TECHNICAL

Elematic’s hollow core concrete slabs are designed and manufactured with precision, using world class technology. A variety of slab thicknesses and widths are available and can be used in combinations to suit the requirements of every project.

Slab Types

We manufacture pre-stressed hollow core concrete slabs in a variety of different slab types and thicknesses. All slabs have a standard 1 hour fire rating, but higher fire ratings can be achieved if required.

	120mm	150mm	200mm	250mm
Standard width (mm)	1200mm	1200mm	1200mm	1200mm
Area of cross section (mm²)	0.100482	0.099222	0.119619	0.149209
Concrete density (kg/m³):	2500	2500	2500	2500
Theretical weight of slab (kN/m):	2.5	2.5	3.0	3.7
Minimum concrete strength at detensioning	30 MPa
Concrete strength at 28 days:	50 MPa +
Accepted bearing tolerance (mm)
- On brickwork	90mm
- On concrete	80mm
- On Steel	75mm
Prestressing strand used:		9.3mm & 12.5mm	diameter stabilized	strand.
Recommended max Span / Depth ration:	Ratio=50
Fire rating		1 hour rating standard;	higher ratings can	be achieved.

Curve Diagrams

Serviceability live load versus span diagrams are available for use in the project budget phase. We do recommend, however, that architectural and/or engineering drawings be forwarded to the Elematic design team (info@elematicsa.co.za ) for a confirmed budget quotation.

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Cross Sections

Cross sections to the different available pre-stressed slab thicknesses are available on request.

Steel Applications

Where steel is required for structural support, Elematic slabs can easily be incorporated in a variety of configurations. For more information on this please contact us. Typical steel support solutions can range from a conventional downstand support beam (beam below the hollow core slab soffit) or an upstand beam where the beam is located within the slab thickness (with only the beam bottom flange visible from below).

Design Parameters

No propping is required
Only a 40mm levelling screed is required over the slab in most cases, however a structural topping may be required from time to time, depending on the loads. Please check with our design department.
Mesh to be used on external areas such as walkways, balconies and staircase landings as these areas are exposed to weather conditions (expansion and contraction)
Mesh to be used internally in areas greater than 16m2
Expansion joints to be utilised in tiled areas (specifications are available from Elematic)
Spans of up to 11m are possible with a 250mm deep slab with a structural topping
Cantilevers can be provided when using Elematic hollowcore concrete slabs

Site Applications / requirements

An area of +/- 7m of clear and level access is required around the building where slabs are to be erected.
This is not Elematic's responsibility.
In order to obtain a flush ceiling on brickwork, the load bearing wall must be level. Avoid internal walls being higher. If brickwork is not level, a mortar bed will be required on top of the brickwork.
Elematic will ensure V joints are straight.
As the panels are designed and manufactured specifically for your project, site dimensions need to be accurate to avoid delays.
Sand and cement for grouting between the pre-stressed panels are to be supplied by the customer. The actual grouting is done by the supplier.
Window and door openings in load bearing walls up to 1.8m wide can normally be spanned by lintels side by side with five courses of brickwork with brick force in every course for slab spans up to 7m. All openings and certainly wider than 1.8m must be referred to the engineer for detailing of additional structural steel beams where required.
Should a panel be required inside a building, a minimum entrance height of 4.5m high by 3.0m wide is needed, provided there is sufficient turning space for trucks.

Screeding

On contracts where hollow core slabs are used indoors and no structural topping is specified a simple 40 - 50mm levelling screed is required.

All loose material is to be removed from the tops of the slabs, which should be thoroughly wetted and screed applied immediately. The levelling screed should comprise 1:4 mix by volume of cement to clean river sand. Water should be added to the mixture to an extent that the mixture is relatively dry but remains easy to float finish.
The screed should be laid to an approximate thickness of 40 - 50mm. After laying the screed it should be steel floated and then wetted for 48 hours to prevent shrinkage cracks.

Further technical information on this procedure is available on request. We are happy to discuss your particular requirements with you.

Tiling

Further technical information on this procedure is available on request.

Lighting

A variety of lighting options can be utilised with Elematic SA's pre-stressed hollow core concrete slabs.

Further technical information on this procedure is available on request.

Fire ratings

All our slabs come standard with a one hour fire rating, which can be increased to a two hour rating if required.

Load bearing

Pre-stressed slab bearing requirements are evaluated as stipulated in SANS 10100 The structural use of concrete, Part 1 Design. Depending on the sub-strata of the supporting element (brick, concrete or steel), and the applied load, a bearing width is prescribed ranging from a minimum of 60mm to 90mm, or more.