Abstract
This paper presents the results of a series of long term survey on carbonation of concrete in structure. Six reinforced concrete model walls, made of conventional concrete with slumps from 12 to 21 cm and flowing concrete with slump of 21 cm fluidized from initial slumps of 8 and 12 cm, and stored in open air were tested for carbonation at 2, 4.5 and 15 years. 25 year survey was conducted only on 2 model walls made of conventional and flowing concrete with slump of 21 cm. The test results indicated that the carbonation was greater for flowing concrete than for conventional concrete. Greater carbonation of flowing concrete can be due to increase in air voids in hardened concrete. Carbonation was found to be accelerated with increase in air voids; indicating 0.5 mm/√<n> increase with 1 % increase in air voids. Carbonation was smaller than the value calculated by C=At^<1/2> and was found to be calculated by C=At^<1/3>. The rate of carbonation correlated closely with 28 day standard-cured cylinder strength. The standard deviation of carbonation increased with time and with carbonation depth, the coefficient of variation was 0.4 regardless of time.
