Pore Structure Degradation of Different Cement Mortars Exposed to Sulphuric Acid

A Study on Mechanical Characteristics of Cement Composites Fabricated with Nano-Silica and Carbon Nanotube

In this study, cement composites were fabricated with various contents of added nano-silica (NS) and multi-walled carbon nanotubes (MWNTs). The compressive and flexural strengths of the resultant cement composites were examined. To explore the microstructures and MWNT distribution, electrical conductivity tests, and scanning electron microscopy were conducted. In addition, the strength results were analyzed based on thermal analysis and porosity evaluations. The electrical conductivity results indicated that MWNTs were satisfactorily distributed in the cement composites. In the mechanical strength tests, the composite with a 0.6% MWNT and 5% NS content and another with a 0.3% MWNT and 5% NS content yielded enhancements in the compressive and flexural strengths of 17.2% and 52% compared with the control samples, respectively. However, composites containing relatively large amounts of both NS and MWNTs showed degradation in the mechanical strength. The enhancement or degradation of the strength was supported by porosity evaluations and thermal analysis results. In particular, the degradation of the strength due to the incorporation of large amounts of both MWNTs and NS was explained by thermogravimetric analysis, which indicated a limited generation of calcium silicate hydrate (C-S-H) hydration products. The lower generation of C-S-H was likely due to the dense microstructure of MWNT/NS-incorporated cement hindering the reactions between calcium hydroxide and the NS.