CRACKS IN CONCRETE DRIVEWAYS

Most of us get colds, and most concrete cracks. We go about our business in spite of the colds, and concrete goes about its business in spite of the cracks. But we'll all agree that colds and cracks are both things to avoid.

Cracks in concrete driveways are usually misunderstood by home owners, and sometimes by home builders. They're often seen as a concrete failure. Too many slabs have been repaired, or removed unnecessarily because of a lack of knowledge concerning cracks.

PLASTIC SHRINKAGE CRACKING (FRESH CONCRETE)

Cause - rapid loss of moisture from the surface while the concrete is still plastic, often before it is even finished.

CONTRIBUTING FACTORS - wind and low humidity most important; also high concrete temperature in relation to air temperature. PREVENTION - minimize rapid evaporation by use of wind breaks, fog sprays, mono-molecular films, etc. Schedule placement for early morning. Avoid placing concrete directly on a vapor barrier. Apply membrane cure immediately after finishing.

EFFECT ON SERVICEABILITY - PROBABLY NONE. After weathering and normal surface wear the cracks will probably be less visible than when they first occurred.

SURFACE CRAZING CAUSE - rapid loss of moisture from a surface with high shrinkage potential during eary hardening.

CONTRIBUTING FACTORS - excess water and fines brought to the surface during placement; early troweling; late application of curing or no curing. PREVENTION - minimize finishing operations, as they increase the amount of fines brought to the surface. Troweling is not a recommended finish for driveways - a broom finish is preferred. Apply membrane cure immediately after finishing.

EFFECT ON SERVICEABILITY - PROBABLY LITTLE OR NONE. Under heavy traffic, some surface wear might occur; with light traffic, there is little chance of any problem.