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Evaluation of the performance of self-healing concrete at small and large scale under laboratory conditions

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Abstract
HEALCON is an EU-FP7 project which aims to develop self-healing concrete to create durable and sustainable concrete structures. While during the first years of the project the self-healing materials (including the healing agents and suitable encapsulation methodologies) and monitoring techniques were designed and tested at lab-scale, large scale elements have been tested near the end of the project to verify the feasibility and efficiency of the self-healing concrete under conditions closer to reality. For this paper, two types of healing agents were investigated for use in mortar and concrete. The first type of healing agent studied was a coated superabsorbent polymer (C-SAP). It is known that the autogenous healing capacity is increased by incorporation of superabsorbent polymers (SAPs) in mortar/concrete. The agents present in the crack can absorb intruding water, swell and block the crack, leading to immediate sealing, but can also exude moisture to the surrounding concrete environment stimulating healing of the concrete by hydration of unreacted cement particles or by CaCO3 precipitation. The disadvantage of these SAPs in the fresh mortar/concrete mix is however that they absorb large quantities of mixing water, leading to unwanted effects (e.g. loss of workability and macro-pore formation). By coating of the SAPs, we want to eliminate this disadvantage. The fluid bed spraying of the different layers was applied by VTT. A second healing agent studied, is a biogenic healing agent, namely a Mixed Ureolytic Culture (MUC). This type of healing agent was developed by Avecom in order to reduce the cost associated with the production of pure bacterial strains. This mixed ureolytic culture is moreover self-protecting and does not need any further encapsulation. At first, the performance of the healing agents itself was evaluated. For the coated SAPs, the swelling performance and swelling rate were determined, showing that the coating can limit the uptake of water during the first 10-15 minutes. For the MUC, the ureolytic and CaCO3 precipitating capacity was determined, immediately after production of the MUC and after 3 months of storage. The results show the potential of these mixed cultures to be used as self-healing agent in mortar/concrete, but also show a decrease of their effectiveness with time. Subsequently, the healing agents were incorporated in mortar mixes at UGent. A dosage of 1 wt% relative to the cement content caused a large reduction of the mechanical properties of the mortar (up to ~ 50%), except for the coated SAP. The sealing efficiency was evaluated with the water flow test, as designed by one of the project partners in HEALCON. The performance of reference mixes was compared to that of self-healing mixes with SAP, coated SAP or MUC (+ urea). Results showed that for cracks with a width less than 0.150 mm, all mortars were sealed (almost) completely after storage for 28 days in wet-dry environment (12 h wet – 12 h dry) after crack creation. For cracks with a larger width, differences were noticed between the different specimens. Moreover, also the immediate sealing effect induced by the presence of SAPs could be noticed. It has to be noted however that the crack width plays an important role but is varying along the crack length (within a specimen) and between specimens, making the analysis more difficult. In order to extend the application to concrete, self-healing and reference reinforced concrete beams (2500 x 400 x 200 mm) were produced at the Danish Technological Institute. The self-healing concretes contained coated SAPs or MUC. Moreover, the beams were equipped with corrosion sensors that are connected to a wireless monitoring system, developed by the Technology-Transfer- Initiative at the University of Stuttgart. The multi reference electrodes (MuRE) were installed alongside the reinforcements and measure the corrosion potential at certain positions. Data is collected in sufficiently dense intervals by battery powered nodes that transmit the data wirelessly to a base station and further on to a database where it can be accessed through a web based application for data analysis over the internet. At the age of 28 days, three-point bending cracks up to 0.6 mm were created in the beams. Subsequently, the beams were regularly sprayed with water (four times one hour per day) for 6 weeks and afterwards, the beams were, once a week, exposed to 3 wt% NaCl solution for 24 h. Evaluation of the self-healing performance by microscopic analysis (crack microscopy and analysis of thin sections) showed that for the reference beam and beam with MUC no significant healing could be noticed (probably because of insufficient supply of nutrients for the bacteria). For the beams with coated SAPs, the smaller cracks (0.1 and 0.2 mm) were partly closed. Continuous corrosion monitoring showed corrosion in the reference and MUC beams already after the first exposure to NaCl solution. Onset of corrosion was delayed in the case the beams contained coated SAPs.
Keywords
self-healing, concrete, microscopy, corrosion, monitoring

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Chicago
Gruyaert, Elke, Brenda Debbaut, Martin Kaasgaard, Henrik Erndahl Sorensen, Jani Pelto, Vanda Branco, Fabian Malm, et al. 2017. “Evaluation of the Performance of Self-healing Concrete at Small and Large Scale Under Laboratory Conditions.” In Durability of Building Materials and Components (XIV DBMC), ed. Geert De Schutter, Nele De Belie, Arnold Janssens, and Nathan Van Den Bossche, 1–12. Paris (France): RILEM Publications.
APA
Gruyaert, E., Debbaut, B., Kaasgaard, M., Erndahl Sorensen, H., Pelto, J., Branco, V., Malm, F., et al. (2017). Evaluation of the performance of self-healing concrete at small and large scale under laboratory conditions. In Geert De Schutter, N. De Belie, A. Janssens, & N. Van Den Bossche (Eds.), Durability of Building Materials and Components (XIV DBMC) (pp. 1–12). Presented at the 14th International Conference on Durability of Building Materials and Components (XIV DBMC), Paris (France): RILEM Publications.
Vancouver
1.
Gruyaert E, Debbaut B, Kaasgaard M, Erndahl Sorensen H, Pelto J, Branco V, et al. Evaluation of the performance of self-healing concrete at small and large scale under laboratory conditions. In: De Schutter G, De Belie N, Janssens A, Van Den Bossche N, editors. Durability of Building Materials and Components (XIV DBMC). Paris (France): RILEM Publications; 2017. p. 1–12.
