What is Joint Spalling?
Joint spalling is the cracking, breaking, chipping or fraying of the edge of a concrete slab next to a joint. It occurs in jointed concrete pavements, on both transverse and longitudinal joints.
FAA AC 150/5380-6C defines it as the breakdown of the slab edge within 2 feet (0.6 m) of the joint. The FHWA Long-Term Pavement Performance (LTPP) manual uses a narrower zone of 0.3 m. A joint spall usually does not go through the full slab thickness. It meets the joint at an angle.
Causes
AC 150/5380-6C names these causes:
- Excessive stress at the joint, caused by soil or stones that collect in the joint and stop the slabs from expanding.
- Weak concrete at the joint, caused by overworking, combined with traffic loads.
- Dowels that are misaligned or do not slip, because of poor placement or poor preparation.
Table 6-2 of the same AC also lists snow plow damage. Joint seal damage lets incompressible material into the joint, and AC 150/5380-6C says this may result in spalling.
How it is rated
The two systems use different criteria.
- FHWA LTPP (JCP 6 and JCP 7). Severity depends on the width of the spall, measured to the joint face. Low is less than 75 mm. Moderate is 75 to 150 mm. High is more than 150 mm. A spall in two or more pieces, or one that contains patch material, is also high. For longitudinal joints, the inspector records the length of joint affected. For transverse joints, the inspector records the number of affected joints. A transverse joint counts as affected when spalling covers 10 percent or more of its length.
- FAA PAVER (distress 74). Severity depends on the spall length (shorter or longer than 2 feet), the number of pieces, and the FOD or tire damage potential. A spall on one edge counts as one slab with joint spalling. A spall small enough to fill during joint resealing is not recorded.
Joint spalling is one of the distresses in the Structural Condition Index (SCI) in AC 150/5320-6G.
Repair
AC 150/5380-6C gives two repairs. For a small spall, remove the loose material, fill with an approved product and reseal the joint. For a larger spall, make a partial-depth repair. The repair keeps the joint open through the full depth of the patch, and the joint is resealed after the patch is placed.
Frequently Asked Questions
- What causes joint spalling?
- Three causes are named in FAA AC 150/5380-6C. Soil or stones in the joint stop the slabs from expanding, so the joint edge takes excessive stress. Weak concrete at the joint, caused by overworking it, breaks under traffic loads. Dowels that are misaligned or do not slip also cause spalling. Snow plow damage is a further cause in the same AC, in its Table 6-2.
- How do the FAA and FHWA rate joint spalling?
- They use different criteria. The FHWA LTPP manual rates the spall width. Less than 75 mm is low, 75 to 150 mm is moderate and more than 150 mm is high. The FAA PAVER manual rates the spall length, the number of pieces and the potential for foreign object debris (FOD) or tire damage.
- How is a joint spall repaired?
- For a small spall, remove the loose material, fill with an approved product and reseal the joint. A larger spall gets a partial-depth repair. FAA AC 150/5380-6C Appendix A8 gives the steps. They include vertical saw cuts at least 2 inches (5 cm) deep, about 3 inches (8 cm) outside the spall.
- Is a joint spall the same as a corner break?
- No. A joint spall usually does not go through the full slab thickness and meets the joint at an angle. A corner break goes vertically through the slab. FAA AC 150/5380-6C makes this distinction for corner spalling and corner breaks.
References
- faa-ac-150-5380-6c
- AC 150/5380-6C, Guidelines and Procedures for Maintenance of Airport Pavements FAA
- faa-paver-concrete
- PAVER Distress Identification Manual, Concrete Surfaced Airfields FAA / U.S. Army Corps of Engineers
- fhwa-ltpp-dim
- Distress Identification Manual for the Long-Term Pavement Performance Program, Fifth Revised Edition (FHWA-HRT-13-092, revised May 2014) FHWA
- faa-ac-150-5320-6g
- AC 150/5320-6G, Airport Pavement Design and Evaluation FAA
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