The influence of air voids and fluid absorption on salt-induced calcium oxychloride damage

Calcium and magnesium deicing salts may damage concrete due to calcium oxychloride formation (CaOXY). Previous work has shown that replacing a portion of the cement in a mixture with supplementary cementitious materials reduce CaOXY formation. AASHTO PP-84 was developed to help specify damage-resistant mixtures by limiting the CaOXY amount in paste. This limit was established based on empirical observations; however, this did not consider other aspects of the mixture such as paste volume or air content. This paper investigates how fluid absorption, paste volume, and air content are all key parameters in determining damage from CaOXY. Concrete with a higher paste volume has more CaOXY and is more susceptible to damage. Concrete with a higher air content is less susceptible to damage as the voids provide space for fluid absorption and CaOXY formation; however this only occurs for mixtures with a specific range of calcium hydroxide (Ca(OH)2) (between 7 and 12 g Ca(OH)2/100 g paste). This paper incorporates these factors to provide a more comprehensive explanation for CaOXY-induced damage in concrete. •Calcium and magnesium deicing salts may damage concrete due to calcium oxychloride formation (CaOXY).•Concrete with a higher paste volume has more CaOXY and is more susceptible to damage.•Concrete with a higher air content is less susceptible to CaOXY-damage for mixtures with Ca(OH)2 content between 7-12 g /100 g paste.•The absorption of fluid appears necessary for substantial CaOXY-induced damage.