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Applications : Repair
Concrete Repair: Development of a high-peformance fiber-reinforced and internally impregnated self-compacting concrete
Innovation:
First application of a high-modulus, polymer, fiber-reinforced and internally impregnated, self-compacting concrete.
Project Description:
The deteriorated covercrete of a 30-year-old railway undercrossing had to be replaced. Due to chlorides from deicing salts severe corrosion has been initiated at the rebars of the load bearing structural walls of the building. The aim of the owner was to apply a repair technique that would prevent any further repair or maintenance of the structure within the next 40 years.
Problem:
The material used for the replacement of the deteriorated covercrete had to fulfill stringent requirements regarding the durability of the repair. In addition to this the new surface had to feature a high visual quality.
Both the risk of surface cracking due to drying shrinkage and the capillary uptake of aqueous solutions of harmful substances had to be taken into account.
Due to the fact that the concrete work had to be performed in confined areas (thickness of the new layer: 60 mm, ongoing traffic during construction, etc.) the utilization of machinery for vibrating compaction had to be circumvented. This was done by applying self-compacting concrete.
All material parameters of the concrete were measured in order to perform numerical simulations of the risk of surface cracking and delamination.
Solution:
The risk of surface cracking was faced by a two-way approach. By optimizing the composition of the binder material (cement, fillers, water and additives) the concrete matrix could be optimized. As a result of this the final shrinakge of the newly developed concrete amounted to less than 70% compared to conventional self-compacting concretes. In addition to this a new generation of polymer-fibers was utilized. These polyvinylalcohol (PVA) fibers have a Young’s Modulus that is about 10 times higher than conventional polymer fibers.
In order to reduce the capillary uptake of aqueous solutions of harmful substances such as chlorides the concrete was impreganted internally in its fresh state. By this measure the capillary suction of the material could be reduced by more than 70% compared to conventional concretes.
After the mix proportion had been established the rheological properties of the concrete such as flowability and viscosity were adjusted in order to achieve self-compacting behaviour. This step had to guarantee both good surface quality and that the concrete completely fills the narrow gap between the old concrete wall and the one-sided formwork.
The ready mix concrete plant and the contracting company were consulted in order to fulfill the requirements regarding the production and application of this high performance concrete. This was part of the quality assurance system.
Client:
Building Authority Zurich, Switzerland
© Concretum Construction Science Inc., Zurich, Switzerland www.concretum.ch
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