Presentation on theme: "Oklahoma DOT Perpetual Pavement Test Sections at the NCAT Test Track."— Presentation transcript:
Oklahoma DOT Perpetual Pavement Test Sections at the NCAT Test Track
Perpetual Pavement Structure and materials are designed to provide a long service life (50 years +)
Early Texas Perpetual Pavements 1.5 PFC 2.0 SMA mm SP mm SP mm 2% air voids 6.0 crushed stone 3.0 SMA mm SP mm SP mm 2% air voids Waco Cotulla McAllen 10.0, 19 mm or 25 mm SP mm 2% air voids 1.5 PFC 2.0 SMA 8.0 lime-treated salvaged aggregate
1.5 PFC 2.0 SMA mm SP mm SP mm 2% air voids 6.0 crushed stone 3.0 SMA mm SP mm SP mm 2% air voids Waco Cotulla McAllen 10.0, 19 mm or 25 mm SP mm 2% air voids 1.5 PFC 2.0 SMA 8.0 lime-treated salvaged aggregate 20.5 Total HMA 16 Total HMA 16.5 Total HMA
How thick is too thick? Cost of 5 Miles of Pavement Assume 80 width, $50 per ton Save 1 in over-design: $650,000 Save 2 in over-design: $1,300,000 Save 4 in over-design: $2,600,000
How thin is too thin? If the perpetual pavement structure is designed too thin, the risk of bottom-up cracking increases dramatically, defeating the purpose of the design and resulting in an expensive rebuild.
To design the appropriate pavement thickness, stresses and strains Max Flexural Strain Pavement Foundation High Modulus Rut Resistant Material (Varies As Needed) } 3to6 High Shear Zone in. PFC, SMA, etc. To design against potential bottom-up cracking, certain strain thresholds cannot be exceeded.
Limiting Strain Theory Based on laboratory beam fatigue data Small strains will never induce cracking Limiting strain at 75 to 125 microstrains No bottom-up cracking below this level
These strains can be calculated based on total pavement thickness and material properties. However, the calculations would be based on assumptions made from previously collected data.
There are large deviations in the types of environment around the country, the types of materials used and the types of pavement specified. These deviations decrease the reliability of the assumptions made to calculate strains. If the strains could be measured directly, using Oklahoma materials and mix designs, the data would be much more reliable. Estimated Strain
National Center for Asphalt Technology (NCAT) Test Track
ODOTS PERPETUAL PAVEMENT STRUCTURAL SECTIONS AT NCAT TEST TRACK PLAN VIEW SECTION N8 – 150 SECTION N9 – TRANSITION 50 TRANSITION 25 TRANSITION
Max Flexural Strain Pavement Foundation High Modulus Rut Resistant Material (Varies As Needed) in. PFC, SMA, etc. The maximum flexural strain is directly measured using a series of strain gauges installed at the bottom of the asphalt section.
MICROSTRAIN ? If we have determined the strain for a 10 and 14 thick pavement, the thickness at the critical strain level can be interpolated / extrapolated
Instrumentation – N8
Accelerated Loading Compress years into 2 years Heavy triples optimize safety and efficiency Each axle loaded to federal legal bridge limit Heavier loads induce unrealistic damage No bridge spans to overload on NCAT track Average gross vehicle weight 155k pounds
Long Term Response Measurements Weekly - three passes of 5 trucks –Steer axle (12 kip), tandem (40 kip), 5 single axles (20 kip/axle) –45 MPH Measure strain Measure pressure Measure temps Characterize long-term trends in strain response
To design the appropriate pavement thickness, stresses and strains Max Flexural Strain High Modulus Rut Resistant Material (Varies As Needed) Vertical Compressive Strain in. PFC, SMA, etc. The vertical compressive strain is directly measured using pressure plates installed at the top of the subgrade.
Moisture sensors were also placed in the subgrade to continuously monitor soil conditions
Temperature probes were placed in the pavement to continuously monitor temperature at various depths
A datalogger is used to collect information from the different pavement sensors. In addition to the normal slow speed mode that continuously gathers data, a high speed mode can be used to collect 40,000 data points per second.