222-SCF : Simulation of fresh concrete flow
Technical Committee 222-SCF
Deputy Chair: Ms Annika GRAM
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, i.e. mixes without high static and dynamic stability, or mixes with limited workability 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.
Following the first workshop organized in this field at CBI (Sweden) in September 2006, researchers from various research teams across Europe have realized that the numerical techniques they were using were almost as numerous as the researchers themselves. This committee objective is to classify and gather all the techniques used in this young research field. This aim is to be reached with a review of the current state-of-the-art knowledge regarding computational modeling of the flow of fresh concrete. Report of the result will be made with in mind the practical use of this type of science. Pros and cons for each technique will be given along with examples and references to applications to fresh cementitious materials. Moreover, in order to make it easier for new techniques to be developed and broadcast, a reference numerical benchmark flow will be defined in order to compare the various numerical methods around the world.
Terms of reference
42 months The committee comprises a selected membership of those relatively few organisations and research centres worldwide that have been active in developing simulation techniques. It includes universities, research institutes, material suppliers, public agencies and representatives from international associations.
Detailed working programme
_6th of September 2007: First meeting in Gent (SCC 2007)
_June 2008: First working meeting and workshop in Paris at LCPC.
_Autumn 2008: TC meeting
_Winter 2009 TC meeting
_Summer 2009: TC meeting
_Winter 2010: Symposium
_Summer 2010: Final report - RILEM publication
This TC was spotted as a high potential research area by the RILEM TC-209-RFC (chairman: Olafûr Wallevik)
The TC will produce a STATE-OF-THE-ART REPORT associated to a complete BENCHMARK NUMERICAL TEST METHOD.
The TC will organize a symposium.
Group of users
Specific use of the results
See (2 subject matter) where all details have been gathered.