Building in a Saline Environment

Transcription

1 Building in a Saline Environment Urban Salinity Prevention

2 Building in a Saline Environment This advice is of a general nature and detailed advice should be sought from a certified structural engineer. Council has received various requests for salinity information from residents building new homes. As a result a Builders Information Night was held in 1997 from which some of the following information was collated. This sheet presents steps that can be taken to reduce salinity damage to buildings in saline environments. The information is sourced from the Cement and Concrete Association of Australia, Australian Standard 2870 for Footings, the State Bank Building Booklet, council building staff and local businesses. Although some of the products and building practices mentioned would cost slightly more than standard building techniques, the life of your building will be prolonged. Initial estimates on a typical residence show that $2,000 is added to the total building cost with building life increasing by fifty percent. Builders and owners should evaluate the level of salinity risk on their specific building block before making decisions on appropriate products and practices. Obtaining a copy of the Depth to Piezometric Surface Map from council and contacting a consulting engineer (see the Yellow Pages) will assist in assessing your building site. HOUSE SLABS Sand Layer Provide a layer of at least 50 mm of sand under the slab to prevent saline water from soaking into the slab and tearing of the damp proof membrane. House Slab Damp Proof Membrane A damp proof membrane rather than a vapour proof membrane should be laid under the slab. The damp proof membrane differs from the vapour proof membrane in thickness and impact resistance. Membrane product types include black industrial, orange industrial, orange premium and orange super. Note that orange premium and orange super are damp proof. Black industrial and orange industrial are vapour proof and only differ from each other in colour. Ensure the membrane extends up to ground level at the slab edges.

3 Building in a Saline Environment BRICKS Brick Damp Proof Course In areas of high salt and dampness, careful detailing of the damp proof course is required. Ensure material is correctly placed to prevent moisture moving past this point in the wall. Builders are required to install a damp proof course. Extra care should be taken to ensure the damp course is correctly laid and not left short of corners and the outer wall because of aesthetic considerations. On sloping sites, where a large number of bricks occur below the damp course you may consider installing an extra damp proof course just above ground level. Brick Type Bricks resistant to water and salt are more suitable for saline environments. Product qualities will vary between different brick companies eg concrete, extruded clay or dry pressed clay. When buying bricks you might like to ask for the bricks salt and water resistance test results. If these have not been undertaken you could ask the company to test the bricks so you can make an informed decision. Some companies routinely test batches of bricks and class the more resistant bricks as exposure quality bricks. Alternatively you may have to pay for testing to be done yourself. Factors such as clay type and location in the kiln may affect brick resistance to salt and water. There is little cost difference between brick types. Masonry Blocks & Concrete Bricks These come in a range of types and strengths. The manufacturer should be contacted for their recommendations regarding the suitability of their product for saline environments. Mortar The correct mortar type should be used below the damp course and may have waterproofing added. Ensure mortar is not stronger than the bricks to prevent bricks from cracking.

4 CONCRETE Concrete Mix Concrete is made more resistant to saline water by: Increasing concrete strength to reduce permeability. Use Normal Class 32 Mega pascals (N32) strength concrete. The concrete strength needed depends on the site s salinity level. OR Using cement that will reduce reinforcement corrosion. Use a Type SR (Sulphate Resisting) cement with a water cement ratio of 0.5 water weight divided by cement weight. Some general purpose cements are sulphate resisting. Your supplier will be able to will be to advise you about this. Both methods one and two will reduce the permeability of concrete and slow the rate at which saline water can infiltrate concrete. This helps protect the reinforcement from corrosion. Method one is preferred as a standard concrete mix can be ordered, and ideally the cement used could be a sulphate resisting. Minimum Concrete Cover in Slabs As per Aust standard (not a salinity specific standard). Cover for reinforcement shall be 40mm to unprotected ground, 40mm to external exposure, 30mm to a membrane in contact with the ground, and 20mm to an internal surface. The State Bank s building booklet recommends minimum concrete cover of 65mm for strip or slab reinforcement in saline environments. Minimum Concrete Cover of Reinforcing in Beams and Strip Footings (Whether or not a damp proof membrane is used): 50mm minimum is a Wagga Wagga City Council Steel standard. This also helps protect reinforcing steel from corrosion.

