In concrete pavement contraction design (CPCD), the following distresses require FDR:
- transverse cracks due to temperature/moisture variations and/or wheel load stress that extend through the depth of a slab (but not plastic shrinkage cracks which occur when the rate of evaporation from the surface exceeds the rate at which the bleed water is available – the depth of plastic shrinkage cracks is limited to about 1 to 2 inches from the surface), where load transfer efficiency has been significantly degraded
- shattered slabs and corner breaks
In continuously reinforced concrete pavement (CRCP), the following distresses require FDR:
Transverse cracks in CPCD that extend through the depth of a slab are caused by improper slab lengths and deficient slab thickness (design issues), concrete with high coefficient of thermal expansion or modulus (materials issues), or non-uniform or insufficient base support (construction issues). Shattered slabs and corner breaks result from insufficient slab thickness (design issue) and base support (design/construction issue). Punchouts in CRCP are caused by excessive wheel loading applications and insufficient structural capacity of the CRCP, such as deficient slab thickness (design issue) or subbase support (design/construction issue). It is manifested by block(s) of concrete connected by transverse and longitudinal cracks, where the block(s) are depressed. Typically, longitudinal steel at the transverse cracks of the punchouts eventually ruptures. Punchouts are the most serious distress type in CRCP. Figure 1 shows typical punchouts. Note the asphalt patch was applied to restore the surface elevation, implying that the concrete block was pushed into the subbase.
Spalling is another distress type in CRCP. Spalling is the breaking, chipping, or fraying of concrete at the cracks. There are several causes for spalling. Spalling may be more prevalent when certain types of coarse aggregates are used. The depth of spalling varies widely, from less than half an inch to as deep as half the slab thickness. Shallow spalling causes functional rather than structural problems in PCC pavement. However, deep spalling cause substantial structural damage to the pavement and requires FDR. Figure 2 shows deep spalling. It was confirmed that the spalling extended to the middle of the slab.
Unlike punchouts, it’s not easy to distinguish deep versus shallow spalling. Non-destructive testing using ground penetrating radar (GPR) or low-strain seismic devices such as the portable seismic pavement analyzer (PSPA) can be used to evaluate spall depth. Alternatively, coring may be used.
Original article content and pictures contributed by TxDOT.