Slab on Ground

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Slide 1: 5.1 Slab on ground Click to edit Master subtitle style U S 9671 CONSTRU 11/21/10 Slide 2: 22 U S 9671 CONSTRU 11/21/10 Contents • • • • • Foundation uses Preparation for slab construction Concrete floors Slab pour Curing and crack control Slide 3: 33 U S 9671 CONSTRU 11/21/10 What is a foundation? A foundati on is a structure th at transmits lo ads from a building to th e underlying ground. A footing is a slab element th at acts as the founda tion, transferring loads from the superstruct ure to the Slide 4: 44 U S 9671 CONSTRU 11/21/10 What is a slab? Slide 5: CONCRETE FLOORS • A recent survey showed that approximately 80% of new houses in New Zealand are built on a concrete ground floor slab. 11/21/10 U S 9671 CONSTRUCTION 55 Slide 6: 66 U S 9671 CONSTRU 11/21/10 • Polished concrete floors and benchtops have become more and more popular. Coloured Concrete is created by adding coloured oxides. These can further enhance the colours of the aggregates Slide 7: Concrete Floors • • COST CONSIDERATIONS One of the reasons for the popularity of concrete slab is that they are cost competitive with timber floors. On a flat site a concrete slab floor may be 5% to 25% cheaper than a suspended timber floor (with concrete perimeter wall, concrete piles, bearers, joists and a particleboard floor). • 11/21/10 U S 9671 CONSTRUCTION 77 Slide 8: 88 U S 9671 CONSTRU 11/21/10 CONCRETE FLOORS • • • • • For buildings within the scope NZS 3604 the requirement is for an ultimate bearing pressure of 300 kPa. It may be assumed that the ground complies with this requirement if: the foundations of adjacent buildings are satisfactory there are no buried services there have been no land slips in the vicinity A ground test maybe necesary Slide 9: 99 U S 9671 CONSTRU 11/21/10 Preparation for slab 1. 2. 3. 4. 5. 6. 7. 8. 9. Site set out Excavator to scrape back organic top soil. Put up formwork Dig out footings Services Sand blinding Vapour barrier Reinforcing T.A. sign off Slide 10: Preparation for slab • Site set out 11/21/10 U S 9671 CONSTRUCTION 1010 Slide 11: 1111 U S 9671 CONSTRU 11/21/10 Excavator scrape off top soil Slide 12: 1212 U S 9671 CONSTRU 11/21/10 Put up formwork Slide 13: Dig out footings Thickened edge 11/21/10 U S 9671 CONSTRUCTION Foundation wall 1313 Slide 14: Sketch the brick veneer foundation shown on previous 11/21/10 U S 9671 CONSTRUCTION 1414 Slide 15: 1515 U S 9671 CONSTRU Services 11/21/10 Slide 16: 1616 U S 9671 CONSTRU 11/21/10 Concrete Floors Hardfilling provides a solid base for the concrete slab and may be: • Sand. (NZS 3604 7.5.3.2) • Material such as rock or scoria (clean) • AP19 (All passing 19) or AP40 • Excavated fill which has been approved by an engineer. Slide 17: Concrete Floors • Granular fill must be placed in layers not exceeding 150 mm. Where the required granular fill exceeds 600 mm specific design by an engineer is necessary. U S 9671 CONSTRUCTION Plate Compactor 1717 11/21/10 Slide 18: 1818 U S 9671 CONSTRU 11/21/10 Concrete Floors • When there is high groundwater, granular filling which acts as a capillary break must be laid. Capillary action can lift the water table a considerable distance. Slide 19: Concrete Floors Table 2 Capillary lifting capability of soils Type of soil Approximte Water rise Clay Silt Fine sand Coarse Sand 3.5 m 3.5 m 2.25 m 0.8 m 2.25 1919 11/21/10 CONSTRUCTION Contaminat U SedGravel 9671 Slide 20: 2020 U S 9671 CONSTRU 11/21/10 Sand blinding • • • Blinding is a layer of material that protects the damp proof membrane and is also a means by which the sub course is flattened. The surface of the granular base or hardfilling may have sharp projections which can puncture the damp – proof membrane. (NZS 3604 7.5.6.2) Slide 21: 2121 Sand blinding U S 9671 CONSTRU 11/21/10 Slide 22: 2222 U S 9671 CONSTRU 11/21/10 Concrete Floors • • • • • • Blinding The surface of the granular base or hardfillling may have sharp projections which can puncture the damp – proof membrane. Protection must be provided to the damp proof membrane by A sand binding layer (NZS 3604 7.5.6.2) A layer of heavy weight building paper. Smooth site concrete. (NZS 3604 Figure 7.16) Slide 23: 2323 U S 9671 CONSTRU 11/21/10 Concrete Floors Damp Proof Membrane (D.P.M.) must be used under concrete slabs to stop moisure rising The presence of moisture may cause: • Floor coverings lifting up. • Mould and mildew in carpets • Furniture absorbing moisture • Increased heat loss through floor • Increased humidity Slide 24: 2424 U S 9671 CONSTRU 11/21/10 Concrete Floors • The most suitable membrane for application on top of sand blinding is a sheet material such as 0.25 mm thick polythene or laminated polythene lapped 150 mm at joints and securely taped. The DPM must be continuous under any thickenings for beams