Coatings on Alkali-Resistant Glass Fibres for the Improvement of Concrete

In general, a sizing is shown to significantly affect both the population and size of flaws on the fibre surface by healing effects. Different alkali-resistant glass (ARG) fibres are coated with special polymer dispersions to provide superior alkali resistance and compared with HTA carbon fibres. Durability testing in highly concentrated NaOH-solutions at ambient and elevated temperatures revealed significant reduction of sizing content of the ‘‘as received’’ ARG fibres after short-term testing. Improved durability of the ARG fibres identified by increased sizing retention is achieved by additional coatings. Styrene–butadiene dispersions proved to be most resistant of those tested. The assessment of changes in the fibre surface chemical properties assisted by nanomechanical investigation is essential for understanding the fibre bulk mechanical fracture behaviour. Sizings and coatings on glass and carbon fibres, respectively, and especially on polymer films, were found to significantly influence both tensile strength of alkali-resistant filament yarns and adhesion strength of coated fibres with cementitious matrices investigated by single fibre pull-out. It would be very advantageous if one could predict higher composites strength of fibrereinforced cement by increasing the tensile strength of the reinforcement fibres. A series of coated yarns showed different mechanical behaviour as a separate phase compared with tensile test results, when a few multifilament bundles were only partly impregnated by the cementitious matrix. The chemistry of the glass fibre sizings and their conditions of interaction (dry or wet state) gives rise to a variation of adhesion strength and modified interphases. Finally, the chemistry of the interaction between both sizing and coating with the cementitious matrix, the concentration of the coating, and the mechanical properties of the coatings were found to significantly influence the strength and failure behaviour with a cementitious matrix. A roving pull-out test allows a rough estimation of the failure behaviour for differently sized and coated reinforcement yarns and their interaction with cementitious matrices.