The Correct Concrete Driveway Mix

Use a high-performance, air-entrained concrete mix

A high-performance concrete mix may cost a bit more per square foot initially than a basic mix, but in the long run it could save you the expense and headaches of repairing cracks and other problems caused by an inadequate mix design. Keep in mind that your driveway will be subject to vehicle traffic, freeze/thaw conditions (in most climates), and possibly deicing chemicals. You'll need a durable, low-permeability mix to withstand these conditions.

Here's what to ask for:

• A compressive strength of at least 4000 psi.
• An air content of around 6%. In cold climates, air entrainment (which involves adding an air-entraining admixture to fresh concrete at the batch plant to cause the development of microscopic air bubbles) allows any moisture that does enter the concrete to expand in the air pockets during a freeze-thaw cycle instead of putting internal pressure on the concrete (see Protect Against Freeze-Thaw Cycles to Improve Durability).
• A water-cement ratio below 0.50, to improve concrete durability and strength (see Use a Low Water to Cement Ratio).

Avoid adding excess water to the mix at the jobsite

Excess water should not be added to the concrete mix at the project site, since this will dilute the water-cement ratio. Instead, ask your contractor to use a mix containing fly ash and water-reducing admixtures to provide long-term strength gain and improve workability without the need for additional water. Also make sure finishers do not sprinkle water on the surface while finishing, since this can lead to scaling or crazing.

Designate the proper slump

For driveway paving, the slump (or stiffness of the mix) should be about 4 inches. Slumps greater than 5 inches should be avoided, warns PCA. An overly wet mix can lead to finishing problems and a weak surface.

For information on testing fresh concrete, see Air Content and Density (Unit Weight).

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