Polymer impregnated concrete consists of polymers or epoxies which are used to impart certain special properties to concrete. Various applications of polymers in concrete and their properties is discussed.
The polymers are used in the concrete due to the following reasons:
- Polymers improve the strength and durability of hardened concrete
- The chemical resistance and the impermeability of hardened concrete is increased
- The flow properties of fresh concrete can be modified based on the required specifications
- The bond characteristics between old and new concrete can be improved
Some of the polymers that are used popularly are:
- Urethanes: Urethanes are produced by the reaction of isocyanates with the polyols
- Acrylics: These are esters of acrylic and methacrylic acids
- Epoxies: These are type of synthetic fibers
- SBR or Styrene Butadiene Resins: These are synthetic rubbers in the solution
Applications of Different Polymers in Concrete
The different ways in which the polymer is introduced into the concrete (hardened concrete) will vary widely based on the commercial objective. The polymers can be employed in concrete in different ways. They are:
- Polymer Impregnated Concrete (PIC)
- Polymer-Modified Concrete (PMC)
- Polymer Concrete (PC)
- Polymer as Protective Coating
- Polymer as Bonding Agent
- Other Applications
Polymer Impregnated Concrete
In the case of polymer impregnated concrete, the prepolymers or the low viscosity liquid monomers are partially or completely impregnated with the pore system of the hardened cement composite structure. After this procedure, the whole treated structure is allowed to polymerize.
The normal curing procedure of the hardened concrete results in the gain of a considerable amount of free water in its voids. These water-filled voids account for a significant amount of the total volume of the component. It ranges from 5% in the case of dense concrete and 15% in the case of gap-graded concrete.
In the case of polymer impregnated concrete, it is these voids (water filled pores) that must be filled with the chosen polymer. Hence the major factor that affects the monomer loading is the: moisture content in the hardened concrete and the air voids in the concrete.
Procedure for Polymer Impregnated Concrete Manufacture
Operations involved in the impregnation process to develop polymer impregnated concrete are:
1. A well-designed cement concrete is made available. They must adequately moist cured and gain an optimum strength.
2. The moisture is removed by drying the concrete. The drying is carried out by heating the structural element to surface temperature of the order 120 to 150 degree Celsius. An air oven can be used to dry small specimens.
If the element has large surface, a thick blanket can be used, say, 10mm thick, to prevent from any thermal gradient. Another sophisticated application is the use of Infrared heaters.
For complete removal of moisture from the concrete, 6 to 8 hours of heating is required.
3. After the complete removal, the concrete surface is cooled to safe levels. This can go to a temperature of 35 degree Celsius. This temperature will avoid flammability.
4. The concrete is now taken to a vacuum sucker, where the whole air within the concrete structure is removed. The quantity of the monomer that is impregnated will decide the time and the degree of application of vacuum.
5. The concrete after adequate removal of air is dipped in a solution of monomer. It is soaked for a long time till the desired depth of penetration of monomer is obtained.
The soaking time is dependent on the viscosity of the monomer, the preparation of the specimen and the main characteristics of the concrete.
To reduce the time taken to acquire the desired penetration, it is preferred to use external pressure like air or nitrogen gas. This facilitates speedy penetration.
6. After the above procedure, the surface is covered with plastic sheet. This helps to prevent the evaporation of the monomer.
7. The thermal catalytic method of polymerization is carried out. This method involves the polymerization by heating the catalyzed monomer to the required temperature level. This will range from 60 degrees to 150 degree Celsius. The temperature range chosen depends on the type of monomer.
The heating can be carried out under the water or by low-pressure steam injection, or by means of infrared heaters or in an air oven. The heating decomposes the catalyst and hence initiate the polymerization reaction.
Once the monomer has penetrated the concrete, the polymerization can also be initiated using the ionization radiation such as the gamma rays. The polymers when fully polymerized or when they are cross-linked, they act as solids that occupy the voids into which they are impregnated.
8. The concrete structure is then allowed to cool.
The whole procedure from 1 to 8 can only be carried out in a precast factory. The Monomers like acrylate, styrene and the vinyl chlorides etc are used commonly for impregnating into concrete. Another widely used monomer is Methyl Methacrylate (MMA).
Properties of Polymer Impregnated Concrete
1. The polymer concrete gains cube compressive strength more than 100N/mm2. This strength is irrespective of the strength of the conventional concrete.
2. The flexural strength of polymer impregnated concrete is usually about 15N/mm2. This is slightly higher than the highest strength plain concrete that is made from normal ingredients.
3. The elastic modulus lies in the range from 30 to 60N/mm2. This value is similar to the value that is obtained from high strength concrete (i.e. about 45N/mm2)
4. The polymer impregnated concrete possesses lesser creep and shrinkage problems due to a lesser number of pores.
5. The polymer impregnated concrete is highly resistant to acid attack, sulfate attack and chloride attack when compared with PCC.
Applications of Polymer Impregnated Concrete
The applications of polymer impregnated concrete in different areas of construction are explained below:
1. Surface Impregnation of Bridge Decks: The bridge decks are allowed to undergo impregnation to avoid the intrusion of moisture, chemicals as well as chloride ions.
The bridge decks constructed in the areas of high salt water and moisture exposure can be protected by this method.
2. Repair of the structures: The damaged structures can be improved by the method of polymer impregnation. The life period of structures which cannot be reconstructed can be increased by this method.
This method hence helps in restoration as well as the preservation of the stone monuments.
3. Underwater and Marine Applications: The ability of Polymer impregnation help in improving the structural properties, resistance to water absorption, and impermeability properties of the concrete structure. This makes them be widely used in underwater construction and for marine structures.
The structures constructed in desalination plants and sea floor structures use this method of concrete construction. It has been observed that the partial impregnation of the concrete piles in the sea water reduces the corrosion of steel reinforcement by 24 times.
4. Application in Irrigation Structures: The use of conventional methods in the repair and rehabilitation of dams and other important hydraulic structures are found to be ineffective and imperfect.
These are later found to cause a large loss in the benefits that are obtained from the irrigation, power generation, flood control etc. But the method of impregnation work best.
The concrete from the severely damaged area is removed, patched and dried. This area is later treated by means of a polymer impregnation.
5. Structural Members: The polymer impregnated concrete have a great potential as a structural material. The PIC also shows remarkable improvements over the conventional concrete.
The internal cracks and voids are the basic factor behind all the issues in conventional concrete structure. As the polymer impregnation stops the root cause, it is best used in structural members.