Redrow Homes, Hampshire – Pocket Cutting, Precision Concrete Removal Case Study
Pocket Cutting in Reinforced Concrete Suspended Slab: Precision Concrete Removal
- Sector: Civil Engineering
- Task: To carry out precision ultra high pressure robotic hydro- demolition to form 8no pockets in suspended reinforced concrete slabs. Additional reinforcement could then be installed to meet design change/requirements prior to concrete repour.
- Location: Lymington, Hampshire
- When: August 2014
- Client: Redrow Homes
- Main contractor: Foundation Developments Limited
- Concrete hydrodemolition sub-contractor: RGL
- RGL plant: Ultra high pressure portable diesel driven water jetting unit (24 litres per min. /2500 bar) with X/Y Axis remote control cutting frame. Single high velocity pencil nozzle. Portable noise reducing acoustic working enclosure, waste water pumps, filtration and Ph adjustment equipment.
RGL were approached by Foundation Developments Limited (FDL) early in 2014 to provide a quotation for some Hydrodemolition works involving the removal of concrete from 8 locations. The requirement was to remove the top 150mm of concrete from areas measuring 3.5 metre squared. After a site visit undertaken by Jeremy Twigg, Commercial Director of RGL, the formal quotation for the works was issued. RGL were required to provide detailed Safety, Health, Environmental and Quality information to FDL in order to become an approved supplier.
Prior to an order being placed FDL requested a noise survey, which was provided, as the work was to be undertaken opposite Lymington railway station and strict noise level limits were in place. Following this submission a visit to a live site was requested to be undertaken by FDL with their client Redrow Homes in order to gain a clearer understanding of RGL’s Hydrodemolition process. Not only to see the cutting method in action but also experience the noise generated.
Once this visit was completed both parties were satisfied that Hydrodemolition was the best method to employ for the project, and an order was issued following additional site meetings to finalise the scaffolding requirements for the project. Due to the noise restraints in place it was decided that a full working enclosure was required, and that this would be covered with timber sheets and acoustic barriers on the external face, with debris netting covering the top.
Bob Mullen from Redrow Homes commented:
“By using the robotic precision Hydrodemolition system, RGL were able to perform a top quality job for us. Our task suited the system well and it is a great step forward from traditional hand held breaking methods”
A further factor had to be considered, which was waste water filtration and Ph adjustment. It was imperative that discharge consent was obtained from the local council prior to the works commencing, along with a suitable plan as to where the treated water would be discharged too.
The method of Hydrodemolition used for this project was ultra high pressure semi-robotic meaning all of RGL’s operatives were away from the work face during the works. This eliminates many of the hazards typically associated with water jetting as the operatives, set up the system and leave the work area once the jetting work starts. The water jetting work is then controlled via a hand held remote control panel. The control is used to stop and start the jetting unit, and control the pace of the nozzle as it traverses and moves across the area to be removed. This method of Hydrodemolition is one that RGL are keen to utilise and employ wherever possible due to the additional health and safety benefits it provides. A major benefit of using the X/Y axis cutting frame and a key factor in reducing noise and flying debris created during this process is the use of a protective rubber debris deflection disc, which is placed directly behind the jetting nozzle.
No separate pockets were required to be cut to accurate depth so that extra reinforcement could be installed. The total volume of concrete to be removed was 14.7m3 (1.8375m3 per location). The project ran for 14 shifts and was a great success, with the work being finished on schedule, with all waste water treated and discharged into an onsite drainage system as per the consent criteria. There were no complaints of noise from any stakeholders and the finished job left the pockets as required enabling additional steel reinforcement to be added.