A Rigid Pavement
1. A rigid pavement is on a highway with two lanes in one direction, and the pavement is conservatively designed. The pavement has an 11-inch slab with a modulus of elasticity of 5,000,000 lb/in2 and a concrete modulus of rupture of 700 lb/in2, and it is on a soil with a CBR of 25. The design drainage coefficient is 1.0, the overall standard deviation is 0.3, and the load transfer coefficient is 3.0. The pavement was designed to last 20 years (initial PSI of 4.7 and a final PSI of 2.5) with 95% reliability carrying trucks with one 18-kip single axle and one 28-kip tandem axle. However, after the pavement was designed, one more lane was added in the design direction (conservative design still used), and the weight limits on the trucks were increased to a 20-kip single and a 34-kip tandem axle (the slab thickness was unchanged from the original two-lane design with lighter trucks). If climate change has caused the drainage coefficient to drop to 0.8, how long will the pavement last with the new loading and the additional lane (same volume of truck traffic)?
2. A four-lane northbound section of interstate has rigid pavement and was designed with an 8-inch
slab, 90% reliability, a 700 lb/in2 concrete modulus of rupture, a 5 million lb/in2 modulus of elasticity, a 3.0 load transfer coefficient, and an overall standard deviation of 0.3. The initial PSI is 4.6 and the TSI is 2.5. The pavement was conservatively designed (assuming the upper limit of the W18 design lane load) to last 20 years, and the CBR is 25 with a drainage coefficient of 1.0. A design mistake was made that ignored 1000 total northbound (daily) passes of trucks with 22-kip single and 30-kip tandem axles. What slab thickness should have been used?
3. A flexible pavement is designed with 4 inches of an experimental asphalt wearing surface that has a structural layer coefficient of 0.575, with 4 inches of a hot-mix asphaltic base, and 10 inches of a crushed stone subbase (all drainage coefficients are 1.0). The roadway is designed to accommodate 200 delivery trucks per day and each truck has one 12-kip single front axle and one 20-kip single rear axle. The subgrade CBR is 8, the initial present serviceability index is 4.5, the TSI is 2.5, and the overall standard deviation is 0.5. How confident would you be that this pavement would last 20 years?
4. suppose that a rigid pavement was designed with a 12-inch slab (modulus of rupture of 900 lb/in2, modulus of elasticity of 6.0 × 106 lb/in2, load transfer coefficient of 3.2, and drainage coefficient of 1.0) for the four-lane northbound direction described in Practice Problem 4.4 (all other traffic and PSI information is the same as in that problem). How confident would you be that this rigid pavement would have a PSI above 2.5 after 20 years?
5. A rigid pavement on a multilane highway (two lanes each direction) has been conservatively designed (for its design-lane traffic). The pavement engineer uses an 11-inch slab, Ec of 4 × 106 lb/in2, a concrete modulus of rupture of 695 lb/in2, a load transfer coefficient of 2.8, an initial present serviceability index of 4.2, and a TSI of 2.5. The overall standard deviation is 0.6, the subgrade CBR is 20, and the drainage coefficient is 1.0. The pavement was designed for four hundred 30,000 lb triple axles, nine hundred 20,000 lb tandem axles per day, and twelve hundred 10,000 lb single axle loads per day. If the pavement was designed to last 40 years, what reliability was used?
