ready super slab design and installation manual · pipe work can be run within the depth of the...

READY SUPER SLAB DESIGN AND

INSTALLATION MANUAL

Consult your Allied Concrete representative for specialised information0800 4 ALLIED (0800 4 225 433) • www.alliedconcrete.co.nz

REVISION HISTORY

Revision Prepared by Description Date

A RJF Draft 20 March 2013

B AE Draft 17 April 2013

DISCLAIMER

This document has been prepared solely for ALLIED CONCRETE. The use of and reliance upon the information or opinions contained in this document by others without prior written consent from HFC Foundations Limited will be at such person’s risk. HFC Foundations Limited accepts no responsibility or liability for the consequences of the unauthorized use of this document.

ALLIED READY SUPER SLAB - DESIGN AND INSTALLATION MANUAL

HFC: Civil and Structural (foundations) Ltd: ref: w12889

CONTENTS

1.0 GENERAL ................................................................................................................................................3

2.0 ALLIED SUPER SLAB COMPONENTS ........................................................................................4

2.1 Polystyrene Pods .............................................................................................................................4

2.2 Topping slab and rib reinforcement [FIGURE 4.1] ...........................................................4

2.3 Concrete ..............................................................................................................................................5

3.0 STANDARD DESIGNS AND LIMITATIONS ................................................................................6

3.1 Structures Supported by the standard Allied Super Slab .............................................6

3.2 Ground conditions ..........................................................................................................................7

3.3 Lateral resistance ............................................................................................................................7

4.0 STANDARD DETAILS: NEW ZEALAND .....................................................................................8

5.0 SPECIAL DETAILS: CANTERBURY REGION ............................................................................9

6.0 INSTALLATION INFORMATION ...................................................................................................10

6.1 Site preparation .............................................................................................................................10

6.2 Set out & boxing ............................................................................................................................. 11

6.3 Damp proof membrane (DPM) ............................................................................................... 12

6.4 Pod set out ....................................................................................................................................... 12

6.5 Perimeter foundations ................................................................................................................ 13

6.6 Internal ribs ...................................................................................................................................... 14

6.7 Mesh .................................................................................................................................................... 14

6.8 Reentrant corners ......................................................................................................................... 14

6.9 Concrete placing, finishing and curing. ............................................................................... 15

6.10 Saw cutting and control joints. ................................................................................................ 16

7.0 LANDSCAPING AND ONGOING MAINTENANCE............................................................... 17

7.1 Paving and landscaping heights ............................................................................................. 17

7.2 Excavation and retaining walls ................................................................................................ 17

7.3 Drainage of the site ...................................................................................................................... 17

7.4 Gardens, trees and shrubs ......................................................................................................... 18



1.0 GENERALThis document details the design and construction requirements for the Allied Super Slab system.

The document covers the components, general site requirements, details and construction of a standard Allied Super Slab. In addition more specific special details are provided for guidance only.

This document does not replace the requirement for specific engineering design and documentation by a professional engineer as part of the consent process.



2.0 ALLIED SUPER SLAB COMPONENTSThe Allied Super Slab floor system consists of polystyrene void formers separated by 100mm wide spacers set out in a grid pattern. Concrete is poured on top of the pods and within the 100mm wide gap between the pods to form a ‘waffle raft’.

A standard design consists of 85mm topping over a 200mm pod creating an overall slab thickness of 285mm.

2.1 Polystyrene Pods

Polysytrene pods are typically 1100mm x 1100mm in plan and 200mm thick.

Depending on supply in some cases 1200mm x1200mm x 200mm pods are used.

Pod thickness is increased in some cases and in the Canterbury Region 300mm pods are used as standard to comply with the requirements of the Department of Building and Housing for TC2 sites.

Where topsoil thickness is such that imported hardfill is required to bring the slab up to level then the thicker 300mm pod and resulting 385mm thick floor system can be used to reduce the thickness of hardfill required.

Once a level platform has been created with a combination of compacted hardfill, a blinding layer and a layer of damp proof membrane (DPM) then the pods can be set out in a grid pattern to create 100mm wide ribs.

