Concrete durability: method to assess carbonation in freeze-thawing conditions

The interaction between the reinforced concrete structures and the aggressiveness of the
environment, when different actions occur simultaneously, provides their early degradation.
Thus, their durability is put in jeopardy and the operating time for which they were designed
is reduced. Between the several mechanisms of concrete deterioration, carbonation and
freeze-thaw cycles were object of study of this work. The isolated or joint action of these
mechanisms causes irreversible damages in the concrete structures, with serious consequences
on their stability and safety.
To assess the behavior of the concrete in relation to carbonation and freeze-thaw cycles, an
accelerated carbonation test device was developed where cylindrical test samples with
different maturing conditions, in lab and under natural exposition conditions, are submitted to
high concentrations of CO2 and different relative humidity. The accelerated carbonation tests
were focused on standard test samples deteriorated by the action of successive freeze-thaw
cycles. In the standard test samples have been used concentrations of 15, 30 and 60% of CO2
and the relative humidity had a variation between 32, 60, 75 and 90%. The test samples
deteriorated by the action of 8, 12, 16 and 20 freeze-thaw cycles were submitted to the
accelerated carbonation test under 60% of CO2 and 75% of RH. Standard concrete
characterization complementary tests were also performed in relation to its durability through
capillary and compressive strength absorption tests, microstructure and chemical composition
through dispersive energy spectroscopy tests and mercury intrusion porosimetry, respectively.
The latter were performed before and after carbonation.
It was found that the greatest advance of the carbonation front measured with phenolphthalein
is achieved under exposition conditions of 60% of CO2 and 75% of RH. The increase of the number
of freeze-thaw cycles provides a higher degradation on the test samples, leading to critical
carbonated depths. With 16 and 20 freeze-thaw cycles, the carbonated depth obtained on test
samples matured in lab is around twice the carbonated depth tested on standard test samples.
For the same number of cycles, the sample tests matured in natural conditions carbonate at
100%.
Thus, it is possible to affirm that the accelerated carbonation test device developed make it
possible to access the effects of carbonation and freeze-thaw in concrete with precision.

Master Dissertation in Civil Engineering-Construction of Joana Filipa Lopes dos Reis, 2014.

Dissertação mestrado Joana Reis 2014

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