Synergistic Microstructures, Mechanical Properties, and Piezoresistive Performance Improvement of Nanoengineered Cementitious Composites by CNT and GNP

Graphene Nanoplatelets (GNPs) and Carbon Nanotubes (CNTs) are important components for smart infrastructure and structural health monitoring, as they possess excellent mechanical and piezoresistive properties. However, current research on GNP-CNT nanoengineered composites remains in its infancy. Herein, the effects of GNP-CNT admixtures with varying contents on the mechanical strength, microstructures, and piezoresistive properties of cement-based materials were investigated. Scanning electron microscopy (SEM) observations confirmed the uniform dispersion of GNPs and CNTs in the cement matrix (with no severe agglomeration), and physical interactions between these nanomaterials contributed to enhanced pore filling. Mechanical tests showed that GNP-CNT admixtures maintained compressive strength but significantly improved flexural strength. Specifically, at a total nanomaterial content of 0.5%, the flexural strength was enhanced by more than 30%. Both CNTs and GNPs exhibit favorable piezoresistive performance at low stress, while CNTs dominate the piezoresistive performance at high stress. A four-probe method revealed that CNTs can effectively improve the linearity of piezoresistive performance, enabling distinct resistivity changes even under high stress (attributed to unclosed tiny interfacial gaps). Additionally, the admixture of 0.25% GNPs + 0.25% CNTs yielded optimal piezoresistive performance. These results deepen the understanding of synergistically nanoengineered cementitious composites by CNT and GNP and provide GNP-CNT modified composite materials in smart self-monitoring infrastructures.