Working with Concrete

Transcription

1 Working with Concrete Call: Measure & Order Work out how much Concrete is required? Concrete is measured and purchased in cubic metres. Follow these easy steps to work out the volume of concrete required. Work out the Area Area in square metres = Length (m) x Width (m). Using a typical garage floor as an example: Area = 10m x 3m = 30m² Cubic Meters to Order Area m² Thickness (mm) Decide what Thickness This may depend on your excavation, but in any case, minimum thickness should be: Paths 75mm Driveways 100mm Garage Floors 125mm For our example, thickness = 125mm Work out the Volume Read the volume required from this chart. For our example: Area = 30m² Thickness = 125mm Volume = 3.8m³ Alternatively, Volume in cubic metres = Area in m2 x thickness / 1,000 For our example: Volume required = 30 x 125 / 1,000 = 3.75m3 The nearest available quantity = 3.8m3 It is wise to add a little extra for wastage and variations in depth. For our example we would order 4.0m3. Page 1 of 5

2 Tools you'll need for concreting Below is a list of Concreting tools and equipment that would set you up to do two house slabs around the 200m2 each at the same time. We suggest a minimum of 4 6 workers in a crew - 3 Shovel hands and 3 Screeders / finishers. Tool List Screeds Boxing Boxing tools (Hand) 1.2 meter 15 x 6 meter 190 x 45 Twisters x meter 15 x 6 meter 140 x 45 Hammers x 4 3 meter x 2 4 x 4.8 meter 140 x 45 Sledge hammers x 4 4 x 4.8 meter 190 x 45 Hand saws x 4 Hand tools (concrete) 6 x 6 meter 90 x 45 Nips x 2 Trowl x 2 long x 2 short 120 x 1.2 meter 70 x 35 (Braceining) Bar cutters Stippler x 2 6 x 6 meter 70 x 45 Mesh Cutter (Bolt cutters) Edger bull nose x 1 small x 2 Star Pickets Crow bar Grover x 2 900mm x 80 Peg puller Mag Float x 2 450mm x 80 String lines x 6 Knee Boards 1000mm x 30 Paint rollers x 2 Brackets x 80 (for Waffle slabs) Square mouth shovels x 4 Concrete extension tools Concrete rakes x 4 Bull float x 1 large x 1 small Boxing tools (battery/ powered) Post hole shovels x 2 Stick Trowel x 1 Nail Gun spirit level Extension Pole Makita cordless drills (set) Circular saw Concrete Machinery Laser level $700 Chopper x 1 36" Wacker x 1 Pressure Washer x 1 Vibrator Jack Hammer Grinder 5" Prepare the Ground Working to specific plans and measurements you ll first need to mark and survey and set up your lines: 1. Hammer Steel pegs into the ground to mark out the area you want to concrete. 2. Use Star Pickets.600 or.900 depending on ground and slab conditions these must be driven solidly into the ground. 3. Stretch string lines between the surveying pegs to set your lines to work to 4. When setting up refer to your plans for RL (Reference Levels or Datum points) to get your heights to work to, these can include TBM/RL, FFL (Finished Floor Level), Ground level, Top of Concrete. 5. Remove turf or loose soil from the marked-out area. 6. Compact rock as a base approx. 50mm thick compacted and levelled. The more it settles - the better the foundation for the concrete. Page 2 of 5

3 Cut & Place Formwork What is "Formwork"? Formwork is the walls that support the concrete until its set. It forms a mould. The best material for formwork is timber at least 35mm thick and equal in width to the concrete thickness. Formwork for Concrete Paths Use Structural timbers and or hard woods such Oregon. For curved paths, hardboard or 7mm plywood is suitable but requires more supporting pegs. Forms must be strong, smooth on the top edge and well supported with stout pegs. (A good test for the strength of formwork is its ability to withstand a reasonable kick). Formwork must be deep enough to hold the thickness of concrete placed and to prevent slurry escaping underneath and additionally we braced. Place reinforcement All structural foundations require reinforcing Mesh and Bars. Local building regulations almost always demand the use of reinforcement. Generally the mesh will be defined in the engineering plans. However a good rule to follow is in foot paths SL62 Mesh, in Driveways, Garages and Sheds SL72 or grater. Check your measurements Once you ve got the formwork sorted and a few other preparations are complete, do one final check on the quantity of concrete you require. IMPORTANT! Check the THICKNESS. Remember - if your slab has an average thickness of 10% more than your original measurements you will need at least 10% more concrete to complete your job. Placing the Concrete How concrete is delivered If the area you want the concrete delivered is level and the way is clear for the truck to drive in or reach over the area with its chute, then trucks can discharge concrete directly into your formwork. Limited access If your site can't be reached by truck - direct the driver to discharge the concrete into a wheelbarrow. Have your helpers ready with barrows when the truck arrives. Load the barrows, wheel them to the concreted area and tip the concrete into the formwork. Plan for a simple spreading job by placing the mounds so they can be evened out - it's easier to move concrete on wheels first than to move it by shovel later. For a sloping site - tip your barrows progressively up the slope - don't start at the top. Page 3 of 5

