Many Factors Can Affect Concrete's Integrity

Driveways poured at the end of a dead-end street or cul-de-sac need additional protection. Every time a car or truck uses the street, the pavement pushes at the driveway, which can cause major failure of the concrete, especially if the street slopes toward the driveway. (Photo courtesy of Art Today.)

A: It is possible that the concrete has failed, but I have some other theories. Keep in mind that concrete is guaranteed to crack eventually; however, the following explains more serious problems that might occur.

Preparation: The area where the concrete is to be placed has to be well compacted and drained. Concrete poured over disturbed soils or in poorly drained areas has a high potential for failure.

Failed concrete: Concrete has to be mixed properly, depending on weather conditions and where the concrete is to be used. For a residential driveway, the concrete is usually a minimum 3,000-pound test mixture. If the mixture is less than that, normal everyday use of the driveway can cause serious cracking and fractures.

Weather: When concrete is poured in cold weather, the contractor sometimes may request that the supplier use hot water in the mixture. Since concrete starts to harden in a chemical process that gives off heat, adding hot water speeds up the hardening process and the concrete "sets" faster than normal.

Finishing: If the contractor tried to finish the concrete too quickly, the "soup" of cement mixture that forms on top of the slab hardens and traps water between the thin layer of cement and the remainder of the slab. In the winter, the trapped water freezes, leaving a pocked and blistered finish on the driveway.

Movement: Failure to install expansion or control joints can result in a cracked and buckled driveway. Concrete moves with the seasons or because of runoff water from the yard. Gravity also affects concrete. If the driveway is on a slope, gravitational forces will pull the driveway downhill. Expansion joints cushion the movement in an attempt to keep the concrete from breaking.

Cul-de-sac: Driveways poured at the end of a dead-end street or cul-de-sac need additional protection. Every time a car or truck uses the street, the pavement pushes at the driveway, which can cause major failure of the concrete, especially if the street slopes toward the driveway. I have seen homes where the street has pushed the driveway, which in turn has pushed the garage off its foundation. One way to protect your investment is to install an expansion barrier.

(Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home-improvement questions at PO Box 268, Evansville, IN 47702 or send him e-mail at d.barnett@insightbb.com.)