PRACTICAL APPLICATIONS OF BACTERIA-BASED PROTECTIVE SYSTEMS: SELF-HEALING CONCRETE AND REPAIR STYSTEMS

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1 PRACTICAL APPLICATIONS OF BACTERIA-BASED PROTECTIVE SYSTEMS: SELF-HEALING CONCRETE AND REPAIR STYSTEMS Virginie Wiktor (1), Henk M. Jonkers (1) (1) Department of Structural Engineering, section Materials and Environment, Delft University of Technology, Delft, The Netherlands Abstract The development of bacteria-based systems for the protection of concrete structures has gained lot of attention over the past few years as it could contribute to lower the maintenance cost and increase the durability of concrete structures. These systems are based on Microbial Induced Precipitation (MIP), a method by which calcium carbonate precipitation is induced by bacteria. This paper gives an overview of field applications with the bacteria-based systems developed at the Delft University of Technology (the Netherlands): self-healing concrete and repair systems. Field applications in collaboration with stakeholder parties involve casting of self-healing concrete as linings for irrigation canals in Ecuador (July 2014), patch repair for the waterproofing of leaking cracks with self-healing mortar ( ) and improving the freeze-thaw resistance and sealing of cracks in parking decks with the application of a liquidbased repair system ( ). These large scale applications proofed the functionality and market potential of these bacteria-based protective systems. 1. INTRODUCTION Corrosion of steel reinforcement has many economic and societal consequences. It is estimated that in the United States alone the annual direct cost for maintenance and repair of concrete highway bridges due to reinforcement corrosion amounts to 4 billion dollars [1]. These costs are however crucial to maintain the useful lifetime of a structure and to ensure appropriate safety of the user. One of the reasons for this lies in the short-term efficiency of conventional repair products which is together with the use of environmental unfriendly materials a burden for the repair industry. A promising alternative approach to this problem is the application of bacteria-based protective systems for concrete. Engineered for self-healing concrete or concrete repair [2] and subsequent crack-sealing, these systems are based on Page 1

2 Microbially Induced Carbonate Precipitation (MICP). MICP is the process where calcium carbonate is produced as the result of the metabolic activity of bacteria under suitable conditions. Various metabolic pathways are involved in MICP processes but in each case the system is composed of specialized alkaliphilic bacteria, nutrients for the bacteria (urea, organic salt ) and a calcium rich solution. MICP applied to concrete material has demonstrated its efficiency for crack sealing not only at the laboratory scale [3] but also through several recent applications on concrete structures. Excellent illustration of the technology potential were made for section of irrigation canals in Ecuador [3] or parking garages in the Netherlands [4]. This paper gives an overview of field applications with the bacteria-based systems developed at the Delft University of Technology (the Netherlands). The authors also discuss the challenges that remain in order to ensure the long-term durability of the bio-based systems. 2. BACTERIA-BASED SELF-HEALING CONCRETE IRRIGATION CANALS IN ECUADOR The first field application of bacteria-based self-healing concrete was done in the highlands in Ecuador in July 2014 in collaboration with the Catholic University of Santiago de Guayaquil [5]. The bacteria-based healing agent is composed of alkaliphilic bacterial spores and nutrients for the bacteria immobilized in porous light-weight aggregates (LWA). Bacteria-based healing agent with LWA targets applications which does not require high strength concrete such as irrigation canals for instance. The irrigation canals ditched in the province of Tungurahua (Ecuador) features concrete linings which were casted in order to limit water loss due to infiltration into the soil. However, soon after the casting (within a year) the concrete linings started to crack what resulted still in water loss. Application of bacteriabased self-healing concrete reinforced with natural fibres has been proposed in order to improve the durability of these irrigation canals. Based on previous work of Mera Ortiz, Abaca fibre, natural fibre found in Ecuador, has been used as reinforcement in order to control and limit the crack width of the material. The concrete mix was designed based on the materials available on site (Figure 1) and on the strength requirements for the concrete linings. Three meters long sections of concrete linings were casted from 110-litres batches of self-healing concrete and another three meters of control concrete (no healing agent). The healing agent composed of bacterial spores and calcium lactate immobilized into LWA was prepared on site and consists of impregnation without vacuum of warm saturated calcium lactate solution. The local farmers who own the canals prepared the formwork and helped in preparing and applying the concrete mixtures (Figure 2). The formwork was removed 3 days after casting and 2 days later the water flow was reopened. Five months after casting no signs of cracking or deterioration have been noticed. Monitoring is still in progress. Page 2

