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This study aimed to evaluate the repeatability of locked-wheel skid trailer (LWST) and sideway-force coefficient routine investigation machine (SCRIM) measurements and investigate the influences of test speed and test temperature on the friction measurements. This study selected 14 test sections from the NCAT Test Track with different surface texture and friction characteristics. The LWST and SCRIM tests were conducted at different test speeds and test times (or temperatures) on the two consecutive days. The repeatability analysis indicates that both LWST skid number (SN) and SCRIM reading (SR) measurements were most repeatable at a test speed of 50 mph and tangent section. The SN measured in the late afternoon and SR measured at noon were more repeatable than those measured at other times. This study recommended an acceptable precision of friction measurement be within 2.5 SN or 3 SR units. In addition, this study concluded that the SN and SR had a good linear correlation. The statistical regression analysis demonstrates that test speed, air temperature, pavement mean profile depth, and pavement type were significant variables affecting asphalt pavement friction. The developed regression models for SN and SR were helpful to correct the friction measurements to a reference speed or temperature. [ABSTRACT FROM AUTHOR]

The objective of this study was to examine the effectiveness of using shotblasting treatment to improve surface friction of asphalt pavements. This study selected six pavement sections with low skid resistance from the National Center for Asphalt Technology Test Track for shotblasting abrasion. These sections included three surface mixture types (open-graded friction course and dense-graded asphalt with and without reclaimed asphalt pavement material) and four coarse aggregate types (limestone, granite, dolomite and sandstone). The dynamic friction tester and lock-wheel skid trailer were used to measure the surface friction of these sections at the different traffic polishing cycles. In addition, the pavement performance including rut depth, cracking and surface roughness were periodically monitored. The test results indicated that shotblasting treatment was effective in improving the friction performance of asphalt pavements and had no detrimental impact on pavement performance in terms of cracking, rutting and surface roughness. The friction improvement by shotblasting treatment was significantly dependent on surface mixture type and coarse aggregate type. [ABSTRACT FROM AUTHOR]

The quality of hot mix asphalt is affected by the quality and consistency of input aggregates and the control of the production process. To improve the quality of hot mix asphalt, both the aggregates gradation and the process variables must be considered. Current practice involves taking samples from actual production and analyzing them in the lab. The entire process can take two hours, which, along with being expensive, is not amenable to real time online process control or even in knowing how much product is actually out of specification. In this paper, an online control system is proposed that can be used to significantly decrease the analysis time and adjust production by using discrete time stochastic simulation combined with algorithmic optimization. Additionally, the system can readily show when a mix is out of specification without lag time or physical experimentation. Results show that this approach can effectively control the production process resulting in improved quality. This is the first known such application in hot mix asphalt online process control. [ABSTRACT FROM AUTHOR]

Among the many applications of the phase-locked loop (PLL), a device used extensively in telecommunications and electronics, is the demodulation of modulated carrier signals. The PLL contains a voltage controlled oscillator (VCO) that tracks a reference signal whose frequency may be changing. This is accomplished through a feedback mechanism--the VCO's frequency is adjusted by a control signal that, after filtering, depends mostly on the phase difference between the reference and VCO output. Phase-lock describes an operating state for which this phase difference remains constant. During nearly phase-locked operation, the filtered signal controlling the VCO approximates the demodulation of the reference. A standard model is used to give a rigorous mathematical explanation of the described operation of the PLL in a physically realistic operating regime. While the model does not allow strict phase-locking, a theorem is formulated and proved that predicts operation near an attracting torus with quasi-periodic flow in the state space. The proof uses high-order averaging, a new result on extension of the averaging estimate to the forward infinite time-scale, and continuation theory for invariant manifolds. For the averaged system (equivalent to a simplified model that assumes ideal filtering), we obtain an approximation for solutions on an attracting invariant torus (for quasi-periodic reference signal modulation of sufficiently small amplitude and frequency), in which the dominant response of the filtered control signal is the demodulation of the reference signal, up to a rescaling and constant shift. Furthermore, we show that the full model (allowing nonideal filtering) also has an attracting torus, on which solutions exhibit the same dominant response. In addition, some results on continuation of invariant manifolds, which may have applications beyond the PLL, are proved. [ABSTRACT FROM AUTHOR]

