Effect of water and nano-silica solution on the early stages cement hydration

The nanoscopic young's modulus of cement paste during early ages of hydration in water and nano-silica was investigated by the application of atomic force microscopy (AFM). Peak-Force Quantitative Nano Mechanical (PFQNM) imaging mode in atomic force microscopy was used to determine elastic modulus of cement paste before and after immersion in water and nano-silica solution. The results clearly show how mechanical and physical properties of cement grains changes progressively to higher values during the hydration process in water and nano-silica. Moreover, an empirical theory on mechanism of hydration development is proposed in the current study based on experimental observations. Average Young's modulus of condensed cement powder was changed from about 15 GPa, for unhydrated state, to 11.3 GPa after two hours of hydration in water environment. The average roughness trend was also altered from 8.31 nm to 18.2 nm during hydration process. Results show that the cement hydration rate in nano-silica solution is much higher than water environment. Moreover transition zone between C-S-H colonies have much higher mechanical properties than the hardest colonies in every ages. In the presence of nano-silica, transition zone has a width of less than 10 nm and a surface area of 5% of the overall surface area. 2016 Elsevier Ltd. All rights reserved.