Computational Modeling of Concrete Flow: State of the Art

1. INTRODUCTION To benefit from the full potential of fluid concretes such as Self-Compacting Concrete (SCC) tools for prediction of the form filling of SCC are needed. Such tools should take into account the properties of the concrete, the shape and size of the structural element, the position of rebars, and the casting technique. The present lack of such tools may lead to selection of highly flowable mixes with tendency to segregate or mixes without high static and dynamic stability, increasing the risk of improper form filling. Although substantial progress has been made in the field of fluid concretes, we must not forget that the most suitable concrete to cast a given element is a concrete which is just sufficiently fluid to fill the formwork. Additional and thus unnecessary fluidity will always have a cost, e.g. in terms of increased super-plasticizer amount, increased porosity causing loss of mechanical resistance and durability and increased risk of segregation. Important requirements to the hardened concrete are total form filling and bond to reinforcement, homogeneity with regard to paste composition, aggregate distribution and air void content, and high quality surfaces without surface air voids (" blowholes "). All these aspects condition the future hardened properties of the material. Segregation could increase the local porosity and thus the permeability of the concrete to aggressive substances. Varying content of cement paste causes heterogeneous shrinkage and creep in a given concrete element. Moreover, high heterogeneity will increase the probability that these time-dependent phenomenon yield high internal stress gradients and thus cracking. Computational modeling of flow could be used for simulation of e.g. total form filling and detailed flow behavior as particle migration and formation of granular arches between reinforcement (" blocking "). But computational modeling of flow could also be a potential tool for understanding the rheological behaviour of concrete and a tool for mix proportioning. Progresses in the correlation between mix proportioning and rheological parameters would of course result but, moreover, the entire approach to mix proportioning could be improved. Indeed, just as numerical simulations of the loading of concrete structures allow a civil engineer to identify a minimum needed mechanical strength, numerical simulation of the casting process could allow the same engineer to specify a minimum workability of the fresh concrete that could ensure the proper filling of a given formwork. This paper describes the present status regarding computational modeling of the flow of fresh …