PIC Lift Thickness & Surface Tolerance 3 — Questions and Answers
Question 1: AASHTO and most state DOTs specify that the maximum particle size in a hot mix asphalt lift should not exceed what fraction of the compacted lift thickness?
- One-half (Correct answer)
- Two-thirds
- Three-quarters
- The full lift thickness
Correct answer: One-half
Maximum aggregate size must not exceed one-half the compacted lift thickness to prevent bridging and ensure uniform compaction through the full depth.
Question 2: An inspector observes that a 2-inch wearing course lift is being placed over a base course with 0.5-inch surface irregularities. What is the likely consequence for surface tolerance?
- The wearing course will self-level and meet tolerance
- The irregularities will telegraph through, causing out-of-tolerance finished surface (Correct answer)
- Compaction will eliminate the irregularities
- Tack coat will bridge the surface variations
Correct answer: The irregularities will telegraph through, causing out-of-tolerance finished surface
Surface irregularities in underlying courses telegraph through thin lifts because the paver screed follows the existing surface, reproducing variations in the finished mat.
Question 3: What is the primary purpose of a profilograph or inertial profiler in pavement inspection?
- Measuring lift thickness during placement
- Evaluating longitudinal surface smoothness after compaction (Correct answer)
- Determining in-place density of the compacted mat
- Checking transverse cross-slope grade
Correct answer: Evaluating longitudinal surface smoothness after compaction
A profilograph or inertial profiler measures the longitudinal profile of the pavement surface to quantify ride quality and identify areas exceeding smoothness tolerance.
Question 4: International Roughness Index (IRI) is expressed in units of:
- Inches per mile
- Millimeters per kilometer (Correct answer)
- Feet per 100 feet
- Slope variance per mile
Correct answer: Millimeters per kilometer
IRI is expressed in millimeters per kilometer (or equivalently inches per mile), representing the accumulated suspension travel of a reference vehicle per unit distance.
Question 5: A specification requires a base course compacted thickness of 3.0 inches with a tolerance of –0.5 inch. A core shows 2.4 inches. This result:
- Is acceptable since it is within 10% of design
- Fails the specification because it is below the minimum allowable 2.5 inches (Correct answer)
- Must be averaged with adjacent cores before a decision
- Passes if density meets spec
Correct answer: Fails the specification because it is below the minimum allowable 2.5 inches
The minimum allowable thickness is 3.0 – 0.5 = 2.5 inches; a core measuring 2.4 inches is deficient and fails the thickness specification regardless of density.
Question 6: Why is it critical that each lift be fully compacted before the next lift is placed?
- To allow the binder to cure and harden completely
- To prevent shoving of the lower lift under paver load and ensure stable support (Correct answer)
- To meet cooling time requirements for tack coat adhesion
- To reduce thermal cracking in cold weather
Correct answer: To prevent shoving of the lower lift under paver load and ensure stable support
An uncompacted lower lift can shove or rut under paver and roller loads from the subsequent lift, resulting in unstable support and non-uniform thickness in both layers.
Question 7: When cores are taken to verify lift thickness on a project, the minimum number of cores per lot as specified by many state DOTs is typically:
- 1 core per 1,000 tons
- 3 to 5 cores per sublot or per day (Correct answer)
- 10 cores per lane mile
- 1 core per truck load
Correct answer: 3 to 5 cores per sublot or per day
Most state DOT specifications require 3 to 5 cores per sublot or per day's production to provide a statistically representative sample of lift thickness.
PIC Lift Thickness & Surface Tolerance 3
AASHTO and most state DOTs specify that the maximum particle size in a hot mix asphalt lift should not exceed what fraction of the compacted lift thickness?