Rigid (Portland Cement Concrete) Pavement
Joints and load transfer
Rigid pavement performance is mostly a story about joints. Transverse contraction joints control cracking and are sawed to roughly one-quarter of the slab thickness, inside a sawing window: too early and the saw ravels the concrete, too late and the slab cracks randomly. Dowel bars are smooth, coated bars that transfer load across transverse joints; tie bars are deformed bars that hold longitudinal joints tight and keep lanes from separating. Never let a question swap those two. A useful rule of thumb for joint spacing is 24 to 30 times the slab thickness in inches, expressed in feet - a 9-in slab gives 18 to 22.5 ft, so a 20-ft spacing is reasonable.
Concrete placement and acceptance
Check subbase grade and smoothness, form line and grade or slipform stringline, reinforcement position and cover, and embedment of dowels before paving. During placement monitor slump, air content (critical for freeze-thaw durability), concrete temperature, and consolidation. Curing follows immediately - curing compound at the specified rate on a properly finished surface, or wet cure for the specified duration. Acceptance covers thickness (cores or formed edges), strength (compressive cylinders or flexural beams), smoothness, and surface texture such as tining. Opening to traffic waits for the specified strength.
Traps
Cylinders must be field-cured the same way the pavement cures if they are to represent the slab. Curing compound applied to a bone-dry surface or at half rate fails quietly. Sealant reservoirs must be dry and correctly shaped, not simply filled.
Worked example: specify the transverse joint spacing for a 9-in slab. 9 × 24 = 216 in = 18 ft; 9 × 30 = 270 in = 22.5 ft. Choose a spacing in that range, typically 20 ft, and keep it uniform.