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HOLLOWCORE

Hollowcore is a prestressed concrete slab manufactured with continuous voids to reduce weight and cost. It is primarily used as a floor and roof deck system. Hollowcore flooring systems provide safe, solid and secure flooring for your needs. This unique product is both strong and durable allowing for increased floor load capacity.

Benefits of Hollow Core Slabs Structures:

  • Assured quality of concrete elements.
  • Excellent surface finish ready to paint
  • Quick and easy installation with less labour.
  • Excellent fire resistance.
  • High load capacity and rigidity with low water/cement ratio.
  • Easy project implementation giving designers greater versatility
  • Easily adapted to enable mounting of ancillary building systems
  • Reduced self-weight elements
  • Huge cost savings
  • Efficient span/depth-ratio leading to reduced storey height
  • High durability and load resistance
  • Long spans without the need of temporary supports
  • Excellent thermal properties and acoustic insulation
  • Green product reduced use of raw material
  • Can be used in seismic zones
  • Production flexibility

Hollowcore Slabs are prestressed elements cast with advanced extrusion technique. Cores are made in the thickness running along the length with special steel tubes. The slabs are manufactured in 150, 200, 240, 265, 320, 400 and 500 mm thick elements as standard products. Slabs with other thicknesses may be designed and supplied. The standard width of the slabs is 1200 mm. Slabs with narrower width can be provided based on design requirements. The length of hollowcore slabs is fabricated to span up to approximately 21 meters dependent upon the loading conditions.

Hollowcore slabs are prestressed concrete slabs of varying lengths and thicknesses.

Hollowcore slabs are lighter by 40-50% than the conventional reinforced concrete slabs of the same dimensions. It is calculated and found that lot of concrete in the slab is extra and just adding to the weight of the element. In Hollowcore slabs this extra weight is removed from the slabs by making cores. Reduced weight of the slabs results in considerable overall savings in construction costs. With the reduced slab weight, the structural frame can be constructed lighter. The reduced combined weight of the frame and flooring leads to reduced dimensions of the foundations.

In addition to the saving in cost of the structures, additional saving is achieved in time. While supporting elements i.e. beams or walls are beings constructed, Hollowcore slabs can be fabricated separately and fitted when the structure is ready. This results in considerable saving in construction time and costs.

With minor change in end detail, it can emulate cast-in-situ slab in respect to overall stability of structure.

Longer spans and greater strengths of hollowcore slabs is specially advantageous for long span buildings e.g. cinema halls, auditoriums, car parks, shopping complexes where unobstructed space is required.

Application

Hollowcore slabs are used in all applications where floors or roofs are required. HCS have also been utilised in constructing facades of industrial sheds and boundary wall. These include:

  • Commercial buildings
  • Car parks
  • Cinema Halls
  • Auditoriums
  • Residential complexes
  • Private houses and villas
  • Industrial sheds (roof sheet supporting structures)

Listed below are advantages of using hollowcore slabs:

  • No cracks for service loads.
  • No positive deflection for normal dead loads.
  • Smaller deflection for super imposed loads.
  • Longer span and greater loads then conventional slabs of same depth.
  • Longer span, meaning less beams and columns required which gives more unobstructed space and saving for the client.

Inventaa manufactures prestressed hollowcore slabs of following thicknesses: 150, 200, 240, 265, 320, 400 and 500 mm. Depending upon the load conditions, slabs upto length of 21 meters can be designed, produced and erected at the site.

Hollowcore slabs are cast using concrete extruders. Inventaa uses Elematic extruders which are worldwide used for this purpose. The concrete used in production of these slabs is manufactured under controlled conditions in its own batching and mixer plants employed specifically for captive use only.

The reinforcement strands are prestressed as per the standards with special equipment ensuring all the strands are properly stressed. After the slabs are cast in its casting beds, they are covered with sheets and left as it is to develop the initial strength. The concrete strength is at least 60% of the design strength before tension in the prestressed strands is released from abudments. After the strands are cross cut, strand slippage must remain within the permitted limits.

Quality Control

Quality control is performed according to Inventaa standard quality procedures in the well equipped laboratories. The testing equipment is calibrated and maintained at fixed intervals to ensure the test results are at par. 

Structural tests are carried out on final product at regular intervals to determine the actual shear and bending capacity of the slabs. 

After production, all slabs are visually checked for cracks, broken edges, finish and strand slippage before they are released for delivery.

All Hollowcore slabs are cured as per Inventaa standard and company procedures. During the curing period, the slabs are regularly watered and kept covered with polythene sheets to retain the moisture around them.

A full schedule of company standard quality control procedures can be requested from the Quality Department.

