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Moisture Conditions and Frost Resistance of Concrete in Hydraulic Structures

Rosenqvist, Martin LU (2013)
Abstract
Owing to the winter conditions in Sweden, the effects of frost action may have a considerable impact on the deterioration of concrete. Both superficial and internal damage, which are suspected to have been caused by frost action, have been found in concrete in hydraulic structures. These observations have raised questions about the long-term behaviour of hydraulic structures in cold regions.



Superficial damage, similar in appearance to salt scaling of concrete, can be seen at the waterline of hydraulic structures, such as hydro power structures. Progressive damage to the concrete surface results in exposure of coarse aggregate and also exposed reinforcing steel in the long-term perspective.



A possible... (More)
Owing to the winter conditions in Sweden, the effects of frost action may have a considerable impact on the deterioration of concrete. Both superficial and internal damage, which are suspected to have been caused by frost action, have been found in concrete in hydraulic structures. These observations have raised questions about the long-term behaviour of hydraulic structures in cold regions.



Superficial damage, similar in appearance to salt scaling of concrete, can be seen at the waterline of hydraulic structures, such as hydro power structures. Progressive damage to the concrete surface results in exposure of coarse aggregate and also exposed reinforcing steel in the long-term perspective.



A possible deterioration process of concrete at the waterline is leaching of the concrete surface, which takes place during the snowmelt runoff period. The concrete surface is thus more susceptible to frost action. During the following winter, the surface layer is damaged by frost action and later removed due to ice abrasion. During the next snowmelt runoff period, the process starts all over again. Experimental results obtained in this work confirm this deterioration process.



Spalling of concrete has been observed below the water level in water retaining concrete structures subjected to long periods of freezing temperatures in winter. The hypothesis is that either poor quality concrete or the effects of aging make hardened concrete susceptible to macroscopic ice lens growth, i.e. ice segregation. Given constant thermal conditions, ice segregation occurs in undamaged concrete with water to cement-ratio (w/c-ratio) 0.9 or higher. In frost-damaged concrete, ice segregation occurs within a few days regardless of the w/c-ratio. Ice segregation may also occur in concrete with cavities or imperfections. The period of freezing required to facilitate ice segregation increases with decreasing w/c-ratio. Hence, the risk of concrete spalling in actual structures cannot be overlooked since unfavourable temperature and moisture conditions may exist in winter.



Knowledge about concrete deterioration is important in order to improve the efficiency of maintenance of hydraulic structures. However, the overall purpose of gathering knowledge about damage mechanisms is to secure and to be able to safely extend the service life of hydraulic structures. (Less)
Abstract (Swedish)
Med avseende på de svenska förhållandena vintertid kan frostpåverkan antas ha betydande inverkan på nedbrytningen av betong i vattenbyggnader. Både ytliga och inre skador, vilka misstänks ha orsakats av frostpåverkan, har upptäckts på betong i exempelvis vattenkraftkonstruktioner. Nämnda observationer har väckt frågor om vattenbyggnaders beständighet i ett kallt klimat.



Ytligt belägna skador, vilka utseendemässigt påminner om avskalningar orsakade av tösaltning, kan i många fall ses längs vattenlinjen på vattenbyggnader. En successiv avskalning av betongytan leder till friläggandet av grövre ballastkorn, samt i ett längre perspektiv även till friläggandet av armeringsjärn.



Ett möjligt scenario för... (More)
Med avseende på de svenska förhållandena vintertid kan frostpåverkan antas ha betydande inverkan på nedbrytningen av betong i vattenbyggnader. Både ytliga och inre skador, vilka misstänks ha orsakats av frostpåverkan, har upptäckts på betong i exempelvis vattenkraftkonstruktioner. Nämnda observationer har väckt frågor om vattenbyggnaders beständighet i ett kallt klimat.



Ytligt belägna skador, vilka utseendemässigt påminner om avskalningar orsakade av tösaltning, kan i många fall ses längs vattenlinjen på vattenbyggnader. En successiv avskalning av betongytan leder till friläggandet av grövre ballastkorn, samt i ett längre perspektiv även till friläggandet av armeringsjärn.



Ett möjligt scenario för nedbrytningen av betongytan längs vattenlinjen är att den utsätts för urlakning under snösmältningsperioden. Betongytan blir därmed känslig för frostpåverkan och skadas således under den följande vintern. På våren nöts det skadade skiktet bort av is och under nästa snösmältningsperiod börjar processen om på nytt. Erhållna resultat från försök i detta arbete styrker nämnda scenario för betongytans nedbrytning.



