Demidec

What is Demidec?

Demidec is a thin precast concrete plate, typically 60mm deep, although this can vary depending on the use. The plate is supplied with a projecting steel lattice girder system that enables it to provide permanent formwork and integral tension reinforcement for insitu concrete toppings.

How is Demidec made?

All Demidec floors are manufactured in a state of the art carousel plant on precision engineered flat steel pallets. Shutters are held in place using magnets thereby ensuring that the quality of the pallets is not compromised. Sockets, channels and electrical boxes can be cast into the units along with conduits.

For what applications can Demidec be used?

All Demidec units have an excellent soffit finish and so are suitable for a variety of different applications:

Floors for: Permanent Formwork for:
Residential Car Park Decks
Commercial Bridge Decks
Industrial Jetties
Hotels Water Retaining Structures
Accommodation Blocks Insitu Concrete & Post Tensioned Floors

Why choose Demidec Flooring?

Flat Soffit Demidec floors are flat and have no camber.

Quality Finish Demidec floors produce a soffit ready for direct decoration. Each plank is cast with a small chamfer along the horizontal edge. Units are nominally 2400mm wide, although this can be varied to suit the geometry of the site so that the joints between units can be expressed.

Thermal Mass Effect By choosing Demidec floors, there is no need for a suspended ceiling and thus the thermal mass effect can be maximised as the concrete soffit is left exposed.

Thermal Performance Part L1A of the Building Regulations shows a k-value of 138kJ/mK² from above and a k-value of 230kJ/m²K from below. When compared to a timber floor with a plasterboard ceiling which has k-values of 24kJ/m²K and 9kJ/m²K from above and below respectively, the effect that the thermal mass has on thermal performance becomes apparent. This cannot be surpassed by any other form of construction.

In the drive for low carbon buildings, designers are consistently selecting exposed concrete soffits as their material of choice because of its latent thermal mass.

This can be further enhanced by selecting heavyweight wall construction such as CCP’s Crosswall Construction including Thermowall Insulated Sandwich Panels.

Sound The density of the product reduces sound transmission.

Speed of Erection Due to the increased nominal width of units and the simple lifting arrangements, large areas of floor can be erected in a very short space of time.

Cost Demidec flooring compares favourably with the cost of insitu concrete solutions as well as providing an instant working platform and a high quality soffit.

What is Demidec made from?

Demidec is made from Ecocrete environmentally friendly concrete which is responsibly sourced with a minimum of 80% secondary content in all products.

Are Demidec floors suitable for use with different types of construction?

Demidec floors are far more versatile than prestressed concrete floors as they can be adapted to suit many different environments. For example, cover to reinforcement can be varied for different fire ratings or exposure classes, although this will affect the reinforcement design. They are also used as permanent formwork for an insitu concrete floor or as part of a composite solution where the reinforcement in the Demidec unit is integral to the overall design solution.

Is Demidec a flexible system?

Each Demidec element is designed in the most efficient way for the particular part of the structure and its loadings. Sufficient reinforcement can be added to cope with localised additional point loads as well as trimming around openings. Unlike prestressed floors, the need for additional supports around openings can usually be avoided. Furthermore, slabs can be designed to cantilever.

Does Demidec always require propping?

Demidec flooring and permanent formwork utilises the lattice girder which gives the units the stiffness required to take the imposed loads from the insitu concrete. Generally, the greater the stiffness required, the more lattice girders will be required. As a rule of thumb, Demidec flooring comes with three propping options:
 
Propped Units are propped with one single row of props placed prior to the insitu concrete pour.
 
Multiple Props For longer spans, additional props are added, typically at 2500mm to 3000mm centres, although this would be designed specifically for each project.
 
Unpropped Additional lattice girders would be used in the Demidec design to give the units sufficient rigidity to allow for the insitu concrete.
 
For Health & Safety reasons, units are generally post propped so that passive fall systems can be installed prior to the erection of the floors.
 

What are Demidec’s capabilities?

Below is an indicative load span table to be used only as a guide. Every Demidec application will be reviewed by our in-house design team in order to find the solution which most meets our customers’ needs.

For details please contact Cornish Concrete Products Ltd

As can be seen from the graph the additional tension reinforcement improves the performance of the floor. Unlike other types of floor, Demidec’s performance can be improved greatly if floors can be designed as continuous spans. There is alternate negative and positive bending along the spans and because of this, the amount of reinforcement can be reduced, which will also have its effect on cost.

General Structural Information

Lattice girders are the essential element in Demidec flooring. They are generally placed at 600mm centres and ensure that the panels span the required distance in the temporary condition. They also assist the floor in its composite state with any top reinforcement being tied into the elements. The top reinforcement in the slab will be also designed by CCP.

Progressive Collapse

Demidec flooring deals simply with progressive collapse as all the elements are tied together in a monolithic structure.
 

Hollow Core Applications

By adding polystyrene void formers at the factory to the Demidec floors, the overall selfweight of the floors is reduced, thereby improving performance and reducing the dead load on the overall structure where the polystyrene creates a “hollow core” within the overall floor slab. Void formers are generally 400mm wide and are fixed between the lattice girders which are usually at 600mm centres.
 

Lightweight Concrete

Demidec can also be made in lightweight concrete using “Lytag” with a specific density of 1.8 compared to 2.4 of normal structural concrete. “Lytag” is also a waste product and hence its inclusion would not alter the secondary content of the concrete. However, if the precast is made of a lightweight concrete, the insitu topping will also need to be of a similar density. Alternatively, the precast elements can made in normal density concrete and the poured insitu topping in lightweight concrete.
 

On Site

Demidec elements are designed to be lifted with the hooks of the lifting eye positioned under the diagonal of the lattice.
 
Joints between elements will need to be sealed prior to the insitu concrete pour to prevent grout loss. On site reinforcement will need to be placed and insitu concreting will be carried out in accordance with the specification.
 
More detailed technical guidance notes are available on our website, and specific technical guidance notes will be issued with each contract.