High-temperature protective hybrid impregnation and coating for carbon reinforcement in concrete structures

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Carbon reinforced concrete is an innovative construction material with high potential for future application, but the use for strengthening and new building structures is limited due to material’s poor high temperature resistance. Concrete spalling, polymer softening and degradation as well as oxidation of the carbon fibre can occur at high temperatures and lead to deterioration of the composite’s mechanical properties like the strength. Still further research on the material behaviour under high temperatures is needed to generate an extensive and reliable database. Unfortunately test methods for material characterisation known so far are inconsistent, elaborate and barely suitable for high temperature experiments. Hence, development of standardized test procedures is a research aim.To prevent premature failure of carbon reinforced concrete structures exposed to high temperatures we propose to modify known and suitable fine grained high strength concrete mixtures by addition of PP fibres. Furthermore, carbon fibre strands will be saturated with a temperature stable, hybrid particle based impregnation. Second, a protective coating based on kaolinite hybrid particles will be applied. The platelet-like kaolinite particles, each chemically functionalised with a combination of flame retardant, intumescent and charring polymers by grafting procedures, assemble into a stacked sheet all around the fibre strand, while adhesives assure the attraction to both impregnation and concrete matrix. In case of high temperatures or fire, the resulting dense and stable char, reinforced by platelet-like nanoclay particles, features an excellent interface barrier for oxygen in one direction and for volatile combustion products on the other way. Furthermore it forms a heat shielding barrier. Thereby, it decelerates the polymer softening and prevents its degradation. The flame retardant moiety smothers the existing flame and prevents spontaneous combustion of flammable polymeric material, while the intumescent component merely compensates for the mass loss of the clay during phase transition.The newly developed impregnation and coating will be applied on fibre strands and examined in tensile and bond tests regarding its high temperature resistance via the developed test setups (including specimen geometry, load introduction, measuring system, heating method). The project will provide a fundamental knowledge on (1) effect of kaolinite coatings on hybrid silica particle impregnated carbon fibre strands as a protective layer against decomposition at high temperatures; (2) mechanical properties of such fibre strands embedded in concrete examined at room and under high temperatures, and (3) recommendations for the composition of concrete in combination with carbon fibre strands with reduced spalling. Finally, improved test setups are expected to be available for determining the basic mechanical properties of carbon reinforced concrete under high temperature load (4).