Are You Meeting All Six Requirements for Quality Flatwork?

Requirement #1
PROPER SUBGRADE PREPARATION

• Subgrade is the existing soil after the topsoil is removed.

• Any pockets of soft soil that cannot be uniformly compacted must be removed and replaced with suitable material.

• Slope the subgrade away from structures enough to ensure good drainage.

• Never place concrete on frozen or muddy subgrade.

Requirement #2
PROPER SLAB DESIGN

• Use a minimum thickness of 4 inches.

• Control joints should be 10 feet apart each way, and should be at least a depth of one inch, made by sawing or tooling.

• Use a center line control joint when driveways are more than 10 feet wide.

• Isolation joints are required at existing slabs, structures, and objects. Isolation joints should run the full depth of the slab.

Requirement #3
PROPER CONCRETE MIX DESIGN

• The mix must be a minimum 4500 psi air entrained concrete meeting the following requirements:

• A water/cement ratio of .45.

• Air content when placed: 6 percent, plus or minus 1 percent.

• Slump: 4 inches, plus or minus 1 inch.

• Coarse and fine aggregate: shall meet Wisconsin Department of Transportation specifications.

• Note: The air content and strength of the mix will be affected by any re-tempering water added at the jobsite.

Requirement #4
PROPER PLACING AND FINISHING

• Place the concrete as near to final position as possible.

• No finishing operations shall be performed when there is excess moisture or bleed water on the surface.

• The only finishing operations required are:
screeding or strike-off; bull floating prior to the appearance of any bleed water; a waiting period for the water sheen to disappear; edging and jointing; and a broom texture (the safest and most durable final finish).

• Protection of the concrete from the hot sun, high winds, or freezing temperatures is required until the concrete has a chance to cure properly.

• All concrete should be placed within 90 minutes from the time the truck was loaded. Hot-weather practices call for shorter placement time limits.

Requirement #5
PROPER CURING AND SEALING

• Curing is a process where a satisfactory moisture content and temperature must be maintained.

• Curing greatly increases the strength and durability of the concrete and therefore its resistance to freezing and thawing and de-icer salts.

• Mid-April to Mid-September: Use a sprayed on curing compound, applied according to the
manufacturer’s recommendations.

• Mid-September to Mid-April: Use waterproof covers and maintain curing for at least 7 days at temperatures above 40 degrees Fahrenheit. Air dry for an additional 30 days and follow with a concrete sealer to prevent intrusion of deicing salts. Use caution and wise cold-weather practices when placing exterior concrete during these months.

Requirement #6
PROPER AFTERCARE

• Don’t drive on new concrete for at least 7 days.

• Don’t allow drain water to undermine the slab and cause settlement cracks.

• Don’t allow snow and ice to accumulate on the slab during the first year.

• Don’t allow the use of de-icing chemicals for snow and ice removal the first winter. Sand can be used for traction.

• Never use de-icers fertilizer ingredients such as ammonium sulfate and ammonium nitrate. They attack and destroy concrete by chemical action.

• Promptly remove build up snow and ice in winter and broom off areas where deicing salts drop from vehicles.

• If wear shows in high traffic areas (as sometimes happens after five or more years), clean the surface and reseal for further protection.