Mechanical and durability performance of hybrid nano clay–CNT concrete: Experimental investigation and data-driven polynomial regression modeling

Abstract

Concrete remains the most widely used construction material, yet its brittleness, microcracking susceptibility, and durability limitations continue to challenge the development of long-lasting infrastructure. At the same time, reducing the environmental impacts associated with cement production requires innovative materials that improve concrete performance. Nanomaterials such as nano clay and carbon nanotubes (CNTs) offer potential for modifying the cementitious matrix and enhancing mechanical and durability properties. However, their combined effects, particularly when integrated with predictive modelling, remain insufficiently investigated. This study evaluates M35 concrete incorporating 0–6% nano clay as a partial replacement of Ordinary Portland Cement and 0–0.20% multi-walled carbon nanotubes (MWCNTs). Compressive, flexural, and split tensile strengths were evaluated at 7, 14, and 28 days, while water absorption was considered as a durability indicator. The optimum hybrid mixture containing 4% nano clay and 0.10% CNTs exhibited improved mechanical performance compared with the control mixture. Second-degree polynomial regression models were developed using nano clay content, CNT dosage, and curing age as predictor variables. The models demonstrated high predictive capability, with R² values ranging from 0.94 to 0.99. Sensitivity analysis identified nano clay content, CNT dosage, and curing age as important parameters influencing concrete performance. The combined incorporation of nano clay and CNTs improved strength and reduced water absorption, indicating enhanced matrix densification and resistance to crack initiation and propagation. The proposed experimental and data-driven framework provides a useful approach for predicting the performance of hybrid nanomaterial-modified concrete and supports the development of durable and sustainable concrete for long-term infrastructure applications.