Many aspects influence the skid resistance of a pavement surface including surface texture, tire characteristics, vehicle operations, and environmental factors. The objective of this paper is to quantify the temperature influence on the skid number of asphalt pavement surfaces when measured by the locked-wheel friction tester. Specifically, this study aims to determine an adjustment factor for friction readings to a standard reference temperature, removing the seasonal temperature variations influencing measurements. This allows agencies to improve the comparison of pavement sections and to provide a more objective assessment of pavement conditions for safety. The friction database employed is from the National Center for Asphalt Technology Test Track facility. The data includes friction measurements with a locked-wheel trailer on sections from the 2000 and 2003 research cycles. The approach calculates the temperature adjustment factor, CT, from a grouping of the data by temperature values at the time of the measurements. The results show that it is possible to define a reference temperature to adjust friction measured at any other temperature value. The reference temperature identified is between 19.5°C (67.1°F) and 20.2°C (68.4°F). The study concludes that when testing, if the air temperature is greater than the reference temperature, the friction reading is biased by a positive quantity. Therefore the adjustment factor, CT, reduces the measured friction, whereas for measurements performed at temperatures lower than the reference temperature, CT increases the measured friction. [ABSTRACT FROM AUTHOR]

Cold in-place recycling (CIR) is one of the most effective methods to rehabilitate asphalt pavements. In fact, most CIR roads have performed well at low cost in Iowa since the first CIR road was constructed in 1986. However, some CIR roads have reached failures earlier than their expected design lives because there is no design standard for designing CIR roads with a limited amount of past performance information. Some of the most prominent problems seemed to have come from selecting CIR in areas where there are poor subgrades. Therefore, it is critical to collect CIR performance data along with falling weight deflectometer (FWD) data in order to develop performance models. The main purpose of this paper is to document that effort. The performance models were developed on the basis of historical data collected from CIR roads in Iowa. First, an inventory of CIR roads was created which includes construction information, subgrade and base characteristics, and traffic levels. In consideration of pavement age, level of traffic, and subgrade condition, 26 test sections were selected from the inventory of CIR roads and pavement surface distress surveys were conducted on these roads using an automated image collection system. Distress data were then compiled to compute pavement condition index (PCI) for each test section. FWD data were collected from each test section to determine its relative soil support condition. Finally, to determine their long-term performance, the PCI values were plotted against the pavement age for each group of pavements categorized by their soil support conditions and traffic levels. Overall, it can be concluded that the CIR roads in Iowa, all under traffic level of annual average daily traffic of 2,000, have performed very well and predicted to last up to 25 years before reaching the poor condition (PCI=40) when the pavements are to be rehabilitated. The CIR roads with a good subgrade support, however, are predicted to last up to 35 years. [ABSTRACT FROM AUTHOR]

With a limited maintenance budget and unprecedented construction cost increases, many owner/agencies in the United States are beginning to rehabilitate existing distressed pavements. Cold in-place recycling (CIR) provides an economical rehabilitation method and has been widely used in the past 20 years. However, recycled roads have experienced inconsistent performance and that has hindered the application of CIR. The objective of this paper is to study the cause and effect relationships between factors, such as traffic loading, support condition, and aged engineering properties of the CIR materials, and pavement performance. Twenty-four roads in Iowa were examined through field and lab tests. Statistical analyzes show that, within the range of data in this study, better performance was observed on CIR roads with lower CIR modulus value and/or higher air voids. [ABSTRACT FROM AUTHOR]

