Cement Polymer Composite Coating System for Corrosion Protection of Reinforcing and Prestressing Steels

Approach adopted in new technology to evade technological gap in the exiting one

State of Art Technologies – International Scenario

In USA corrosion of concrete bridges is a very serious problem During 1982, the annual cost of corrosion damage to bridge deck and support structures was estimated to be in the range of $165 to $500 million. The annual cost of repair of parking garage dueo to corrosion was estimated at $300 to $400 million. Out of 500,000 bridges in USA, 200,000 were reporte to be under severe distress. Remaining 300, 00 also needed repair and rehabilitation measures of cost replacement of 300,000 bridges was worked out to be around $112 billion.

Currently, the bridge deck maintenance in USA is considered as a trillion-dollar proble. Many repair techniques such as overlay, fusion bonded epoxy coating, cathodic protection etc. had been tried on an experimental basis in few selected bridges. Among these, fusion bonded coating has been widely used. Epoxy coating can no longer be considered a viable primary protective system, as it suffers from the following disadvantages.

Being a barrier type of coating, it facilitates localized pitting corrosion through pinholes. This was very much evident in the Florida Bridge by undercutting of the fusion-bonded epoxy coated reinforcing bars.

• It affects the bond strength between steel and concrete.
• It undergoes degradation on long term exposure to sunlight and hence necessitates storing of the coated reinforcement under sheltered condition.
• It shows generally poor alkali resistance.
• It needs additional electrical interaction of the rebars to facilitate cathodic protection and other electrochemical process that may needed for then and there maintenance of the structures.

Above all, the application of fusion bonded epoxy coating needs carefully prepared surfaces. This poses difficulties in field preparation and the long-term performance is not satisfactory. Realizing these difficulties, CECRI has developed a cement polymer composite coating system which may be a suitable substitute for fusion bonded epoxy coating system but with a better-cost benefit ratio. The findings will create new solution to the existing to the existing corrosion problem.

Advantages:

• It is a factory process amendable for field repair and rehabilitation.
  Coating has high flexibility
  
• As per BIS2770 part it has sufficient bond strength
• Coating can withstand high tensile stresses and hence applicable to prestressing steels
• As per ASTM & Indian standards, it has good corrosion resistance and chemical resistance
• It has good weathering resistance (UV resistance)
• As per ASTM & Indian standards, it has good abrasion resistance

Brief description

The base metal used as rebar, namely iron, contains electrons which gets readily released in any corrosive environment (e.g. atmospheric oxygen) leading to oxidation with the formation of Fe2O3 (the rust), a principal deterrent. To prevent this oxidation, a surface coating capable of interacting / nullifying the released electrons should be provided. Further, prestressing and reinforcing steels during service are exposed to an alkaline medium and this necessitates additional measure by way of a topcoat, which should be compatible to primer and and alkaline environment. To meet these two requirements, a primer and a compatible topcoat as mentioned above are proposed.

CECRI has developed CEMENT POLYMER COMPOSITE COATING (CPCC) system for corrosion protection of reinforcing steel. The coating system consists of a primer and a sealing coat. The process covers the following patents.

• An improved formulation for a rapid setting primer useful for corrosion protection of reinforcing and prestressing steels.
• Indian Patent No.481/DEL/93 dated 13.05.93
• An improved coating composition for corrosion protection of reinforcing steel and prestressing steel.

Indian Patent No.259/DEL/92 dated 25.03.92

The polyblend of polyacrylics and polyquinones is p electrons rich and hence can readily chemisorb via ¶ electrons with unfilled "d" orbital of iron surface to prevent corrosion in prestressing and reinforcing steel. So the products proposed to be evaluated involve solution blending process for preparation of polyblends based on acrylic copolymers and quinine copolymers which offer a flexible and water resistance layer on steel for corrosion protection. The flexibility of acrylate copolymer, its film forming capability and water repellency characteristics of quinine based polymers are carefully tailored through the formation of a single phase in the polyblend which offers the necessary mechanical and physical properties. Besides, this precursor has the possibility of accepting rust as a filler in the polyblend film which facilitate the application of surface coating derived from this polymer precursor or rusted steel surface thus making surface preparation non critical one. Further, the cement polymer composites based on these polymers is expected to serve as precursor for the formulation of a topcoat which will tae care of the alkaline environment that is anticipated in the concrete structure. Additional feature of this system is that the curing time of the coating can be manipulated to suit the specific process requirement (minutes to hours).

Advantages: A Novel Coating System for Rebar Protection

Reinforced concrete bridges and structures are expected to serve for their design life without undue maintenance. Material contamination coupled with industrial and environmental pollution causes corrosion of steel reinforcement leading to accelerated deterioration of concrete structures.

CECRI has been carrying out R&D activities in this vital area over four decades and more recently it has come out with a novel coating system is actually a composite coating system designed and tailor made utilizing the desirable attributes of Portland cement and a polymer.

Uniqueness of the System

Primer :

Chemical bondage with rebar surface leads to better adhesion.

Primer with Rapid setting Properties:

Amendments for Mechanism

Cement Polymer Seal Coat :

Good compatibility with base primer and surrounding concrete. Assured bond Strength

Rapid setting Properties :

Amendable for Mechanism

Special Features

Flexibility :

Coated rods can be bent and fabricated as per the requirements of building codes.

Bondability :

Bonding strength equivalent to that of uncoated rebar as per standard Pull out Test

Weatherability :

The system designed to have better UV resistance CPCC coated prestressing strands under tension and exposed to aggressive open environment – coating was intact even after 3 years.

Durability :

A durability factor of more than 10 is obtainable under most aggressive environmental conditions

Applicability :

By brushing, dipping or any other suitable method

Feasibility :

Automation; Site application and Insitu repair

Applications:

Protection of steel reinforcement inconcrete from corrosion.

Detailed Description

Cement polymer composite coating (CPCC) technology has developed for the protection of steel einforcement rods against corrosion in aggressive marine atmosphere after analyzing the merits and demerits of various protective coatings systems currently in operation including FBEC and our own earlier technology of cement – slurry anticorrosive system. The CPCC technology has been evolved & custom designed from the consorted inputs originating from polymer science and electrochemistry (corrosion is an electrochemical reaction) to meet the structural engineering requirements of steel reinforcement rod.

The data are confidentially documented after a careful R&D practice and also by following the internationally prescribed standards (ASTM). Based on these R&D strength, CECRI has evolved a code of practice for standard tests to be followed in maintaining the highest quality of CPCC by the manufacturers and applicators of this coating to give better performance. Incidentally, the code of practice prescribed for CPCC imparted rods has a better ease in handling and transportation than the set of conditions prescribed in your own addition letter appended to the main construction.

Chemical Features of CPCC System

The basic resin matrix based in which coating formulation arrived at our custom designed specifically to counter the corrosion reactions of concrete structures in marine environment susceptible to severe corrosion. They possess required chemical feature to provide spontaneous adhesion and corrosion resistant and the over all coating process adaptable both in the field and shop floor

Technology Transfer Assistance Offered:

Know-how, Training

Extent of Commercialisation:

Seeking to license or sell this innovation

Contact for more information:

Director
Central Electrochemical Research Institute (CECRI),
Karaikudi -630 006,
Tamil Nadu, India