Pavement Structural Evaluation at the Network Level: Final Report

Section 508 Captions

Figure 5. Flowchart. Idealized approach to successful accomplishment of project's objectives. This figure shows a flowchart of an idealized approach to the successful accomplishment of the project's objectives. Five major activities are identified in the left section of the flowchart. Item 1 is to establish pavement structural condition threshold values. Under item 1, there are six steps which include (1) define typical categories of pavements (e.g., flexible pavement with thick hot mix asphalt (HMA) representing interstate highways); (2) define modes of failure (e.g., alligator cracking of HMA); (3) establish ranges of pavement structures; (4) Define structural-related responses that causes each failure mode (e.g., tensile strain at bottom of HMA); (5) Select candidate deflection basin parameters (e.g., Surface Curvature Index (SCI)); and (6) define threshold value for each structural-related response (e.g., 100 microstrain). Item 2 is to relate structural-related responses to deflection parameters measured with high-speed deflection devices (TSDDs). Under item 2, there are five steps which include (1) select a validated numerical model that predicts structural-related responses and the TSDD-measured parameters (e.g., 3D-Move); (2) carry out a numerical study to understand TSDD estimated deflection-parameters; (3) evaluate feasibility of estimating candidate deflection basin parameters from TSDD measured parameters; (4) establish sensitivity of each structural-related responses to each TSDD index (e.g., tensile strain at bottom of HMA to TSD SCI) for each pavement category; and (5) select most sensitive TSDD indices for further considerations. Item 3 is to establish ideal measurement characteristics for TSDDs (from items 1 and 2). Under item 3, there are five steps which include (1) numerically establish the minimum and maximum likely values of each deflection parameter for each pavement category; (2) compare the minimum and maximum deflection parameters with each TSDD sensor specification; (3) numerically establish the minimum and maximum likely values of critical stresses/strains anticipated from each TSDD; (4) establish the desired precision of the TSDD parameters; and (5) establish the desired accuracy of the TSDD parameters. Item 4 is to evaluate TSDDs under different operational conditions and pavement structures. Under item 4, there are four steps which include (1) carry out a field evaluation plan to establish accuracy of TSDDs; (2) carry out a filed evaluation plan to establish precision of TSDDs; (3) establish operational limitations of TSDDs; and (4) validate 3D-Move using Minnesota's Cold Weather Pavement Testing Facility (i.e., MnROAD) data. Item 5 is determining the best strategies for implementing TSDDs in network-level evaluation. Under item 5, there are four steps which include (1) recommend appropriate (most sensitive to structural pavement condition) TSDD index; (2) recommend optimal operational parameters for the TSDDs; (3) recommend the most appropriate algorithm for structural condition assessment; and (4) draft necessary protocols.

Back

Figure 186. Graph. Variation of maximum horizontal strain at bottom of AC layer in simulated pavement combinations. This bar graph shows the variation of maximum horizontal strain at the bottom of the asphalt concrete (AC) layer in the simulated pavement combinations. The y-axis shows maximum horizontal strains at bottom of AC from 0 to 0.0003 strain, and the x-axis includes 36 simulated pavement combinations. These combinations includes three AC thicknesses (3, 6, and 12 inches (76.2, 152.4, and 304.8 mm)) with three moduli (200, 500, and 800 ksi (1,378, 3,445, and 5,512 MPa)), two subgrade moduli (10 and 20 ksi (68.9 and 137.8 MPa)), and two speeds (30 and 60 mi/h (48.3 and 96.6 km/h)). The maximum horizontal strain for the combinations with an AC thickness of 3 inches (76.2 mm), an AC moduli of 200 ksi (1,378 MPa), and a subgrade modulus of 10 ksi (68.9 MPa) at 30 and 60 mi/h (48.3 and 96.6 km/h) is about 0.00026 strain, while the combinations with the same specifications except subgrade moduli of 20 ksi (137.8 MPa) is 0.00028. The same trend is observed for other combinations with an AC modulus of 3 inches (76.2 mm). It was concluded that in the combinations with thin AC (3 inches (76.2 mm)), when subgrade modulus increases, the strain increases. Maximum horizontal strain for the combinations with an AC thickness of 3 inches (76.2 mm), AC moduli of 200 ksi (1,378 MPa), and subgrade moduli of 10 ksi (68.9 MPa) at 30 and 60 mi/h (48.3 and 96.6 km/h) is about 0.00026 strain, while the combinations with the same specifications except AC thickness of 6 inches (152.4 mm) is 0.0002. The same trend is observed for other combinations when AC thickness increased. It was concluded that when AC thickness increases, the strain decreases. Maximum horizontal strain for the combinations with an AC thickness of 3 inches (76.2 mm), AC moduli of 200 ksi (1,378 MPa), and subgrade moduli of 10 ksi (68.9 MPa) at 30 and 60 mi/h (48.3 and 96.6 km/h) is about 0.00026 strain, while the combinations with the same specifications except AC modulus of 500 ksi (3,445 MPa) is 0.00022. The same trend was observed for other combinations when AC modulus increased. It was concluded that when AC modulus increases, the strain decreases.

Back

Figure 187. Graph. Variability of relationships of R1 with maximum horizontal strain at bottom of AC layer for various AC thicknesses. This bar graph shows the variability of relationships between radius of curvature (R1) with maximum horizontal strain at the bottom of the asphalt concrete (AC) layer for various AC thicknesses. The y-axis shows the R square value from 0 to 1, and the x-axis shows R1 indices, which include R1 subscript 8, R1 subscript 12, R1 subscript 18, R1 subscript 24, R1 subscript 36, R1 subscript 48, and R1 subscript 60. The R square value for the R1 indices is shown for four datasets: all data points with 36 data points, AC thickness of 3 inches (76.2 mm) with 12 data points, AC thickness of 6 inches (152.4 mm) with 12 data points, and AC thickness of 12 inches (304.8 mm) with 12 data points. For all data points, the R square value varies from 0.87 to 0.96, and all indices except R1 subscript 60 have R square values greater than 0.9; however, no value is shown for R1 subscript 8. For AC thickness of 3 inches (76.2 mm), the R square value varies from 0.21 to 0.93, which show drastic changes. The values are available only for three indices (R1 subscript 8, R1 subscript 12, and R1 subscript 18), and only R1 subscript 8 has an R square value greater than 0.9. For AC thickness of 6 inches (152.4 mm), The R square value varies from 0.36 to 0.98, and four indices have R square values greater than 0.9 (R1 subscript 8, R1 subscript 12, R1 subscript 18, and R1 subscript 24). Finally, for AC thickness of 12 inches, The R square value varies from 0.90 to 0.99; however, no value is shown for R1 subscript 8.

Back