As a special service, we can offer a full Quality Control Report for the individual project consisting of casting dates, cube test and other quality checks for the particular project. This service shall be agreed with our sales department.

Erection

Erection of the hollowcore slabs is a simple process.  Inventaa trained erection crew lead by experienced supervisors ensures that installation fulfil the required specifications.

Erection is carried out in a continuous operation. On steel and precast structures the Hollowcore slabs are placed directly on top of the support. On in situ concrete structures the Hollowcore slabs are placed on plywood shims for levelling purposes.

The erection process will in most cases takes 1 day for approximately 400m2 depending upon the complexity of job.

After the slabs are erected, levelling of slabs will be done within 2 days of erection.

Trained Inventaa crew carries out the erection work thus giving you the maximum expertise and saving of time.  Provided certain requirements are observed, contractor’s crew may carry out the erection work.
In this case it is important that lifting and handling of the slabs is done correctly by following the procedure specified by Inventaa.

Inventaa will not take any responsibility for the slabs during lifting, handling and erection if the erection is done by the contractor. We will only guarantee for the slabs after completion of grouting and tamping according to our specifications.

Lifting of slabs:

Slabs are lifted directly from the trailer and into position.   
Full slabs are lifted using the specially designed lifting equipment.

When lifting part slabs (width less than 1200mm) and slabs with cutouts near the end, sling belts will be used.

When lifting with clamps safety chains are used underneath the slab. The chain should not be released until the slab is about 100 mm from the support.

Inventaa products are designed as per quality standards. Inventaa is equipped with state of art software and computers to design hollowcore slabs for any application. Its experienced designers understand and meet any requirement of the client. 

Load tables:

Load tables are designed in accordance with Inventaa Standard. For simple supported slabs, value for load capacity and deflections are given in load tables for the various thicknesses.
To acquire the load tables please contact our local Sales or Design department.

Hollowcore slabs are produced in standard width of 1200mm. Special width and cutouts can be made under certain conditions.

Dimensions and tolerances are shown in the table below:

Dimensions

Tolerances

Length

Up to 4.5 m
4.5 m to 6 m
6.0 m to 12 m
>12 m

+ 10 mm
+ 12 mm
+ 18 mm
+ 24 mm

Width bottom

1200 mm

+0 mm
-3 mm

Depth

150 mm
200 mm
240 mm
265 mm
320 mm
400 mm
500 mm

+3 mm
-7 mm

Width of part slab

 

+ 20mm

Flatness (maximum deviation from 1.5m straight edge)

 

+ 20mm

Camber

Calculated value

+ 50 %

Variation in camber closely associated units

 

9 mm

Positions of strands (Maximum deviation from position)

 

5 mm

Size and positions of cut-outs as required with respect to detailed structural analysis

 

+ 20mm

Noise reduction (dB):

Noise reduction properties of Hollowcore Slabs are according to the following table:
 

HCS

HCS WITH SCREED

SOLID CONCRETE SLAB

HCS 150: 
50 dB

HCS 150+75 mm Screed: 54 dB

200 mm:
55 dB

HCS 200: 
53 dB

HCS 200+75 mm Screed: 57 dB

250 mm:                     
57 dB

HCS 240: 
55 dB

HCS 240+75 mm Screed: 60 dB

290 mm:                     
60 dB

HCS 265: 
56 dB

HCS 265+75 mm Screed: 61 dB

320 mm:
61 dB

HCS 320: 
58 dB

HCS 320+75 mm Screed: +62 dB

350 mm:                     
62 dB

HCS 400: 
60 dB

HCS 400+75 mm Screed: 65 dB

450 mm:                     
65 dB

HCS 500: 
63 dB

HCS 500+75 mm Screed: 68 dB

560 mm:                     
67 dB

 

Fire resistance

Hollowcore slabs elements meet the very highest requirements for non – flammability and fire resistance. 

Slab Joint
The joints between the slabs can be filled without the need of shuttering.

Bearings
Under normal conditions the Hollowcore slabs will need a minimum bearing not less than 60mm.

Bearing will, under normal conditions, always be designed as 75mm in order to allow for tolerances in the main load bearing structure. For spans more than 12m, the designed bearing should be 100mm due to the increased tolerances.

For erection on concrete beams, cast in-situ or block walls, a 18 mm joint is required to take the variances of the level of the support and secure a uniform bearing stress.

For erection on steel structure, the slabs can be placed directly on the steel beams or on a strip of roofing felt or similar.

Nominal and minimum bearings depend on the loading conditions and type of construction. Please contact the Design Departments at your respective locations for advise for specific project.

Joint reinforcement
Reinforcement can be placed in the joints to act as a horizontal structure bracing if required.

Using voids for services
Electrical conduits can easily be installed through the voids after erection of the slabs is planned correctly.