Carl L Monismith

Analytically Based Approach to Rutting Prediction

An analytically based (mechanistic-empirical) procedure was conducted to estimate the development of rutting in asphalt pavements as a function of both traffic loading and environment as defined by pavement temperatures. The procedure uses permanent strain determined for a representative asphalt concrete mix as a function of load repetitions, shear stress, and elastic shear strain. It combines multilayer elastic analysis for determining key shear stresses and strains in the asphalt concrete resulting from traffic loading to be used in the permanent strain expression with a time-hardening procedure for the accumulation of permanent strain as a function of both traffic loading and environment. The WesTrack test sections were used to calibrate the methodology, with results of rutting predictions evaluated for four different test sections from that experiment. Based on the results of the regression analyses, an expression can be used to determine coefficients for use in the permanent strain expression that reflect the permanent deformation characteristics of a specific mix as measured in repeated simple shear test at constant height. In addition to the WesTrack examples, results illustrated the use of the approach to predict rutting development in a controlled loading condition at 50°C (122°F) using the heavy vehicle simulator.

Development and Evaluation of Dynamic Flexural Beam Fatigue Test System

Although both mix variables and environmental variables are known to affect the fatigue response of asphalt-aggregate mixes, other factors—including specimen fabrication procedure and test equipment and procedures—are equally important. The development of a dynamic flexural beam fatigue test system is described, and the effects of specimen compaction method and equipment type on the precision of in situ fatigue lives of asphalt-aggregate mixes predicted by using laboratory strain-life relationships are discussed. Results indicate a coefficient of variation of 41 percent in fatigue life for the new fatigue equipment compared with one of 93 percent for an earlier electropneumatic version. The specimen compaction method was also found to influence significantly the precision of the predicted fatigue life. A 33 percent difference in coefficients of variation between the fatigue response of rolling wheel—compacted specimens and kneading-compacted specimens was observed. Consequently, twice as many specimens ar...

APPLICATION OF WEIBULL THEORY IN PREDICTION OF ASPHALT CONCRETE FATIGUE PERFORMANCE

The objectives are to present the feasibility of utilizing the Weibull proportional hazards (PH) model and the Weibull accelerated failure time model of survival analysis to predict in situ pavement fatigue performance from laboratory fatigue test results. A set of WesTrack temperature sensitivity fatigue tests is used as an example to demonstrate how the Weibull PH model works. An example utilizing the deflection data from a heavy vehicle simulator test is given to verify the feasibility of the failure time model. The relationship between mode factor and controlled-deformation fatigue test is discussed using the same example. The Weibull theory approach has potential for use in recursive mechanistic-empirical design procedures.

Field Investigation into Effects of Vehicle Speed and Tire Pressure on Asphalt Concrete Pavement Strains

An asphalt concrete section on a test track in the PACCAR Technical Center in Mount Vernon, Washington, was fitted with strain gauges at the surface and in pavement cores and tested using an instrumented truck operated at different speeds and with different tire pressures. The field test results are presented. The results indicate that the effects of both vehicle speed and tire pressure-contact area on pavement strains are significant: increasing vehicle speed from 2.7 Km/hr (1.7 mi/hr) to 64 km/hr (40 mi/hr) caused a decrease of approximately 30 to 40 percent in longitudinal strains at the bottom of the asphalt concrete layer, which was 137 mm (5.4 in.) thick. The speed effect on transverse strains is lower, causing only a 15 to 30 percent decrease. Reducing tire pressure from 620 kPa (90 psi) to 214 kPa (30 psi) caused a decrease of approximately 20 to 45 percent in the horizontal strains at the bottom of the asphalt concrete layer. The pressure effect on surface strains was significantly lower, causing...

Three decades of development and achievements: the heavy vehicle simulator in accelerated pavement testing

The purpose of this paper is two fold. First, it will provide a brief description of the technological developments involved in the Heavy Vehicle Simulator (HVS) accelerated pavement testing equipment. This covers the period from concept in the late 1960s, to the current state-of-the-art HVS Mk-IV Plus and HVS-A Mk-V. Second, an overview of the research performed by the various accelerated testing programs currently using the HVS as their accelerated testing tool will be provided. The overview will focus on the South African experience, where the HVS was developed. Brief descriptions of HVS research and summaries from other programs worldwide are also provided. These include the Partnered Pavement Research Center (California), the U.S. Army Corps of Engineers Engineering Research and Development Center (CRREL and WES), the Swedish and Finnish HVS-Nordic program and the Florida DOT HVS test programs.

