1.0 Introduction

In Canada, the main causes of concrete deterioration are the corrosion of the reinforcing steel and the action of frost, or freeze-thaw cycles in the presence of de-icing salts. The City of Montreal’s dry-mix shotcrete specification document for concrete repairs specifies the use of inorganic corrosion inhibitors, commonly known as calcium nitrites, in air-entrained dry-mix shotcrete. These concrete admixtures are commercially available throughout most major concrete admixture manufacturers in North America.

A shotcrete rehabilitation condition survey in 2004-2005 revealed that most air-entrained
dry-mix shotcrete used in the field with the addition of corrosion inhibitors produced significant increases in the compressive strength and variations in the air void distribution/spacing factor.

As a result of this survey, a test program was initiated to determine the effects of liquid corrosion inhibitors when added to the mixing water of air-entrained dry-mix shotcrete on various plastic and hardened properties. Parameters such as plastic consistency, set time, air void distribution, compressive strength and freezing and thawing cycles with the presence of de-icing salts would be examined.

The test program was a join venture between the City of Montreal’s Materials Laboratory, King Packaged Materials Company (Pre-packaged shotcrete materials manufacturer) and Grace Canada Inc. (Manufacturer of corrosion inhibitors).

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