Ett flertal exempel på spjälkning av betong har påträffats under vattennivån i dämmande betongkonstruktioner. Dessa konstruktioner har vintertid varit utsatta för långa perioder av frostpåverkan. En hypotes är att dålig betongkvalitet eller effekterna av åldring möjliggjort makroskopisk islinsbildning i betong. Erhållna resultat visar att vid stationära temperaturförhållanden kan spjälkning inträffa i oskadad betong med vattencementtal (vct) 0.9 eller högre. I frostskadad betong inträffar däremot spjälkning redan inom några få dagar oavsett betongens vct. I betong med håligheter eller andra svagheter kan också spjälkning inträffa. Dock krävs det allt längre perioder med frostpåverkan i takt med ett lägre vct. Risken för spjälkning av betong i verkliga konstruktioner kan således inte förbises, eftersom ofördelaktiga temperatur- och fuktförhållanden kan existera vintertid.



Kunskap om betongens nedbrytning är viktig i syfte att förbättra och effektivisera underhållet av betong i vattenbyggnader. Det övergripande syftet med kunskap om skademekanismer är dock att kunna säkerställa och möjliggöra säker förlängning av livslängden för vattenbyggnader. (Less)
Please use this url to cite or link to this publication:
author
supervisor
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Hydraulic Structures, Hydro Power, Concrete Dams, Concrete, Frost Resistance, Scaling, Spalling, Moisture Absorption, Macroscopic Ice Lens Growth
pages
78 pages
publisher
Building Materials, LTH, Lund University
external identifiers
  • other:TVBM-3173
language
English
LU publication?
yes
id
3abe1c7d-ed07-4561-8a38-e603d489c6f8 (old id 4180243)
date added to LUP
2016-04-01 14:00:10
date last changed
2018-11-21 20:22:09
@misc{3abe1c7d-ed07-4561-8a38-e603d489c6f8,
  abstract     = {Owing to the winter conditions in Sweden, the effects of frost action may have a considerable impact on the deterioration of concrete. Both superficial and internal damage, which are suspected to have been caused by frost action, have been found in concrete in hydraulic structures. These observations have raised questions about the long-term behaviour of hydraulic structures in cold regions.<br/><br>
<br/><br>
Superficial damage, similar in appearance to salt scaling of concrete, can be seen at the waterline of hydraulic structures, such as hydro power structures. Progressive damage to the concrete surface results in exposure of coarse aggregate and also exposed reinforcing steel in the long-term perspective.<br/><br>
<br/><br>
A possible deterioration process of concrete at the waterline is leaching of the concrete surface, which takes place during the snowmelt runoff period. The concrete surface is thus more susceptible to frost action. During the following winter, the surface layer is damaged by frost action and later removed due to ice abrasion. During the next snowmelt runoff period, the process starts all over again. Experimental results obtained in this work confirm this deterioration process.<br/><br>
<br/><br>
Spalling of concrete has been observed below the water level in water retaining concrete structures subjected to long periods of freezing temperatures in winter. The hypothesis is that either poor quality concrete or the effects of aging make hardened concrete susceptible to macroscopic ice lens growth, i.e. ice segregation. Given constant thermal conditions, ice segregation occurs in undamaged concrete with water to cement-ratio (w/c-ratio) 0.9 or higher. In frost-damaged concrete, ice segregation occurs within a few days regardless of the w/c-ratio. Ice segregation may also occur in concrete with cavities or imperfections. The period of freezing required to facilitate ice segregation increases with decreasing w/c-ratio. Hence, the risk of concrete spalling in actual structures cannot be overlooked since unfavourable temperature and moisture conditions may exist in winter.<br/><br>
<br/><br>
Knowledge about concrete deterioration is important in order to improve the efficiency of maintenance of hydraulic structures. However, the overall purpose of gathering knowledge about damage mechanisms is to secure and to be able to safely extend the service life of hydraulic structures.},
  author       = {Rosenqvist, Martin},
  language     = {eng},
  note         = {Licentiate Thesis},
  publisher    = {Building Materials, LTH, Lund University},
  title        = {Moisture Conditions and Frost Resistance of Concrete in Hydraulic Structures},
  url          = {https://lup.lub.lu.se/search/ws/files/3718424/4180251.pdf},
  year         = {2013},
}