Controlling the workability properties of self-compacting concrete used as ready-mixed concrete

Title: Controlling the workability properties of self-compacting concrete used as ready-mixed concrete
Author(s): S. Kordts, W. Breit
Paper category : conference
Book title: International RILEM Symposium on Self-Compacting Concrete
Editor(s): O. Wallevik and I. Nielsson
Print-ISBN: 2-912143-42-X
e-ISBN: 2912143713
Publisher: RILEM Publications SARL
Publication year: 2003
Pages: 220 - 231
Total Pages: 12
Nb references: 8
Language: English

Abstract: Self-compacting concrete (SCC) is characterized by its special workability. However, the self-compacting property can be achieved only by rigorous optimization of the constituent materials and of the production procedure. When SCC is used as ready-mixed concrete it is important to ensure that the concrete has the required workability at the moment of placement. The aims of the investigation were to determine the influence of fluctuations in the composition of self-compacting ready-mixed concretes on the fresh concrete properties and to develop correction procedures which might be needed when the workability is no longer adequate. It was proposed that the workability of a SCC should be represented in a diagram with funnel velocity and slump flow as the parameters, and should be assessed with respect to self compaction, sedimentation and stagnation on the basis of a workability region. The investigations were carried out on SCCs of the powder type. The self-compacting workability property was determined on laboratory concretes and checked in a ready-mixed concrete plant under practical conditions. A CEM I 32,5 R Portland cement and a CEM III/A 32,5 N blastfurnace slag cement were used as the cements. The concrete additions were fly ash and limestone meal. Water contents were investigated which differed by ± 7 l/m3 from the level established in the preliminary investigations in order to determine the influence of the spread normally found in practice. The influence of the superplasticizer addition level on the behaviour of the workability with time was also investigated. Subsequent addition of up to 0.2 wt.% superplasticizer (wrt cement) was investigated as a means of correcting concretes which no longer had sufficient workability. The investigations showed that the ideal composition for a SCC must be determined by preliminary tests based on the powder, additions and aggregates to be used. The behaviour of the workability with time can be assessed objectively using the proposed workability diagram, in which the limits of workability have to be checked and specified for the SCC. Deviations from the target composition can be recognized and quantified within the workability window. In these tests, for example, deviations in the added water content of ± 7 l/m3 caused appreciable changes in the flowability and the mix stability. In the same way, higher addition levels of superplasticizer produced a selectively adjustable extension of the workability time. When the slump flow and funnel velocities were no longer sufficient it was possible to obtain adequate workability properties again, even after fairly long transport or storage times, by subsequent addition of the superplasticizer. The fresh and hardened concrete properties under practical conditions showed good agreement with the laboratory results.

Online publication: 2003-08-21
Publication type : abstract_only
Public price (Euros): 0.00