Project duration: 2023 - 2025

Joints are integral components in concrete structural elements, e.g. industrial surfaces, parking and traffic areas, retaining walls, etc., in order to avoid unwanted forced cracking. Particularly in movement and dummy joints, the thermally or hygric-induced inherent deformations of the concrete component are concentrated. Depending on the intensity and duration of the effects, joint deformations of several millimeters to centimeters can occur.
Liquid media, including pollutants contained therein (chlorides, sulfates, alkalis, hydrocarbons, etc.), can penetrate through the joints and enter the concrete via the joint flanks, possibly impairing the durability of the component. To avoid this, joints are sealed with bituminous compounds, plastics or rubber-based joint profiles. However, the durability of these sealing compounds and profiles is limited to a few years. As a rule, they have to be replaced after about 5 to 10 years at corresponding expense. In addition to the direct costs, the maintenance and renewal of the joints often results in further impairments due to the necessary blocking of the surfaces.
Thus, joints are inherent weak points in the system, which may represent considerable restrictions in the use of the concrete surfaces, irrespective of the structural design and the quality of workmanship and maintenance. From the point of view of finishing and use, it would therefore make sense to avoid joints as far as possible. Usually, this is made possible by the classical reinforced concrete construction method, although high reinforcement proportions are necessary to adequately limit crack widths. At the same time, the reinforcement located in the edge zone is usually subject to a high risk of corrosion.
In the research project applied for here, an alternative solution concept for the joint problem described is to be fundamentally investigated. The principle is to cover joints in unreinforced or only weakly reinforced concrete components with thin, textile-reinforced concrete layers. Carbon fiber reinforcement, which is characterized by very high corrosion resistance and comparatively high (tensile) load-bearing capacity, is the preferred material for this purpose. The relatively large singular joint movements in the base component would show through in the form of wide individual cracks in a conventional concrete cover layer applied over it. However, the fine high-strength reinforcement in such a "carbon concrete layer" (Carbon Reinforced Concrete or CRC) transforms these singular deformations into plural, much smaller cracks. With sufficiently small cracks, the penetration of fluid media into the overall system is prevented. At the same time, this cementitious-reinforced system can be expected to have a durability similar to that of comparable concrete structures, which considerably reduces or even eliminates the need for maintenance and servicing, including indirect deterioration. Overall, a significantly more durable and serviceable structure can be predicted with this type of joint closure.