Effect of Nano-Silica, Nano-Alumina, and Nano-Calcium Carbonate on Fresh and Mechanical Properties of High Performance Concrete

The incorporation of nanomaterials into high-performance concrete (HPC) offers a promising pathway for enhancing mechanical performance and durability. This study presents a systematic experimental investigation on the effects of three nano-additives—nano-silica (nS), nano-alumina (nA), and nano-calcium carbonate (nC)—on the fresh and mechanical properties of HPC. A total of 16 concrete mixes were prepared, including one control mix and 15 nano-modified mixes with dosages ranging from 0.5% to 3.0% for nS, 0.5% to 2.0% for nA, and 1.0% to 5.0% for nC by weight of cement. Fresh properties were evaluated through slump, compacting factor, and fresh density tests. Mechanical properties including compressive strength (7 and 28 days), split tensile strength, flexural strength, and modulus of elasticity (28 days) were determined according to IS and ASTM standards. Results demonstrate that all three nano-additives enhance the mechanical properties of HPC at optimal dosages. The optimal dosages were found to be 2.0% for nS, 1.0% for nA, and 3.0% for nC. The optimal nS mix achieved a 25.7% increase in 28-day compressive strength, while nA and nC achieved 15.4% and 15.9% increases, respectively. Split tensile strength improvements of 22.4%, 13.8%, and 8.6% were observed for optimal nS, nA, and nC mixes at 28 days. Flexural strength improvements of 23.7%, 15.8%, and 10.5% were recorded. Modulus of elasticity increased by 19.4%, 14.7%, and 11.3% for the optimal nS, nA, and nC mixes, respectively. The enhancements are attributed to pozzolanic reactivity, nucleation effects, filler effects, and microstructure densification. The results provide practical guidance for selecting nano-additives for specific performance requirements in HPC applications.