of Civil Engineers- Construction Materials, 164(1), 29±41
Kawaai, K., Okuno, H., and Ujike, I (2017) Alginate Capsules Encapsulating Aerobic and
Anaerobic Microorganism for Repairing Cracks in Concrete The 6th International
Conference on Self-Healing Materials
Khalifa, S F (2016) Fabrication and characterization of antibacterial herbal drug loaded polylactic acid/cellulose acetate nanocomposite nanofibers for wound dressing applications http://dar.aucegypt.edu/handle/10526/4609
Krajewska, B (2018) Urease-aided calcium carbonate mineralization for engineering applications:
A review Journal of Advanced Research, 13, 59±67
Lee, Y S., Kim, H J., and Park, W (2017) Non-ureolytic calcium carbonate precipitation by
Lysinibacillus sp YS11 isolated from the rhizosphere of Miscanthus sacchariflorus Journal of Microbiology, 55(6), 440±447
Li, V C., Lim, Y M., and Chan, Y.-W (1998) Feasibility study of a passive smart self-healing cementitious composite Composites Part B: Engineering, 29(6), 819±827
Li, W., Dong, B., Yang, Z., Xu, J., Chen, Q., Li, H., Xing, F., and Jiang, Z (2018) Recent Advances in Intrinsic Self-Healing Cementitious Materials Advanced Materials, 30(17), 1705679
M Koda, H Mihashi, T Nishiwaki, T Kikuta and S.M Kwon (2011) Self-Healing Capability of
Fiber Reinforced Cementitious Composites International RILEM Conference on Advances in Construction Materials Through Science and Engineering
Mahmoodi, S., and Sadeghian, P (2019) SELF-HEALING CONCRETE: A REVIEW OF RECENT
RESEARCH DEVELOPMENTS AND EXISTING RESEARCH GAPS
Matsushita, Y., Shinichiro, O., Yasuhara, H., and Ujike, I (2010) Development of crack repairing method of concrete using microbial metabolism Vol.32(No.1)
Mihashi, H., Ahmed, S F U., and Kobayakawa, A (2011) Corrosion of reinforcing steel in fiber reinforced cementitious composites Journal of Advanced Concrete Technology, 9(2), 159±
Mihashi, H., and Nishiwaki, T (2012) Development of engineered self-healing and self-repairing concrete-state-of-the-art report Journal of Advanced Concrete Technology, 10(5), 170±184
9 Mitchell, J K., and Santamarina, J C (2005) Biological considerations in geotechnical engineering
Journal of Geotechnical and Geoenvironmental Engineering, 131(10), 1222±1233
2WVXNL 1 DPDGD 7 ,PDPRWR DQG 2VDGD 2XWOLQH RI ³3UDFWLFDO *XLGHOLQH IRU
Investigation, Repair and Strengthening of Cracked Concrete Structures -2013-´Concrete Journal, 52(8), 638±643 https://doi.org/10.3151/coj.52.638
Otsuki, Nobuaki, Miyazato, S., and IMAMOTO, K (2015) Practical Guideline for Investigation,
Repair and Strengthening of Cracked Concrete Structures Japan Concrete Institute, 53(11), 1017±1018
Putri, P Y., Ujike, I., and Kawaai, K (2019) Application of bio-based material for concrete repair:
Case study leakage on parallel concrete slab MATEC Web of Conferences, 258, 01013
Ramachandran, S K., Ramakrishnan, V., and Bang, S S (2001) Remediation of concrete using micro-organisms ACI Materials Journal-American Concrete Institute, 98(1), 3±9
Rao, M S., Reddy, V S., Hafsa, M., Veena, P., and Anusha, P (2013) Bioengineered concrete-a sustainable self-healing construction material Research Journal of Engineering Sciences ISSN, 2278, 9472
Rao, MV Seshagiri, Reddy, V S., and Sasikala, C (2017) Performance of microbial Concrete developed using Bacillus Subtilus JC3 Journal of The Institution of Engineers (India): Series
Reinhardt, H W., Jonkers, H., Van Tittelboom, K., Snoeck, D., De Belie, N., De Muynck, W.,