3 Figure 1. Preparation of the materials for the casting of the linings of irrigation canals Figure 2. Preparation with the farmers of the formwork for the linings of irrigation canals Page 3

4 3. BACTERIA-BASED REPAIR MORTAR PATCH REPAIR OF A VERTICAL LEAKING CRACK A number of field trials involving repair of damaged concrete structures with the bacteriabased repair mortar developed at Delft University of Technology have been done on several outdoors locations in the Netherlands [6]. Treatments focused on the structural repair of leaking cracks. An example is the repair of vertical leaking crack on water treatment plant site. The leakage was evidenced by discoloration observed at the surface of the crack before repair. Sierra-Beltran and Jonkers were assisted by a company specialised in concrete repair for the preparation of the crack before repair. The crack was first cut open and half was patch repaired with conventional repair mortar and the other half with the bacteria-based repair mortar in October The first inspection was performed 6 months later (Figure 3) and observations showed no evidence of delamination or cracking for both the bacteria-based and conventional repair mortars. However, discoloration of the conventional repair mortar only was noticed. This could be due to the leaking water or oxidation of the mortar components. Monitoring is still in progress. Figure 3. Picture of the crack after patch repair top section repaired with conventional repair mortar, bottom section treated repaired with bacteria-based repair mortar Page 4

5 4. BACTERIA-BASED LIQUID REPAIR SYSTEM SEALING OF CRACKS AND IMPROVED RESISTANCE TO FREEZE-THAW The bacteria-based system has successfully been applied in practice on several concrete structures in the Netherlands. This liquid-based system transports bacteria and their nutrients into cracked or porous concrete. The bacteria are from the genus Bacillus. They are added as endospores, dormant bacterial cells with characteristic round compact shape. When the environmental conditions are favourable (presence of water, oxygen and nutrients) these endospores germinate and grow into rod-shaped vegetative bacterial cells. The system is composed of 2 solutions: (i) Solution A Sodium-silicate (alkaline buffer), Sodium-gluconate (source of organic carbon for bacteria growth), alkaliphilic bacteria. (ii) Solution B Calcium-nitrate (calcium source for CaCO3 precipitation), alkaliphilic bacteria. When the solutions are mixed together a gel is formed due the reaction between the silicate-based compound and the calcium ions. Although not very strong, this gel allows a rapid sealing of the crack (within few hours) and provides an optimum environment for the bacteria to precipitate calcium carbonate. By the time the gel becomes too weak, substantial amount of CaCO3 has been precipitated to seal the crack. The ph of the solution (A+B) is 10.5 which is around the optimum for these bacteria to grow but is also compatible with the concrete material. The first field application of the bacteria-based repair system was performed on a 8 yearsold underground car park [4]. The treatment focused on the repair of two type of damages commonly encountered in such structures: (i) leaking cracks on the parking deck, (ii) damaged concrete pavement due to freeze/thaw (and de-icing salt) (Figure 4). The two solutions (A and B) were sprayed at the surface of cracks and on the concrete pavement at the entrance of the parking garage. The crack sealing efficiency of the repair system was assessed with water permeability test performed in-situ 8 weeks after the treatment with bacteria. Rectangular wooden frames (1x0.5m) were placed on top of 3 treated- and 3 untreated cracks on the concrete deck. The wooden frames were sealed with silicon glue prior pouring 5L tap water. As the crack goes through the whole thickness of the deck, the sealing efficiency was assessed by monitoring, from the other side of the deck, how much water was dripping through the crack. Also, 6 cores were drilled from two different locations on the concrete pavement: 3 from the treated area and 3 from an untreated part of the pavement as control specimens. The resistance to freeze/thaw and de-icing salt was then evaluated in laboratory. Page 5

