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Form Pressures Generated by Self-Consolidating Concrete
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.ORCID iD: 0000-0002-1526-9331
2005 (English)In: Concrete International, ISSN 0162-4075, E-ISSN 1944-7388, Vol. 27, no 10, 35-42 p.Article in journal (Refereed) Published
Abstract [en]

Since its development, it has been generally assumed that self-consolidating concrete (SCC) would generate hydrostatic formwork pressure due to the rate at which it can be cast and the long time before it starts to set. However, in 1998 when the first bridges were cast using SCC in Sweden, measured form pressures were even lower than the design values for conventional concrete. To investigate the need for special formwork design considerations when using SCC, a series of eight wall specimens were cast, and the resulting form pressures were monitored.

Place, publisher, year, edition, pages
2005. Vol. 27, no 10, 35-42 p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-24057OAI: oai:DiVA.org:kth-24057DiVA: diva2:343054
Note
QC 20100812Available from: 2010-08-12 Created: 2010-08-12 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Form pressure generated by self-compacting concrete: influence of thixotropy and structural behaviour at rest
Open this publication in new window or tab >>Form pressure generated by self-compacting concrete: influence of thixotropy and structural behaviour at rest
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Self-compacting concrete (SCC) offers rational and fast casting process since it merely has to be poured, or pumped, into the formwork without any compaction work needed. But this can be at the cost of high form pressure. However, reported results show that SCC can act thixotropically, i.e., build up a structure at rest, and this can reduce the form pressure considerably. Thus, in order to utilise the favourable possibilities to increase effectiveness without risking form collapses, the need arises for deeper and broader understanding of the mechanisms behind this thixotropic behaviour.

Methodologies have been developed for the characterisation and measurement of the structural build-up at rest, both for the fluid (micro mortar) phase and the concrete itself. Hypotheses state that thixotropic mechanisms originate within the colloidal domain and, thus, motivate studies on the fluid phase comprising this domain. The stress-strain methodology is based on the hypothesis stating that the magnitude of the structure is represented by the maximum elastic stress the fresh material can withstand before the structure breaks. An instrumented steel tube is used to simulate various casting heights and rates.

Results show that both micro mortar and SCC are thixotropic and this behaviour is influenced by every measure taken influencing the interparticle colloidal forces. The time-dependent structural build-up of SCC is a function of an irreversible structure (slump-loss) and a reversible, thixotropic structure.

There is apparently a threshold value of the structural build-up necessary to reach before obtaining any significant form pressure reduction. Housing SCC´s, with W/C = 0.58, show low degree of structural build-up and pressure decrease while civil engineering SCC´s can show the opposite, but this often at the cost of slump-loss.

Recommendations are presented and for the nearest future, suggesting a conservatism regarding design of formwork systems when SCC is used. If the behaviour of a SCC is known it should be used to optimise the formwork. If not, calculating with hydrostatic pressure should be done or the knowledge missing should be gained by using this methodology. A third option is given and this is to monitor the form pressure in real time using sensors.

Place, publisher, year, edition, pages
Stockholm: Byggvetenskap, 2006. xiv, 91 p.
Series
Trita-BKN. Bulletin, ISSN 1103-4270 ; 85
Keyword
self-compacting concrete, thixotropy, structural build-up, form pressure, rheometer, viscometer, instrumented pressure tube
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-4144 (URN)91-7178-464-0 (ISBN)
Public defence
2006-10-27, Sal F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100812Available from: 2006-10-10 Created: 2006-10-10 Last updated: 2010-09-10Bibliographically approved

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