ExoLeaf® UHPFRC column strengthening – Elmer Approach

The scope

Freyssinet’s Technical Solutions team designed the ExoLeaf® UHPFRC strengthening system and defined the site works sequence, which included the installation and operation of a forced‑action mixing plant.

The surfaces of each column were prepared in order to get the aggregate exposed to allow bonding between the existing concrete and the Ductal material.

• A number of proprietary ‘spiders’ (small steel plates) were installed in all four faces of each column.
• The UHPFRC pouring would be from the level above the column, so a 100mm hole was cored close to each column.
• Following surface preparation, spider installation and coring of the slab, the formwork was installed and secured.
• The specialist mixing plant for the concrete, including a metallic fibres silo, conveyor belt, water collection unit was delivered and commissioned on site.
• The fresh UHPFRC was then unloaded into petrol wheelbarrows and taken to the pouring location using a hoist. As the quantity of concrete remains modest, simple handling means could be used, generating more savings.
• Once the UHPFRC is poured it was cured for seven days before striking the formwork.
• The top kicker of the columns (available gap for pouring the UHPFRC) was then cast using R4 high class repair concrete.

The benefits of ExoLeaf®

• Reduced percussion drilling, and all associated issues: dust, noise, HAVS, microcracking of the existing columns.
• Reduced quantity of materials to be delivered on site (no rebars, less concrete). This in turn reduced the impact on the residents and nearby premises.
• Reduced size of the finished columns, therefore maximising the living space in the refurbished building.
• Fast construction on site providing benefits to the Client. Site works were carried out within the site boundaries, controlled by the Client. Freyssinet works were undertaken over level 3 to level 9 of the building and segregated from the public.