4 Placing the Concrete Continued A bit of teamwork will help get the concrete placed quickly if you're barrowing it to the forms. 1 or 2 people can wheel and tip the concrete while another can spread it. Note: If your job needs less than 3m3 of concrete the truck driver allows 20 minutes to unload it that s 20 minutes to place the concrete before it starts to 'cure' or 'set'. Drivers allow 7 minutes for each additional cubic metre ordered. This time is sufficient if you are ready to start when the truck arrives. Use shovels and concrete rakes to spread the concrete evenly over the ground. Work a shovel up and down in the concrete just inside the formwork to assist with settling or vibrating the concrete to ensure best compaction on these edges use a concrete Vibrator to remove air bubbles. Ensure the concrete has filled right to the corners and sides of your formwork. Levelling Use a laser level, height pins and timbers to ensure you have reference points to screed to, pride lies within the finished product and if it s not level it can be a very costly process to repair or even replace concrete work. Screeding Screed the concrete to create a smooth level concrete surface. Screeds come in various sizes and types the most common is a aluminium square tube screed, this has a smooth edge and a cutting edge on it, when screeding you want the cutting edge facing you and the smooth edge away. It is important to ensure you have a steady hand and pull the concrete back evenly and not to cut in to your boarders or to leave ripples in the concrete as these will show up in final product if they are too deep to be removed with a chopper (power trowel) Water may appear on the surface of your concrete after the screeding process known as bleeding. This is normal. Some of the water will run off or evaporate, the rest will be drawn back into the concrete when the "setting process" commences. Finishing the Concrete Surface Using a Bull Float If you want a smooth finish there are several processes that will lead to this, most importantly is the Bull Float, the bull is an aluminium flat surface with rolled edges, this is used to flatten the surface of the concrete and remove screed lines, using a bull float is not an easy task and requires skill to ensure a quality finish. "Floating" agitates the surface, compacts the material and brings sand and slurry to the surface to fill the voids. Use the float with light pressure - tilted slightly upwards into the direction you are pushing it. For a textured finish Page 4 of 5

5 For a rough texture - use a Steel stipple float to swirl the concrete or draw a broom or brush over the surface. A steel trowel finish may be used on garage floors, but the surface will become slippery when wet. Not recommended for external driveways, patios, etc. Stamp Impression Stamp Impression is a less common finish however it creates a beautiful finished product, stamp imprints can be of texture, design such as stone or brick and even custom designs. Stencil Finish Stencil finishes can be of various design similar to stamp however a stencil is a polymer material that has been cut with specific designs and is placed on the concrete before it has completely set off, this is then covered with an oxide colour and stippled or trowelled in, and once completed the stencil is then removed. For a smooth finish For a very smooth finish, use a steel trowel in multiple passes as the concrete is setting off. Take care not to add excess water or fine material to the surface as this can create staining, powdering or blemish the final finish. Start trowelling as soon as the "shiny water sheen" disappears, but while concrete is still soft and damp. Edging should be started whilst the concrete is still wet, and can be redone and touched up with several passes as the concrete firms up until the pass when you are happy with the finish. Concreting in cold / Hot weather and Additives The time between screeding and finishing processes varies in summer and winter, during Summer retardant is added to the concrete to slow the exothermic chemical reaction the sets off concrete, and during winter hardener is added to set it of quicker. IMPORTANT NOTES: Where concrete is being placed in sections greater than 3 metres long (eg. driveway or long path) - evenly divided grooves should be made across the concrete surface with the grooving tool. The distance between grooves should be less than 3 metres. Grooves help prevent the concrete cracking these should also be positioned at every weak point such as corners and joins. Use flat side of the screed board as a support and guide when making grooves. Remove the Formwork When the concrete has enough strength to support its self and it has almost completely gone off you can carefully start stripping the timbers and Peg and bracing. Be careful not to damage the concrete surface when stripping timbers and DO NOT vibrate timbers as you may weaken and cause the concrete to drop or crack. If you've used form oil, the forms will be easier to remove and use again on other projects. Page 5 of 5