This session highlights the beneficial use of accelerated pavement testing for pavement design in the papers received this year.
Calibration of Asphalt Strain Transducers Using Digital Image Correlation
Thomas Burnham, Minnesota Department of TransportationShow Abstract
Santiago Huerta, Minnesota Department of Transportation
Steven Olson, Minnesota Department of Transportation
Full-scale pavement testing often utilizes embedded instrumentation to measure the effect of traffic loading. As with any scientific measurement, confidence in the data from these sensors relies on proper calibration and installation. Manufacturers of sensors typically perform calibration tests before shipment, but these tests are not standardized. In addition, some manufacturers provide only one calibration sheet covering a batch of sensors, while others provide calibration results for each sensor. Many transducers are calibrated to produce voltage sensitivity factors, however not all data acquisition systems accept these as inputs. This was the case at the MnROAD pavement testing facility, whereby a new data acquisition system required simple gauge factors. This paper describes the development of a bench calibration testing procedure using a digital image correlation system to determine gauge factors for two types of asphalt strain transducers. Calibration results clearly show that each transducer has a unique gauge factor that should be used when transforming raw strain data. No simple correlation could be found between the TGF values determined in this study and the manufacturer supplied sensitivity factors or gauge factors. While the procedure that was developed produced fairly consistent transducer gauge factors between tests, several improvements are recommended. The variations in gauge factors found in this study demonstrate the need to fully understand the calibration of strain transducers and the data acquisition systems they are connected to.
Performance Evaluation of Cracking on Thin Roller-Compacted Concrete Pavements
Moinul Mahdi, Louisiana Transportation Research Center (LTRC)Show Abstract
Xiaohui Sun, LTRC
Zhong Wu, Louisiana Transportation Research Center (LTRC)
Tyson Rupnow, Louisiana Department of Transportation and Development
Roller compacted concrete (RCC) pavement is an economical, fast-paving and durable candidate for many pavement applications. This paper documents the cracking performance of thin RCC-surfaced pavements that may be used as a viable design alternative for low volume highways where heavy and overloaded trucks are often encountered. Six full-scale pavement sections with three RCC thicknesses (4-, 6-, and 8- in.) and two types of stabilized base were tested under an accelerated pavement testing (APT) experiment. Instrumentation, in situ pavement testing and crack-mapping were employed to monitor the load-induced pavement responses and pavement cracking performance. In general, the results indicated that a thin RCC pavement (thickness of 4 to 6 in.) would eventually have a structurally fatigue cracking failure under the repetitive traffic and environmental loading due to a combined effect of pavement cracking and pumping. The visible cracks were first showed up on pavement surface as a single or several fine cracks along the longitudinal traffic direction within the wheel paths. The longitudinal cracks were then extended and gradually propagated to transverse and other directions under the continued loading, and finally merged into a fatigue cracking failure. Post-mortem trenching results showed that the majority of the cracks were bottom-up, but some did show as a top-down. A finite difference pavement model was developed to investigate the mechanistic rationale of the possible longitudinal or transverse cracking initiations happened on thin RCC pavements under loading. The cracking failure of thin RCC pavement was found initiated as a bottom-up cracking at saw-cut joints and subsequently at the bottom of thin RCC slabs. To predict a pavement fatigue service life, the APT field results were used to develop a set of fatigue models of thin RCC pavements. Based on the field forensic results and the finite difference analysis, a cracking development mechanism on thin RCC pavements under loading was presented.
Accelerated Pavement Testing and Finite Element Modeling of Airfield Pavement Under High Tire Pressure Loading
Hao Wang, Rutgers, The State University of New JerseyShow Abstract
Maoyun Li, Rutgers, The State University of New Jersey
Navneet Garg, Federal Aviation Administration (FAA)
This paper aims to investigate airfield flexible pavement responses through an integration of full-scale testing and numerical modeling. Accelerated pavement testing was conducted at the two acceptance test strips using the state-of-art heavy vehicle simulator – airport version (HVS-A) at different loading and tire pressure levels. An advanced three-dimensional (3-D) finite element (FE) model was developed to predict pavement responses for the testing section. The FE modeling results agreed well with full-scale testing results when the nonlinear anisotropic model was considered for aggregate base material. In particular, it was found that the non-linear behavior of granular base affected the tensile strains and compression strains in the asphalt layer significantly. The critical pavement responses in the asphalt layer increase slightly as tire pressure increased from 1.45 MPa (210 psi) to 1.75 MPa (254 psi). However, the loading magnitude affects pavement responses in the asphalt layer significantly, especially for strain responses related to rutting. The accelerated pavement testing results indicate that the rutting differences between two pressure levels (1.45 MPa and 1.75 MPa) were not significant as the total rut depth was relatively small without tertiary flow. This is consistent with the calculated results using the mechanistic-empirical performance transfer function. The numerical modeling can support and supplement the full-scale testing results and provide valuable suggestions for mechanistic-based airfield pavement design under heavy aircrafts with high tire pressure.
Testing to Compare Performance of Full Depth Reclamation with Foamed Asphalt Under Three Different Environmental Conditions
David Jones, University of California, DavisShow Abstract
Full-depth reclamation (FDR) with foamed asphalt has been successfully used as a rehabilitation strategy in California since 2001. Long-term field monitoring on a number of projects combined with a comprehensive laboratory study resulted in the preparation of guidelines and specification language in 2008. However, the design criteria were essentially empirical in line with California design procedures for this level of rehabilitation project. Recently, there has been growing interest in the use of cement, engineered emulsion, and no stabilizer full-depth reclamation strategies in addition to foamed asphalt, and in the use of mechanistic design in a greater range of rehabilitation projects. Consequently, the research initiative was extended to a second phase to include accelerated load testing on an instrumented test track constructed with these four different FDR strategies to gather data for the development of performance models that can be included in mechanistic-empirical rehabilitation design procedures. This paper summarizes the results of three of the eleven tests in this accelerated loading study, which compared the performance of foamed asphalt under three different environmental conditions (dry, wet, and at elevated temperature). All three sections performed well; however, performance was clearly influenced by the wet conditions and the higher asphalt concrete surface temperatures, and these factors need to be considered when undertaking rehabilitation designs where full-depth reclamation is being considered.