Concrete Repair Chemicals
Chemicals that are used to repair damaged sections or members of any concrete structure is called concrete repair chemicals.
Concrete repair chemicals are of various types. While some are used for increasing bond strength between old concrete and new concrete; others are used for water repellant or corrosion resistance purpose.
Depending upon the materials from which they are produced, they can be groped into following 3 primary groups.
- Epoxy Resin based
- Acrylic Polymer based
- SBR based
1. Epoxy Resin Based Concrete Repair Chemicals
This group of chemicals consists of two components – resin & hardener. Resins are the product of plants or it can be manufactured in factory. Hardener is mixed with resin to start the process of polymerisation. (Polymerisation is a chemical process that combines several monomers to form a polymer or polymeric compound). Resin possesses adhesive quality and they are insoluble in water.
The common form of using epoxy resin chemicals is to prepare an epoxy bonded concrete. this type of concrete is used when the depth of repair is at least 40 mm. to prepare an epoxy resin based mortar, mix 100 parts of epoxy, 60 parts of hardener and 20 parts of silica sand by weight. This mix is applied on the surface of old concrete. This will increase the bond strength of new concrete with old concrete. This will also help to transfer the load from steel to concrete.
Epoxy based chemicals are also used for crack repair works. A low viscosity epoxy is generally used to repair small static cracks ranging from 0.02 mm to 6 mm in width.
Steel bars can also be coated with epoxy based chemicals to increase its corrosion resistance capacity. This is done by mixing 100 parts of epoxy with 50 parts of hardener by weight and then applying this solution on steel bar.
2. Acrylic Polymer Based Concrete Repair Chemicals
The problem with epoxy based chemicals is that it requires skilled persons to use it. Because there are many factors that can affect its properties, such as time of mixing and area of application.
To avoid this problem polymer based repair chemicals were developed. It is much cheaper than epoxy based chemicals but costlier than cement. The primary advantage of using polymer based chemicals is that, they make the concrete or mortar much stronger with less shrinkage.
Polymer chemicals can be used in many different from as given below.
As polymer cement bonding coat
This bonding coat is prepared by mixing one part of cement and one part of polymer chemical by weight. Then mix it thoroughly with suitable amount of water so that it can be applied with a brush. First clean the surface on which it is to be applied with a jet of water. Leave it for 24 hours. Apply the above prepared slurry on this surface. Then we place mortar or concrete on this layer before it dries.
As polymer cement grout
This is used for repair grouting cracks. Generally mix 1 kg of polymer + 2 kg of water + 3 kg of cement. Then mix it with a mechanical mixer before using it.
As polymer modified mortar or concrete (PMM / PMC)
A polymer modified mortar (PMM) can be made by mixing 1 part of cement + 4 parts of quartz sand + 0.25 part of water + 0.15 part of polymer chemical by weight. This is used when depth of repir is upto 75 mm.
A polymer modified concrete (PMC) can be prepared by mixing 1 part of cement + 2 parts of quartz sand + 3.75 parts of aggregate + 0.35 part of water + 0.6 part of polymer chemical by weight. This is used when depth of repair exceeds 75 mm.
Before using PMM or PMC, first apply a coat of polymer cement bonding coat on the old concrete surface. Leave it for 24 hours. There after apply another coat of polymer cement bonding coat at right angle to the first coat. Then apply PMM or PMC as the case may be.
3. SBR Based Concrete Repair Chemicals
The term SBR stands for styrene butadiene rubber. This is a single pack aqueous polymer that can be mixed with cement. It is a copolymer latex, specially modified to be compatible with cement based mixes. This type of chemical is cheaper than polymer based chemicals. It can be used in the same way as in the case of polymer based chemicals. The modern modified SBR chemical has resistant to UVR.