5 Building in a Saline Environment Admixtures (optional) These substances may be used to extend the normal design life of concrete by Waterproofing. Waterproofing admixtures are used to reduce concrete permeability and help keep salts out. Corrosion prevention. Corrosion inhibitors improve the resistance of the reinforcing steel to corrosion. Concrete Vibration Compact the concrete through vibration to reduce spaces that water and salt can move into. Note that concrete can be over-compacted causing aggregate to sink to bottom of the pour. Cure the Concrete Concrete should be cured for at least seven days to ensure a hard dense surface that reduces saline water infiltration rate. This includes exposed slab surfaces and edges. PIPES WATER & PLUMBING Water Supply Pipes Galvanised iron pipes will corrode in a saline environment. Copper piping is now generally used and is reasonably tolerant against salt attack. Some grades of non metal pipes, such as polybutylene or polyethylene may be used, subject to some restrictions. Contact your plumber or Riverina Water County Council Plumbing Inspector for further details. Plumbing Pipes (Waste Water) Use Unplasticised Polyvinyl Chloride (UPVC).

6 THE GARDEN Garden Design Correct site drainage, garden design and watering of your garden will protect foundations and footings. It will also reduce the amount of water seeping past plant roots and into the groundwater system. Some practices include: Trees Plant trees but keep large trees a safe distance from your home. This will prevent uneven drying of soil and foundation cracking. A tree s root system will usually spread out as far as the tips of its branches. Soil type is another important factor with clays more likely to cause problems. Garden Beds Do not locate garden beds close to your house. Excessive or irregular watering may affect foundations. A garden bed situated up against a house wall may make the damp course ineffective. Rising damp in this situation can move past the damp course. Water Pipes Check and repair water pipe leaks as soon as possible. Watering Do not excessively water gardens or lawns - this will reduce the amount of water reaching the groundwater system. Plant a water wise garden, mulch, use a tap timer, reduce lawn area and put in plants with deeper roots like shrubs and trees that need little watering, water in the cool of the morning or evening. SHEDS, PATHS & DRIVEWAYS Materials used in these structures should be built with consideration of the above information eg damp proof membranes under shed slabs and paths & paver resistance to salt.

7 Why Do We Have Urban Salinity? Urban salinity is caused by rising watertables. A watertable is the upper surface of groundwater below which layers of rock, sand and gravel are saturated with water. In a balanced system the watertable usually stays well below the soil surface. Water seeps into the Wagga Wagga groundwater system in a number of ways including: 1. Over watering gardens and recreation areas. 2. Tree clearing in urban area. 3. Leaking water pipes. 4. Disruption of natural drainage lines. 5. Backyard rubble pits.

8 These factors cause the watertable to rise. A watertable rising toward the surface carries with it dissolved salts that are normally locked in the soil and rocks. The salts concentrate at the soil surface causing the salinity problems we currently see in Wagga Wagga such as poor plant growth, underground pipe corrosion and damage to roads and buildings. WHAT YOU CAN DO Be water wise in the garden Buy a tap timer so you can t leave taps on, or set an alarm clock to remind you. A forgotten sprinkler wastes about 1000 litres every hour. Mend dripping taps. Water in the morning or evening to reduce water loss through evaporation. Avoid watering on very windy days and mulch garden beds. Avoid fine mist sprays, use low trajectory sprinklers. Sweep paths rather than water them and use the leaves for mulch. Divert roof water from your rubble pit if you have one Install a water tank and pump the water to the street if the water cannot be used on the garden. Connect to the stormwater system if possible. Check water pipes for leaks Read the water meter before going to bed and again next morning. If the numbers have increased you may have a leak. Call a plumber. For further information & your comments Ph Wagga Wagga City Council (October 1999)

9 SOME USEFUL INTERNET SITES: ********************************************* The built environment site of the CSIRO. This excellent Monash University site has on line salinity and hydrology information and makes reference to other useful sites. A CSIRO media communique about encroaching salinity in regional areas including Wagga Wagga. Environment Canada: This site has some groundwater quizzes together with some basic groundwater information. It also has an interactive model of leachate migration from a landfill. The site has terrific graphics explaining the movement of groundwater through the profile and the use of peizometric bores, and the way water is held in the soil profile. *top site. A farm note from the Department of Agriculture in Western Australia on monitoring salt land 92 The Commonwealth Government. The Salinity process. Murray Darling Basin Hydrological Map Series and salinity information.

10 Those Contributing to the Booklet Include: The Cement & Concrete Association of Australia Wagga Wagga City Council Building Staff Boral Bricks, Wagga Wagga Boral Concrete, Wagga Wagga Hudsons Timber & Hardware, Wagga Wagga Pioneer Construction Materials, Wagga Wagga Rivcrete Brick & Block, Wagga Wagga Sherwood Sales, Wagga Wagga Willis Bricks, Wagga Wagga CITY OF WAGGA WAGGA Printed by Active Print, Wagga Wagga. Ph: (02)