Abstract—The aim of this work is to investigate the pozzolanic activity of nano-silica (NS) prepared by sol-gel method and to study its application for improving physical, mechanical and structural properties of hardened blended cement. The NS was mixed with calcium hydroxide (CH) by different ratios 10%, 20%, 30% and 50% using water to CH ratio of 0.35, the mixtures were kept at relative humidity 100% for 7 days. After curing for 7 days, the reactions mechanisms were investigated by differential scanning calorimeter (DSC), X-ray diffraction (XRD) and scanning electron microscope (SEM).
It was found that, NS consume the CH and produce calcium silicate hydrate (CSH) (strength responsible phase in cement). The ratio of CH consumed increases with increasing NS ratio. The studied NS was characterized by great reactivity i.e. it is a good pozzolanic material that can be used for improving cement and concrete properties. Blended cement paste samples were prepared by partial replacement of cement by different ratios of NS 0.5%, 1%, 1.5%, 2 % and 2.5 %. The compressive strength, capillary water absorption and microstructure of NS-blended characteristics were studied at 28 days of curing. An enhancement in compressive strength by about 21% was obtained at 2% of NS. Capillary water absorption was reduced with increasing NS ratio. The reduction rate was 18.29 % at 2% of NS. The microstructure of NS-blended cement appeared quite dense and compact with less micro pores.

Index Terms—Pozzolanic activity, cement, nano-silica, DSC, XRD, SEM, TEM.

The authors are with Physics Dept., Faculty of Science, king Khalid University, Abha, Saudi Arabia (e-mail: mahmoudgawati@gmail.com).

Cite: A. E. Al-Salami and M. A. Al-Gawati, "Pozzolanic Activity of Nano-Silica and Its Application for Improving Physical, Mechanical and Structural Properties of Hardened Cement," International Journal of Applied Physics and Mathematics vol. 3, no. 6, pp. 376-380, 2013.