Estudo de ensaios e parâmetros de transporte de cloretos no concreto para aplicação em modelos preditivos de vida útil
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2022-03-31
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Universidade Federal de Goiás
Resumo
In a contemporary engineering context, a performance approach and the design of more
durable, sustainable and efficient structures are required. Corrosion of reinforcement is one of
the main mechanisms of degradation of reinforced concrete structures, especially in the
marine environment, and can lead to its collapse if there is no intervention. To meet this
approach, predictive models have been developed, with the objective of predicting the useful
life of structures, considering different degradation mechanisms; among them, the corrosion
of the reinforcements. Thus, the objective of this work is to study different parameters of
chloride transport in concrete with three water/cement – w/c ratios (0.40; 0.55 and 0.70) for
application in prediction models of service life. For that, four different test methodologies were
used to evaluate the transport of chlorides, over four months. Two migration tests were then
considered – NT Build 492: 1999 (in non-steady state); LMDC test (steady state) – and a nonsteady
state diffusion test: NT Build 443: 1995, carried out in two different ways, according to
the standard (exclusive diffusion mechanism, with the concrete continuously submerged) and
by means of weekly cycles of wetting and drying (hybrid mechanism, containing capillary
absorption in the convection layer and diffusion in the deeper saturated layers). The results of
the experimental program, as expected, showed a tendency for the coefficients to increase
with increasing w/c ratio and a decrease in these parameters with increasing maturity of the
cement matrix (age effect). Despite having different principles, the coefficients obtained by
different methods showed good correlations: with the results of the NT Build 492 and NT Build
443 standards being close to each other and about 10 to 16 times greater than the effective
coefficient (steady state) obtained by the LMDC test. The application of prediction models
indicated the importance of a more assertive definition of the input parameters of these
models, especially the diffusion coefficient used. Among the methods studied, the use of the
effective diffusion coefficient (LMDC test) as an input parameter resulted in service lives more
in line with reality. Among the models applied, Life-365 stood out for considering different
influential factors and getting closer to reality. Regardless of the model applied or the
coefficient considered as an input parameter, the w/c ratio strongly influenced the calculated
service life: it reduced, on average, 40% of concrete with w/c ratio 0.40 for concrete with w/c
ratio c 0.55, reduced by 50% when the w/c ratio increased from 0.55 to 0.70 and 70% from
0.40 to 0.70.
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LOPES, R. C. Estudo de ensaios e parâmetros de transporte de cloretos no concreto para aplicação em modelos preditivos de vida útil. 2022. 229 f. Dissertação (Mestrado em Geotecnia, Estruturas e Construção Civil) - Universidade Federal de Goiás, Goiânia, 2022.