Concrete Bonding Agent -Functions & Usage

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Concrete bonding agents are natural or synthetic materials used to join the old and new concrete surfaces. This agent can also be used to join the successive concrete layers. This chemical helps to allow different concrete surfaces to behave like a single unit.

The properties, functions, and types of concrete bonding agents are explained briefly in this article.

Functions of Concrete Bonding Agent

The cement present in a concrete mix does not have any bonding agent within it. When a layer of fresh concrete is added over an existing or old concrete layer, they exist as two separate layers without any bond. So a bonding agent must be introduced between the layers.

The use of a bonding agent helps the different concrete layers to behave like a single unit, thus increasing the strength and performance of the structure.

The bonding agent is applied over the existing surface of the concrete so that the new layer of fresh concrete successfully adheres to the old layer. The two main factors that affect the bonding between old and new concrete are:

1. Surface preparation and cleanliness of the existing surface
2. Strength and integrity of the old surface

Characteristics of Bonding Agents

The main characteristics of bonding agents are:

1. Bonding agents are easy to use and apply.
2. They reduce cracks formed in shrinkage
3. The permeability of concrete is reduced
4. The use of bonding agents improves adhesion between the layer of concrete.
5. The tensile, flexural and bond strength of the concrete or mortar are increased
6. Bonding agents have high resistance against frost and chemical actions

How to Use Concrete Bonding Agent?

The application of bonding agent is performed by the following procedure:

1. Initially, the existing concrete surface is cleaned. Any dirt, dust, oil, efflorescence on the surface must be removed completely to facilitate the proper working of the bonding agent. Excessive dirt on concrete surfaces can be cleaned by pressure washing or vacuum shot blasting.
2. After the concrete surface is cleaned, the admixture is prepared. The chemical is shaken before use. It is diluted with water and mixed properly. It is always recommended to look through the manufacturer's guidelines to clearly follow the application procedures.
3. The next step is to properly mix the mixture. The manufacturer's guidelines would give an idea about the time within which the mix must be applied once the chemical is diluted with water.
4. A primary layer of bonding agent is applied on the existing surface over which the fresh concrete mix is placed. The concreting must be done before the primary coating starts to dry.
5. After placing the concrete layer, it is smoothened using a trowel and later cured.

Different Types of Concrete Bonding Agents Used in Construction

Different concrete bonding agents are

1. Epoxy Bonding Agents

This is an ideal resin for high performance and lightweight concrete parts. This resin wets-out fast. They impart high compressive strength, strong adhesion, and high chemical resistance. They are not only used to bond concrete layers but also to join concrete and steel.

2. Acrylic Latex Bonding Agents

This agent is primarily used to bond fresh concrete with a surface of old concrete. These are a combination of polymers and copolymers which is milky white in color. Acrylic latex bonding agents are applied on the surface either by brush, or trowels or rollers.

3. Polyvinyl Acetate( PVA)

This agent is mainly used for the repair works in concrete. PVA offers great water resistance, ultraviolet stability, and aging characteristics. It has gained popularity due to its compatibility with cement.

Also Read: How to pour new concrete over old concrete?