Westminster City Council King Street Low Carbon Trial - Client Report

The excavator would also have been easily charged with their own power pack, but they needed to provide a separate adapter to connect to the feeder pillar. As the excavator was offered as a free trial, no other options were considered, however other suppliers such as Kubota and Caterpillar are developing their own electric mini excavators.

Speedy Hire supplied the following equipment:

• WackerNeuson AP1850WE wacker plate

• Hasqvarna K535i disc cutter

To retain the look and feel of the St James’s area it was decided not to deviate too far from the existing artificial stone paving. This meant there was limited scope for reducing the carbon through a specification change. Across other parts of the City, it may be possible to explore other materials, such as recycled slabs or asphalt, which would require a larger input from the design team and a longer lead time. MATERIALS The Welfare Unit was adapted to run off electricity and solar rather than a diesel generator. This worked well as it was silent when switched on and the benefits were that the site team could use the Unit earlier without being a nuisance to the residents. The one drawback was that the hut could not be relocated as it was connected to the feeder pillar. Under normal circumstances they seldom need to be moved, however, due to an unexpected incident outside of our control involving loose masonry on an adjacent building, a scaffold needed to be erected overhead. This meant that the Welfare Unit and compound could not be used until it was safe to do so which resulted in a time delay. These items were used when required and worked almost as well as their fossil fuel powered counterparts. The wacker plate was quite heavy and difficult to manoeuvre but there was not any significant difference in terms of performance or time taken to carry out the activity. The disc cutter worked quite well cutting through the slab, assisted by the fact they were only 50mm thick. However, the battery needed to be changed after every eight cuts, meaning that a fully charged spare battery needs to be ready each time the saw is used. Another concern was its ability to cut through granite kerb if required, as this would take longer, and the battery may not be powerful enough to cope. SPECIFICATION Following discussions with the paving supplier Marshalls it was decided that the slab could be reduced to 50mm thick instead of the usual 63mm. To ensure that there was no reduction in strength Marshalls also designed the foundation. Mortar bedding with primer was specified to provide extra cohesion than sand and cement, which also enables the slab to take the impact of vehicle overrun in the same manner. The deviation from the standard also allowed the team to use a less carbon intensive C10 concrete instead of C20 without any reduction in performance. It was hoped that a low carbon concrete could also be trialled, however, it is not yet readily available as a dry, lean mix used for this type of works. Usually, the kerb line is then reinstated to match the existing carriageway. On King Street this was replaced with GreenPatch, a product manufactured with recycled asphalt and no petroleum-based ‘cut back’ solvents and hand-laid cold. STORAGE To reduce the size of the storage area on site and to replicate the workings of a centralised depot, a separate compound area was set up on Carlton House Terrace. This was less than a mile from site and allowed ‘just-in-time’ deliveries and reduced vehicle movements to King Street.

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