Guidelines for Exterior Concrete - Residential
(Driveways, patios, and sidewalks)
The following guidelines are as suggested by the Atlantic Concrete Association.
Step One: Determine the Required Thickness
Step Two: Prepare the Subgrade and form the Pavement Area
Step Three: Order the Concrete but be ready to use it
Step Four: Place and Finish the Concrete)
Step Five: Curing and Jointing
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1. Determine the Required Thickness
Cars only --- 100mm
Cars and light trucks --- 125mm
Occasional heavy trucks (rarely necessary) --- 150mm
Sidewalks and patios --- 100mm
At junctions with other concrete such as the street or sidewalks, the slab thickness should be increases 50% for a distance of at least 300mm from the joint.
Plan Joints - isolation, control, and contraction.
Reinforcement is not required or recommended if jointing is done properly.
Concrete should be placed directly on the Subgrade if possible.
Sometimes granular fill will have to be used as a leveler or to bring over-excavated areas up to grade.
Top of Subgrade = bottom of slab. Therefore, determine slab thickness first.
Subgrade should be uniform and compacted --- replace extra solid or soft spots.
Slope away from buildings (2% if possible).
Isolate abutting construction (buildings, sidewalks) with asphalt impregnated fiberboard.
Use stiff wood forms to keep them in line by nailing pegs not more than 1m apart. Top of pegs should be flush with top of form, all at finish grade.
Form curves with thin plywood, using pegs to keep the line true.
Oil or wet form work shortly before placing concrete ---not the day before.
Specify DURA-MIX® for all exterior concrete applications
Ask your concrete supplier how much you need.
Make sure adequate labour is available to do the job. Minimum requirement is three people. More are required for large jobs or on hot and dry days.
Mix the concrete for one minute just before starting to unload the truck.
Have a roll of plastic sheeting handy in case of rain or very hot conditions.
4. Place and Finish the Concrete
Dampen the subgrade before placing the concrete. If water isn't available use the hose on the truck.
Use a straight board on edge to strike off the concrete even with the top of forms (screening).
Tap forms to consolidate edges.
Consolidate and smooth the concrete with a long handled bull-float. This work should be completed before water appears on the surface of the concrete. WAIT - until bleedwater evaporates and concrete begins setting up before finishing.
Float with either a magnesium or aluminum float. Wooden floats should not be used because they tend to tear the surface. Steel trowels must not be used.
Final finish should give a non-skid surface. This can be done with a burlap drag or stiff broom.
If you are placing the concrete on a hot day, evaporation will be rapid. To prevent premature cracking, cover the surface until the slab is stiff enough to begin finishing. If water still remains on the surface, it will disappear quickly when uncovered.
Edging and grooving should also be done at this time.
DO NOT ALLOW power floats or trowels to be used on the slab. This extra finishing is not required and will reduce the durability of the slab. Scaling may result.
Curing means retaining moisture in the slab so it will become more durable.
Curing should begin as soon as concrete has been finished.
If a curing compound is used, follow the manufacture's guidelines.
Water curing gives the best cure --- soaker hoses, wet burlap, waterproof paper, or polyethylene sheeting will keep the surface wet.
Curing should continue as long as possible but a minimum of 7 days is recommended. (With curing a compound, the curing continues until the material wears off).
Before salt is used on the slab, allow a 30-day air-drying period.
Do not use ammonium-based deicers.
Care should be exercised when placing concrete in hot weather and late in the construction season when cold temperatures are anticipated. Do not use deicing chemicals during the first winter for concrete places late in the season. Contact your APRMCA concrete producer for advice about proper placing, curing and the use of deicing chemicals.
Joints: Isolation joints are placed between the slab and abutting construction before concrete is placed.
Control joints are either grooved into the slab while the concrete is still soft or sawcut 4-24 hours after the concrete has set. A power saw with either a carborundum or diamond blade will do the job.
Joints should not be more than 3m apart and panels should be planned to be square (if possible). Cut the joints to a minimum depth of 25mm or 1/4 the depth of the slab, whichever is greater.