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Gewählte Master / Diploma Thesis:

Matthias Hummelbrunner (2012): Einfluss der Konsistenz auf die Scherfestigkeit von Frischbeton.
Master / Diploma Thesis - Institut für Geotechnik (IGT), BOKU-Universität für Bodenkultur, pp 72. UB BOKU obvsg

Data Source: ZID Abstracts
Recently, damages caused by bleeding of freshly cast concrete are often observed in foundation engineering practice, e.g. cast-in-place piles and diaphragm walls. The sus-ceptibility of fresh concrete to bleeding depends on a number of factors, e.g. aggregate, workability, concrete pressure etc. The pressure in fresh concrete is difficulty to determine because fresh concrete shows both solid-like and fluid-like behaviour. One possible approach to determine the concrete pressure is based on the earth pressure theory of Coulomb, where the strength parameters of fresh concrete are needed. This thesis is a continuing examination and presents an experimental study on the shear strength of fresh concrete with different degrees of consistency. The shear parameters, i.e. friction angle φ and cohesion c are determined based on direct shear tests in a large size shear apparatus of 50 cm x 50 cm. The tests are carried out at different setting times after placement in the mould. The strength parameters enable the calculation of time dependent concrete pressure based on the earth pressure theory of Coulomb. The concrete is mixed according to the recipes of an augured pile of the strength class C25/30. The strength parameters are determined for three different concrete mixtures of F45, F59 and F70 with various degrees of consistency. The degrees of consistency correspond to the different setting times of 0, 60, 180 and 300 min after placement. Altogether some thirty three tests are carried out. Moreover, the consistency is changed by additives, which delay the hardening of concrete. The effect of these additives on the strength behaviour of fresh concrete is investigated. Higher consistency gives rise to lower strength. Consistency has large influence on cohesion but small influence on friction angle.

Beurteilende(r): Wu Wei

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