Investigation of Backcalculated Moduli Using Deflections Obtained at Various Locations in a Pavement Structure

The AASHTO pavement design model is one of the most widely used empirical design models for flexible pavement design. A factor complicating its utility is the use of an abstract quality, the structural number (SN), to quantify the strength of the total pavement structure. A consequence of the use of SN is the need for structural layer coefficients to characterize the component materials of the pavement structure. These layer coefficients are difficult to assess directly. However, a method for determination of layer coefficients with a falling weight deflectometer (FWD) that are representative of the in situ behavior of the pavement materials is presented. This method is based on a model provided in the 1993 edition of the AASHTO Guide for Design of Pavement Structures for assessment of the effective SN. The Vermont Agency of Transportation (VTrans) has established a procedure that uses FWD data and the AASHTO effective SN model to characterize layer coefficients for Vermont pavement materials. VTrans found that the layer coefficients determined for unbound subbases were reasonable, whereas layer coefficients estimated for asphalt cement concrete materials were generally 25 to 35 percent higher than AASHTO’s implied maximum of 0.44. However, a statistical analysis indicates considerable support for the predictive qualities of FWD-derived layer coefficients to approximate the in situ layer coefficients estimated by an elastic layer simulation.

“…), p = loading plate pressure applied by the FWD (lbf/in. 2 ), a = loading plate radius (in. ), D = depth of the pavement structure (in.…”

Section: Aashto Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Procedure for Use of Falling Weight Deflectometer to Determine AASHTO Layer Coefficients

Pologruto¹

2001

“…It is capable of evaluating HMA pavement structure containing up to five layers. The program uses an iterative approach to find a set of moduli that would provide a calculated deflection basin closest to the measured deflection basin as characterized by the root-mean-square (RMS) error (5).…”

Section: Backcalculation Of Hma Modulusmentioning

confidence: 99%

Comparison of Moduli of Kansas Superpave Asphalt Mixes

Gedafa

Hossain

Romanoschi

et al. 2010

Currently, hot-mix asphalt (HMA) mixture design and pavement structural design are not fully integrated, although Superpave® asphalt mixture design is somewhat project specific. The objective of this study was to compare elastic moduli assumed during structural design of pavements with the backcalculated moduli of HMA layers obtained from the falling weight deflectometer (FWD) tests and the dynamic modulus values measured in the laboratory. Five newly built Superpave pavements, designed by using the 1993 AASHTO Design Guide, were selected as study sites in this research. Deflection data were collected with a Dynatest 8000 FWD on a 1,000-ft test section at each site. The HMA layer moduli were then backcalculated by using an elastic-layer analysis program. Full depth cores were taken from each section and tested in the laboratory for dynamic moduli. The results showed that backcalculated and laboratory moduli were somewhat comparable for all practical purposes. The laboratory dynamic moduli increased with the loading frequency, indicating the need for consideration of vehicle speeds in the HMA pavement structural design. HMA design moduli, assumed by the Kansas Department of Transportation during pavement structural design, are lower than both backcalculated and laboratory dynamic moduli. Thus, current HMA design moduli are achievable in the field through Superpave mixture design, despite the fact that the pavement structural design and mix design processes are not integrated.

“…In the quality-control and -assurance procedure, long pavement sections are divided into homogeneous segments, and FWD tests are conducted on each layer of the segments at intervals of 10 to 20 m. Statistical tests are conducted on measured deflections in order to evaluate the construction quality as well as to identify weak points. Zhou et al additionally suggested that the coefficient of variation (COV) of the measured deflection be calculated for each homogeneous segment in order to evaluate the uniformity of construction (7).…”

Section: Deflection and Stiffness Target Valuesmentioning

confidence: 99%

Quality Assessment During Road Formation and Foundation Construction: Use of Falling-Weight Deflectometer and Light Drop Weight

Livneh

Goldberg²

2001

Mechanistic empirical-based specifications, which focus on the mechanical properties of materials, facilitate quantitative evaluations of alternative construction practices and materials such as reclaimed materials. Thus, to represent these mechanical properties, quality-control and-assurance testing would be expected to include stiffness along with density measurements. In two case studies, a falling-weight deflectometer (FWD) was used during the construction of two major interchanges in Israel. FWD testing was found to be very useful in identifying local spots with poor performance, thus enabling execution of the required remedy actions. The two studies also indicated that, for a given feature, both a representative central deflection at the 95 percent reliability level and a coefficient of variability of measured deflections may serve as potential quality-control indicators. The possible use of the German light dropweight (LDW) device for measuring the mechanical properties of the formation of flexible pavements was also examined. Based on the cost per test, rate of testing, and quality of the data, the German LDW can serve as a cost-effective testing device for quality control and assurance during subgrade and capping-layer compaction.