Lviv Polytechnic National University, Department of construction production
Lviv Polytechnic National University, Department of Building Production
Lviv Polytechnic National University, Department of Building Production

The application of engineering cementitious composites (ECC) – a specially developed class of cement-based material reinforced with fibers – allows to enhance the loading capacity, stability under static and dynamic influences, as well as durability of building structures due to controlled cracking process. The design of engineering cementitious composites is based on the concept of micromechanics, which includes the strength and energy criteria of deformation strengthening throughout the wide range from the macro- to the nanostructural level. This concept based on the ability of the dispersed fibers to perceive the load and absorb energy. However, the high volume of cementitious materials in ECC, often up to 70 %, results in a large drying shrinkage, limitation on dimensional stability and negative effects on material cost. The flowability and strength of engineered cementitious composites based on binary and ternary systems of binder materials with different content of dispersed fibers are researched. It is established that an increasing of fiber amount leads to a significant reduction in the flowability of cementitious composites, so the fiber content of 1.5–2 % is optimal. When the disperse fibers are introduced, part of it works on tension, and some of it prevents particle displacement, ensuring the integrity of the system under the action of external loading. It is shown that the combination of fly ash and ultrafine mineral additives with high surface energy in the ternary system of binder materials, the use of polycarboxylate superplasticizer, as well as reinforcement of the engineered composites structure with dispersed fibers in optimum amounts contribute to their mechanical properties both at an early and later hardening period compared to composites based on binary system of binder materials. With the use of a complex of mineral additives that provides a dense packing of particles, filling space between cement grains, an early pozzolanic reaction, obtaining of additional hydration products, the coefficient of crack resistance increases to 0.227-0.240 compared with 0.216 for the EСC based on the binary system of binder materials.

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