Mapei were asked by the contractors, Freyssinet, to look at a possible solution using Mapei’s extensive range of Reinforced Fibre Composite materials, that would redistribute the loads around the holes cut through the 280mm thick PT slab.
Their composite engineer submitted a strengthening solution utilising Mapewrap C UNI-AX 300 and the Mapewrap C Fiocco system. Mapei supported their recommendation by providing a design report and drawings.
The design was based on Mapewrap C UNI-AX 300, a high strength unidirectional carbon fibre fabric with very high modulus of elasticity, and Mapewrap C Fiocco, a unidirectional high strength carbon fibre cord for systems. Mapewrap C Fiocco was used to make “structural connections” between the two sides of the slab.
To avoid any loss of stress in the PT tendon, Freyssinet installed Mapewrap C UNI-AX 300 in stages, enabling the tendency of the slab to expand under axial load to put in the Mapewrap Carbon Fibre in tension.
Before proceeding with the sequence of cuts into the concrete, the PT tendons needed to be tracked, and longitudinal strips of Mapewrap C UNI-AX 300 were applied underneath the slab as flexural strengthening following the position of the PT cables. Once completed, 12mm diameter holes were drilled through the slab, in predetermined locations, allowing the Carbon Fibre anchoring system to be installed at a later stage of the works.
The carbon fibre strips were applied transversely to the direction of the hole, from the top to the bottom of the slab, and folded though the hole. Once the sequence of cuts was completed, holes were predrilled and Mapewrap Primer 1 was applied. The predrilled holes were then filled with Mapewrap 31 adhesive. Next, the Mapewrap C Fiocco cord was inserted into the hole, creating 150mm of cord at the ends of the hole which was then splayed out evenly around the hole and completely encapsulating with previously applied Mapewrap 31 adhesive.
The use of Mapei’s range of carbon fibre solutions was ideally suited to the time-critical project due to the speed of installation compared to alternatives. Thanks to the properties of the Mapei products used, the installation caused minimal disruption with noise and dust virtually eliminated by Freyssinet during installation.