DEPTH OF CARBONATION TEST
The carbonation
test was carried out to determine the depth of concrete affected due to the
combined attack of atmospheric carbon dioxide and moisture and causing a
reduction in the level of alkalinity of concrete. The carbonation of concrete
also lowers the number of chloride ions needed to promote corrosion and reduces
the protection of steel against corrosion.
The indicator
used is a solution of phenolphthalein in diluted ethyl alcohol, which changes
from colorless to purple-pink as the pH value rises above 10. Consequently, the
outer, carbonated layer of concrete remains its natural color while
non-carbonated concrete is stained pink. This test was conducted in accordance
with BS EN 14630:2006 and BS 1881-201:1986.
The test results are presented in the buildings' reports.
AIM AND SCOPE
The method of testing consists of determining the depth of the carbonated layer on or from the surface of hardened concrete using an indicator. This method can be carried out; on specimens taken from completed structures (site specimens) and be used for testing on-site.
Carbonation affects various properties of hardened concrete. Primarily, the protection of the reinforcing steel against corrosion, which is originally guaranteed by the highly alkaline pore solution of the cement paste, becomes lost.
A change in color shows the difference in alkalinity between carbonated and uncarbonated concrete. In contrast, the carbonation of concrete occurs when the PH of the concrete (normally 11 or 12) drops to a range between 9 and 10, according to BRE Information Paper No. IP6, 1981.
This test will be carried out as per BS 1881-201:1986
PRINCIPAL APPLICATIONS
Knowledge of the depth of carbonation combined with the age of the concrete may be useful when assessing potential durability and the likelihood of corrosion of reinforcement. This test may also be useful in conjunction with some of the near-to-surface test methods to ensure that the depth of carbonation is insufficient to influence results.
PROCEDURE
- On the freshly extracted concrete core, clear the
surface immediately of dust and loose particles using a clean cloth.
- Apply phenolphthalein, a chemical indicator, by wiping
using a clean paintbrush or by spraying immediately.
- Evaluate
if carbonated or uncarbonated by a change in color
- Observe
measurements from the side surfaces or the broken surface.
- If weak
coloration or none appears on the surface, then repeat the spray test
after the surface has dried.
Phenolphthalein indicator appears pink in contact with alkaline concrete with pH values above 9 and colorless at lower levels of pH.
