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  • 1.
    Billberg, Peter
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Development of SCC static yield stress at rest and its effect on thelateral form pressure2005In: SCC 2005, Combining the Second North American Conference on the Design and Use of Self-Consolidating Concrete and the Fourth International RILEM Symposium on Self-Compacting Concrete, 2005, p. 583-589Conference paper (Refereed)
  • 2.
    Billberg, Peter
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Form pressure generated by self-compacting concrete: influence of thixotropy and structural behaviour at rest2006Doctoral 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.

  • 3.
    Billberg, Peter
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Mechanisms behind reduced form pressure when casting with SCC2005In: RILEM Proceedings PRO 42 / [ed] Yu ZW; Shi C; Khayat KH; Xie YJ, 2005, Vol. 42, p. 589-598Conference paper (Other academic)
    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.

  • 4.
    Billberg, Peter
    KTH, Superseded Departments, Structural Engineering.
    Some rheology aspects on fine mortar part of concrete1999Licentiate thesis, monograph (Other scientific)
  • 5.
    Billberg, Peter
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Time-Dependent Growth of Static and Dynamic Yield Stress of SCC2006In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873Article in journal (Other academic)
  • 6.
    Billberg, Peter
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Silfwerbrand, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Holmgren, J
    SCC Structural Behaviour at Restand Its Influence on Form Pressure2006In: RILEM Materials and Structures Journal, ISSN 1359-5997Article in journal (Refereed)
  • 7.
    Billberg, Peter
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Silfwerbrand, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Österberg, Thomas
    Form Pressures Generated by Self-Consolidating Concrete2005In: Concrete International, ISSN 0162-4075, E-ISSN 1944-7388, Vol. 27, no 10, p. 35-42Article in journal (Refereed)
    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.

  • 8.
    McCarthy, Richard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Billberg, Peter
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Silfwerbrand, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    An Investigation and Comparison of International Design Methods for Vertical Formwork2007In: 5th International RILEM Symposium on Self-Compacting Concrete / [ed] G. De Schutter and V. Boel, 2007, p. 479-484Conference paper (Other academic)
    Abstract [en]

    Concrete construction and reinforcing works have traditionally been laborious and time consuming. Self Compacting Concrete (SCC) offers an improved working environment and increased degree of mechanisation. Despite these advantages, the share of SCC in on-site casting is currently quite low. A few known factors may explain the low share. One is the formwork technique. The technique developed for conventional, vibrated concrete is not optimal for SCC. The special attributes of SCC, e.g. fast concrete filling, bottom to top form filling, casting against an overhead form, are not considered. The formwork design is highly dependent on the pressure and the movement of concrete in the formwork. An ongoing research project in Sweden aims at developing new design codes suitable for Swedish conditions, covering both SCC and conventional concrete, through benchmarking of international methods. This paper discusses the need for further and deeper understanding of how SCC influences the lateral formwork pressure. Currently, there is a lack of methods designing formwork for SCC. Most likely, they will be developed from the ones for conventional concrete. Therefore, a comparison has been made of the current design codes for conventional concrete in Sweden, Germany, U.K., USA and Japan.

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