Verstraete, W., Wang, J., and Mechtcherine, V (2013) Recovery against environmental action In Self-Healing Phenomena in Cement-Based Materials (pp 65±117) Springer
Samanya, M., and Yamauchi, K (2002) Histological alterations of intestinal villi in chickens fed dried Bacillus subtilis var Natto Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 133(1), 95±104
Schlegel, H (1995) General microbiology 7th edition Cambridge University Press, Cambridge
Souradeep, G., and Kua, H W (2016) Encapsulation technology and techniques in self-healing concrete Journal of Materials in Civil Engineering, 28(12), 04016165
7RGDU 7RGDUảV RQOLQH WH[WERRN RI EDFWHULRORJ\ 7KH JHQXV %DFLOOXVUniversity of
Wisconsin-Madison, Department of Bacteriology
Ujike, I., Kubo, F., Kawaai, K., and Okazaki, S (2014) Influencing factors affecting microbial metabolic processes of bio materials used for leaking repairs Concrete Solutions 2014, 127
Van Tittelboom, K., and De Belie, N (2010) Self-healing concrete: Suitability of different healing agents ,QWHUQDWLRQDO-RXUQDORI5ảV, 1(1), 12±21
Van Tittelboom, Kim, and De Belie, N (2013) Self-healing in cementitious materials²A review
Van Tittelboom, Kim, De Belie, N., De Muynck, W., and Verstraete, W (2010) Use of bacteria to repair cracks in concrete Cement and Concrete Research, 40(1), 157±166
Wang, J (2013) Self-healing concrete by means of immobilized carbonate precipitating bacteria
Wang, J., Jonkers, H M., Boon, N., and De Belie, N (2017) Bacillus sphaericus LMG 22257 is physiologically suitable for self-healing concrete Applied Microbiology and Biotechnology,
Wang, J Y., Soens, H., Verstraete, W., and De Belie, N (2014) Self-healing concrete by use of microencapsulated bacterial spores Cement and Concrete Research, 56, 139±152
10 Whiffin, V S (2004) Microbial CaCO3 precipitation for the production of biocement [PhD Thesis]
Wu, M., Johannesson, B., and Geiker, M (2012) A review: Self-healing in cementitious materials and engineered cementitious composite as a self-healing material Construction and Building
Zhu, T., and Dittrich, M (2016) Carbonate precipitation through microbial activities in natural environment, and their potential in biotechnology: A review Frontiers in Bioengineering and
Zhu, Y., Yang, Y., and Yao, Y (2012) Autogenous self-healing of engineered cementitious composites under freeze±thaw cycles Construction and Building Materials, 34, 522±530
Literature review of self-healing
General introduction
In 2009, the state-of-the-art report about autogenous healing in cementitious materials was published and summarized their findings,QDVSHFLDOLVVXHRI³-RXUQDORI$GYDQFHG&RQFUHWH7HFKQRORJ\´ in Japan, which aims at summarizing progress in self-healing cementitious materials, was published Through the studies, three main contents are the quantitative evaluation of self-healing performance, such as water leakage control and loading damage recovery, the investigation into self-healing mechanism, and application of the non-destructive tests to identify self-healing results Every year, with the rapid increase in the number of publications in the world, research teams in Japan have worked on many projects involving self-healing techniques in concrete Also, the Japanese industry has a high interest in self-healing materials, especially concrete In 2019, as the first time a conference
RI ³6HOI-+HDOLQJ 0DWHULDOV &RPPXQLW\´ ZDV KHOG LQ DQ $VLDQ FRXQWU\ ³7KH WK ,QWHUQDWLRQDO Conference on Self-KHDOLQJ0DWHULDOV,&6+0´LQ