Effect of joint grinding of nanosilica and Portland cement on the performance of cement pastes

Portland cement has important properties that, over time, have led to its development as the main component of one of the most consumed products in the world: concrete. However, in order for Portland cement to continue with various applications, it is necessary to have full knowledge of its properties and the development of others through scientific research in academic and industrial centers. The addition of new components to the cementitious matrix and the aid of Nanoscience provided advances in the search for improvement of cement properties and this is the objective of this scientific work. Nanosilica, a product formed by silicon dioxide (SiO₂), was added to Portland cement with prospects of influencing the properties of this cement and, in an attempt to solve the dispersion / homogenization problem, the mechanical energy from the grinding was used as resource. For the development of this research, it was necessary to investigate two parameters, the first, the influence of grinding on the properties of the materials and, second, the addition of nanosilica to the cement matrix in different percentages (1% and 2%). In this way, the tests were divided in two stages, Step 1, responsible for the analysis of the materials in powder form, and Step 2, stage characterized by the execution of tests in the specimens and cement pastes. The results of Step 1 showed that milling markedly decreased the average particle size of cement, increased its surface area to a level (above 5000 cm² / g), which according to the literature, may be a proof of Mechanical Activation. The X-ray diffraction showed a reduction in the intensity of the peaks caused by the milling and the disappearance of the gypsum. Thermal analysis indicated a decrease in the decomposition temperatures after grinding, but both the not ground and ground CP II-F presented a fire loss within the limits of the standard. In Step 2, the calorimetry test indicated an increase in the total heat released as a function of grinding and the addition of nanosilica to the cement, especially when both were milled together, which may be an indication of the dispersion potential of the mechanical energy of the grinding. Finally, the mechanical properties such as modulus of elasticity and flexural strength did not show significant changes in the addition of nanosilica or after milling, but when ground together, there was an increase, which can be inferred in a certain capacity of the energy of grinding to promote a dispersion of the nanosilica in the matrix. The compressive strength has increased, both as a function of the grinding and the nanosilica, as well as the water absorption also decreases. From the results, it is concluded that it is possible to improve the performance of the pastes when nanosilica is added and the milling energy is used as the dispersing agent. (author)