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Mechanisms behind reduced form pressure when casting with SCC
KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
2005 (Engelska)Ingår i: RILEM Proceedings PRO 42 / [ed] Yu ZW; Shi C; Khayat KH; Xie YJ, 2005, Vol. 42, s. 589-598Konferensbidrag, Publicerat paper (Övrigt vetenskapligt)
Abstract [en]

Among the topics within the more than 10 year experience from use of self-compacting civil engineering concrete in Sweden there is the fact that the lateral form pressure can be lower than the design values for conventional concrete. This is in total contradiction to results from different parts of the world where pressures close to or equal to hydrostatic pressure have been reported. A project has been started and partly carried out in order to investigate on fresh SCC behaviour at rest. The hypothesis is that this extremely flowing concrete can build up a structure at rest withstanding the load of the concrete layers above with limited effect on the increasing lateral form pressure. A new methodology has been developed using rheometers for both SCC and its micro mortar phase. The mechanism behind the thixotropic behaviour is to be found in the latter phase where colloidal forces dominate. In the present stage of this project it has been established that SCC indeed develops a structure at rest. The magnitude of this structure is dependant on the concrete constituents.

Ort, förlag, år, upplaga, sidor
2005. Vol. 42, s. 589-598
Serie
RILEM PROCEEDINGS ; 42
Nyckelord [en]
Construction & Building Technology; Engineering, Civil
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
URN: urn:nbn:se:kth:diva-14401DOI: 10.1617/2912143624.063ISI: 000243127200063OAI: oai:DiVA.org:kth-14401DiVA, id: diva2:332349
Konferens
First International Symposium on Design, Performance and Use of Self-Consolidating Concrete, SCC’2005
Anmärkning
QC 20100804Tillgänglig från: 2010-08-04 Skapad: 2010-08-04 Senast uppdaterad: 2012-02-13Bibliografiskt granskad
Ingår i avhandling
1. Form pressure generated by self-compacting concrete: influence of thixotropy and structural behaviour at rest
Öppna denna publikation i ny flik eller fönster >>Form pressure generated by self-compacting concrete: influence of thixotropy and structural behaviour at rest
2006 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Stockholm: Byggvetenskap, 2006. s. xiv, 91
Serie
Trita-BKN. Bulletin, ISSN 1103-4270 ; 85
Nyckelord
self-compacting concrete, thixotropy, structural build-up, form pressure, rheometer, viscometer, instrumented pressure tube
Nationell ämneskategori
Husbyggnad
Identifikatorer
urn:nbn:se:kth:diva-4144 (URN)91-7178-464-0 (ISBN)
Disputation
2006-10-27, Sal F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Handledare
Anmärkning
QC 20100812Tillgänglig från: 2006-10-10 Skapad: 2006-10-10 Senast uppdaterad: 2010-09-10Bibliografiskt granskad

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