As obras disponibilizadas nesta Biblioteca Digital foram publicadas sob expressa autorização dos respectivos autores, em conformidade com a Lei 9610/98.
A consulta aos textos, permitida por seus respectivos autores, é livre, bem como a impressão de trechos ou de um exemplar completo exclusivamente para uso próprio. Não são permitidas a impressão e a reprodução de obras completas com qualquer outra finalidade que não o uso próprio de quem imprime.
A reprodução de pequenos trechos, na forma de citações em trabalhos de terceiros que não o próprio autor do texto consultado,é permitida, na medida justificada para a compreeensão da citação e mediante a informação, junto à citação, do nome do autor do texto original, bem como da fonte da pesquisa.
A violação de direitos autorais é passível de sanções civis e penais.
The seek for low environmental impact materials has become one of
the priorities of construction building materials engineers. One of the
reasons is the massive growing contribution of cement production industry
in worldwide CO2 emissions. In this scenario, the dissemination of
nanotechnology into varied areas is drawing attention for enabling new
possibilities. The idea of the present thesis is to associate a material
provided from a natural source with the potential benefits of
nanotechnology to modify conventional cement pastes regarding their
chemical, physical and mechanical aspects. Nanocellulose arises as an
alternative that meets an eco-friendly source with remarkably properties
expected from nanomaterials. There are different types of nano cellulosic
materials that may be tailored to achieve desired compatibilities with varied
cementitious materials. In this work, nanofibrillated cellulose (NFC) in the
form of gel, and microcrystalline cellulose (MCC) particles were
investigated, so a comparison could be traced between them. The use of
both NFC and MCC in cementitious materials is recent and there are
important gaps regarding their effect. For that reason, the feasibility of MCC
and NFC to act as reinforcement on cement pastes was evaluated through
compressive and flexural tests. Then, the possible mechanisms behind the
effect of MCC and NFC on the microstructure of cement pastes were
investigated through distinct chemical and physical analyses. Moreover, the
total and autogenous shrinkage were characterized, as well as the dynamic
and static rheological behaviors. Due to rheological modifications, the
mixture of cement pastes with NFC was facilitated by a superplasticizer, especially for percentages higher than 0.050 percent wt. The MCC and NFC
promoted the reinforcement of the cement pastes, regarding flexural and
tensile stresses, increasing the composite strength and modulus. It was
observed that he water present in the NFC gel is not totally available as
mixing water due to the morphology and hydrophilicity of the fibrils. If
associating certain levels of inclusions and water ratio, the NFC inclusion
led to a decrease in autogenous shrinkage. The addition of 0.040 percent of NFC
resulted in similar outcomes to 1.000 percent of MCC regarding their ability to
increase yield stress and viscosity.