Causes of PCC Distress
The following table summarizes the types of distresses that may be identified during a PCI survey of PCC pavements, as well as brief descriptions and probable causes of each distress type.
| Distress Type | Distress Description | Probable Cause of Distress |
|---|---|---|
| Alkali-Silica Reaction (ASR) | Pattern cracking and breakdown of the PCC due to an internal chemical reaction. | Chemical reaction between silica compounds in the aggregate and alkalis from the cement. The reaction releases a gel that swells significantly when wet; leading to cracking of the surrounding concrete. |
| Blowup | Upward movement and pavement breakdown at a joint or crack. | Expansive forces caused by incompressible materials in joints or cracks. |
| Corner Break | A crack across the corner of a slab. Must be located all within one-quarter of the slab or it is an LTD crack. | Load repetition combined with loss of support and curling stresses. |
| Durability Cracking | Pattern of fine cracks and disintegration, close to and predominantly parallel to joints. | Concrete’s inability to withstand environmental factors such as freeze-thaw cycles. |
| Faulting/Settlement | Vertical displacement across a joint. | Upheaval or consolidation. |
| Joint Seal Damage | Joint seal no longer prevents water and incompressible material from entering the joint. | Stripping of joint sealant, extrusion of joint sealant, weed growth, hardening of the filler (oxidation), loss of bond to the slab edges, or absence of sealant in joint. |
| Longitudinal, Transverse, and Diagonal (LTD) Cracking | A crack that divides a slab into two or three pieces, which does not fit entirely into one-quarter of the slab. | Combination of load repetition, curling stresses, and shrinkage stresses. |
| Patching (Small and Large) | Removal and replacement of material to repair distresses or for utility cuts. Size break between large and small is 5 sf (1.5 m). | A patch is often used to repair pavement distresses, or repair the pavement after a utility cut has been made. |
| Popouts | Small holes in the concrete surface caused by expansion and loss of individual aggregate particles. | Freeze-thaw action in combination with expansive aggregates. |
| Pumping | Water, soil, and fine particles from base material pushed up through joint or cracks. | Poor drainage and/or poor joint sealant. |
| Scaling | Surface deterioration unrelated to durability cracking or ASR. | Overfinishing of concrete, deicing salts, improper construction, freeze-thaw cycles, or poor-quality aggregate. |
| Shattered Slab | Slab divided into three or more pieces by structural cracking. | Load repetition. |
| Shrinkage Cracking | Cracks that do not progress across the entire slab (and not caused by durability cracking or ASR); includes map cracking if there is no scaling. | Setting and curing of the concrete. |
| Spalling (Joint and Corner) | Breakdown of the pavement at a joint or corner. | Excessive stresses at a joint caused by infiltration of incompressible materials or traffic loads; weak concrete at joint combined with traffic loads. |