PAVEMENT EVALUATIONS provide important information about asphalt concrete (HMA) performance and service life. They determine an existing pavement’s structure, confirm its structural adequacy and help determine why it failed and how it will perform with various maintenance alternatives. Pavement evaluations are invaluable in determining the best and most economical pavement design and rehabilitation approach based on an annual cost analysis.
There are two components to a pavement evaluation: physical evaluation and visual evaluation.
A pavement evaluation uses two test methods to determine a pavement system’s structural capacity and its ability to handle the stresses created by repetitive traffic loads. Each test method provides slightly different data depending on the pavement materials, layer thicknesses and moisture contents, data that is essential for high performing, long-lasting pavement.
The first is deflection testing, a non-destructive method of evaluating a pavement’s flexibility, the resilience of structural layers, and how it has been affected by the type and volume of traffic as well as the effects of temperature and moisture. Although there are several different testing devices, the goal is to measure the total deflection from a load applied on the surface of the pavement. Typically, a generator applies a vertical oscillating force on a pavement section and the motion-sensor measures the magnitude of deflection. PEI uses California Test Method 356 (CTM 356).
The second is core testing, which determines how well a foundation distributes repetitive stresses caused by traffic. Coring measures existing pavement thicknesses and determines the type of native soils that form a pavement’s subgrade or structural foundation.
On existing pavement, core samples are taken about every 500 feet and separated into layers. The subgrade or foundation layer, primarily composed of native soils or a combination of soil and aggregate, is tested by applying a vertical pressure to determine how well the fully moisture-saturated soil sample resists deforming under stresses representative of heavy wheel loads. The resulting data is referred to as the R-value, or resistance value, which fixes or determines the depth of the subgrade necessary to support the aggregate base and asphalt concrete surface layer in order to carry the expected amount of traffic and wheel loads. When used in pavement design, the R-value helps determine the required thickness of foundation layer for the expected traffic conditions. PEI tests R-values using California Test 301, ASTM Test D2844 or AASHTO Test T190.
Once test data are gathered and analyzed, PEI visually evaluates the pavement for fatigue characteristics such as raveling, transverse and longitudinal or block cracking, and alligator cracking. The visual evaluation focuses not just on pavement condition but also on factors that affect performance, including site drainage, water sources from roof drains and landscaping, tree roots, and loading conditions from trucks, buses, garbage trucks or other heavy wheel loads. The visual evaluation also can include an optional compliance review for ADA parking and access or an assessment of sitework concrete for potential liability concerns. All this information is then analyzed to develop a customized multi-year maintenance plan that allows clients to plan and budget for current and future pavement maintenance.