Trade Journals for the Concrete Industry

Reinforced concrete is considered the most important construction material in the building industry on account of its versatile formability. The advantages – high strength and comparatively simple processing at low cost in addition to formability – are, however, opposed by a decisive disadvantage: the susceptibility of the reinforcement to corrosion. Concrete is highly alkaline and forms a so-called passive layer on the steel that protects it against corrosion. Substances penetrating into the concrete from the outside can lower the alkalinity in time and damage the passive layer, allowing the steel reinforcement to corrode. This usually results in spalling of the concrete, which reduces the durability of the entire structure and in extreme cases leads to the failure of the construction. In particular structures from the 1950s to the 1970s such as bridges, which in addition must withstand high stresses, can exhibit such serious damage after 15 to 20 years that cost-intensive and elaborate repairs are necessary. In order to prevent that, the steel reinforcement must be protected by a sufficiently dense and thick concrete covering which, according to current standards, must be at least 35 mm thick for outdoor structural elements. In the case of façade panels in particular, this results in slab thicknesses of at least 100 mm in order to guarantee durable structural elements. If the steel reinforcements are now replaced by non-metallic reinforcements, for example textile reinforcements, a few millimetres suffice to ensure the durability and the bond between the concrete and the reinforcement. Façade panels with thicknesses of between 20 and 30 mm can thus be manufactured and 70 to 80% of the concrete can be saved, which in turn has a positive effect on the transport and assembly costs of precast elements manufactured in this way. Textile reinforced concrete is equally suited to the manufacture of new structural elements and the reinforcement of existing ones – where existing buildings are concerned, for example, buildings threatened by demolition can be repaired and resources saved. Like steel reinforced concrete, the tensile forces freed during the formation of cracks in the concrete are absorbed by the textile reinforcement. Flat, mesh-like structures are used, which are usually manufactured as a non-woven fabric made of alkali-resistant glass fibres (AR glass) or carbon fibres. The fibres are characterised by extremely high strengths, which are five to six times higher than is the case with conventional reinforcing steel. The main properties of the fibres and the concretes are described below.