EFFECT OF TEMPERATURE ON THE CHLORIDE BINDING OF PORTLAND CEMENT EXPOSED TO CaCl_2

摘要

When concrete is exposed to calcium chloride (CaCl_2) deicing salts the concrete may deteriorate or the reinforcing steel may corrode due to the transport of ionic species through it's pore structure. As the chloride ions enter the concrete pore structure the ions will either react or be bound by hydration products or will remain free in the pore solution. This work examines the potential reaction that may occur between the CaCl_2 and the calcium hydroxide (Ca(OH)_2) from the paste resulting in the formation of calcium oxychloride. To better understand the role of calcium oxychloride on binding this study investigates the effect of temperature when CaCl_2 solutions are present in Type Ⅰ and Type Ⅴ cements at -5,10, 23 and 40 °C (23, 50, 73.4 and 104 °F). The results indicate that the chloride binding due to calcium oxychloride increases with decreasing temperature. A two part Freundlich isotherm was developed to fit the chloride binding behavior of hydrating cement paste with the first portion considering the common forms of binding (absorption, Friedel's and Kuzel's salts) while the second portion considering binding due to calcium oxychloride formation.