Q: What causes spalling in concrete parking lots?
A: Spalling can occur after stones, dirt, and debris get into joints when they are open. Then, when the joints attempt to close in hot weather, localized resistance causes breakage. As these cycles are repeated, spalling at joints can become extensive. Non-air-entrained concrete that is repeatedly exposed to deicing salts or to freeze/thaw cycles in the saturated condition also can exhibit spalling.
To avoid problems with spalling, provide joints of proper design and spacing, seal joints using good materials, use air-entrained concrete that is properly cured, and refrain from applying deicers during the first winter.