What is Concrete replacement?
Concrete replacement is a repair technique to restore or enhance the original load-bearing capacity of compromised concrete structures. This method includes patching localized areas or replacing the general concrete cover, using concrete or mortars applied via hand, re-casting within formwork, or spraying.
Replacement of concrete necessitates prior actions such as removing defective concrete, substrate preparation, cleaning and replacing corroded reinforcement, adding corrosion protection, and casting new concrete.
What is Concrete replacement used for?
This repair method is, in general, suitable for all deterioration processes such as:
How does Concrete replacement work?
The concrete replacement process begins with identifying the cause and extent of the damage, followed by removing contaminated or defective concrete and preparing the substrate.
Reinforcements are cleaned, replaced, or added as needed, with corrosion protection applied often to them.
Then new concrete is cast into the void ensuring a good bond between old and new, crucial for successful, long-lasting repairs that can reinstate load bearing capacity.
Methods such as chemical and mechanical cleaning, and mechanical and abrasive preparation like rotomilling, or needle scaling are used to increase interfacial bond strength between the repair and existing unit. Often the top surface is texturized or its coarse aggregate exposed to give the repair concrete something to grip onto.
How do I carry out and control Concrete replacement on concrete structures?
For replacement of concrete in existing structures the relevant standards to consult are then BS EN 1504 series for concrete repair.
These outline the principles for the protection and repair of concrete structures and while there is no one document that lays out a start to finish procedure for concrete replacement, all required information can be found in the ten individual standards. For example:
Assessing the extent of damage and planning the repair (BS EN 1504-9).
Removing contaminated or damaged concrete (BS EN 1504-10).
Preparing the substrate and cleaning reinforcements (BS EN 1504-10).
Applying corrosion protection to reinforcement (BS EN 1504-7).
Selecting and applying suitable concrete or polymer repair mortars (BS EN 1504-3).
Ensuring a good bond between the existing and new concrete (BS EN 1504-10).
A general step-by-step guide for concrete replacement as a repair technique, integrating best practices and principles from various global standards, might involve steps such as:
Identify and evaluate the extent of concrete damage.
Excavate damaged or contaminated concrete to reach sound substrate.
Clean the exposed surfaces and reinforcements.
Apply any required repair measures to ensure deterioration methods such as corrosion or alkali aggregate attack have stopped and conditions have been removed so they cannot restart.
Replace corroded reinforcement and increase the number and density of reinforcement bars if required, ensuring compatibility with existing materials.
Choose an appropriate repair material based on structural needs and environmental conditions.
Apply repair material using methods like casting, hand application, or spraying, ensuring thorough compaction and void filling.
Allow the repair material to cure, adopting methods that ensure moisture retention.
Finish the surface to match the surrounding areas and restore aesthetic and functional properties.
Inspect the repair for any defects and ensure the bond between old and new concrete is secure. Pull off testing is commonly used to measure this.
What equipment and expertise are required for Concrete replacement on concrete structures?
Concrete replacement does not require specialised labour and only minimal equipment which could be found on the majority of construction sites. This includes:
Demolition tools such as jackhammers or chisels for removal of damaged concrete.
Concrete mixers.
Reinforcement cutting and bending tools like hydraulic rebar cutters, rebar bending machines, bolt cutters, angle grinders, etc.
Concrete finishing tools such as trowels for smooth surfaces, edger trowels for creating clean edges, float blades for levelling and compacting, and brooms for textured finishes.
What are the advantages of Concrete replacement for concrete structures?
Restores structural integrity and load-bearing capacity.
Offers sustainability by extending the lifespan of structures.
Ensures compatibility and durability with appropriate material selection.
What are the disadvantages of Concrete replacement for concrete structures?
Can be costly and labour-intensive.
May require significant downtime for the structure.
Potential for incompatibility with existing materials if not properly matched.
What are the limitations of Concrete replacement for concrete structures?
Difficulty in achieving perfect material compatibility (thermal expansion, creep, elastic modulus).
Environmental impact from demolition and construction processes.
Challenges in addressing the root cause of deterioration, risking recurrence of issues.
Ancillary information
Service disruption: Yes
Preliminary works: Yes
Posterior works: Yes
Time consumption: Medium
Cost: Medium
