Self-Healing Concrete
Document identifier: oai:DiVA.org:ltu-76527
Keyword: Engineering and Technology,
Teknik och teknologier,
Materials Engineering,
Other Materials Engineering,
Materialteknik,
Annan materialteknik,
Cementitious materials,
Self-healing,
Exposure,
Fly ash,
Calcite,
C-S-H,
Cracking,
Byggmaterial,
Building MaterialsPublication year: 2019Relevant Sustainable Development Goals (SDGs):
The SDG label(s) above have been assigned by OSDG.aiAbstract: Concrete is a brittle material prone to cracking due to its low tensile strength. Crack repairs are not only expensive and time-consuming but also increase the carbon footprint. Designing a novel concrete material possessing the ability to self-repair cracks would enhance its sustainability. Self-healing can be defined as a material’s ability to repair inner damage without any external intervention. In the case of concrete, the process can be autogenous, based on an optimized mix composition, or autonomous, when additional capsules containing some healing agent and/or bacteria spores are incorporated into the binder matrix. The first process uses unhydrated cement particles as the healing material while the other utilizes a synthetic material or bacteria precipitating calcite which are released into the crack from a broken capsule or activated by access to water and oxygen. The main disadvantages of the autonomous method are the loss of the fresh concrete workability, worsened mechanical properties, low efficiency, low survivability of the capsules and bacteria during mixing and the very high price. On the other hand, the autogenous self-healing was found to be more efficient, more cost effective, safer, and easier to implement in full-scale applications. Knowledge related to mechanisms and key factors controlling the autogenous self-healing is rather limited. Therefore, the aim of this research work was to better understand the autogenous self-healing process of concrete and to optimize the mix design and exposure conditions to maximize its efficiency. This licentiate thesis summarizes the main findings of the first 2.5 years of the PhD project. Several factors affecting autogenous self-healing were studied, including the amount of unhydrated cement, mix composition, age of material, self-healing duration and exposure conditions. The process was investigated both externally, at the surface, and deeper inside of the crack, by evaluating the crack closure and chemical composition of formed self-healing products. In addition, the flexural strength recovery was also studied. It was observed that a large amount of cement in the concrete mix does not ensure an efficient autogenous self-healing of cracks. A very dense and impermeable binder microstructure limited the transport of calcium and silicone ions to the crack and diminished the precipitation of the healing products. Addition fly ash increased the crack closure ratio close to the crack mouth, but its presence did not support the recovery of the flexural strength, presumably due to a very limited formation of load bearing phases inside the crack. Calcium carbonate was detected mainly at the crack mouth, whereas calcium silicate hydrate (C-S-H) and ettringite were found deeper inside the crack. The formation of C-S-H and ettringite presumably resulted in a regain of the flexural strength. On the other hand, calcite crystals formed close to the surface of the specimen controlled conditions inside the crack through its external closure. Healing exposure based on pure water appeared to be inefficient even despite the application of different temperature cycles and water volumes. The application of a phosphate-based retarding admixture in the curing water resulted in the highest self-healing efficiency. The admixture presumably inhibited the formation of a dense hydration shell on the surface of the unhydrated cement grains and promoted the precipitation of calcium phosphate compounds inside the crack. In addition, water mixed with microsilica particles caused a regain of the flexural strength through formation of C-S-H in the crack.
Authors
Magdalena Rajczakowska
Luleå tekniska universitet; Byggkonstruktion och brand
Other publications
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Andrzej Cwirzen
Luleå tekniska universitet; Byggkonstruktion och brand
Other publications
>>
Karin Habermehl-Cwirzen
Luleå tekniska universitet; Byggkonstruktion och brand
Other publications
>>
Hans Hedlund
Luleå tekniska universitet; Byggkonstruktion och brand
Other publications
>>
Erik Schlangen
Delft University of Technology
Other publications
>>
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header:
identifier: oai:DiVA.org:ltu-76527
datestamp: 2021-04-19T12:37:03Z
setSpec: SwePub-ltu
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recordCreationDate: 2019-10-28
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978-91-7790-491-5
http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-76527
titleInfo:
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lang: eng
title: Self-Healing Concrete
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type: alternative
lang: swe
title: Självläkande Betong
abstract: Concrete is a brittle material prone to cracking due to its low tensile strength. Crack repairs are not only expensive and time-consuming but also increase the carbon footprint. Designing a novel concrete material possessing the ability to self-repair cracks would enhance its sustainability. Self-healing can be defined as a material’s ability to repair inner damage without any external intervention. In the case of concrete the process can be autogenous based on an optimized mix composition or autonomous when additional capsules containing some healing agent and/or bacteria spores are incorporated into the binder matrix. The first process uses unhydrated cement particles as the healing material while the other utilizes a synthetic material or bacteria precipitating calcite which are released into the crack from a broken capsule or activated by access to water and oxygen. The main disadvantages of the autonomous method are the loss of the fresh concrete workability worsened mechanical properties low efficiency low survivability of the capsules and bacteria during mixing and the very high price. On the other hand the autogenous self-healing was found to be more efficient more cost effective safer and easier to implement in full-scale applications. Knowledge related to mechanisms and key factors controlling the autogenous self-healing is rather limited. Therefore the aim of this research work was to better understand the autogenous self-healing process of concrete and to optimize the mix design and exposure conditions to maximize its efficiency. This licentiate thesis summarizes the main findings of the first 2.5 years of the PhD project. Several factors affecting autogenous self-healing were studied including the amount of unhydrated cement mix composition age of material self-healing duration and exposure conditions. The process was investigated both externally at the surface and deeper inside of the crack by evaluating the crack closure and chemical composition of formed self-healing products. In addition the flexural strength recovery was also studied. It was observed that a large amount of cement in the concrete mix does not ensure an efficient autogenous self-healing of cracks. A very dense and impermeable binder microstructure limited the transport of calcium and silicone ions to the crack and diminished the precipitation of the healing products. Addition fly ash increased the crack closure ratio close to the crack mouth but its presence did not support the recovery of the flexural strength presumably due to a very limited formation of load bearing phases inside the crack. Calcium carbonate was detected mainly at the crack mouth whereas calcium silicate hydrate (C-S-H) and ettringite were found deeper inside the crack. The formation of C-S-H and ettringite presumably resulted in a regain of the flexural strength. On the other hand calcite crystals formed close to the surface of the specimen controlled conditions inside the crack through its external closure. Healing exposure based on pure water appeared to be inefficient even despite the application of different temperature cycles and water volumes. The application of a phosphate-based retarding admixture in the curing water resulted in the highest self-healing efficiency. The admixture presumably inhibited the formation of a dense hydration shell on the surface of the unhydrated cement grains and promoted the precipitation of calcium phosphate compounds inside the crack. In addition water mixed with microsilica particles caused a regain of the flexural strength through formation of C-S-H in the crack.
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lang: eng
authority: uka.se
topic: Engineering and Technology
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lang: swe
authority: uka.se
topic: Teknik och teknologier
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authority: uka.se
topic:
Engineering and Technology
Materials Engineering
Other Materials Engineering
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topic:
Teknik och teknologier
Materialteknik
Annan materialteknik
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topic: cementitious materials
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topic: self-healing
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lang: eng
topic: exposure
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topic: fly ash
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lang: eng
topic: calcite
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lang: eng
topic: C-S-H
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topic: cracking
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authority: ltu
topic: Byggmaterial
genre: Research subject
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dateIssued: 2019
publisher: Luleå tekniska universitet
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