Influence of Casting Conditions on Durability and Structural Performance of HPC-AR: Changes in Workability and Air-Void System of Concrete due to Pumping

Project Details









Dimitri Feys, Kyle Riding, Daniel Galvez Moreno, Alexis Salinas, Alexandra Wehar




Air voids, Bridge decks, Casting, Concrete pavements, Durability, Pumped concrete, Self compacting concrete (SCC), Workability

Project description

This report summarizes the research performed on the influence of pumping operations on the changes in workability, rheology, air content, air-void system, freeze-thaw and scaling resistance of self-consolidating concrete (SCC). This project is a collaboration between the RE-CAST Tier-1 UTC the ACI Foundation, the Kansas State University (through funding from the Kansas DOT), EllisDon and CBM St-Marys. A portion of the results are summarized in the K-DOT report based on a research project on the effect of pumping on properties of low-slump concrete mixtures for bridge decks, as well as a paper in Materials and Structures. This report discusses the continuation of the research work, as some dramatic results were observed especially for SCC. When pumping concrete, a portion of the material is subjected to very high shear rates, and the lower the yield stress, the larger the concrete volume in the pipe which is exposed to shear. Shearing can cause substantial changes in rheology and workability, while a combination of pressure and shearing can induce major changes in the air-void system. Figure 1 shows the change in spacing factor, which is the difference between the spacing factor of the pumped and non-pumped concrete, due to the pumping process. These results were obtained in an experimental campaign with EllisDon and CBM-St-Marys in Toronto, ON, Canada in May 2015. No major changes were imposed on the different SCC mix designs, apart from the workability level. Figure 1 shows that the spacing factor increases more with a faster flow rate, due to the increase in applied pressure and in shearing. The use of a reducer (triangles), also increases the change in spacing factor, due to the same reasons. It should also be mentioned that one of the tests when using a reducer caused segregation of the SCC. However, the most striking results are the magnitude of those changes: the spacing factor increased with values between 250 and 550 μm, significantly above the acceptable limits. Normal concrete shows changes up to 100-150 μm, making SCC more sensitive. This is why further investigation on SCC is necessary.