Plastic Shrinkage Cracking in Concrete
The 1st International Conference on Smart Materials for Sustainable Construction
Document identifier: oai:DiVA.org:ltu-76796
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10.3390/proceedings2019034002Keyword: Engineering and Technology,
Cement type,
Byggmaterial,
Capillary pressure,
Bleeding,
Evaporation,
Settlement,
Water-cement ratio,
Admixtures,
Materials Engineering,
Cracking,
Plastic shrinkage,
Annan materialteknik,
Materialteknik,
Teknik och teknologier,
Other Materials Engineering,
Building MaterialsPublication year: 2019Relevant Sustainable Development Goals (SDGs):
The SDG label(s) above have been assigned by OSDG.aiAbstract: Plastic shrinkage cracking in concrete is mainly a physical process, in which chemical reactions between cement and water do not play a decisive role. It is commonly believed that rapid and excessive moisture loss, due to evaporation is the primary cause of the phenomenon. Once the concrete is cast, its solid particles start to settle due to gravity, causing an upward water-flow from the concrete interior and through its pore system to the surface, i.e., bleeding regime. When the amount of the evaporated water exceeds the amount of the water accumulated at the concrete surface, i.e., bleed water, concrete enters the so called drying regime, during which water menisci form inside the pores causing a build-up of a negative pore pressure, also known as capillary pressure. The progressive evaporation gradually decreases the radii of the menisci, which causes a further increase of the pore pressure and solid particles consolidation. Eventually, the skeleton of the concrete becomes stiff enough to resist the gravitational forces, which means that the vertical deformation of the concrete either completely stops or continues at a much lower rate. At this point, the capillary pressure is no longer able to further consolidate the concrete and move the pore water towards the surface. Instead, the developed tensile forces reduce the inter particle distances and the horizontal deformation continues. If the concrete member is restrained (e.g., due to reinforcement, variation in sectional depth, the friction of the form, etc.), the shrinkage can lead to tensile stresses accumulation. Once the tensile stresses exceed the early age tensile strength of the concrete, cracks start to form, preparing passageways for ingress of harmful materials into the concrete interior, which eventually may impair the durability and serviceability of the structure. This abstract reports the findings of a PhD research, carried out at Luleå University of Technology (LTU) to investigate the impact of parameters such as, admixtures, water-cement ratio (w/c), cement type, dosage of superplasticizer (SP), and steel fibers, on concrete’s cracking tendency while in plastic state. The results show that presence of accelerators, retarders, coarser cement particles, high w/c, and more SP increases the cracking risk, while stabilizers, air entraining agents (AEA), shrinkage reducing admixtures (SRA), and steel fibers notably decrease the cracking potential. Based on the findings of the above mentioned investigation a new model is proposed to estimate the severity of plastic shrinkage cracking, based on the initial setting time and the amount of the evaporated water from within the concrete bulk. The experimental results of the PhD research, alongside those reported by other researchers, were utilized to check the validity of the proposed model. According to the outcomes, the model could predict the cracking severity of the tested concretes with a good precision.
Authors
Faez Sayahi
Luleå tekniska universitet; Byggkonstruktion och brand
Other publications
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Mats Emborg
Luleå tekniska universitet; Byggkonstruktion och brand
Other publications
>>
Hans Hedlund
Luleå tekniska universitet; Byggkonstruktion och brand
Other publications
>>
Andrzej Cwirzen
Luleå tekniska universitet; Byggkonstruktion och brand
Other publications
>>
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header:
identifier: oai:DiVA.org:ltu-76796
datestamp: 2021-04-19T12:54:31Z
setSpec: SwePub-ltu
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recordCreationDate: 2019-11-21
identifier:
http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-76796
10.3390/proceedings2019034002
titleInfo:
@attributes:
lang: eng
title: Plastic Shrinkage Cracking in Concrete
abstract: Plastic shrinkage cracking in concrete is mainly a physical process in which chemical reactions between cement and water do not play a decisive role. It is commonly believed that rapid and excessive moisture loss due to evaporation is the primary cause of the phenomenon. Once the concrete is cast its solid particles start to settle due to gravity causing an upward water-flow from the concrete interior and through its pore system to the surface i.e. bleeding regime. When the amount of the evaporated water exceeds the amount of the water accumulated at the concrete surface i.e. bleed water concrete enters the so called drying regime during which water menisci form inside the pores causing a build-up of a negative pore pressure also known as capillary pressure. The progressive evaporation gradually decreases the radii of the menisci which causes a further increase of the pore pressure and solid particles consolidation. Eventually the skeleton of the concrete becomes stiff enough to resist the gravitational forces which means that the vertical deformation of the concrete either completely stops or continues at a much lower rate. At this point the capillary pressure is no longer able to further consolidate the concrete and move the pore water towards the surface. Instead the developed tensile forces reduce the inter particle distances and the horizontal deformation continues. If the concrete member is restrained (e.g. due to reinforcement variation in sectional depth the friction of the form etc.) the shrinkage can lead to tensile stresses accumulation. Once the tensile stresses exceed the early age tensile strength of the concrete cracks start to form preparing passageways for ingress of harmful materials into the concrete interior which eventually may impair the durability and serviceability of the structure. This abstract reports the findings of a PhD research carried out at Luleå University of Technology (LTU) to investigate the impact of parameters such as admixtures water-cement ratio (w/c) cement type dosage of superplasticizer (SP) and steel fibers on concrete’s cracking tendency while in plastic state. The results show that presence of accelerators retarders coarser cement particles high w/c and more SP increases the cracking risk while stabilizers air entraining agents (AEA) shrinkage reducing admixtures (SRA) and steel fibers notably decrease the cracking potential. Based on the findings of the above mentioned investigation a new model is proposed to estimate the severity of plastic shrinkage cracking based on the initial setting time and the amount of the evaporated water from within the concrete bulk. The experimental results of the PhD research alongside those reported by other researchers were utilized to check the validity of the proposed model. According to the outcomes the model could predict the cracking severity of the tested concretes with a good precision.
subject:
@attributes:
lang: eng
authority: uka.se
topic:
Engineering and Technology
Materials Engineering
Other Materials Engineering
@attributes:
lang: swe
authority: uka.se
topic:
Teknik och teknologier
Materialteknik
Annan materialteknik
@attributes:
lang: eng
topic: plastic shrinkage
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lang: eng
topic: cracking
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lang: eng
topic: admixtures
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lang: eng
topic: cement type
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lang: eng
topic: water-cement ratio
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lang: eng
topic: settlement
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lang: eng
topic: evaporation
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lang: eng
topic: bleeding
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lang: eng
topic: capillary pressure
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lang: swe
authority: ltu
topic: Byggmaterial
genre: Research subject
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lang: eng
authority: ltu
topic: Building Materials
genre: Research subject
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languageTerm: eng
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conference/other
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Published
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Byggkonstruktion och brand
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Byggkonstruktion och brand
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Byggkonstruktion och brand
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originInfo:
dateIssued: 2019
publisher: MDPI
relatedItem:
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type: host
titleInfo:
title: Proceedings 2019 SMASCO 2019
subTitle: The 1st International Conference on Smart Materials for Sustainable Construction
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type: series
titleInfo:
title: Proceedings
partNumber: 34(1)
identifier:
2504-3900
2504-3900
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url: http://ltu.diva-portal.org/smash/get/diva2:1371871/FULLTEXT01.pdf
accessCondition: gratis
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form: electronic
typeOfResource: text