In Germany the properties of textile concretes have been investigated intensively for more than 20 years. At first, essentially textiles on the basis of polypropylene or polyvinyl alcohol were used as reinforcement. As these polymers have only a low modulus of elasticity they can lead to relative large crack widths in the cementitious matrix. Therefore the research activities focused then preferentially on fibres, rovings and fabrics made of alkali-resistant (AR) glass, later on intensified on the material carbon, because this material is more alkali-resistant and thus more durable compared to AR-glass. Carbon-concretes require, compared to conventional reinforced concrete, only a small concrete cover of the reinforcement. For this reason very thin and slight components can be produced with this building material.
Beside the construction properties, the environmental compatibility of construction products becomes more and more important. Whereas at present it is assumed in Germany that standardised construction products or such which have a technical approval fulfil all requirements regarding the environmental compatibility, for new unknown products this has to be proved where necessary (ABuG, 2017) according to the “Principles for assessing the effects of construction products on soil and groundwater” of the Centre of Competence for Construction (DIBt).
Goal of the research project was to generate a broad, scientific verified data base via corresponding leaching and shower tests (laboratory and outdoor tests) on carbon-concrete test specimen with different concrete covering of the carbon-fibres as well as with different percentages of the carbon-fibres to evaluate the environmental compatibility of the new, innovative composite building material “carbon-concrete”. Based on this carbon-concretes can be classified if applicable I such a way, that further environmental testing is preferably not necessary (Without Further Testing (WFT)).
The work of the VDZ gGmbH in the joint research project “Environmental compatibility of C3” focused on characterisation studies on dry mixed fine concretes, cement/binders, fillers and carbon fibres as well as on leaching tests according to the European long term tank test DSLT (DIN CEN/TS 16637-2:2014) on unreinforced and reinforced fine concrete specimens. The “DSLT” leachates of the four carbon fibres studied indicate that they release practically no polycyclic aromatic hydrocarbons to the leachate. The “DSLT” leachates of the unreinforced and carbon fibre reinforced fine concretes have shown that only very small quantities are leached out for most of the parameters and the limiting values of the model building code technical building rules are complied with. Furthermore it was found that no significant difference of the leaching behaviour of the unreinforced and the reinforced fine concretes occurs for the individual parameters. The results available so far suggest that the new material carbon concrete can be classified as environmentally compatible and that no further environmental tests are necessary. This could avoid unnecessary testing costs for the industry concerned.
C³- Carbon Concrete Composite was funded by the Federal Ministry of Education and Research's "Twenty20 Partnership for Innovation" program (Project number 03ZZ0328A).