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Title: Effect of nano-TiO2 on C–S–H phase distribution within Portland cement paste
We investigate the mechanisms by which titanium dioxide nano-particles (nano-TiO2) interact with cement hydration products. To this end, we synthesize nanomodified cement samples with 1 wt% and 5 wt% of TiO2. We investigate the physical properties using depth-sensing based methods such as statistical nano-indentation and microscopic scratch testing. Fourier transform infrared spectroscopy yields the chemistry, whereas micromechanics modeling provides insights into the nanostructure. The macroscopic plane strain modulus increases by 16% and 83%, respectively, and the macroscopic indentation hardness increases by 37% and 40%, respectively. The fracture toughness rises by 3% and 11%, respectively. Environmental scanning electron microscopy reveals a 30% reduction in crack width for TiO2 cement nanocomposites compared to plain cement. Meanwhile, Fourier transform infrared spectroscopy and statistical deconvolution show an increase in the fraction of high-density calcium silicate hydrates (by 22% and 12% respectively), and in the fraction of calcium hydroxide (by 101% and 251% respectively). Within the framework of the colloidal and granular models of C-S-H, the increase in stiffness and strength after nano-TiO2 modification of cement paste is due to the closely-packed structure and the high atomic coordination number of high-density C-S-H. Similarly, due to the high dimensional stability of high-density C-S-H and calcium hydroxide, our results explain the reported improvements in drying shrinkage and creep properties following cement modification with nano-TiO2.  more » « less
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Journal of materials science
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Medium: X
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National Science Foundation
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