As part of the validation effort to evaluate the consistency of a new cold in-place recycling using foamed asphalt (CIR–foam) mix design process for the Iowa Department of Transportation, the dynamic modulus and repeated load tests were conducted to evaluate the performance characteristics of CIR–foam mixtures over a wide range of loading and temperature conditions. The main objective of this research is to study the impacts of the foamed asphalt contents and reclaimed asphalt pavement (RAP) material characteristics on dynamic modulus and flow number. Dynamic modulus and repeated load tests were conducted on CIR–foam mixtures with RAP materials collected from seven different CIR project sites located throughout Iowa. Dynamic modulus values of the RAP materials varied depending on the sources and foamed asphalt contents. Coarse RAP materials with a small amount of residual asphalt content exhibited a higher modulus value at 4.4°C but exhibited a lower dynamic modulus value at 37.8°C than fine RAP materials with a large amount of residual asphalt content. Flow numbers were varied significantly depending on their RAP sources and foamed asphalt contents. Fine RAP materials with a hard residual asphalt binder exhibited a higher flow number than coarse RAP materials with a soft residual binder. The relative rankings of RAP materials in terms of the flow number did not change when the foamed asphalt was increased from 1.0 to 3.0%, which supports the repeated load test being consistent in evaluating a rutting potential of RAP materials. [ABSTRACT FROM AUTHOR]

The main objective of this study is to validate a new mix design procedure for cold in-place recycling using foamed asphalt (CIR-foam) developed for the Iowa Department of Transportation. First, reclaimed asphalt pavement (RAP) materials were collected from seven different CIR construction sites located across the state of Iowa. To determine the consistency of a new CIR-foam mix design procedure, the mix design was performed seven times using these RAP materials. The test specimens were prepared using gyratory compactor rather than Marshall hammer because it produced more consistent mixtures for various foamed asphalt contents and curing conditions. The indirect tensile strength test was performed on the vacuum-saturated specimens prepared using each of seven RAP material sources for five different foamed asphalt contents (1.0, 1.5, 2.0, 2.5, and 3.0%), given a fixed moisture content of 4.0%. As the foamed asphalt content increased from 1.0 to 3.0% at 0.5% increments, air voids in the CIR-foam mixtures decreased gradually. The indirect tensile strength of CIR-foam specimens cured for two days at 60°C was significantly higher than that of CIR-foam specimens cured for three days at 40°C. Based on the new mix design procedure, the optimum foamed asphalt contents were consistently found at values between 1.5 and 2.5% for all seven different RAP materials. The stiffer residual asphalt required more foamed asphalt, whereas the higher residual asphalt content did not require a smaller amount of foamed asphalt. The raveling test result was very sensitive to the curing time and the foamed asphalt content, such that RAP materials with a large amount of stiff residual asphalt would exhibit more potential for raveling. [ABSTRACT FROM AUTHOR]

Exact solutions are obtained for a model of the longitudinal displacement along an elastic tapered bar due to a force applied at its blunt end. A formula for velocity amplification is given; it specifies the velocity of the pointed end of the bar shortly after it feels the influence of the force. For a bar. with an exponentially decreasing cross-sectional area, the velocity is magnified by twice an exponential function of length. This result has applications in the design of piezoelectric drills. In addition, we discuss the differences between the motions of rigid and elastic bars during the transient before one complete reflection of the wave induced by a force applied to an end of the bar. hi this regime, force is proportional to velocity for elastic bars with constant cross-sectional areas. While the force-velocity relationship is more complicated for tapered elastic bars, their exact relationship is determined. [ABSTRACT FROM AUTHOR]

A well-established model for simulation of the chain-scission process of polylacticacid (PLA) during thermal processing has been simplified and revised. The key assumption in the new model is that the total number of monomer units is invariant as reactions progress. Surprisingly, this seemingly obvious assumption appears to have been previously overlooked. The revised model no longer requires solution of simultaneous differential equations and, for isothermal conditions, an analytical solution is readily available. The present model is in excellent agreement with the more complex model and experimental results for PLA degradation reported in the literature. This simplified model has potential to be applied to other thermoplastics. [ABSTRACT FROM AUTHOR]