Rolands Cepuritis

Effect of the Fibre Type on the Rheological and Mechanical Properties of Cementitious Composites for Thin Overlays

Polypropylene (PP), nylon and polyvinyl alcohol (PVA) micro-fibres with different geometries were used at 1 vol. % dosage to investigate rheological and mechanical properties of cementitious composites to be used for thin overlays. Slump-flow and visual stability index methods were used to characterise the rheological properties. Single crack tension and bending studies were carried out to evaluate the tensile and bending strength, as well as the post-cracking behaviour. The results show that fibre geometry (L/d ratio and specific surface area) has a pronounced influence on the fresh state rheological properties of the cementitious composites. The results also surprisingly indicated that the nylon fibres are able to significantly increase the pre-cracking tensile and bending strength. All tested composites showed tensile strain softening and insignificant deflection hardening after cracking and a major strength loss. The results indicate single crack tension method to be the most appropriate for evaluation of mechanical properties of cementitious composites used for thin overlays.

Method development to evaluate steel fiber performance in concrete with expansive additives under restrained hardening conditions: preliminary results

Novel steel molds in form of a rigid cubical shell were developed in order to investigate single steel fiber pull-out resistance in concrete with expansive additive under restrained hardening conditions. The developed steel molds simulate internal (from steel fibers) and external (from friction against sub-base) restraints that hinder expansion of the concrete in a flooring slab structure installed on ground. Samples with a single hooked-end steel fiber, with and without expansive additive were manufactured and tested in the developed mold geometry. The results show that restrained concrete expansion positively affects single fiber pull-out behavior, i.e. fiber delamination resistance is increased by 29.7 % and pull-out peak load by 10.8 %.