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Carbonation of concrete caused by carbon dioxide, salt attack, etc. may lead to serious damages to concrete structures. In order to prevent the concrete's damages caused by losing the durability of concrete through carbonation, it is very important to measure the degree of carbonation.There are many tests that can be used to measure the degree of carbonation. Among these tests, phenolphthalein test has been used in field measurement on account of portability, economical efficiency, and immediate determination. But, This test has low reliability because it tends to easily make measurement errors with measurement time, concentration, and so on. Even though researches, which are carried out to improve the reliability of phenolphthalein test through standardization of usage, are being conducted, this test still has no good reliability. Besides low reliability, the test can not determine early carbonation because of determining it in accordance with pH 8.9.In this study, indicators are selected in accordance with selection conditions, which are hiding power (30%), end point and discrimination between base and acid color (30%), economical efficiency (30%), simplicity preparation of stock solution (10%), and noxiousness (advisability), to improve reliability, substitute for phenolphthalein and to determine early carbonation.