Concrete Bonds: Uses, Working, Benefits and More
Does Concrete Bond to Concrete?
Yes, concrete can bond to concrete through a chemical reaction called hydration. Proper surface preparation, including cleaning and roughening the existing concrete surface, is important for a strong bond. The use of bonding agents can further enhance the bond strength. Good construction practices and consideration of other factors such as mix composition and curing conditions are also important for a reliable and durable bond.
How Concrete Adhesion Works?
Concrete adhesion refers to the ability of fresh concrete to bond with existing or hardened concrete. The process of adhesion involves the formation of chemical and mechanical bonds between the two concrete surfaces. Here is how concrete adhesion works:
1. Surface Preparation: Proper surface preparation is crucial for achieving good adhesion between concrete surfaces. The existing concrete surface should be clean, free from contaminants, and roughened to provide a suitable bonding surface. Common methods for surface preparation include sandblasting, scarifying, or using chemical cleaners to remove dirt, oil, or loose particles.
2. Hydration: When fresh concrete is placed against existing or hardened concrete, a chemical reaction called hydration takes place. Hydration is the process by which cementitious materials, such as Portland cement, react with water to form a strong and durable matrix. During hydration, calcium silicates present in the cement react with water, releasing calcium hydroxide and forming calcium silicate hydrate (C-S-H) gel. This gel fills the gaps and voids between the aggregates, binding them together and providing strength.
3. Interfacial Zone: The interface between the fresh and existing concrete is known as the interfacial zone. It is a transition zone where the chemical and mechanical bonds form. The hydration products from the fresh concrete penetrate into the existing concrete, creating a zone of interlocking crystals and chemical bonds. This interfacial zone plays a vital role in transferring stresses and load between the two concrete surfaces.
4. Bonding Agents: In some cases, bonding agents or bonding compounds are used to enhance the adhesion between concrete surfaces. These agents are applied to the existing concrete before placing the fresh concrete. They act as an intermediary layer, promoting adhesion by providing a chemical bond and improving bond strength. Bonding agents can be in the form of epoxy, acrylic, or polymer-modified materials.
5. Mechanical Interlocking: Along with chemical bonding, mechanical interlocking also contributes to concrete adhesion. The roughened surface of the existing concrete creates a better surface area for the fresh concrete to adhere to. As the fresh concrete is placed, it fills in the voids and irregularities of the existing surface, creating a mechanical interlock between the two concrete layers.
6. Proper Construction Practices: Adherence to proper construction practices is essential for achieving optimal adhesion between concrete surfaces. Adequate consolidation of the fresh concrete, ensuring proper curing conditions, and following recommended construction techniques contribute to a strong and durable bond.
What are the purposes of using concrete bonding agents?
A concrete bonding agent is used to enhance the adhesion between new and existing concrete surfaces. In short, here are the reasons why you need to use a concrete bonding agent:
1. Improved Bond Strength: A bonding agent creates a strong and reliable bond between the fresh and existing concrete. It enhances adhesion by providing a chemical bond and improving bond strength, ensuring a durable connection between the two surfaces.
2. Surface Compatibility: Sometimes, existing concrete surfaces may not have the ideal characteristics for optimal bonding with fresh concrete. A bonding agent acts as an intermediary layer, promoting adhesion and compensating for any surface deficiencies, such as smoothness, contamination, or variations in porosity.
3. Overcoming Compatibility Issues: When different concrete mixes or curing conditions are used for different sections of a project, a bonding agent can help overcome compatibility issues. It facilitates the transition between different concrete mixes and ensures a seamless connection without compromising the bond strength.
4. Minimizing Delamination: Delamination refers to the separation or detachment of layers within concrete. By using a bonding agent, the risk of delamination is significantly reduced. The bonding agent helps to create a strong bond that prevents the fresh concrete from separating or debonding from the existing concrete surface.
5. Repair and Restoration: In repair and restoration projects, where new concrete is applied over existing surfaces, a bonding agent is essential. It ensures that the repaired or restored sections bond effectively with the existing concrete, preventing future issues and maintaining structural integrity.
How To Prepare the Surface for Concrete Bonding?
Proper surface preparation is crucial for achieving effective concrete bonding. Here are the general steps to prepare the surface for concrete bonding:
1. Clean the Surface: Start by cleaning the existing concrete surface thoroughly. The bonding process may be hampered by loose particles, dirt, dust, grease, oil, or other contaminants. Use a broom, brush, or vacuum to ensure the surface is clean and free from debris.
2. Remove Existing Coatings: If there are any existing coatings, such as paint, sealers, or epoxy, they should be completely removed. Use appropriate methods like grinding, sandblasting, or chemical strippers to strip away the coatings and expose the bare concrete surface.
To learn more, watch the following video tutorial.
Video Source: Swimming Pool Steve
3. Roughen the Surface: Next, it is important to roughen the surface to provide a better bonding surface for the fresh concrete. The goal is to create a rough texture that allows the new concrete to adhere effectively. Several methods can be used for surface roughening, including sandblasting, shot blasting, scarifying, or grinding. The specific method depends on the condition of the existing concrete and the desired surface profile.
4. Repair Cracks and Imperfections: Inspect the surface for any cracks, spalling, or other imperfections. Repair these areas using appropriate concrete repair techniques. Fill in cracks, patch holes, and ensure a smooth and even surface. Follow recommended repair procedures and allow sufficient curing time before proceeding.
5. Clean the Surface Again: After roughening and repairing the surface, clean it once more to remove any dust or debris generated during the preparation process. Use compressed air or a broom to eliminate loose particles. This step ensures a clean surface ready for the application of a bonding agent or the fresh concrete.
6. Apply a Bonding Agent: Depending on the project requirements, a bonding agent may be necessary to enhance the bond strength between the existing and new concrete. Follow the manufacturer's instructions to apply the bonding agent to the prepared surface. Use a brush or roller to ensure even coverage. Allow the bonding agent to dry or reach the specified tackiness before proceeding with concrete placement.
