Experimental Study on Activation Energy and Microstructure of Nano- and Micro-Sized Pozzolanic Materials as Cementitious Composite Binder

Silicate-based nano- and micro-sized binders were used with ordinary Portland cement to evaluate their influence on the setting time, activation energy, mechanical properties, and microstructure. It was found that the setting time was reduced due to the pozzolanic reaction of the silicate-based binders and the densification of the microstructure. However, there is a lack of research on nano-sized pozzolanic materials. Therefore, in this study, research on activation energy and microstructure was conducted. The compressive strength increased owing to a reduction in the porosity in the microstructure, and activation energy also tended to decrease. Moreover, using both micro-silica and a small proportion of nano-silica was more effective in reducing the setting time and activation energy than using any of them individually. The study established that adding a small proportion of nano-silica could reduce the setting time and increase the compressive strength because it positively influenced the pozzolanic reaction and filled the pores between micro-silica and cement, which were composed of relatively larger particles, with smaller particles. Because nanomaterials may degrade flowability due to their large specific surface area, it is deemed necessary to consider the addition of chemical admixtures during mix design. A characteristic has been revealed when nanomaterials are used, and special attention to the particle size distribution characteristics is required because the imbalance in particle size distribution may increase the porosity inside the microstructure. Therefore, it is recommended to use micro-sized pozzolanic materials together when using nano-sized pozzolanic materials.

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