Estudo da carbonatação natural de concretos com diferentes adições minerais após 10 anos de exposição
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2013-04-29
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Universidade Federal de Goiás
Resumo
Among lots of pathologies that attack the concrete structures stands out the corrosion of the
reinforcements, that may be triggered by the phenomenon of carbonation of the concrete,
which consists in a physico-chemical process between the carbon dioxide (CO2) from the
atmosphere and the cement paste compounds, which has as main result the calcium carbonate
precipitation (CaCO3) in a region of the concrete cover, with the formation of a layer that has
less alkalinity than that not affected by this phenomenon. The carbonation moves from
outside to inside the concrete through a carbonated front, that when it reaches the depth of the
reinforcement causes destabilization of the protective passive layer, providing the onset of
the corrosion. How many researches are conducted by accelerated carbonation tests, it is of
paramount importance that the evaluation process by comparing it with data obtained from
samples that have suffered natural carbonation. Facing this reality, this research is conducted
based on samples that are exposed in the natural environment (external housed) for a period of
ten years, with the general objective of evaluating the results (coefficients and carbonation
depths) of natural carbonation process of concrete with different mineral additions,
water/binder ratios and curing conditions (moist and dry) over this period. For this realization,
samples of concrete produced in 2002, produced in Castro's dissertation (2003). The variables
included in the experimental program are: concretes with five types of mineral additions
(silica fume (10%), rice husk ash (10%), metakaolin (10%), fly ash (25%), blast furnace slag
(65%), these amounts being in partial replacement of cement mass) and the reference
concrete, without mineral addition; three water/binder relationships (0.40 , 0.55 and 0.70) and
two curing conditions (moist and dry). Measurements were made of natural carbonation
through of pH indicator based on phenolphthalein, elaborating a database along time, through
measurements with periods of exposure of 0.25 years (91 days), 0.50 years (182 days), 0.82
years (301 days), 3 years, 7 years, 9 years and 10 years, allowing comparative performance
evaluation of various concrete containing mineral additions, taking as a base carbonated
depths and natural carbonation coefficients data. The results showed that there are significant
differences of behavior between different concretes studied and that in the overall analysis of
the carbonation natural coefficients, the reference concrete showed the best alone
performance, showing that the alkaline reserve is still the predominant effect in terms of
against carbonation, but the microstructure refinement provided by additions (physical effect)
approaches such chemical aspect, as detected, for example, in concrete with metakaolin. In
the correlation between the accelerated carbonation coefficients and the natural carbonation
ones, was verified a relation of direct proportionality between the coefficients found for the
two procedures, with the coefficient signifying accelerated approximately 7.4 times the
natural ratio. The useful life predictions showed periods of time until the carbonation front
reaches the cover thickness ranging from 4 years up to 241 years, for the different concretes
and situations analyzed.
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FERREIRA, Murillo Batista. Estudo da carbonatação natural de concretos com diferentes adições minerais após 10 anos de exposição. 2013. 197 f. Dissertação (Mestrado em Geotecnia, Estruturas e Construção Civil) - Universidade Federal de Goiás, Goiânia, 2013.