MLA
Gruyaert, Elke, Brenda Debbaut, Martin Kaasgaard, et al. “Evaluation of the Performance of Self-healing Concrete at Small and Large Scale Under Laboratory Conditions.” Durability of Building Materials and Components (XIV DBMC). Ed. Geert De Schutter et al. Paris (France): RILEM Publications, 2017. 1–12. Print.
@inproceedings{8557589,
  abstract     = {HEALCON is an EU-FP7 project which aims to develop self-healing concrete to create durable and
sustainable concrete structures. While during the first years of the project the self-healing materials
(including the healing agents and suitable encapsulation methodologies) and monitoring techniques
were designed and tested at lab-scale, large scale elements have been tested near the end of the
project to verify the feasibility and efficiency of the self-healing concrete under conditions closer to
reality.
For this paper, two types of healing agents were investigated for use in mortar and concrete. The
first type of healing agent studied was a coated superabsorbent polymer (C-SAP). It is known that
the autogenous healing capacity is increased by incorporation of superabsorbent polymers (SAPs) in
mortar/concrete. The agents present in the crack can absorb intruding water, swell and block the
crack, leading to immediate sealing, but can also exude moisture to the surrounding concrete
environment stimulating healing of the concrete by hydration of unreacted cement particles or by
CaCO3 precipitation. The disadvantage of these SAPs in the fresh mortar/concrete mix is however
that they absorb large quantities of mixing water, leading to unwanted effects (e.g. loss of
workability and macro-pore formation). By coating of the SAPs, we want to eliminate this
disadvantage. The fluid bed spraying of the different layers was applied by VTT. A second healing
agent studied, is a biogenic healing agent, namely a Mixed Ureolytic Culture (MUC). This type of
healing agent was developed by Avecom in order to reduce the cost associated with the production
of pure bacterial strains. This mixed ureolytic culture is moreover self-protecting and does not need
any further encapsulation.
At first, the performance of the healing agents itself was evaluated. For the coated SAPs, the
swelling performance and swelling rate were determined, showing that the coating can limit the
uptake of water during the first 10-15 minutes. For the MUC, the ureolytic and CaCO3 precipitating
capacity was determined, immediately after production of the MUC and after 3 months of storage.
The results show the potential of these mixed cultures to be used as self-healing agent in
mortar/concrete, but also show a decrease of their effectiveness with time.
Subsequently, the healing agents were incorporated in mortar mixes at UGent. A dosage of 1 wt\%
relative to the cement content caused a large reduction of the mechanical properties of the mortar
(up to {\texttildelow} 50\%), except for the coated SAP. The sealing efficiency was evaluated with the water flow
test, as designed by one of the project partners in HEALCON. The performance of reference mixes
was compared to that of self-healing mixes with SAP, coated SAP or MUC (+ urea). Results
showed that for cracks with a width less than 0.150 mm, all mortars were sealed (almost)
completely after storage for 28 days in wet-dry environment (12 h wet -- 12 h dry) after crack
creation. For cracks with a larger width, differences were noticed between the different specimens.
Moreover, also the immediate sealing effect induced by the presence of SAPs could be noticed. It
has to be noted however that the crack width plays an important role but is varying along the crack
length (within a specimen) and between specimens, making the analysis more difficult.
In order to extend the application to concrete, self-healing and reference reinforced concrete beams
(2500 x 400 x 200 mm) were produced at the Danish Technological Institute. The self-healing
concretes contained coated SAPs or MUC. Moreover, the beams were equipped with corrosion
sensors that are connected to a wireless monitoring system, developed by the Technology-Transfer-
Initiative at the University of Stuttgart. The multi reference electrodes (MuRE) were installed
alongside the reinforcements and measure the corrosion potential at certain positions. Data is
collected in sufficiently dense intervals by battery powered nodes that transmit the data wirelessly to
a base station and further on to a database where it can be accessed through a web based application
for data analysis over the internet.
At the age of 28 days, three-point bending cracks up to 0.6 mm were created in the beams.
Subsequently, the beams were regularly sprayed with water (four times one hour per day) for 6
weeks and afterwards, the beams were, once a week, exposed to 3 wt\% NaCl solution for 24 h.
Evaluation of the self-healing performance by microscopic analysis (crack microscopy and analysis
of thin sections) showed that for the reference beam and beam with MUC no significant healing
could be noticed (probably because of insufficient supply of nutrients for the bacteria). For the
beams with coated SAPs, the smaller cracks (0.1 and 0.2 mm) were partly closed. Continuous
corrosion monitoring showed corrosion in the reference and MUC beams already after the first
exposure to NaCl solution. Onset of corrosion was delayed in the case the beams contained coated
SAPs.},
  author       = {Gruyaert, Elke and Debbaut, Brenda and Kaasgaard, Martin and Erndahl Sorensen, Henrik and Pelto, Jani and Branco, Vanda and Malm, Fabian and Grosse, Christian and Price, Eric and Kr{\"u}ger, Markus and De Belie, Nele},
  booktitle    = {Durability of Building Materials and Components (XIV DBMC)},
  editor       = {De Schutter, Geert and De Belie, Nele and Janssens, Arnold and Van Den Bossche, Nathan},
  isbn         = {978-2-35158-159-9},
  keyword      = {self-healing,concrete,microscopy,corrosion,monitoring},
  language     = {eng},
  location     = {Ghent},
  pages        = {1--12},
  publisher    = {RILEM Publications},
  title        = {Evaluation of the performance of self-healing concrete at small and large scale under laboratory conditions},
  year         = {2017},
}