Chemicals that are used to repair damaged sections or members of a concrete structure are called concrete repair chemicals.
There are different types of concrete repair chemicals. While some are used to increase the bond strength between the old concrete and the new concrete; Others are used for water repellent or corrosion resistance purpose.
On the basis of the material from which they are produced, they can be divided into the 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 and hardener. Resins are plant products or can be manufactured in a factory. The hardener is mixed with the resin to initiate the polymerization process. (Polymerization is a chemical process that combines several monomers to form a polymer or polymeric compound). The resin has adhesive properties and is insoluble in water.
The common form of using epoxy resin chemicals is to prepare a epoxy bonded concrete, This type of concrete is used when the repair depth is at least 40 mm. To prepare an epoxy resin-based mortar, mix 100 parts epoxy, 60 parts hardener, and 20 parts silica sand by weight. This mixture is applied over the surface of the old concrete. This will increase the bond strength of the new concrete with the old concrete. It will also help transfer the load from the steel to the concrete.
Epoxy based chemicals are also used for crack repair works. A low viscosity epoxy is typically used to repair small static cracks ranging from 0.02 mm to 6 mm in width.
Steel bar can also be coated with epoxy based chemicals to increase its corrosion resistance ability. This is done by mixing 100 parts of epoxy with 50 parts hardener by weight and then applying this solution to a steel bar.
2. Acrylic Polymer Based Concrete Repair Chemicals
The problem with epoxy based chemicals is that it requires skilled individuals to use it. Because there are many factors that can affect its properties, such as mixing time 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 ways as outlined below.
Polymer cement as bonding coat
This bonding coat is prepared by mixing one part cement and one part polymer chemical by weight. Then mix it well 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 solution on this surface. Then we pour mortar or concrete over this layer before it dries.
polymer cement as grout
It is used to repair grouting cracks. Generally mix 1kg polymer + 2kg water + 3kg cement. Then mix it with a mechanical mixer before using.
As polymer modified mortar or concrete (PMM/PMC)
A polymer modified mortar (PMM) can be made by mixing 1 part cement + 4 parts quartz sand + 0.25 parts water + 0.15 part polymer chemical by weight. It is used when the depth of the repir is up to 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 parts of water + 0.6 part of polymer chemical by weight. It is used when the repair depth is more than 75 mm.
Before using PMM or PMC, first apply a coat of polymer cement bonding coat to the surface of the old concrete. Leave it for 24 hours. Next apply another coat of polymer cement bonding coat at right angles 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. It is a single packed 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. Modern modified SBR chemicals are resistant to UVR.