Concrete is a high quality, versatile construction material preferred by home owners, home builders and developers for its durability, attractive appearance and long service life.
Concrete provides trouble-free service for many years, if the following six guidelines are followed:
1. SUBGRADE PREPARATION
Topsoil and organic matter should be removed. A granular base (stone or sand)
may be necessary, and fill materials must be compacted uniformly. Because
"flat" pavements can collect water, the subgrade should be sloped.
Exterior pavements, such as patios, driveways, walkways, and parking areas, should
slope at least 1/8 inch per foot. At the time concrete is placed, the subgrade
should be sprayed with water so that it is moist but not muddy.
2. PERFORMANCE CONCRETE
Ask your contractor or ready mixed concrete producer to specify performance concrete
for your exterior concrete projects. Performance concrete should include:
Strength: 4,000 pound per square inch (psi) in 28 days
Air Entrainment: 6% ± 1 %
Slump: 4 inches ±1 inch
3. PLACING & FINISHING
Concrete should be placed, then screeded to the proper elevation. The surface
should be bullfloated before bleed water accumulates on the surface. Finishing
must be delayed until water sheen has disappeared from the surface. The least
amount of finishing should then be done: do not add water to or overwork the surface.
A broom finish is recommended for exterior concrete, except when special textured
finishes (like exposed aggregate or stamped or impressed finishes) are desired.
In hot weather, fresh concrete should be
protected from the sun and wind - even
before it is finished. Confilm, a surface
evaporation retarder, is one way to protect
concrete in hot weather. Concrete can
also be safely placed in cold weather
when proper precautions are taken.
4. PROPER DESIGN
For patios, walkways and most driveway pavement, a 4" to 5" thickness
is satisfactory. Control joints should be set 8 feet to 10 feet apart each way.
They should be 1 inch deep and should be made by sawing or tooling. Sawed joints
must be cut as soon as possible without raveling the concrete. Control joints
need not be filled. Isolation joints should be used at garage doors, where driveways
abut sidewalks and the street, or where patios abut the house. Isolation joints
should extend completely through the slab and provide total separation between
new and old slabs. Isolation joints should contain premolded joint filler 1/4
inch to 1/2 inch thick.
5. PROPER CURING
Proper curing greatly increases the durability of concrete. Concrete should be
cured with a curing compound sprayed on the surface immediately after the final
finishing, or by approved moist curing methods. Concrete should cure 3 to 7 days
before being put in service. (For driveways, car traffic may begin after 3 days;
trucks and other vehicles, 7 days.) A cure and seal compound with an ultraviolet
(UV) protectant is recommended to keep your concrete from gaining a yellow tint.
6. PROPER AFTERCARE
Water repellent concrete sealers can help to prevent surface defects from cold
weather by keeping water from getting into the surface pores. Most sealer applications
are effective for about a two year period. (Note: Use of some sealers can cause
darkening of your concrete surface - ask your sealer distributor if the sealer
will darken the color of your concrete pavement.)
Never use deicing chemicals on new or recently
placed concrete. If traction is needed during the pavement's first winter, the
Portland Cement Association recommends spreading sand or cinder chips. Washing
off road salt that drips from your vehicles is also recommended. After the first
winter, deicing chemicals containing sodium chloride (common salt) or calcium
chloride may be used.
Exterior residential concrete flatwork has no equal
in terms of quality, value, dependability, good looks and long service life, if
the concrete is designed, produced and installed correctly.
And while concrete's initial costs can be higher
than other materials, its good looks, durability and long service life mean life-cycle
costs are much lower.