A continuously reinforced concrete pavement is designed to carry 9x106 ESAL on the design lane over the design period. The Portland cement concrete has a 28-day compressive strength of 4000 psi and a modulus of rupture (Sc) at 28 days of 600 psi. The load transfer coefficient (J) is 3.
The concrete pavement will be placed on top of a 8-inch cement-treated subbase with a modulus of 750,000 psi. The drainage is good and the subbase is subject to moisture level near saturation 5% of the time. The resilient modulus of the subgrade is 8,000 psi and a geological study showed that there is rock (rigid foundation) 10 ft below the surface. [Use R=0.95, so=0.3, PSIi=4.5, and PSIt=2.5.]
A. Compute the effective composite modulus of subgrade reaction (please consider the subbase, the presence of a relatively shallow rock foundation, and the potential loss of support).
B. Determine the thickness of slab required to the nearest ¼ in.
C. Design the longitudinal reinforcement using No. 5 bars (determine the bar spacing) using the crack width criterion only. The magnitude of the wheel load due to construction traffic is 20,000 psi, concrete shrinkage is 0.0004 in/in, thermal coefficient of steel is 5x10-6in/in/oF, thermal coefficient of concrete is 4x10-6in/in/oF, and the design temperature drop is 60oF.
D. What is the average crack spacing for that reinforcement?