Ready-mix concrete is a preferred material for driveways because of its inherent strength, minimal maintenance requirements, and ability to withstand heavy traffic and harsh weather. However, the many benefits of concrete pavements can be compromised if not correctly designed and constructed.
To maximize the value of your investment, follow these six steps during installation.
Step 1: Prepare the subgrade
The subgrade is the existing soil after the topsoil is removed. To prevent the driveway from cracking, the subgrade must be uniformly compacted and graded to slope away from structures by ¼” per linear foot to ensure adequate drainage. Before pouring, make sure that the subgrade is thawed and dry.
Step 2: Design slabs with proper control and isolation joints
Concrete slabs should have a minimum thickness of 4 inches. Directly after pouring the concrete, place control joints at a spacing of 2 to 2 1/2 times the thickness of the slab converted to feet. For a 4-inch slab, this means placing control joints every 10 feet. Do not exceed 15-foot spacing for control joints; place them with a minimum depth of 1/4 the slab thickness or 1 inch, whichever is larger. When a new pour touches an existing slab, structure, or object, add isolation joints running the full depth of the slab.
Step 3: Get the mix right
The strength of concrete is affected by the ratio of air and water to cementitious materials. The mix must have a maximum water/cementitious ratio of .45 air-entrained concrete, equating to a minimum of 4500 psi. However, the air content and strength of the mix will be affected by any re-tempering water added at the job site. When properly installed, the mix should meet the following requirements:
- Air content when placed: 6 percent, plus or minus 1 percent.
- Slump: 4 inches, plus or minus 1 inch.
- Coarse and fine aggregate meeting Wisconsin Department of Transportation specifications
Step 4: Ensure proper placing and finishing
Pour concrete within 90 minutes of being placed in the truck; during hot weather, the placement time is shorter.
The safest and most durable final finish is applying a broom texture before any bleed water appears on the surface. Other finish operations include screeding or strike-off.
Protect freshly poured concrete from the hot sun, high winds, and freezing temperatures.
Step 5: Maintain optimal conditions during curing
Curing begins immediately after placement and typically takes three to seven days, depending on weather conditions. Curing helps to ensure the newly placed concrete maintains adequate moisture and temperature conditions so it can develop the strength and durability it was designed to achieve. The most common curing method is applying a spray-on compound according to the manufacturer’s recommendation.
Step 6: Seal and protect from chemical damage
Keep vehicles off the freshly poured concrete for at least seven days, and seal it after it has completely air dried for a minimum of 30 days. Sealing applies a protective coating or penetrating water repellent material to prevent moisture and contaminants from seeping into the concrete. To extend the life of your concrete pavement, you can re-seal aged concrete every few years.
Never use deicers with fertilizer ingredients, such as ammonium sulfate, ammonium nitrate, calcium chloride, and magnesium chloride, as these chemicals will cause the concrete surface to deteriorate and crack.
Use County Materials’ Ready-Mix for your next project by contacting our Central Wisconsin Region Ready-Mix Dispatch Team at (715) 845-2100.