Where the geometry of the slab dictates the pods need to be cut to ensure the 100mm wide rib spacing is maintained and perimeter footing widths are correct.

2.2 Topping slab and rib reinforcement [FIGURE 4.1]

The thickness of concrete over the polystyrene pods is typically 85mm.

Reinforcement within the topping is either 665 mesh for areas of low seismicity or SE62 ductlile mesh in areas with high seismicity. It is recommended that the ductile SE62 mesh is used.

Thicker toppings and a variety of mesh sizes are also used to accommodate under floor heating or higher superimposed design loads in some cases.

The reinforcement in the bottom of the 100mm wide ribs is a single HD12 E bar and these run in two orthogonal directions following the rib lines.

Perimeter reinforcement typically consists of 2 HD12 E bottom bars as well has HD12 E starters bars lapping with the top mesh reinforcement.

Bar chairs and spacers are used to ensure the correct cover to reinforcement as well as ensuring the mesh is lifted off the pods to provide the correct top cover.

Additional reinforcement is provided for specific design cases such as to accommodate higher loads, spanning between piles or highly expansive soils.

All reinforcement shall be deformed bar to AS/NZS4671:2001. Stirrups, links and binding shall be plain bar of the above grade or wire to AS/NZS4671:2001.

Welded mesh shall be to AS/NZS4671:2001.



2.3 Concrete

Allied Super Slab Mix should be used for all Allied Super Slabs.

For sites located away from corrosive environments 20 Mpa concrete strength is required. For sites in more corrosive environment (such as sea spray zones) or for additional strength 25 Mpa concrete is used.

Mix code 252RSS is used for 25 Mpa applications.

Mix code 202RSS is used for 20 Mpa applications.

The design documentation will specify the required mix code for each design.

Where good access exists around the site and sufficient labour is employed then the concrete can be placed directly from the truck using the chute or wheel barrows. If this is the case then it is important that the mesh reinforcement and pods are protected from wheel barrow traffic and correct covers are maintained.

Alternatively a slump pump can be used with either 13mm or 19mm aggregate.

At the time of ordering it is important to state the method of concrete delivery so that any adjustments in concrete mix can be made by Allied Concrete.



3.0 STANDARD DESIGNS AND LIMITATIONSThe standard Allied Super Slab is an extremely strong and durable foundation system and can accommodate a wide variety of loading combinations.

The following sections outline the general loading requirements for a standard Allied Super Slab.

Specific designs for more onerous design cases can be carried out for any project and they normally only require a minor variation to the standard design. All designs are carried out by a Chartered Engineer with specific plans and details provided at consent stage.

3.1 Structures Supported by the standard Allied Super Slab

The standard Allied Super Slab is designed to support lightweight timber framed houses generally satisfying the requirements of NZS3604:2011. Solid masonry construction is excluded from the standard design but can be accommodated by specific designs in most cases.

The criteria for complying with NZS3604:2011 include but are not limited to:

• Building founded on ‘good ground’

• Importance level 1 and 2 structures

• Total height to the highest point of the roof up to 10m

• Open ground snow loading up to 1kPa

• Buildings with floors not exceeding 3kPa uniformly distributed or 2.7kN concentrated loads excluding garages

• Garage loading up to 2.5 kPa uniformly distributed or 13 kN concentrated loads for vehicles up to 2500 kg tare.

• Exterior cladding to be either lightweight or masonry veneer up to 220 kg/m2 with a maximum height of 7m above finished ground level.

• Masonry construction is excluded from the standard design case but can be accommodated through specific design

• Timber framed upper level floors up to 3 levels

• The slope of any roof plane shall not be steeper than 60 degrees.

• From low to Very High wind zones

• A maximum heavy veneer height of 5.5m on gable ends



3.2 Ground conditions

The standard Allied Super Slab can be used on ‘good ground’ in accordance with NZS3604:2011 section 3.1.3 which includes (but is not limited to) a geotechnical ultimate bearing capacity of 300 kPa (equivalent to 100kPa allowable bearing).

