Managing a Concrete Pour

The Process

Where to use it

• Ensure there is safe and clear access to the site for concrete trucks
• Check if reinforcing is required. Learn about Ready Floor steel fibre reinforced concrete as an option.
• Sub-grade preparation, level and flat. Check if a vapour barrier such as polythene is necessary
• Confirm the type of concrete, slump and volume that is required. Check the weather, accelerator or retarders may be required to cope with hot or cold conditions
• Work out the speed of supply. Taking into consideration travel time, how close together the concrete trucks are required?
• Have your account details or method of payment, contact phone number and site address available
• If concrete cutting is required ensure that it is done as soon as possible after placing

Placing

• Choose an experienced concrete placer, ask to view some of their recent work
• Monitor water added to concrete on site, (check with the batcher to ensure that the maximum water content is not exceeded). Adding extra water will reduce the concrete strength
• Vibrate or rod the concrete to ensure adequate compaction
• Screed the concrete to the correct level
• Float off to close the surface (smooth off). Take care not to overwork wet concrete (this will bring too much cement paste to the surface) and do not add water to the surface when troweling, either action will weaken the final surface

Finishing

• The finishing process can only begin when the concrete has stiffened sufficiently and the bleed water has evaporated from the surface. The timing of this will depend on both the weather and the concrete temperature
• Determine how dense and hard wearing you want the concrete surface to be. Depending on the requirements different finishing methods are available, these include:- Mechanical power floating: for a hard wearing smooth surface (standard internal finish)- Bull float: applicable for most external surfaces, can be broomed to add grip- Decorative finishes: exposed aggregates, ground or polished.

Curing

• Concrete should be protected from early loss of moisture; this loss can cause shrinkage cracking, as little strength development has occurred to withstand the stresses resulting from the volume change (due to loss of water)
• A good curing environment should exist immediately after finishing, and for best results for seven days
• After finishing and before curing can take place without damaging the surface, an evaporation retardant might be required to slow moisture loss in hot weather

Curing Methods

• Ponding: build a sand bund around the perimeter and fill with water to cover slab
• Spraying: the use of sprinklers to keep slab continuously wet
• Covering: impermeable covering such as plastic sheet will trap moisture on concrete surface and minimise evaporation
• Curing compounds: apply after finishing when bleed water disappears (use with caution, these products may affect follow on trades like paint, tiles, vinyl, adhesives)