Abstract
Mechanical and deformational properties of concrete are markedly improved by the addition of long structural fibres. This addition, however, not always improves the durability of concrete. One important factor for an estimation of concrete durability is to assess the permeation and diffusion characteristics of the surface layer. The research was performed by means of the TORRENT permeability method and the method for determination of the non-steady-state migration coefficient of chlorides in concrete – NORDTEST. The addition of long polypropylene fibres contributes to increasing the permeability of the surface layer for air and chloride solution, but no too significantly. The higher permeability was determined in concrete with concrete recyclate and polypropylene fibres. The measured results by both used methods are partially comparable and can be used for raw estimation of durability of concretes. The higher values of permeability indicate the expected lower durability of tested concretes.
Highlights
According to the Guidance Paper F to the European Construction Products Directive of December 2004, the durability of concrete can be defined as the ability of a product to maintain its required performance over a given or long time, under the influence of foreseeable actions
If we accept the fact that the durability of concrete is considerably determined by the permeability of its surface layers [5], it seems to be reasonable to determine the permeability of the surface of the tested concretes by one of the modern non-destructive methods, e.g. TORRENT for air and NORDTEST for a solution of chlorides in water
2.2 Principles of TORRENT and NORDTEST testing methods The TORRENT testing method is suitable for determining the air permeability of the surface layer of concrete and it can be used both on the test specimens, and on the construction site
Summary
According to the Guidance Paper F to the European Construction Products Directive of December 2004, the durability of concrete can be defined as the ability of a product to maintain its required performance over a given or long time, under the influence of foreseeable actions. Fibre concretes are modern building materials with the sufficiently proven mechanical and deformation properties. Long polymer fibres purposefully improve the mechanical properties of the concrete composite. The diffused fibres are able to improve the low tensile strength of concrete, at the cost of exceeding the critical shear stress of the fibre-cement contact. Poor adhesion of fibres to the cement matrix, the exceeding of the shear stress, or corrosion can lead, according to some authors, to an increase in permeability and subsequently to a decrease in the durability of the cement composite.
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