105 Victoria Street

The scope, under a JCT Design and Build subcontract, comprised the delivery of the two-storey basement and superstructure concrete, with collaborative development and testing of ultra-low carbon solutions and a reduction in the overall volume of concrete used. CDP elements included: basement waterproofing and sewer connections; rebar detailing; precast stairs, landings, and core capping slabs. Meticulous planning of concrete pours and deliveries was required in this sensitive Westminster area, where unforeseeable over-runs are not an option.

Early on in the planning, the project required our in-house M-Tech jumpform rig, as proprietary systems on the market could not jump the rig at the reduced strengths of the low-carbon concrete. The rig is uniquely suited for projects requiring a quick cycle time, exposed concrete finish and low-carbon concrete, all while keeping tower crane dependency low. The rig is designed to jump at concrete strength as low as 12MPa, while also having the ability to store a week’s worth of reinforcement on the top deck, significantly de-risking programme delays due to weather events.

The rig, which has built some of London’s most iconic towers, including 22 Bishopsgate, Principal Place and 1 Leadenhall, was reconfigured for 105 Victoria Street. A team had been working off-site months before the project, refurbishing the alkus ply, which has built these previous projects, bringing it back up to as-new quality to deliver on the visual concrete requirements. No new ply was used on the core construction, which in itself is a great achievement.

The east and west cores were constructed from B2 level up to level 14 (east) and level 16 (west) using the jumpform rig. The total formwork area of the east core was 12,000m2, while the west core was 16,000m2. The core construction included casting in situ lobby slabs and the supply and installation of precast stairs and landings, together with infill with either concrete or grout to all precast plank edges, joints and pockets following installation by the steelwork contractor.

The project made use of recycled and repurposed building materials to reduce embodied carbon, especially deriving from the structure’s foundation, eliminating a large quantity of waste and emissions. Most of the new construction materials were derived from recycled content, while a high percentage of cement replacement in the pre-cast concrete planks and a large proportion of recycled material in the steel structural components helped to minimise the embodied carbon emissions of new materials. We reduced the thickness of the liner walls from 600mm to 300mm, as well as the finished concrete faces on rear areas, also reducing timber.

With 17% of the embodied carbon in the Stage 3 concrete structure, by working with Skanska and our concrete supplier London Concrete we were able to reduce this by 41%. A high GGBS and limestone filler, ultra-low-carbon mix (all the concretes used meet the LCCG-1 benchmark 2024) was developed, which also had a high flow to aid placement around the steel embedment plates, while the design also allowed for a high early-age strength that was required to maintain the one-week cycle time.

We led a pilot initiative with Uploop to create a closed loop circularity where recycled waste concrete was processed and turned into Recycled Concrete Aggregate (RCA) for reuse in ready-mix concrete on the project. These loads were delivered to Victoria Street in London’s first electric-powered concrete lorry. During construction, the requirement was to employ zero fossil fuels and we achieved this.

We also partnered with our reinforcement supplier, Express Reinforcement, to recycle temporary steel props to produce new reinforcement bars for use in the new structure - all 100% recycled in the UK and forged in an electric arc furnace in Wales, saving 400tCO2e and achieving a fully closed-loop waste solution.

The design was awarded BREEAM Excellent for office components, BREEAM Very Good for retail and WELL Platinum.