Keywords: fibre-concretes, reinforced fibre concretes, concrete mixtures design.

Despite a century of development and their exquisite properties fibre-concretes have not undergone a significant expansion in their use by the construction sector. The cause of this fact is uncertainty in acquiring the required properties from the unawareness of principles of fibre-concrete design. While for the design of plain concrete many theories exist, there is no reliable method for fibre-concrete so far.

In this article the results of mathematical modelling of fibre-concrete mixtures of preset granulometry are presented. It follows that while for mortars of small sizes of grains we are not limited in the design of hard micro-reinforcement, the concrete mixtures are more liable to over-batching. With mixtures of optimal granulometry of grains the parameters of micro-reinforcement must strictly correspond to existing principles, otherwise grain opening occurs together with a decrease of the quality.

The principle finding is that for the batching of micro-reinforcement the weight is not crucial but the total length of micro-reinforcement in the unit of volume of fibre-concrete is significant. While with a maximal grain size of D = 4 mm, the total length of the micro-reinforcement in 1m³ of a concrete mixture can reach 530 km, it decreases with grains of maximal size D = 8 mm to 132 km, with grains of D = 16 mm to 33 km, with grains with maximal size 32 mm to 8 km and finally with mixtures with a maximal grain size of 63 mm to only 2 km.

At the end of the paper methodical instructions for the experimental verification of designed fibre-concrete mixtures are presented.

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