ExoLeaf® Ultra High Performance Fibre Reinforced Concrete
The redevelopment of 9-11 Elmer Approach in Southend-on-Sea required two additional floors to be added to the existing 10-storey building as part of its transformation into a 108 room hotel.
To facilitate the load of the new levels, columns throughout the building required strengthening. Freyssinet was enlisted to carry out the strengthening of 52 columns across four levels. Works included the preparation of existing columns, formwork and in-situ pouring of Ultra High Performance Fibre Reinforced Concrete (UHPFRC) shells to strength the columns.
The use of Freyssinet’s ExoLeaf® UHPFRC enables faster, more economical works on site and made the strengthening shell thinner than it would have been using traditional techniques. Only light preparation of the existing concrete is required, which negated the need for intensive percussive drilling in preparation for the strengthening operations.
Freyssinet’s Technical Solutions team designed the ExoLeaf® system. The site works sequence, including the installation and utilisation of forced action mixing plant included:
- 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 selection of ExoLeaf® Ultra High Performance Fibre Reinforced Concrete as a strengthening system provided a number of benefits when compared to traditional solutions:
- 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.
Find out more about Freyssinet’s ExoLeaf® Ultra High Performance Fibre Reinforced Concrete and its uses. Click on the cover image to access our brochure.