Two robotic hydrodemolition robots from Sweden’s Aquajet Systems are being used to remove 220m3 of concrete from the parapet beams and abutment walls on a major overpass near Newcastle.
The A194(M) Havannah Interchange bridges in Washington, on the outskirts of Newcastle, carry the dual carriageway over the large interchange or roundabout.
The Highways Agency, as part of its routine maintenance programme for the Area 14 Managing Agent Contract (MAC), is replacing significant areas of contaminated and spalled concrete over the exposed faces of the reinforced concrete abutments and deck edges that support the steel parapets of the structure.
These refurbishment works will preserve the integrity of the structures, which are over 35 years old and which were suffering from the contamination of the exposed areas within the spray zone from passing vehicles.
Hydrodemolition was specified for these works to minimise the health and safety issues for the operatives
and to reduce the period of time that the trunk road was restricted to the public. A secondary benefit is that hydrodemolition prevents micro-cracking of the concrete which can be experienced with pneumatic or percussion methods of removing the defective concrete.
The £931,000 project is being undertaken by Carillion Regional Civil Engineering with the hydrodemolition
Works sub-contracted to Buxton Water, one of the UK’s leading hydrodemolition specialists.
The refurbishment works are divided into two phases: the removal of 40m3 of concrete from the abutments was completed at the start of June under Phase 1; the remaining 180m3 of concrete removal from the parapets was completed in July under Phase 2.
High volume work
Traditionally, this work would have been undertaken by pneumatic-percussive equipment. However, this method of removing the concrete can cause problems. The most significant of which is that the action of jackhammers creates micro-fractures deep into the structure, mostly around the interface between the reinforcing and the concrete. This significantly weakens the structure as it undermines the cohesion between the concrete and its reinforcing. In addition, jackhammer work is noisy and dusty, and over a period of time the operators may begin to suffer from white-finger nerve damage.
Hydrodemolition has numerous advantages over traditional pneumatic-percussive methods of concrete removal including: no dust, less noise and also it is far quicker. Water is emitted from the nozzle faster than the speed of sound at a pressure of approximately 15,000 psi. When applied to concrete this jet of super-pressured water penetrates the pours of the concrete, compressing the air within, thereby creating a micro-explosion which blows the concrete away leaving the embedded reinforcement intact.
Because the process is vibration-free, it removes the concrete without causing damage to adjacent areas which can often happen when pneumatic tools are employed, leaving the structure prone to stress fractures in the surrounding concrete. When using percussive tools there is also a significant increase in the likelihood of damaging the steel reinforcements thereby further reducing the life expectancy of concrete repairs.
Lance v robots
There are two ways of undertaking concrete removal by high pressure water – hand lancing or robotic.