6 Figure 4: Test location for the application of the bacteria-based repair system. (a) Cracks on the concrete deck, (b) pavement on the side of the access ramp [4]. Page 6

7 Figure 5: Observation of water leaking through the cracks during water permeability test (a-c) control non treated cracks, (d, e) cracks treated with the bacteria-based repair system [4]. The results have shown that only the control cracks (not treated with the bacteria-based system) were still heavily leaking (Figure 5). Also, the bacteria-based system seems to provide surface protection to the concrete as the concrete treated with the bacteria showed 50% less mass loss after the freeze/thaw test compared to the control (non-treated). The performance of the proposed system is directly linked to the efficiency of the metabolic activity of bacteria and biomineral production. It seems then logical to assess the efficiency of such system not only on the basis of the concrete repair e.g. recovery of water tightness, but also with the evaluation of the bacterial involvement in the process and characterization of the biomineral. However, the investigation and proof of the in-situ bacterial involvement in the mineralization process is not an easy task. Indeed, after the crack has been successfully sealed, it is very delicate to determine whether the bacteria facilitated the CaCO3 formation or if it is simply the result of physico-chemical conditions in the crack micro-environment as for instance it can also result from natural carbonation of concrete. Keeping this in mind, in the treatment of another parking garage, in addition to water leakage test, cores were drilled along treated cracks after leakage test, and further analysed in laboratory with environmental scanning electron microscope equipped with X-ray Dispersion element for elemental analysis. Calcium-based minerals featuring rod-shaped imprints were found inside the crack suggesting that the bacteria grew and were involved in the mineral formation [7]. 5. PROSPECTS The results from laboratory experiments and field applications have shown a great potential of the bacteria-based system for the protection of concrete structure. It also shows that MICP can successfully be implemented to concrete material. Page 7

8 The in-situ application of the technology on concrete structure is rather recent (<3years) and challenges remain in order to ensure optimum performance and long term durability of the bio-based treatment. The lack of protocols and guidance as well as the lack of in-situ monitoring tools represent a significant gap in the characterization of the performances of concrete structures exposed to the action of microorganisms [8]. An important aspect is that MICP involves the application of a nutritive solution and foreign bacteria to the concrete material. This raises a number of questions, and in particular whether bacteria or other microorganisms naturally present on the concrete surface, or in the crack, could metabolically convert the nutrient brought during the treatment. How does the treatment affects the microbial communities inhabiting the concrete material and its environment during and after the MICP has taken place? These are important concerns in order to evaluate the effectiveness and the risk of the MICP treatment. Indeed, development of undesired microorganisms can also be a threat to concrete structures and lead to the biodeterioration of the material instead of its bioprotection [8]. The biodeterioration of building materials, i.e. degradation of the material due to microbial activity, have been widely reported in the literature. But, interestingly Ettenauer et al, [9] observed the disappearance of a heterogeneous microbial community replaced by a more homogeneous micro-biota mainly composed of carbonatogenic bacteria after bioconsolidation treatment on limestone historical buildings. The authors concluded that this change could be beneficial as carbonatogenic bacteria can further boost the consolidation treatment and enhance the long lasting effect of the treatment. This might suggest that biobased treatment could also help to limit and/or prevent the biodeterioration of buildings. However, this has to be further investigated for concrete material. Finally, ongoing research on the development of non-destructive methods to monitor and evaluate the effectiveness in-situ of the bio-based treatment will certainly bring the use of biobased methods in the field of concrete repair forward. 6. CONCLUSIONS MICP applied to concrete material has demonstrated its efficiency for crack sealing not only at the laboratory scale but also through several recent applications on concrete structures. Excellent illustration of the technology potential were made for section of irrigation canals in Ecuador or parking garages in the Netherlands. The promising results have led to the creation of a spinoff company, Basilisk Self-Healing Concrete, with the aim to further develop these systems and bring them to the market. Ongoing research on the development of non-destructive methods to monitor and evaluate the effectiveness in-situ of the bio-based treatment will certainly bring the use of bio-based methods in the field of concrete repair forward. ACKNOWLEDGEMENTS The authors would like to thank Eirini Tziviloglou, Renée Mors, Damian Palin, Lupita Sierra-Beltran for valuable discussions on the subject. The authors acknowledge the financial support of European Union Seventh Framework Programme (FP7/ ) under grant Page 8