In addition to good ground sites the standard slab can be specifically designed to accommodate the following (subject to site specific geotechnical information)

• Low bearing sites down to a geotechnical ultimate bearing capacity of 150 kPa (equivalent to 50 kPa allowable bearing)

• Floating slabs on gravel rafts over peat site

• Fully suspended piled slabs [refer figure 4.6]

• Moderately, Highly and Extremely expansive sites

• Bridging over public services [refer figure 4.5]

• Slope stability piles

• Basement retaining walls

• Canterbury region TC1, TC2, TC3 sites [refer figures 5.1 to 5.4]

3.3 Lateral resistance

Lateral resistance to sliding from seismic actions is generally resisted by friction between the slab and the underlying ground surface.

In areas of high seismicity additional resistance to sliding is provided by the use of shear keys. Shear keys consist of drilled piles of 900mm depth spread around the perimeter of the slab to lock the slab into the ground. Where shear keys are required they will me indicated on the drawings provided. [refer figure 4.2]

In some circumstances shear keys are not adopted even in high seismic areas (such as the Canterbury Region).

Where shear keys are not adopted in high seismic zones additional measures need to be taken to protect services which run through the slab from being damaged under a serviceability earthquake event.

Pipe work can be run within the depth of the slab and exit out of the side of the footing with a flexible junction. This method mitigates the likely hood of damage as well as providing an accessible point to repair services should they be damaged. [refer figure 5.3]



4.0 STANDARD DETAILS: NEW ZEALAND

FIGURE TITLE

4.1 Standard slab details

4.2 Typical shear key

4.3 Typical step detail

4.4 Typical block retaining wall detail

4.5 Typical bridging detail for public lines

4.6 Typical fully suspended slab detail



5.0 SPECIAL DETAILS: CANTERBURY REGION

FIGURE TITLE

5.1 Typical edge beam TC2 & TC3 sites

5.2 Typical internal stiffening beam TC2 & TC3 sites

5.3 Typical service penetrations TC2 & TC3 sites

5.4 Re-level able Jacking slab TC3 sites



6.0 INSTALLATION INFORMATIONThe following section outlines the standard installation details for the Allied Super Slab. For specific projects non-standard details may be required and the builder should construct these in accordance with the drawings, the NZ Building Code and good practice.

All construction should be inspected by an engineer, the council and/or an approved representative of Allied Concrete who has been specifically trained.

All bending of bars should be carried out in accordance with NZS3101:Part 1:2006. Minimum bend diameters for main reinforcing bars (between 6-20mm dia.) bar should be 5 x diameter of the bar (db) measured to the inside face of the bend.

All bar laps should be 50 x db or greater.

6.1 Site preparation

The site should be cut to underside of slab level plus any extra allowance for hard fill and blinding layers. All topsoil and organic matter should be removed from under the entire slab area and any soft spots should be excavated and replaced with compacted material to achieve the site specific ground bearing requirements (normally 100 kPa allowable)

The cut platform should not be left exposed to dry out for any length of time particularly in areas where expansive soils have been identified. If necessary on dry cut platforms the site should be thoroughly wetted prior to the placement of hard fill or fines. Failure to do so can result in excessive ground movement and damage to the slab particularly on highly and extremely expansive sites.

Granular fill complying with NZS3604:2011 clause 7.5.3 shall be placed and compacted in layers of 150mm maximum thickness up to a maximum thickness of 600mm (or thicker under the supervision of a geotechnical engineer)



A sand blinding layer of 15mm should be used over the platform to protect the DPM from being punctured by the aggregate within the hard fill.

The cut platform and any compacted hard fill should be inspected and approved prior to continuing on with construction.

6.2 Set out & boxing

Site profiles, levels and position on site should be determined by the builder and/or surveyor

Boxing of correct height and levels should be erected around the perimeter of the slab ensuring that any boxing supports do not penetrate the DPM layer.

Rebates for brickwork, garage door thresholds and joinery should be allowed for in the boxing.

