A study on mechanical properties of cement paste using magnetite-silica nano-composites

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Abstract
Micro- and nano-siliceous particles have been employed as one of major components of Portland cement composites because of their filling effect and pozzolanic reaction. Enhancing the mechanical properties of Portland cement composites using nano-particles without workability reduction and dispersion difficulties is one of the challenges in the cement field of research. In order to overcome disadvantages of nano-particles in cement, a new method was investigated in this study. Magnetite-silica core-shell nano-composites (MS), which have been widely used in biological fields, were employed here as fillers and reinforcements in cement pastes. These nano-composite particles consist of nano-magnetite (NM) cluster and nano-amorphous silica shell. Different types of analysis such as X-ray diffraction, transmission electron microscopy and vibrating sample magnetometer were conducted on these particles to investigate their properties. MS particles were synthesised by coating nano-magnetite particles with tetraethyl orthosilicate (TEOS) as a source of silica. MS particles were used as an additive material in cement paste mixes with cement replacement ratios of 0·05, 0·1 and 0·2%. Additional samples were also made with the same cement replacement ratio of NM and nano-silica (NS). Experimental results indicated that the compressive strength of cement paste can be increased up to 14%. This is mainly attributable to the pozzolanic effect of silica shell in combination with the filler and nuclei effect of these particles. It was also found that the MS does not change the workability of mixes considerably. Additionally, the microstructure of cement pastes was characterised using scanning electron microscopy to evaluate the effect of NM, NS and MS particles on the microstructure of cement pastes.

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