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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 (fcm) and splitting tensile strength (fctm) 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 fcm 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, fctm 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. [ABSTRACT FROM AUTHOR]

The structural foundations in southern Iran face a formidable challenge due to extensive corrosion. To enhance concrete strength and durability, the construction industry in this region typically incorporates micro silica at a rate of 8% by weight of cement. Nonetheless, given that a significant amount, around 70%, of the concrete expenses in these projects can be attributed to micro silica, and the cost of natural pozzolan in proximity to project sites amounts to only 10% of the price of micro silica, the primary goal of this study is to investigate the durability of concrete incorporating both micro silica and natural pozzolan. The aim is to potentially replace a portion of the micro silica with natural pozzolan while maintaining the required durability and strength of the concrete as specified in the project requirements. To achieve this, eight different concrete mix designs were proposed and subjected them to assessments of compressive strength and various durability standard tests, including water absorption, resistance to rapid freezing and thawing, water permeability, chloride migration coefficient, electrical resistivity, and electron microscopy (Scanning Electron Microscopy (SEM)/Energy Dispersive X-ray Spectroscopy (EDS)/MAPPING). The obtained results indicated that the concrete sample containing 4% micro silica and 12.5% natural pozzolan exhibited similar characteristics to the project's mix design with 8% micro silica in terms of the durability and distribution of permeable spaces within the material. In addition, concerning the pozzolanic reaction, one kilogram of micro silica is nearly comparable to three kilograms of natural pozzolan. Moreover, despite the non-uniform nature of the concrete environment, the EDS and MAPPING results, obtained through random sampling of study points, closely mirrored trends observed in other controlled experiments. • Raising the proportion of natural pozzolan in the concrete up to 25% enhances the durability of reinforced concrete. • The mixture with 30% natural pozzolan displays the most significant reduction in compressive strength. • 4% micro silica + 12.5% pozzolan blend excels in durability and compressive strength compared other mixtures. [ABSTRACT FROM AUTHOR]