Chlorides and Concrete

Time-Tested Performance

Calcium chloride has been the most widely used accelerator in the past because of its low cost and predictable performance. However, the use of calcium chloride also comes with these disadvantages:

  1. Corrode the reinforcement steel within the concrete, (particularly if the dosage is large and if it is not properly controlled)
  2. Reduce the concrete’s resistance to sulphate attack.

The presence of chlorides in the concrete, changes the protective quality of the environment of the steel, and is a serious cause of corrosion of the steel reinforcement. The corrosion of steel is a process where ions react with water and oxygen to form rust. The rust formed can occupy a volume over twice the original volume of the steel with internal pressures as high as 30N/mm2. This force is many times greater than the strength of the concrete and is responsible for the cracking and spalling that occurs. The severity of the damage depends on the concentration of the chlorides present in the concrete, as well as the variation of the chloride from one point to another. Soluble components of the rust may be leached through the cracks and appear as rust stains on the surface of the concrete.*

Chlorides can also be carried into the concrete through water migration, therefore keeping chloride penetration to a minimum, is a major factor in controlling the integrity of the steel within the concrete. The chlorides already present in the concrete from admixtures and raw materials are there to stay, but you can do something about the additional chlorides that migrate to the interior of the concrete through water migration. SEAL-IT treats this problem from the source – water migration. SEAL-IT Concrete Sealant penetrates 1 to 1.5 inches into the concrete, chemically reacts with the alkali to form a permanent internal seal. SEAL-IT Concrete Sealant retards the penetration of chlorides, acids, and alkalis from entering the pores and causing irrepairable damage. The service capacity and the safety of the structure will be significantly increased by reducing the damaging effects of chloride penetration.

Rebar that has rusted resulted in costly repairs to the concrete.

*ASTM-C-67 – Section 13. Results: 25% decrease in absorption.
*Concrete Materials and Practice Fifth Edition