Banca de DEFESA: Andreia de Paula

EFFECT OF THE REDUCTION OF APTES CONTENT ON THE FUNCTIONALIZATION OF NANOSILIC ON THE MECHANICAL PROPERTIES AND MICROSTRUCTURE OF CEMENTICIOUS MATERIALS

Nanosilica, Functionalization, Amine groups, Portland cement, Microstructure, APTES.

Nanosilica (NS) is considered a highly reactive pozzolanic addition that, replacing cement, has resulted in an improvement in the resistance of cementitious materials and an increase in resistance to water penetration, which strongly influences durability. Despite this improvement, NS contributes to potentiate undesirable effects in cementitious composites, regarding the rheological behavior, workability and final hardened properties of cementitious composites. Recently, some researchers have investigated ways to mitigate these effects, such as the incorporation of functional groups on the surface of the NS, a procedure called functionalization. Thus, this work aims to verify the effect of NS functionalization with low levels of 3-aminopropyltriethoxysilane (APTES) on the mechanical and microstructural properties of cementitious materials. The properties of five different cement pastes were investigated. The heat of hydration, the compressive strength at 1, 3, 7 and 28 days of hydration, the amount of CH and C-S-H through ATG diffraction techniques were evaluated in cement mixtures. and FTIR and porosity through the mercury intrusion porosimetry test (PIM). Such tests aimed to verify the effect of the functionalization of NS with low levels of APTES in the properties in the fresh and hardened state and in the microstructure of the cementitious materials. The results found for pastes with NSF in the calorimetry test demonstrate that the functionalization of NS increases the time required to reach the maximum heat value, leading to a delay in the hydration reactions. The resistance to compression of the NSF's is superior to that of the REF and the NS, the NSFA4 sample reached at 28 days a resistance 28% greater than the REF and 17% greater than the NS at the same age. Through the results of the ATG test, it was verified that the pastes with NS or NSF had lower levels of CH than the REF paste at all ages analyzed. FTIR assays demonstrate that the process of functionalization of NS with APTES slightly increased the amount of CH of pastes with NSF compared to P-NS. All pastes containing NS or NSF resulted in a lower amount of CH compared to P-REF. The PIM results show that, in general, the additions of NS and NSF lead to a decrease in the total porosity, in relation to the reference mortar.