6.3 Damp proof membrane (DPM)

A continuous damp proof membrane should be placed on top of the sand blinding layer over the entire slab area in accordance with NZS3604:2011.

Where polyethylene (polythene) sheet damp proof membrane is to be used the material should be not less than 0.25mm thick , have lapped joints not less than 150mm wide which are sealed with pressure sensitive plastic tape not less than 50mm wide. The DPM should be protected from damage during construction.



6.4 Pod set out

The polystyrene pods should be placed on the DMP layer within the perimeter boxing as per the set out drawings provided.

The set out of the pods should ensure that the perimeter footing width (normally 300mm wide) is correct and the space between pods is correct (normally 100mm). The drawings and details should be carefully checked as in some cases footing and rib widths are varied to suit site specific requirements.

Internal load bearing walls will be marked on the drawings and these also need to be accommodated in the pod set out (or cut into the pods if preferred).

Where pods require cutting to suit the dimensions and set out of the floor care should be taken to ensure that the remaining pods are no less than 200mm wide. Where narrow < 200mm pod widths occur then the pod should be removed OR the set out merged with an adjacent full width pod to create two narrower pods of 600-800mm wide with a standard 100mm wide rib between.

The maximum pod size in all cases should not exceed 1200mm

6.5 Perimeter foundations

The perimeter edge beam is typically 300mm wide however larger widths are specified when ground conditions or edge detailing of cladding dictate this.

Typically 2 HD12 bars (Grade 500E deformed bars) are used for bottom steel in the footing and 1 HD12 used as top reinforcement where required. The bottom bars should be placed onto bar chairs to achieve 50mm bottom and side cover.

HD12 starter bars are used of varying lengths depending on site conditions and levels of soil expansiveness, and these should be tied to the mesh.

The perimeter footing may have rebates to accommodate exterior cladding details such as bricks, garage door rebates, and full height joinery rebates. The rebates should be coordinated and set out in accordance with the architects drawings.



6.6 Internal ribs

A standard internal rib is 100mm wide and has 1 HD12 bar located in the bottom of the rib with 50mm cover to the DPM.

Extra wide ribs or ribs with additional reinforcement including links can be specified to suit site specific requirements.

Ribs should run from one side of the slab to another in a straight line where possible. HD12 bars should be lapped 600mm where required.

6.7 Mesh

The typical mesh used in the 85mm topping is SE62 grade 500 E mesh.

The mesh should be supported on 40mm chairs for an 85mm topping. The chairs should be located on top of the polystyrene pods and be of sufficient number to ensure the mesh does not sag excessively between support points.

Where the topping is increased above 85mm the mesh size may be increased and the chair size may also need to be increased to achieve 40mm top cover.

6.8 Reentrant corners

At re-entrant (internal) corners additional steel is required to prevent cracks from propagating from the internal corner into the slab. The additional steel will be indicated on the drawings and consist of 2 HD12 bars, 1500mm long placed diagonally across the corners.



6.9 Concrete placing, finishing and curing.

PLACING:

Only Allied Mix code 252RSS should be used for 25 Mpa applications or Mix code 202RSS used for 20 Mpa applications unless specifically varied by the designer or concrete supplier. Failure to use the correct Allied concrete specified may prevent the contractor from obtaining Code of Compliance.

Concrete placing should be carried out by experienced contractors and should be carried out strictly in accordance with NZS3109:1997

No water should be added to the as delivered concrete unless approved by the design engineer within the restrictions of NZS3104 clause 2.9.3.1

Concrete should not be placed until all reinforcement has been inspected by the engineer, council and/or an approved engineers representative. Failure to carry out a pre-pour inspection may result in difficulties in obtaining code of compliance.

Care should be taken during the pouring process to ensure that the polystyrene pods do not move around. Ideally concrete should be placed on top of each pod prior to infilling between the ribs to prevent pod floatation or movement during concrete placing.

The concrete shall be placed so that its working face is generally vertical, and normal to the direction of placing. It should be placed over the width of the slab in such a manner as to minimize segregation.

