New method used

The facility needed to provide the optimum operating platform for the Jungheinrich trucks within the VNA racking system being installed.

With rack heights of 11m and aisle widths of 1.85m the project specification detailed DM2 flatness tolerance (TR34 3rd Edition) with a 225mm slab thickness (175mm base slab and a bonded top slab of 75mm).

Traditionally high tolerance floors have been cast using long strip methods, which allow the contractor to set up formwork, that act as a guide rail for levelling the concrete, however this method is costly and time consuming.  Twintec offered the client a value engineered solution of a large bay ‘jointless’ SFRC, 200mm slab thickness, flood pour with no remedial grinding and the Co-sinus armoured construction joint installed across the aisles to provide smooth vibration-free crossing and load transfer.

The Twintec method involves casting large area ‘jointless’ panels using laserscreed technology and the use of an in-house specialist tolerance team to achieve the required surface levels, prior to the powerfloating operation. This specialist tolerance team are highly skilled in achieving the highest flatness tolerance criteria; DM1, DM2, Cat 1; German DIN standards and ACI Fmin standards.

TR34 determines that the DM2 tolerance is measured based on the MHE truck dimensions, to minimise the amount of static lean when the MHE is operated at height. It considers a tolerance transversely across the aisle and also longitudinally down the aisle to ensure the variations in levels do not affect the MHE operation.

DM2 flatness is measured in four properties, two consider the transverse limits (Properties A and C) and two consider the longitudinal limits (Properties B and D). 

Properties A and C refer to the elevation difference:

•A = between two front wheels

•C = between front and rear axles

Properties B and D refer to the rate in change of elevational difference for each 300mm travelled:

•B = between two front wheels

•D = between front and rear axles

For each property there is a 95% limit and 100% limit to be achieved, therefore multiple measurements are required in order to assess compliance to the flatness specification, highlighting the importance of employing a high tolerance flooring specialist.

Twintec is renowned for producing flat floors worldwide and, following a floor survey by an independent specialist, not only successfully achieved the DM2 flatness specification without any remedial grinding to all 11 aisles, 40m long, poured over two casting days but, in addition, several of the aisles passed the higher flatness tolerance of DM1.