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10981: Durable Repair and Radical Protection of Concrete Structures in View of Sustainable Construction

Quality assessment of concrete structures is complicated because, firstly, concrete itself is a heterogeneous material and, secondly, pouring and vibration of the fresh concrete can further enhance the scatter in the concrete quality (Of course, vibration has also positive effects). The scatter in concrete quality implies that a lot of tests, either destructive or non-destructive, are needed in order to get a complete and reliable picture of the technical status of a structure. Areas with poor quality concrete are susceptible to penetration of hazardous substances, like CO2 and chloride ions, resulting in premature deterioration of the concrete and corrosion of the reinforcing steel. In areas where the concrete quality is really poor repair may be required. Even though the quality of concrete repairs has substantially increased in recent years, it is still well-known that realizing durable repairs is difficult. Even more difficult is the prediction of the long-term performance of concrete repairs. The assessment of the quality of previous concrete repairs, however, must be considered as an inherent part of an overall condition assessment of repaired concrete structures.

Apart from the technical aspects of concrete repair it is well-known that repairing concrete structures is expensive. Directs costs can be high and indirect costs are generally even several times higher than the direct costs. For this reason attempts are welcomed focusing on enhancing the life time and predictability of concrete repairs. A next and ideal situation would be if we can totally refrain from repairing poor quality areas of concrete structures by applying a robust cement-based self-healing coating. These two approaches, i.e. firstly the development of durable and predictable concrete repair and, secondly, the development of cement-based self healing coating, will be studied in detail in this project.

The starting point for this study is the recently developed cement-based material, known as ECC, which stands for Engineered Cementitious Composite. The material has been developed by prof. Victor Li, University of Michigan, USA. This ECC has several specific properties, which makes this material suitable for concrete repairs. ECC is a cement-based material. Fine fibres ensure that multiple cracking, whereby the typical crack width is about 0.05 mm and the strain capacity is in the range of 3-7%. ECC has meanwhile been used as repair material indeed, whereby multiple cracking is an excellent feature of this material in view of relieving stresses induced by deformational incompatibility of repair material and substrate. Because of the stress relieving properties the risk of interface delamination is reduced, which enhances the durability of the repair.

In a currently running PhD project at TU Delft several modifications of the original ECC material have been studied. Preliminary results show that within certain limits modifications are possible. However, fundamental knowledge of the bond properties of the ECC-substrate interface is still lacking. This makes the long-term performance of ECC-based concrete repairs uncertain. In this project the bond properties between repair materials and substrate are, therefore, studied in detail, as well as parameters that affect these properties.

The acquired fundamental knowledge of bond properties will then be used as basis for the development of a cement-based self-healing coating. The ECC-materials is again the starting point for the coating material to be developed. Preliminary studies have revealed that ECC, because of the very fine cracks, has already some self-healing properties. It will be investigated in this project how the self-healing potential of ECC can be ensured in a robust way, even if the thickness of the ECC-based coating is not more than a few millimeters. For both the repair material and the coating it will be demonstrated how the use of these materials can contribute to enhanced performance of concrete structures and to reduction of long-term operational costs and mitigation of the environmental burden.