Efeitos da diatomita em substituição parcial ao cimento portland nas propriedades de concretos convencionais
Concrete is a composite, considered the most used construction material in the world. Its main component is Portland cement, responsible for the formation of calcium silicate hydrates (C-S-H) formed during hydration and which are mainly responsible for the compressive strength of concrete. However,...
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| Médium: | doctoralThesis |
| Jazyk: | pt_BR |
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Universidade Federal do Rio Grande do Norte
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| On-line přístup: | https://repositorio.ufrn.br/handle/123456789/46632 |
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| Shrnutí: | Concrete is a composite, considered the most used construction material in the world. Its
main component is Portland cement, responsible for the formation of calcium silicate
hydrates (C-S-H) formed during hydration and which are mainly responsible for the
compressive strength of concrete. However, currently, the search for alternative, more
sustainable materials has increased, aiming to reduce CO2 emissions and consequently
minimize environmental impacts. This is possible through the use of supplementary
cementitious materials (SCMs), which can be used as a substitute for clinker in the
manufacture of Portland cement and/or as an addition or replacement for cement in the
production of concrete. Diatomite is considered a natural MCS, which with high SiO2
concentration is able to react with calcium hydroxide (CH) released during cement
hydration to produce additional calcium silicate hydrate (C-S-H). Thus, the present work
aimed to study the effects of replacing Portland cement by diatomite in the proportions
of 0%, 10%, 15% and 20% by volume, in the production of conventional concretes with
fck estimated at 30MPa (NBR 8953, 2015). Initially, the starting materials were
characterized as to their physical, chemical, mechanical, structural and microstructural
properties. Then, concretes were produced with a volume ratio of 1: 1.33:2.33 and a/c
ratio=0.44. The concretes were evaluated for their properties in the fresh state (slump
test) and in the hardened state (compressive strength, porosity, water absorption, capillary
water absorption and chloride ion diffusion). Cement pastes with the same proportions of
the concretes were analyzed by XRD (X-ray diffraction) and TG/DTA
(thermogravimetry) techniques at 7, 28 and 91 days. The results showed that the
incorporation of diatomite caused a small reduction in the values of compressive strength
of the concretes. Nevertheless, the concretes produced with 15%v. and 20%v. of
diatomite presented a higher evolution in the values of compressive strength (20.07% and
16.16%, respectively) from 28 to 91 days, as a consequence of the pozzolanic reaction.
While the 0%v. and 10%v. concretes presented an evolution of 4.33% and 5.20%,
respectively. This observation was confirmed in the results of XRD and TGA, where it
was observed that there is a greater consumption of portlandite and a greater amount of
combined water in pastes with diatomite incorporation. The total porosity, water
absorption and capillary absorption decreased in the concrete with 10%v. of diatomite,
due to the filler effect. The incorporation of diatomite reduced the chloride ion diffusion
coefficient of the concretes due to the refinement of the pore structures, presenting the following values 8.389 x 10-12; 5.668 x 10-12 ; 2.241 x 10-12 ; 1.297 x 10-12 , respectively, for the concretes CD-0, CD-10, CD-15 and CD-20. |
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