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The experiments did not reveal any single factor to improve the compactibility nor reduce the risk of segregation. However, the results demonstrated well that the workability and compactibility are not correlated phenomena. The casting of the test structures showed that even though the fluid concrete quickly filled the mould, the required compaction time remained in the same level when compared to the stiff concrete. According to the rheological modelling, the maximum density of concrete is a parameter that is controlled by the selection of compaction time, but it can also be increased by improving concrete properties. The visual estimation and modelling of the optimal vibration time suggest that the optimal vibration cannot remove all the entrapped air. Therefore, the compaction process is always a compromise between the degree of compaction and segregation.
The effects of the superplasticisers during the compaction are complex even though the superplasticiser had minor impact on the rheological properties of the concrete. Since superplasticisers increase the slump value of concrete by decreasing the yield stress, their effect on viscosity is relatively small, and thus, have little influence on the compactibility. While the vibration mechanically breaks down the cement particle interactions, the plasticisers permanently reduce those interactions of the cement particle. Due to the permanent loss of interactions, plasticised concretes are more susceptible for segregation during vibration when compared to the non-plasticised concretes. Moreover, lower viscosity of the cement paste increases the velocity of compaction pores raising upwards, reducing the required time for entrapped air to exit the concrete. The best compaction quality can be achieved with a moderate workability concrete. Importantly, the height of compaction layers, the distance of compaction points, and the compaction times affect greatly the overall compaction quality. As such, the whole compaction process has a significant impact on the quality of concrete.
|Number of pages||126|
|Publication status||Published - 2021|
|MoE publication type||D4 Published development or research report or study|
|Name||Aalto University publication series SCIENCE + TECHNOLOGY|
- entrapped air
- vibration time
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- 1 Finished
01/01/2020 → 28/02/2021
Project: Domestic funds and foundations