Comparative measurements of fracture toughgness combined with visual analysis of cracks propagation using the DIC technique of concretes based on cement matrix with a highly diversified composition

This paper presents comparative measurements of the fracture toughness together with visual analysis of cracks propagation of concretes made of quaternary binders. A composition of the 2 most commonly used mineral additives, i.e. fly ash (FA) and silica fume (SF) in combination with nanosilica (nS), has been proposed as a partial replacement of the ordinary Portland cement (OPC) binder. The primary objective of the proposed tests was to assess: basic mechanical parameters, i.e. compressive strength – fcm and splitting tensile strength – fctm, fracture toughnessKIcS, and fracture processes in quaternary concretes. The modern and precise DIC technique was used, during the studies, in order to realised assumed tasks. It was found that modification of the binder composition with 3 pozzolanic active materials resulted in an increase in the analysed mechanical parameters for each of the combinations compared to the results obtained for the control concrete. Substitution of the binder by 3 additives resulted in a slight heterogeneity of the structure of the quaternary binder concretes. In addition, as content of FA rises throughout each of quaternary concrete series, material becomes more ductile and shows less brittle failure. Therefore composite containing: 80% OPC, 5% FA, 10% SF, and 5% nS – due to its high fracture toughness and lower brittleness – can be used in reinforced concrete structures subjected to dynamic or cyclic loads.