Concrete should be thoroughly vibrated around all steel and against all boxing and formed rebates within the perimeter of the slab.

FINISHING:

The top surface of the slab should be screeded immediately after placing/vibration has been completed.

Screeding should be carried out with a level as a reference to ensure the top surface is finished within tolerance.

A trowel and an edging tool should be used to finish the slab to a U3 finish in accordance with NZS3114:1987. The finish surface should be blemish free with all slab edges tooled off to form a rounded edge to prevent cracking.



CURING:

When the possibility of heat, wind, rain or low humidity could induce premature drying of the top surface the contractor should either delay the pour or take appropriate actions to mitigate plastic cracking forming in the surface of the slab.

Where a risk of plastic shrinkage cracking is present the concrete placer shall apply an anti-evaporation agent over the concrete surface after screeding to prevent excessive evaporation of water from the concrete surface.

Additional curing measures including ponding of water on the surface of the slab, sprinkling the slab surface regularly or the use of wet sacking placed over the slab can also be adopted.

Where a large change in ambient temperature is expected during the first 24 hours such as a very cold night then continuous wet curing via ponding or sprinkling is recommended to mitigate thermal shock and cracking in the slab.

6.10 Saw cutting and control joints.

Saw cut joints should be cut into the slab within the 24 hours after pouring once the slab is sufficiently hard. Early entry soft cutting is recommended.

Saw cuts should be 25mm deep (for the standard 85mm topping). For thicker toppings deeper saw cuts will be required of approximately 1/3rd of the topping thickness. Saw cuts should be made where indicated on the drawings.

For larger slabs, formed control joints are required and they will be indicated on the drawings. It is important that formed control joints are installed where indicated to prevent excessive cracking of long or irregular shaped slabs.



7.0 LANDSCAPING AND ONGOING MAINTENANCEFoundation maintenance should be broadly in accordance with AS280:2011: Appendix B. Particular care should be taken on sites which are Moderately, Highly or Extremely expansive as work and planting around the slab perimeter can have a detrimental effect on the slabs performance.

7.1 Paving and landscaping heights

The level of permanent paved, concreted and landscaped surfaces should be kept within the limits stated in NZS3604:2011 clause 7.5.

For paved or concreted surfaces the minimum step from the internal finished floor level to the finished exterior level should be no less than 150mm

For grassed or permeable surfaces the minimum step from the internal finished floor level to the ground level should be no less than 225mm

7.2 Excavation and retaining walls

Excavation next to the edge of the Allied Super Slab should be avoided where possible. Under no circumstances should excavation take place which will undermine the edge of the slab

Excavation or construction of retaining walls (lower than the slab level) within a 1:4 gradient from the underside of the slab to the base of the excavation/wall should be avoided. A qualified engineer should design all retaining walls within this zone to ensure that loss of vertical and lateral support (during construction or permanently) does not occur.

7.3 Drainage of the site

Sands, silts and clays should be protected from becoming extremely wet by adequate attention to site drainage and prompt repair of plumbing leaks.

The site should be graded or drained so that water cannot pond against or near the building. The ground immediately adjacent to the building should be graded to a uniform fall of 50mm minimum away from the building over the first metre. The site drainage should be maintained for the design life of the building (normally 50 years)

7.4 Gardens, trees and shrubs

The development of the gardens should not interfere with the site drainage requirements. Garden beds immediately adjacent to the slab edge or undermining the slab edge in anyway are not permitted.

Planting of trees should be avoided near the foundations as they can cause damage due to drying of clay and result in excessive seasonal ground movement.



To reduce, but not eliminate, the possibility of foundation damage, tree planning should be restricted to a distance from the house as follows

(1) 1 ½ x mature tree height for extremely expansive sites

(2) 1 x mature tree height for highly expansive sites

(3) ¾ x mature tree height for moderately expansive sites

Where rows or groups of trees are involved the above distances should be increased. Please note that removal of mature trees from the site can also cause issues with ground movement



ready super slab design and installation manual · pipe work can be run within the depth of the...

Documents