Mechanistic study on the influence of nano‑SiO₂ on the properties of smart cementitious composites to sulfate attack: From experiments to evaluation modeling

Abstract

The potential impact of sulfate attack on the self-sensing performance of smart cementitious composites posed non-negligible risks to the accuracy of structural health monitoring. This study aimed to enhance the sulfate attack resistance of those containing multi-walled carbon nanotubes (MWCNTs) by incorporating nano-SiO₂ (NS). Mechanical, electrical, and cyclic piezoresistive properties were determined under sulfate exposure. Microstructure and phase composition were characterized using MIP, FE-SEM, EDS, XRD, and TG-DTG. A new evaluation model integrated the maximum fractional change in resistivity (FCR_max), stress sensitivity (SES), strain sensitivity (SAS), and the stress–FCR vertical offset (SFVO) to yield a self-sensing performance index (SPI). Results showed that 0.5 wt% NS-modified mortar most effectively mitigated self-sensing performance degradation during late-stage erosion. Under varying load amplitudes, the maximum increases in FCR_max, SES, and SAS compared to other samples were 4.0, 10.2, and 6.0 times, respectively; under varying loading rates, these indicators increased by 6.9, 14.0, and 9.1 times; moreover, smaller standard deviation (SD) and coefficient of variation (CV) of SFVO indicated lower volatility and enhanced stability of self-sensing performance. The pozzolanic and nucleation effects of NS and MWCNTs reduced porosity by 4.11–15.97 %, inhibited sulfate ion transport, and decreased corrosion products by 10.1 % after 180 days of erosion. SPI increased with load amplitude but decreased with loading rate; high rates, coupled with corrosion products, accelerated self-sensing degradation, reducing the maximum SPI by 2.89–5.41 % versus low rates. These findings provide a foundation for designing durable smart cementitious composites and predicting their long-term performance in sulfate environments.