Fiber reinforced concretes with high fiber volume fraction - a look in future

Rapport, 2009

Fiber reinforced concretes with high fiber volume fraction – a look in future Can the design determine the fiber amount in concrete in real time in every part of structure in production? RALEJS TEPFERS Department of Civil and Environmental Engineering Structural Engineering, Concrete Structures Chalmers University of Technology ABSTRACT In near future when control and knowledge about the load bearing capacity of only fiber reinforced concrete members can be safely guaranteed, a deletion of ordinary steel reinforcing bars might be possible. For time being it is difficult to change the fiber amount during the casting with to-days techniques. Therefore the fiber concentration has to be determined by the maximum tensile stress in the concrete member resulting in unnecessary fiber addition as in compressed zones. However, if the right amount of fibers could be regulated and added to concrete in real time at pump outlet, a future vision could be to design and produce the structure using FEM controlled equipment. Signals from the calculation result could be provided to the concrete casting system for addition of necessary amount of fibers to take care of the actual tensile stresses in the right position in structure. The casting location could be executed using GPS for positioning of pump outlet for targeting the casting location horizontally and laser vertically. Addition of fibers to the concrete at the outlet of the concrete pump and there proportioning them according to the actual stress situation needs in structure given by the FEM analysis in real time is a future challenge. The FEM analysis has to be based on material properties of only fiber reinforced concrete. This means that the resistance and stiffness of different strength concrete members with varying used fiber content has to be determined in tests and provided to the FEM analysis. The FEM analysis has to be completed before the casting and controlled. Then it can be used as the base for the correct amount of fiber addition to the concrete in every part of the structure. The system for correct amount of fiber introduction in the concrete has to be developed. The fibers have to be added at outlet of concrete pump. May be a system to gunite concrete with electronically controlled fiber addition at outlet is to be preferred? The target point where the concrete comes to rest into the structure has to be electronically noted and sent to the FEM system. The FEM analysis should then immediately send back the information for the correct amount of fibers in that point. This requires a lot of signal system development, but should not be impossible. An integrated system for design and production of concrete structures could be developed excluding the heavy and comprehensive work with steel reinforcing bars. The result could be: • No evaluation of moments and shear forces from FEM analysis for determination of bar reinforcement. • No bar anchorage requirements and reinforcement detailing. • No reinforcement drawings. • No reinforcing bars. • No heavy work with reinforcement. Finally investigations have to be performed concerning demolition of the fiber reinforced concrete structures and how to reuse the material. Fragments of the fiber reinforced concrete might be sticky and a problem for nature. The recirculation of material has to be solved. Key words: Concrete, Fibers, Design, Production, Integration, Real time