Concrete structures may require maintenance, such as patching or resurfacing, in order to correct surface cracks or erosion. However, when the surface is too damaged, these short-term solutions are a waste of time and money. In these cases, the surface will quickly show the same characteristics as the underlying concrete.
Here is a list of conditions under which a complete concrete replacement is recommended:
- Sunken concrete slabs : Concrete slabs can sink when the subgrade has not been properly prepared. Loose dirt may have been used for the subgrade, and this dirt may settle due to water leaking under the concrete. This makes the concrete slab unsupported and susceptible to sinking. Another possibility is that the subgrade was properly compacted, but the concrete slab was overloaded, which caused subsidence.
- Frost damage : In cold climates, frost damage can easily occur on concrete slabs. Frost heave is the elevation of the ground or other surface due to the expansion of groundwater when it freezes.
- Deep Cracks : Some concrete elements may have deep and widespread cracks in places where settlement has occurred. This may be due to heavy loads such as large trucks, inadequate subgrade, erosion or similar reasons.
- Severely Damaged Concrete Surfaces : There are concrete slabs that have a lot of chipping or corrosion on the surface. It is more economical to replace all the concrete than to repair the surface.
- Construction additions : When a structure is modified or renovated, concrete elements that interfere with the project must be removed.
- New Construction : Some structures are demolished when a new building with a completely different purpose or architectural design is planned.
- Defective concrete : If a batch of concrete has a problem that affects the quality of the project, it must be removed and poured again.
Professional construction management services can help you minimize waste.
Concrete Demolition Methods
The main methods used to demolish concrete are summarized below.
Pressure explosion
Pressure bursting is the best option in situations where dust-free, controlled and relatively quiet concrete removal is required. Pressure rupture can be mechanical or chemical: in both cases, holes are made in the concrete and lateral forces are applied.
- In mechanical breaking, the concrete is broken with a hydraulic pressure machine.
- In chemical breaking, the concrete is divided by inserting an expanding paste.
- Once divided, the concrete is removed manually or with a crane.
Pneumatic and Hydraulic Breakers
This method is typically used in demolition projects involving foundations, pavements and bridge decks. The complexity of this method will depend on the strength of the concrete, the amount of steel reinforcement, the size of the hammer and the working conditions.
Machine-mounted breakers can perform demolitions in a range of 100 to 20,000 foot-pounds at 300 to 800 blows per minute. These breakers can be controlled remotely and use a telescopic boom for easy access. Some are even designed for underwater demolition.
Ball and Crane Method
This is one of the oldest and most common demolition methods, where a crane uses a 13,500-pound wrecking ball to demolish concrete structures. The ball falls or swings into the structure, and only highly qualified operators should perform ball and crane demolitions.
Concrete can be easily broken with this method, but additional work may be required to cut through steel reinforcement. Also consider that this method produces a lot of dust, noise and vibration. The size of the building that can be demolished depends on the size of the crane, the available work area, and the proximity to power lines.
Disassembly
Concrete elements can be cut with a saw, thermal lance (in the presence of steel reinforcement) or high-speed water jets. The concrete pieces are then removed by crane, allowing the complete demolition of a structure with little noise and dust and minimal impact on the surrounding area. This method is beneficial when parts of the building, such as slabs or walls, are being removed.
Explosives
Explosives can be used to remove large volumes of concrete. They are inserted and detonated in a series of pre-defined holes, causing the structure to break into smaller pieces. This method is versatile and flexible, but the resulting explosion and vibration can damage surrounding structures if left unchecked. Among all demolition methods, explosives typically have the most stringent safety standards.
Conclusion
Concrete demolition is necessary in many situations, such as major renovation projects or when the material is damaged beyond repair. There are many methods available, each with advantages and disadvantages, and the best option will depend on the needs and surroundings of the project.
Large amounts of waste are generated when concrete is demolished and there are disposal costs and environmental impact. However, recycling concrete is viable in many projects, reducing waste and saving on new materials.
