Methods for characterization of fresh and hardened state of fibre concrete

Abstract Design, preparation and testing of fibre-cement composites are a task of wide range of research workplaces and universities in our country and abroad. However, a question on homogeneity of all cement matrix components and mainly optimal dispersion of fibre reinforcement in a mixture has not been yet solved sufficiently. A research team from the Research Institute for Building Materials has designed new experimental devices for the Discovery Hybrid Rheometer to measure rheological properties of fresh cement-based mixtures. The aim of research works was to find suitable homogenization techniques, design of mixing process and optimal dosing of individual components. By means of these actions it is possible to achieve the best dispersion of selected fibre types in fine-grained cementitious matrixes, which is subsequently verified in hardened composites at first by non-destructive and then by destructive methods. At the first stage non-destructive testing by means of ultrasound waves was carried out at first on a compact test slab with dimensions 500 × 500 × 40 mm and subsequently on individual test specimens with dimensions 250 × 40 × 40 mm, cut from the test slab according to a designed pattern. At the second stage destructive testing of test specimens was performed, mainly evaluation of flexural strength with 4-point bending and subsequently preparation of thin sections from the failure area for observation by means of polarizing microscopy to assess their structural integrity. The aim of research works was to find a method for monitoring homogeneity of cement composites reinforced with both metal and non-metal fibres before being subjected to mechanical loading.