and must be sealed at service pipe penetrations. • Slide 25: 2525 U S 9671 CONSTRU 11/21/10 Concrete Floors Damp Proof Membrane (D.P.M.) • modified bituminous sheet comprising modified bitumen on a polythene backing, with or without fabric reinforcement • synthetic rubber sheet • polyethylene (polythene) sheet having a minimum thickness of 0.25 mm • liquid coatings, such as bitumen or tar emulsions,epoxies and urethanes Slide 26: 2626 U S 9671 CONSTRU 11/21/10 Concrete Floors • • • • • BRANZ recommends That the DPM is stopped at the bottom of the outside face of the perimeter beam. the rate of moisture absorption through the concrete is low enough that the consequences are not serious it is impractical to carry the DPM up the exposed face of the foundation Refer page 120 B.R.A.N.Z. H.B.G. Slide 27: 2727 Reinforcing U S 9671 CONSTRU 11/21/10 Slide 28: B.C.A. sign off = 11/21/10 U S 9671 CONSTRUCTION 2828 Slide 29: 2929 U S 9671 CONSTRU Crack former • 11/21/10 Place the reinforcement and pour the concrete over the key joint. Finish concrete surface to the top of the joint (NOT ABOVE IT). Slide 30: 3030 Crack former • U S 9671 CONSTRU 11/21/10 Position key joint in desired location and drive in the supplied pegs. Note that the LONGEST FLANGE of the key joint always goes TO THE TOP. Slide 31: 3131 U S 9671 CONSTRU 11/21/10 Concrete Floors • • • • Slab thickenings under load-bearing timber or masonry walls must be reinforced with two D12 bars All foundation reinforcing bar must: have the correct concrete cover to reduce the possibility of corrosion during the designed life of the building Refer page 119 B.R.A.N.Z. H.B.G. Slide 32: 3232 U S 9671 CONSTRU thickenings 11/21/10 Slide 33: 3333 U S 9671 CONSTRU 11/21/10 Slab pour Slide 34: 3434 U S 9671 CONSTRU 11/21/10 Slab pour Slide 35: 3535 U S 9671 CONSTRU 11/21/10 Slab pour Slide 36: 3636 U S 9671 CONSTRU 11/21/10 Slab pour Slide 37: 3737 U S 9671 CONSTRU 11/21/10 Slab pour Slide 38: 3838 U S 9671 CONSTRU 11/21/10 Slab pour Slide 39: 3939 U S 9671 CONSTRU 11/21/10 Slab pour Slide 40: 4040 U S 9671 CONSTRU 11/21/10 Slab pour Slide 41: 4141 U S 9671 CONSTRU 11/21/10 Slab pour Slide 42: 4242 U S 9671 CONSTRU 11/21/10 Slab pour Slide 43: 4343 U S 9671 CONSTRU 11/21/10 Slab pour Slide 44: 4444 U S 9671 CONSTRU 11/21/10 Slab pour Slide 45: 4545 U S 9671 CONSTRU 11/21/10 Slab pour Slide 46: 4646 U S 9671 CONSTRU 11/21/10 Slab pour Slide 47: 4747 U S 9671 CONSTRU 11/21/10 Slab pour Slide 48: 4848 U S 9671 CONSTRU 11/21/10 Slab pour Slide 49: 4949 U S 9671 CONSTRU 11/21/10 Earth Bar Slide 50: 5050 11/21/10 Laser screeds U S 9671 CONSTRU Slide 51: Curing Continuously wetting the surface, preventing the loss of moisture from the body of the concrete. (Ponding or spraying the surface are two ”wetting" methods which can be used.) 11/21/10 U S 9671 CONSTRUCTION 5151 Slide 52: 5252 U S 9671 CONSTRU 11/21/10 Curing slab Slide 53: 5353 U S 9671 CONSTRU 11/21/10 Concrete Floors Crack control • During the drying of the concrete shrinkage occurs as the water leaves the wet concrete. • Control joints are put in to the slab either before the slab is cast or later on. • Refer pages 117 & 118 B.R.A.N.Z. H.B.G. Slide 54: Saw-cutting the slab to a depth 25mm . Saw-cutting must be carried out as soon as possible without tearing the11/21/10 (24 hr) U S 9671 surface CONSTRUCTION HBG pages 117 - 5454 118 Slide 55: Where would the information relating to the type of Damp Proof Membrane (DPM) be found? 2. What preparation is required before laying the Damp Proof Membrane (DPM)? 3. Why is it necessary that the Damp Proof Membrane (DPM) layer be fitted carefully to the profile of beams and thickenings beneath the slab? 4. Give two precautions that should be taken when service pipes penetrate the Damp Proof Membrane (DPM). 5. What is the maximum depth of each separate layer when compacting hardfill? 6. Give two reasons for using a sand blinding layer. U S 9671 5555 11/21/10 7. What design requirements will be needed if the 1. CONSTRUCTION Slide 56: • Where would the information relating to the type of Damp Proof Membrane (DPM) be found? Working Drawings or Specification • What preparation is required before laying the Damp Proof Membrane (DPM)? All services in place, compact and level. • Why is it necessary that the Damp Proof Membrane (DPM) layer be fitted carefully to the profile of beams and thickenings beneath the slab? To stop the weight of the concrete damaging the DPM To provide solid bearing for the foundation. • Give two precautions that should be taken when service pipes penetrate the Damp Proof Membrane (DPM). Seal all penetrations , Cover tops of pipes • What is the maximum depth of each separate layer when compacting hardfill? 150mm • Give the reason for using a sand blinding layer. U S 9671 11/21/10 Stop Hardfill from puncturing DPM CONSTRUCTION 5656