Mechanical properties and brittleness of concrete made by combined fly ash, silica fume and nanosilica with ordinary Portland cement

This paper introduced a new concrete composites made by quaternary binder by partially replacing ordinary Portland cement (OPC) with different percentages of supplementary cementitious materials (SCMs). The motivation is to reduce our dependency on OPC to reduce CO₂ emission and carbon foot print. As the main substitute for the OPC, siliceous fly ash was used (FA). Moreover, silica fume (SF) and nanosilica (nS) were also used. This study utilized the following contents of SCMs used: 5% of nS; 10% of SF; 0, 15, and 25% of FA. During examinations the main mechanical properties of concrete composites, i.e. compressive strength (f_cm) and splitting tensile strength (f_ctm) were assed. The brittleness of these materials was also analysed. Based on the conducted studies, it was found that concrete composite based on quaternary blended cements, of series Mix3, has shown the best results in terms of good strength parameters, whereas the worst mechanical parameters were characterized by concrete of series Mix4. On the other hand, concrete including only SF and nS (Mix2 series) were characterized by the greatest brittleness. It was observed that f_cm of concrete composites for series Mix2, Mix3, and Mix4 increase of 41%, 48%, and 31% respectively compared with the concrete without additives, i.e. series Mix1. In addition, f_ctm also increase of 39%, 47%, and 30%, respectively, for the three series mentioned above, compared with the control concrete. Concrete of series Mix3, with high mechanical properties and demonstrating the features of quasi-plastic material, i.e. having lower brittleness, can be used in concrete and reinforced concrete structures subjected mainly to dynamic and cyclic loads. Therefore, it can be used, in the construction of foundation structures for machines and other types of structures in which the above-mentioned loads are dominant.