Textile reinforcement in ultra high performance concrete – a sustainable material composition

Abstract

Nowadays concrete is the world’s most widely used building material. A decisive constituent is cement, which causes in production nearly 10% of the world’s CO2 emissions. Ultra High Performance Concrete (UHPC), a new high-tech concrete with an outstanding compressive strength of 4 to 6 times the strength of standard concrete (NSC), is the most advanced building material in reinforced concrete construction and increasingly used in different countries all over the world. Due to its high compressive strength, building members with remarkable slenderness are enabled and concrete volume can be saved. Even though UHPC requires more cement per volume than NSC, the significant reduction of cross-sections and the partial substitution of cement by adequate fine grain materials such as blast furnace slag, a by-product from steel production, finally lead to a significant reduction in CO2 emission. From a lifecycle perspective, the durability of the material itself can be rated about 3-5 times higher than for normal strength concrete, driven by the very high packing density and low capillary porosity which makes UHPC more resistant against chloride penetration and against freezing-thawing cycles. Without an adequate steel fiber content cracking of the UHPC with respect to reinforcing steel bars leads to similar corrosion topics as known from NSC structures. Concerning the steel fibers, a major disadvantage is the random direction and distribution of the fibers. From an ecological perspective, steel bars as well as steel fibers have a significant negative impact on the ecological indicators. However, non-metallic reinforcing elements such as textile reinforcement are already available as an alternative to traditional reinforcement types; the ongoing research project presented in here combines UHPC material and textile reinforcement, making use of the advantageous material properties of both components and investigating the full potential when combining them. By using textile reinforcement instead of steel fibers and bars, several advantages can be created: A clear orientation of the reinforcement with respect to the main stress axes is ensured and it is possible to fix the reinforcement layers exactly in the designated position. Textile reinforcement has a very high tensile strength, is non-corrosive and its ecological impact is less harmful than that of steel bars or fibers. Another benefit is the recycling option: when using textile reinforcement instead of steel fibers it is possible to separate the two material components with a crushing technique.