Influence of cement and water content on the multifaceted capabilities of a self-sensing cement-based geocomposite: a comprehensive analysis

This study investigates the synergistic effects of cement, water, and hybrid carbon nanotubes/graphene nanoplatelets (CNT/GNP) concentrations on the mechanical, microstructural, durability, and piezoresistive properties of self-sensing cementitious geocomposites. Varied concentrations of cement (8% to 18%), water (8% to 16%), and CNT/GNP (0.1% to 0.34%, 1:1) were incorporated into cementitious stabilized sand (CSS). Mechanical characterization involved compression and flexural tests, while microstructural analysis utilized dry density, apparent porosity, water absorption, and non-destructive ultrasonic testing, alongside TGA, SEM, EDS, and x-ray diffraction analyses. The durability of the composite was also assessed against 180 Freeze-thaw cycles. Moreover, the piezoresistive behavior of the nano-reinforced CSS was analyzed during cyclic flexural and compressive loading using the four-probe method. The optimal carbon nanomaterials (CNM) content was found to depend on the water and cement ratios. Generally, elevating the water content led to a rise in the CNM optimal concentration, primarily attributed to improved dispersion and adequate water for the cement hydration process. The maximum increments in flexural and compressive strengths, compared to plain CSS, were significant, reaching up to approximately 30% for flexural strength and 41% for compressive strength, for the specimen containing 18% cement, 12% water, and 0.17% CNM. This improvement was attributed to the nanoparticles' pore-filling function, acceleration of hydration, regulation of free water, and facilitation of crack-bridging mechanisms in the geocomposite. Further decreases in cement and water content adversely impacted the piezoresistive performance of the composite. Notably, specimens containing 8% cement (across all water content variations) and 10% cement (with 8% and 12% water content) showed a lack of piezoresistive responses. In contrast, specimens containing 14% and 18% cement displayed substantial sensitivity, evidenced by elevated gauge factors, under loading conditions.