Investigation of Joint Spalling on Concrete Runway

During 2 days in October 1994, 4-month-old concrete on a runway developed extensive spalling along transverse joints. Damage was extensive, limited to transverse joints; was located in trafficked areas only; and developed only after the beginning of freezing weather. An investigation into possible causes of this spalling concluded that the concrete probably developed a network of microcracks from premature loading before the concrete had gained adequate strength. The concrete continued to gain strength with time and these cracks were not sufficient to cause spalling. Later, moisture accumulated in the cracks froze, which propagated the original cracking to free the spall fragments. The most likely cause of the original inadequate strength gain was probably poor curing of the concrete in the vicinity of the transverse joints caused by damage to the curing compound membrane during initial sawing of transverse contraction joints. Alternate explanations of the damage were unable to account for all of the observed characteristics of the damage. The remaining concrete is essentially sound, and permanent repair of the runway requires only patching of the spalled areas.