Why is concrete removal required?
Concrete removal is essential when structures exhibit deterioration due to factors such as environmental exposure, leaching, alkali aggregate reaction, internal and external sulphate attack, freeze-thaw cycles, or reinforcement corrosion through carbonation or chloride contamination. The concrete is removed and replaced to the eliminate the problem at its source.
This process often precedes necessary repairs such as the use of corrosion inhibitors or the application of cathodic protection or re-alkalisation.
How do you remove concrete?
There are six main methods for concrete removal commonly used in concrete structures.
Blasting
This technique employs rapidly expanding gas confined within a series of boreholes to produce controlled fractures and allow rapid concrete removal at low cost even when up to 250mm must be removed from the concrete surface. This method is often used to fell large multistorey buildings through destruction of their support columns and beams and requires highly skilled personnel to control the scale of the damage and limit this to only the target area.
Crushing
Concrete crushing employs hydraulically powered jaws for the demolition and removal of concrete.
Boom-mounted mechanical crushers are utilized for extensive demolitions, cutting through concrete in decks, walls, and columns where the shearing depth is usually up to 1.80 meters.
Despite their efficiency, they may damage reinforcing steel beyond reuse .
Alternatively, portable mechanical crushers, requiring two operators, offer a more targeted approach with a shearing depth of up to 300 mm. Though less disruptive in terms of noise and vibration, they have lower production rates, are less widely available and still can damage reinforcement steel beyond reuse.
Cutting
These techniques employ full depth perimeter cuts to disjoint concrete for removal as a unit. The maximum size of the unit is determined by the load carrying capacities of available lifting and transporting equipment.
Forms of cutting include abrasive water jetting, diamond blade saws, diamond edged cutting wires, stitching and thermal melting of concrete.
Impacting
These techniques use the repeated striking of a concrete surface with a large mass to fracture and spall the concrete. Impact methods are sometimes used in a manner similar to cutting methods.
Methods of impacting include boom mounted breakers, spring action hammers and handheld impact breakers. These techniques generally create large amounts of dust , debris and high noise levels and can often damage the remaining concrete causing microcracking
Milling
Milling employs impact-abrasion or cavitation-erosion techniques to strip away surface concrete.
Hydro-milling is used for the removal of deteriorated concrete from the surface of decks and walls. Removal depth depends of the machinery but is usually less than 150mm. This method is costly, requires a significant source of potable water and produces high levels of noise however the steel reinforcement and concrete left behind will be undamaged.
Rotary head milling for removing deteriorated concrete cover from reinforced members such as pavements and decks and is only suitable where contact with the reinforcement is unlikely. High levels of noise, vibration and dust are produced and remaining concrete can be damaged. This method is however significantly less costly than hydro-milling.
Pre-splitting
Pre-splitting involves using wedging forces in a designed pattern of boreholes to produce controlled cracking of the concrete which can then be removed.
Chemical presplitting uses expansive agents to force the concrete apart. Mechanical pre-splitting is used on more massive structures where 250mm or more of material must be removed and comes in the form of piston jacks or plug and feather splitters.
No noise, vibration or flying rock is produced, limited skills are required by the operator and costs are typically lower than for other cutting methods.
