The further development of concrete plasticizer admixture (in particular super-plasticizer) has led to a trend in recent years to increase the production of concretes with a softer consistency. At the same time, concrete manufacturers are keen to reduce the cement paste content in concrete, as cement accounts for a comparably high proportion of costs in concrete production. This development is allegedly supported by the use of modern super-plasticizers.
Along with the trends to softer concretes with reduced paste contents, there have been increasing reports in recent years of unexpected, significant changes in the properties of fresh concrete in prolonged building projects despite the same mix formulations and the same initial constituents. In such cases, undesired deviations from previous behaviour have occurred in concretes, which could previously be repeatedly processed without any difficulties, without any comprehensible reasons and without any prior notice, making concrete placement difficult or even impossible. In particular,
- an accelerated or decelerated strength development,
- a changed consistency, or
- appearances of sedimentation (bleeding)
were established in these practical cases.
Within the framework of the research project, the intention was to identify the most important influence parameters that are responsible for showing unscheduled properties such as changed consistency, signs of sedimentation, or an accelerated or decelerated strength development in certain cases of fresh concretes which are produced over prolonged periods.
In addition, criteria for a blueprint of concrete formulations was to be developed, which had to be met so that among the multitude of influences that can also occur in concrete production and its initial constituents in the economically optimised 5-material system, no undesired fresh concrete behaviour occurs and that the susceptibility to material and production related fluctuations is kept as low as possible.