Mono Slabs

Suspended Slabs:

Mono Block provides professional engineering service for the design, supply and installation of suspended slabs to the construction and building industries in KwaZulu-Natal.

The engineering background to Suspended Slabs:

Essentially suspended slabs ensure that the right construction materials are used in the right place within a slab. Normally a slab is under compressive stress on its top face and under tensile stress on its bottom face. Concrete is very good in compression and reinforcing is very good in tension. Hence, a suspended slab endeavours to maximise the amount of concrete in the compression zone and the amount of reinforcing in the tension zone.

The center of a concrete slab is defined as the neutral axis and does not provide any structural significance besides providing a void between the compression and tension zones within a slab. The greater the void the greater the effective strength of the slab. The central void created by the suspended slab system assists in increasing the gap between the two zones under compression and tension as well as reducing the overall mass of the slab. Essentially it is a more effective use of materials within a slab. The concept may be seen in steel I beams.

The Mono Block system was designed in 2000 by Mr. Peter Erskine, an independent structural engineer. The Mono Block system is based on using a lintel beam 100mm wide by 70mm high pre-stressed with 7 No. 2.64mm diameter crimped wires having an ultimate tensile stress of 1850 Mpa. The beam concrete strength is 40Mpa at 28 days and spacing of the lintels are 510mm for single beams, 610mm for double beams and 710 for triple beams. Three different hollow blocks may be used with these beams. They have heights of 110mm, 140mm and 200mm. The blocks are all 400mm wide at their base. In situ concrete strength of the slab topping is to be a minimum of 25Mpa at 28 days.

The Advantages of the Suspended Slab System :

Speed of installation :

A competent team can install up to 300m2 of the system, using grade polystyrene 14 blocks, in one day. If hollow concrete blocks are used, up to 120m2 can be installed in one day. This installation time frame excludes the placing of the concrete topping.
This installation is done by labor without the requirements of any mechanical equipment.

Speed of construction :

As the suspended slab is pre-stressed, it may be stripped and work may commence below the deck within 14 days of placing the concrete. Brickwork on-top of the slab for the next floor may commence the day after the placing of the 50mm concrete screed.

Cost :

On-average the cost of the completed composite suspended slab system is 30/40 % cheaper than an in-situ system.

Flexibility :

Should the client or the professional team require changes to the slab layout these changes can be incorporated into the slab very quickly due to the flexibility of the suspended slab system as well as due to the location of the production factory.

Shuttering :

The hiring / purchasing of shuttering for the slab soffit is not required.

Fire Rating :

The polystyrene blocks used by Mono Block are manufactured from styFRene which contains a flame retardant and can be used in accordance with SANS 10400 T and is rated by SANS 428 as B / B1 / H&V. Reference: FIRELAB Report F TC06/075.

Thermal Resistance :

The company from which Mono Block purchases their polystyrene blocks is currently undertaking a comparison on the thermal resistance of an equivalent in-situ concrete slab and their polystyrene block with a screed. The results to date indicate that their polystyrene block provide a thermal resistance approximately 26 times better than the traditional in-situ slab. These calculations were based on actual tested results provided by the Concrete Institute and the Expanded Polystyrene Association of SA.

Live Load Carrying Capacity :

The slab design loads are dependent on the span between supports and the thickness of the slab. The suspended slab is not cost effective over spans in excess of 6.5m and is not cost effective if the slab is designed to carry large dead loads.

General Issues regarding Suspended Slabs :

Installation :

The suspended slab needs to be propped for 14 days after the placing of the concrete topping.

Finishes :

The suspended slab needs to be plastered and painted on the slab soffit.

Placing of Reinforcing :

All slabs will require Ref. 193 mesh to be supplied and placed within the 60mm topping to control the micro cracking of the slab.

Equipment :

All slabs will require the hiring of concrete pumps or labour to place the concrete and power floating tools or screeding equipment to finish the concrete surface to specification.