Investigating the mechanical performance of nano additives reinforced high-performance concrete

•- Reducing cement content of concrete, while keeping its mechanical performance by using nano additives.•- Increasing the activity and surface area of NC through chemical exfoliation in addition to thermal activation.•- The enhancement ratios in compressive, splitting and flexural strengths of concrete reached to 33%, 13% and 70% respectively.•- The highest gain in the mechanical performance was obtained from NC modified concrete. It is known that nanomaterials have been broadly employed worldwide as reinforcements for the production of high-strength and high mechanical performance concrete-based structures. Hereinafter, high-performance concrete (HPC) modified with three types of additives were synthesized: exfoliated nano clay (NC), nano-silica (NS), and hybrid particles [silica fume (SF) & limestone (LS)]. The compressive, splitting tensile and flexural strengths, were investigated at 28 days of hydration. The exfoliated NC was simply prepared via exfoliating the thermally activated ordinary clay with the aid of organic ammonium chloride. The results revealed that all types of the employed additives provided an augmentation in the mechanical properties of the hardened concrete mixes especially the mixes with a cement content of 350 kg/m3. Furthermore, the addition of 6% NC has improved the compressive strength of concrete with 350 kg/m3 by 17.06%, the splitting tensile strength by 7.32%, and the flexural strength by 13.21%. Furthermore, the compressive, splitting tensile and flexural strengths of the same concrete were enhanced by 9.57%, 12.1%, and 32.87% respectively, by adding 3% NS. Finally, incorporating (7.5% SF + 2.5% LS) led to an increase in the compressive, splitting tensile and flexural strengths of concrete by 10%, 2.64%, and 51.14%, correspondingly.