9 agreement no (HEALCON), the financial support of European Union Seventh Framework Programme (FP7/ ) under grant agreement no (Marie Curie Program action SHeMat Training Network for Self-Healing materials: From Concepts to Markets ) and the financial support from the Netherlands Enterprise Agency (IOP grants SHM01018, SHM and SHM01018) and the Dutch Technology Foundation STW project number Parts of this review article are based on earlier publications by [3, 10-11]. REFERENCES [1] FHWA-RD (2001) Corrosion cost and preventive strategies in the United States. Report by CC Technologies Laboratories, Inc. to Federal Highway Administration (FHWA), Office of Infrastructure Research and Development [2] N.K. Dhami, M.S. Reddy, A. Mukherjee, Biofilm and Microbial applications in biomineralized concrete, Advanced Topics in Biomineralization. Rijeka, InTech (2012) pp [3] Jonkers HM, Wiktor VAC, Sierra-Beltran MG, Mors RM, Tziviloglou E, Palin D (2015) Limestone-producing bacteria make concrete self-healing. Self-healing materials - pioneering research in the Netherlands, S. van der Zwaag, E. Brinkman (eds.) IOS Press, The authors and IOS Press. p [4] Wiktor V, Jonkers HM (2015) Field performance of bacteria-based repair system: pilot study in a parking garage, Case Studies in Construction Materials, vol 2, pp [5] Sierra-Beltran L., Jonkers HM., Mera-Ortiz W. (2015) Field application of selfhealing concrete with natural fibre as linings for irrigation canals in Ecuador. Proceedings of the 5 th International conference on Self-healing Materials, June 2015, Durham, USA. [6] Sierra-Beltran MG., Jonkers HM. (2015) Carck self-healing technology based on bacteria, Journal of Ceramic Processing Research, vol 16, pp [7] Tziviloglou, E, Tittelboom, K van, Palin, D, Wang, J, Sierra Beltran, MG, Ersan, YC, Mors, RM, Wiktor, VAC, Jonkers, HM, Schlangen, E & Belie, N de (2016). Bio-based self-healing concrete: From research to field application. In Advances in Polymer Sciences (Advances in Polymer Sciences) (pp. 1-41). Dordrecht: Springer [8] Bertron A. (2014) Understanding interactions between cementitious materials and microorganisms: a key to sustainable and safe concrete structures in various contexts, Materials & Structures, (47), pp [9] J. Ettenauer, G. Pinar, K. Sterflinger, M.T. Gonzalez-Munoz, F. Jroundi, (2011) Molecular monitoring of the microbial dynamics occuring on historical limestone buildings during and after the in-situ application of different bio-consolidation treatments, Science of the Total Environment, vol 409, pp [10] Wiktor V, Jonkers HM (2015) Bacteria-based protective system for the conservation of cement-based materials, Proceedings of the 1 st Workshop on Green Conservation of Cultural Heritage, October, Rome (Italy). [11] Wiktor V, Jonkers HM, (2016) Bacteria-based concrete From concept to market, Smart material and Structures Special issue on Self-healing Materials: From concept to market, accepted for publication. Page 9