Hydration process and physical properties of cement systems modified by calcium chloride and multi-walled carbon nanotubes

Abstract

The application of accelerating admixtures is required in construction work where fast-setting is required or in an environment of low temperature. This type of admixtures allows to regulate the setting and hardening time of cement composites and could influence on their strength and performance. The accelerating admixtures are exemplified by chloride, nitrate and other salts. Some investigations demonstrated the application of different types of nano- and complex additives as a method to accelerate the hydration processes of cement composites. The present study focuses on the investigation of the combined action of multi-walled carbon nanotubes (MWCNT) dispersion and various types of accelerating admixtures such as calcium chloride, calcium nitrate and magnesium chloride. The amount of accelerating admixtures ranged from 1% to 3% by weight of cement, the amount of MWCNT for all compositions remained equal to 0.005% by weight of cement. The setting time of cement pastes modified by different types of accelerating admixtures and MWCNT dispersion was determined. The combined effects of MWCNT dispersion and accelerating admixtures on compressive and flexural strength, water absorption and porosity of cement mortar modified by calcium chloride and MWCNT were studied. Besides, the cement hydration products were evaluated by FT-IR spectroscopy and XRD analysis. The individual and combined effects of accelerating admixtures and MWCNT addition are reported in the article.