Synergistic effects of air content and supplementary cementitious materials in reducing damage caused by calcium oxychloride formation in concrete

Abstract

Pavement damage occurs in cold-region concrete exposed to high concentrations of calcium chloride (CaCl2). The damage is caused by a combination of conventional freeze-thaw damage and the formation of a deleterious phase known as calcium oxychloride from a reaction between CaCl2 and calcium hydroxide in the concrete. Much research has focused on calcium oxychloride mitigation in cement pastes, but not on concrete damage due to calcium oxychloride.In this study, the synergistic roles of air and supplementary cementitious materials (SCMs) in reducing damage in concrete exposed to high concentrations of CaCl2 and freeze-thaw conditions is studied. Concrete mixtures were made with different SCM replacement levels and air contents ranging from 1.8 to 8.0% and immersed in 25% CaCl2 solutions and subject to freeze-thaw cycles (-8 °C to 25 °C) for 600 days. Bulk resistivity and visual assessment of damage were found to be excellent descriptors of the damage progression. Damage was reduced as the SCM content and air content was increased. Mixtures which had 20% SCM and 8% air and mixtures which had 35% SCM and more than 4% air showed strong durability against damage due to calcium oxychloride formation.

Durability of concretes exposed to high concentrations of CaCl2 and MgCl2

“…Type I/II ordinary portland cement (OPC), Class F fly ash, and ground granulated blast furnace slag (referred to as slag in the text), were used as cementitious materials in the concretes. The chemical compositions of the cementitious materials obtained from the manufacturer or through X-ray fluorescence testing performed on beads using a calibrated device are given in Table 1 [ 10 , 15 ].…”

“…Much research has been performed on damage mitigation in cement pastes [ 9 – 12 ] and mortars [ 10 , 13 , 14 ], but damage in concrete has been less studied, especially over long-term exposure periods [ 15 – 18 ]. Paste and mortar research has shown that damage is reduced due to the replacement of cement with supplementary cementitious materials (SCMs) [ 7 – 14 ], which consume calcium hydroxide in pozzolanic/latent hydraulic reactions [ 19 ].…”

“…Apart from SCM replacement, paste damage reduces as the curing duration increases from 28 to 91-days, especially for Class F fly ash [ 10 ]. In concrete, in addition to SCM replacement level, the damage reduces as the air entrainment increases [ 15 , 18 ].…”

“…Multiple concrete mixtures with varying air and SCM contents were exposed to these conditions and damage was monitored over the long-term using mass change, bulk resistivity, and visual observation. This study is the third part of a larger project which investigates the damage of cement paste, mortar [ 10 ], and concrete [ 15 ] exposed to high concentrations of deicing salts. In previous work, low-temperature cycles (− 8 °C to 25 °C) and CaCl 2 exposure were studied.…”

“…Damage was reduced as the SCM replacement level and curing time increased. Mortar and concrete generally outperformed cement pastes [ 10 , 15 ].…”