Solution Features and Benefits
• Used to achieve strict tolerances on multi-storey warehouses
• Also used when extensive floor upgrading is required
• Can be Bonded or Unbonded depending on budget and preference
• The CoGri Korea TP-FS is a proven solution
Design and Specification
Topping slabs are sometimes specified if the design of the structure does not allow the structural slab to be constructed to the required tolerance, for example with a Deckplate (composite) slab system which is expected to deflect, typically with multi-storey warehouses.
Topping slabs can also be used when the Main Contractor prefers to construct the structural slab itself – due to programme or building sequence, or when the Client decides at a late stage in the construction that a strict tolerance . The Bonded version may also be used with a Precast slab system.
The critical consideration in the Design is the type of Topping Slab System required, which depends on budget, clear height limitations and personal preference for finished floor. The two types to consider are:
1. The Bonded TP-FS
Where the Topping slab is fully bonded to the structural slab below to create one monolithic slab. The Bonded Topping slab thickness should preferably be no less than 75 mm ay any location, although if the conditions are suitable it can be constructed to an absolute minimum of 60 mm. The key concern is the Bonding as the topping slab will not perform and will break up if de-bonding occurs.
Based on the 20 years experience of the CoGri Group, CoGri Korea recommends that Bonding is provided by good surface preparation to the sub-slab and the use of Shear Connectors to provide a mechanical bonding system. The use of Bonding Agent alone will not be sufficient. No saw cuts will be required – unless the structural slab below has ‘Live’ movement joints, in which case they must be followed through.
The Client must understand that some random cracking due to Shrinkage cannot be avoided, although a technically competent flooring contractor is able to minimise the cracking.
2. The Unbonded TP-FS
If the Client prefers that Shrinkage cracks are avoided, and Unbonded topping is recommended. As an Unbonded Topping will function independently as a Wearing Slab, slab thickness is again critical to avoid any occurrence of the floor defect commonly known as ‘Curling’. BS 8204, Part 2: Concrete wearing surfaces – Code of Practice states that, “to minimise the risk of Curling the slab thickness might need to be increased to 150 mm”. From its experience in specialist floor repairs, the CoGri Group recommends that if possible the minimum Unbonded Topping thickness is 150 mm, although this can be reduced to 120 mm, depending on various factors and conditions – as long as the Client is willing to accept the risk of some Curling at joints.
Generally the Unbonded Topping is designed and constructed as a Slab on Grade, with careful consideration of Joint layout and load transfer required. As with the Sub-Base of a SOG, the structural slab supporting an Unbonded Topping should be as smooth, flat and level as possible in order to prevent any restraint to shrinkage in the Topping, which could result in random cracking. A structural slab tolerance of +/- 15 mm is recommended.
Topping slabs can be constructed to the most stringent tolerances, up to TR-34 Superflat for VNA warehouses and as always CoGri Korea recommends that the specification and Compliance Testing is cleared specified prior to award of the Main Contract.
Construction Methodology
Ground floor Topping slabs can be constructed by Laser Screed and upper floor Topping slabs can be constructed by ‘Copperhead’ walk behind laser screeds, so tolerances up to TR-34 FM2 can be achieved. If a more stringent tolerance is required, say for a VNA warehouse, a Long Strip construction method may be required.
Prior to construction of the Topping Slab, an CoGri Korea Engineer will carry out a complete survey of the structural slab level and condition, in order to confirm the Finish Floor Level. For Bonded Toppings, surface preparation is required to remove any laitance on the surface and create a suitable bond finish, and this can be done by Grinding, Shotblasting or Planning depending on the structural slab condition.
After thorough cleaning of the floor, Shear Connectors are installed, typically using rebar fixed into the structural slab with Epoxy Resin at 1.5 m centres. Secondary reinforcement can be provided by a sheet of Steel Fabric (typically 7x200x200 mm) or minimum 25 Kg/ m3 of Steel Fibres, in order to control the width of any cracks which do occur. However to provide a good mechanical bond, CoGri Korea prefers the use Steel Fabric which the Shear Connectors can be tied to. Unbonded Toppings are constructed as per SOG floors with the slab saw cut at maximum 6.5 m spacing and the use of Armoured Joint systems with dowels for load transfer at construction Joints.
With its 20 years of experience constructing industrial concrete floors around the world, you can be sure that the CoGri Group and CoGri Korea TP-FS is a proven and low risk solution which will provide a hardwearing and low maintenance wearing slab with the highest possible performance. Recent Clients in Korea to have enjoyed the benefits of the CoGri Korea Topping Slab Floor System include Prologis, Schenker Logistics and Nong Shim.
