Quality Thru Product Innovation

Understanding effects of corrosion in reinforced concrete.


Although well known for its durability, concrete is subject to corrosion as a result of the onslaught of humidity and chloride-ion penetration, which does not only have a destructive impact on the concrete itself, but also on the reinforcement steel used to improve the tension of the structure. When rebar corrodes, the rust expands cracking the concrete, and unbonding the rebar from the concrete. The water in the pores of the cement is normally alkaline-and in such environment steel is passive and does not corrode. However, the carbon dioxide from the air reacts with the alkaline in the cement and makes the pore water more acidic.  The acidity in combination with humidity leads to corrosion of the rebar – and the process is hastened by the presence of chloride ions.

All this destructive reactions require water. Hence, keeping the concrete dry is an important feature for concrete protection and maintenance. Bituminous coatings are reported to have limited durability and after a while the corrosion process will start due to its weak interfacial film failure that occurs overtime. The limited mechanic ability and penetrabili ty to protect the surface deeper from the concrete surface does not provide the protection needed due to attack of anions toward the passive steel in the concrete matrix. At the same time rendering bituminous coatings prone to adhesion failure, wherein durability is weakened by the elements over varying weather conditions.

Proven effectiveness of Silicon Emulsions


Water based silicon emulsions based on various types from siloxanes, and silane derivatives however, have been considered as the latest solution to contain corrosion. Tests conducted on the use of siloxane emulsions on roadwork applications such as tunnels and bridges by independent and authorized institutes in Germany and Sweden, have proved their efficiency. Recent tests for US highway applications according to National Cooperative Highway Research Program Report 244-11 have also confirmed the European results. The main subjects of the tests were water absorption, drying (vapor permeability) and chloride-ion absorption. Water-repellant protection via integral (i.e. mixing with cement, aggregate, sand, and water) provides the most effective corrosion protection possible in freshly poured concrete, wherein all dimensions of the concrete are protected while at the same time leaves the concrete continuously surface breathable (vaporpermeable) and reduces (or suppresses) the chloride ion penetration.


References:
(1) SP, Swedish National Testing and Research Institute, Boras, Sweden.
(2) US Highway Research Program, Report 244-11, Maryland, US.