Study on Critical Content of Chloride Ion for Initiation of Steel Corrosion in Concrete or Mortar with Mineral Admixtures
Takao UEDA, Kenta MIURA, Hiromi IWABUCHII, Akira NANASAWA and Masayuki TSUKAGOSHI
Abstract:Considering environmental impact of construction materials, especially concrete, mineral admixtures like fly ash or blast furnace slag should be used as much as possible. Such concrete using mineral admixture generally has dense micro pore structure and high durability due to high resistance performance against the ingress of damage factors into concrete can be expected. However, as the chemical reaction of mineral admixtures consumes Ca(OH)2 in concrete, the pH value decreases with the age of concrete. Such dropping of pH value may decrease the critical chloride content for the initiation of steel corrosion in concrete. This study experimentally investigated the critical chloride content in some cases of concrete or mortar with mineral admixtures including the cases of combination of blast furnace slag cement and fly ash. As a result, although the combination of blast furnace slag cement and fly ash could realized highly dense pore structure, Cl-/OH- molar ratio in mortar pore solution extracted by high compressive pressure remarkably increased compared with the case of normal mortar because of the synergistic effect of reduction of OH- concentration and the rise of Cl- concentration. However, correlation between Cl-/OH- molar ratio and half-cell potential was not so clear, which suggested that Cl-/OH- molar ratio is not the unique factor to determine the initiation of steel corrosion. Key Words:Concrete, Mortar, Blast furnace slag cement, Fly ash, Critical chloride content for initiation of steel corrosion, Pore solution, Cl-/OH- molar ratio