Pic 1: Carbonation ProblemCorrosion of reinforcement is one of the major durability challenges, which leads to a reduction in the design life of reinforced concrete. Due to an increasing demand for longer service lives of infrastructure (typically 100–120 years) and the high cost involved in building and maintaining it, protective measures of reinforced bars in concrete structures has become extremely important.
Pic 2: Spalling ConcreteOne of the most significant durability issues is the corrosion of steel reinforcement, which leads to rust formation, cracking, spalling, delamination and degradation of structures. This is considered to be the main factor causing damage in bridges, commercial buildings, flyovers, residential buildings and other infrastructure. Atmospheric corrosion, galvanic corrosion and stress corrosion cracking can impact the performance and appearance of concrete structures. Therefore, to deal with these issues, research around the globe is oriented towards developing methods or materials to prevent corrosion of steel in concrete.
Corrosion of Steel in Concrete
In general, when metals and alloys interact with their environment chemically, biochemically or electrochemically, surface loss occurs, and they convert to their oxides, hydroxides, or carbonates, which are more thermodynamically stable. This process is termed as corrosion. Along the surface of an embedded steel bar, when there is a difference in electrical potential, the concrete acts as an electrochemical cell that consists of anodic and cathodic regions on the steel, with the pore water in the hardened cement paste acting as an electrolyte. This generates a flow of current through the system, causing an attack on the metal with the more negative electrode potential (i.e. the anode), while the cathode remains undamaged. Thus, corrosion of rebar is initiated.
Mechanism of Corrosion of Steel in Concrete
As soon as the hydration of cement starts, steel in concrete develops a protective passive layer on its surface which consists of γ-Fe2O3 adhering tightly to the steel with a thickness in the range of 10−3 to 10−1 μm. This layer blocks the movement of ions between the steel and surrounding concrete, thereby reducing the corrosion rate. The presence of this oxide layer prevents damage of steel. It is only stable at high pH i.e. 12–14. For corrosion to take place, this layer must be broken down. This occurs in the presence of carbonation or chloride ions or poor quality concrete, and, in the presence of water and oxygen, corrosion occurs.
Chloride-Induced Corrosion
Pic 3: Chloride - Induced CorrosionTo protect and prevent corrosion from reinforcement bars in concrete structures and to extend the service life, CSIR-CECRI (Central Electrochemical Research Institute) Karaikudi, one of a chain of 40 national laboratories under the aegis of the Council of Scientific and Industrial Research, has come up with a user-friendly, economical admixture named CLEANFLO STEELCARE – a Corrosion Resistant Admixture as an alternate to rebar coatings.
The product has been developed by CSIR-CECRI after 20 years of R&D and field trials and the technology has been transferred to Cleanflo India Pvt Ltd, New Delhi. CLEANFLO STEELCARE is very economical and easy to use; while making concrete just add it in recommended doses. It is suitable for all structures like residential and commercial buildings, bridges, airports, flyovers, dams etc built in mild, moderate, marine and high chloride environment conditions. The product is available in 5, 10, 20 and 200 liter packing.
CLEANFLO India is a 40-year-old ISO 9001:2015, 14001:2015 & OHSAS 18001:2007 certified company, with its own NABL-accredited lab and has been managing water and corrosion since 1979. It has a complete range of Water Treatment Chemicals for Raw & Waste Water, Boiler, Cooling Towers, complete range of Water Treatment Plants, Environmental and Corrosion Management.
