The Significance of Chlorides in Concrete Trial Mixes


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Title: The Significance of Chlorides in Concrete Trial Mixes


Publication: CIA



Appears on pages(s):


Date: 2/14/2011

The concentration of acid-soluble chlorides in concrete has been used to determine the risk of corrosion of reinforcing steel despite indications that the level of free chloride ions may be overestimated by this test, which may result in the rejection of otherwise suitable aggregates. To assess the influence of sample size on the test results, 100mm diameter x 200mm long concrete cylinders were ground to 150μm and analysed for acid-soluble chloride in accordance with AS 1012.20, modified to improve accuracy. The concrete was found to contain between 0.03% and 0.04% chloride by weight. The same concrete was extracted in boiling water. The water soluble chloride content was no more than 1/35 of that measured by acid extraction. The constituents of the concrete mix were then analysed by acid extraction and total chlorides determined. Hardened concrete samples of the mix were made and analysed for chloride by acid extraction, with the quantity of chloride found to be within 0.1% of the quantity of chloride in the constituents. Water extraction found nil chlorides. Additional samples of the concrete mix were prepared containing an added known quantity of sodium chloride and analysed. The chloride was recovered quantitatively using acid and water extraction, with water extraction finding nil chlorides.

Concrete Institute of Australia, International Partner Access.

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