The TR-34 ‘Superflat’ floor classification required for VNA applications with MHE lift heights of more than 13.0 m and the American equivalent – ACI Fmin100 is the most stringent floor flatness specification in use.  The Superflat tolerance will only be achieved by experienced and Specialist Superflat Flooring Contractors such as CoGri Korea and requires the application of ‘Long Strip Construction’ whereby the floor is constructed in Bays of 4-6 m width with joints placed below racking.  A series of skilled procedures are required to achieve the required tolerance.  Some Contractors use Dry Shake Toppings to fill hollows in the slab surface although the proven method applied by CoGri Korea does not require the use of Dry Shakes.  This reduces the risk of delamination and dusting during remedial grinding.  It should be noted that even with an experienced Specialist it is expected that up to 5% of the VNA aisle length will require minor remedial grinding to achieve the ‘Superflat’ tolerance. 

Of course if the programme or budget makes Long Strip Construction prohibitive, CoGri Korea’ patented ‘Laser Grinder?’ can be used to Grind a general floor to Superflat tolerances. 

For a Jointed SOG, Drying Shrinkage cracks can be minimized or prevented through good practice including control of the Sub-Base tolerance and correct layout, design and installation of Joints.  Attention to detail is critical to construct a high quality SOG floor!

For Suspended Slabs and fully reinforced Ground Supported Slabs, Shrinkage cracks cannot be entirely eliminated and can only be minimized and controlled by good design, Concrete Mix Design, Good Curing and high standards of Quality Control throughout all stages of the floor construction.  Of course there are many other types of Cracks which can occur in concrete slabs including:- Plastic Shrinkage Cracks, Surface Micro-Cracking and Thermal Cracking. 

Formed Free Movement Joints (Contraction Joints) are installed as Day Joints and designed to provide a minimum of restraint to Drying Shrinkage and Thermal Movements in the slab.  Dowels are required to provide load transfer across the joints and prevent any vertical movements under traffic and loading.  There are a number of proprietary cast in place Joint Systems available – with different Arris-protection systems and Dowel types.  The most important consideration is the cast in place armoured steel plates which should be two plates of 10 x 50 mm Cold Rolled Steel for long term duability.  CoGri Korea was the first company to use a Cast in Place Armour Joint system with Diamond Dowels in Korea – in 2002. 

The Client must note that these Armour Joints are designed to open up to 25 mm and frequently do.  The Contraction Shrinkage in SOG floors is unpredictable and can vary a great deal depending on various factors.  It may take 12 months or more for the Joints to open up to the maximum width.  The Client must be aware of this when considering the Racking system or any other Equipment and storage system which will be fixed to the floor! 

Somero Enterprises, Inc revolutionised the concrete flooring industry with the invention of the S-240 Laser Screed? in 1987.  However it is important to understand the differences in the different types of Laser Screed machines.  Experienced flooring contractors such as LGA Logis can generally achieve tolerances up to TR-34 FM2 Special or ASTM Ff 35/ Fl 40 using the larger drive-on Laser Screeds such as the S-240 owned by LGA Logis. 

For fully reinforced slabs it is not practical to use the drive-on Laser Screeds and the Somero Copperhead? XDTM 2.0 Laser Screed should be used.  This is a walk behind model and although a very good piece of equipment requires far more skill to construct very high tolerances with.  We advise you to be aware of the different types of Laser Screeds available and confirm the methodology when contracting with Flooring companies.  If a Flooring Contractor is claiming to be able to achieve tolerances over and above those stated above, simply ask to see a Certified Floor Survey Report from a Specialist Testing company!  Link to ‘10 Steps to a Perfect Floor’ or LGA Logis Equipment.  Link to downloads of Floor Survey Certifications.