Calibration of Mechanistic–Empirical Models for Flexible Pavements Using California Heavy Vehicle Simulators

Calibration of mechanistic-empirical models for pavement design is a very complex process. The heavy vehicle simulator (HVS) is ideal for the first step in this calibration process. The short test section can be carefully constructed with well-characterized materials and instrumented to measure the pavement response. The climatic conditions may be controlled or monitored closely, all load applications are known exactly, and perhaps most important, the pavement may be tested until it fails. This overcomes the problems of real pavements, which have uncertainties with regard to materials, loads, and climatic conditions and which are normally designed with a high reliability leading to very few failures. The mechanistic-empirical models of an incremental-recursive computer program, known as CalME, have been initially calibrated using data from 27 flexible pavement test sections tested with the two HVSs owned by the California Department of Transportation. Most sections were instrumented with multidepth deflectometers to compare the measured pavement deflections (at several depths) to the deflections predicted by the mechanistic model. Resilient deflections were compared for the complete time history of each test, and each test was carried to failure in regard to rutting (12.5 mm), cracking (2 m/m2), or both. This involved the calibration of models for changes in layer moduli, including the effects of asphalt fatigue. The comparison of measured and predicted response is essential to ensure that the pavement response is predicted reasonably well by the mechanistic model. Once this was achieved, models for permanent deformation of the individual pavement layers were calibrated against the measured permanent deformation of the layers, again using the complete time history of each test.

Using the three-stage weibull equation and tree-based model to characterize the mix fatigue damage process

The primary purpose of this paper is to demonstrate the applicability of the three-stage Weibull equation to describe the fatigue damage process using flexural controlled deformation fatigue tests. A data set of 179 beam fatigue tests originally designed for exploring the fatigue performance of conventional dense graded asphalt concrete (DGAC) and asphalt-rubber hot-mix gap-graded (ARHM-GG) mixes was used to inspect the three-stage Weibull parameters that were estimated using a genetic algorithm. The tree-based regression-category models were then used to uncover the data structure of the estimated parameters as a function of material properties, conditioning methods, temperatures, compaction methods, and strain levels. In general, the three-stage Weibull equation provides satisfactory fitting results for the three-stage fatigue damage process occurring in a beam test. It was found that the tree-based models of three-stage Weibull parameters associated with the crack initiation stage were statistically ad...

Pavement Rutting Performance Prediction by Integrated Weibull Approach

This paper demonstrates the applicability of the integrated Weibull approach to simulate the in situ rutting performance of asphalt concrete mixes by applying appropriate correction factors to laboratory models. The goal was to verify and calibrate the laboratory models according to accelerated pavement test results. The results of the repeated simple shear test at constant height (RSST-CH) were used to estimate the permanent deformation accumulation mechanisms. General regression equations were shown to successfully represent the Stage I and Stage II permanent deformation accumulation phases for mixes containing different binder types according to the results of RSST-CH. Correction factors were used to calibrate the laboratory equations according to the deflection data from four heavy vehicle simulator test sections to estimate in situ rutting performance. The results indicate that phase separation occurs at higher repetition values with increasing shear stress. Moreover, only Stage I of the laboratory models was actually valid at the high shear stress levels used for in situ rutting performance prediction. The simulations further confirm that the integrated Weibull approach is a successful and reliable method for prediction of the in situ rutting performance of flexible pavements and provides high coefficient of determination values.

WESTRACK FATIGUE PERFORMANCE PREDICTION USING MINER'S LAW

The objectives of this paper are to present an approach using statistical analysis and Miner’s law to predict the fatigue performance (crack initiation) of the WesTrack test sections. A strain function, calculated by a layered-elastic program, was statistically determined in terms of temperature at the bottom of the asphalt layer, temperature gradient, subgrade modulus, air-void content, and asphalt content. With integration of laboratory fatigue test results, strain calculation, and Miner’s law, the methodology produces the output in terms of cumulative fatigue damage versus cumulative repetitions for both wander and no-wander cases. Lack of consideration of nonlinear stiffness deterioration of asphalt concrete, crack propagation, and an appropriate correction factor makes long-term fatigue performance prediction conservative and not fully compliant with the condition survey data from WesTrack. The simulation indicated that the WesTrack coarse mixes took longer to initiate fatigue cracks than the fine and fine-plus mixes did but may propagate cracks faster in cold weather.

Truck Pavement Interactions: Requisite Research

A framework for consideration of the effects of dynamic loads on pavement performance is presented. The paper discusses requisite research which will permit both the pavement engineer and the truck designer to effectively utilize such a framework to arrive at optimal solutions which will result in overall savings to the agencies responsible for design, construction, maintenance, and rehabilitation of pavement facilities and to the users of the facilities as well. Included is a discussion of needed research to evaluate: the dynamic response of jointed portland cement concrete pavements to load, the influence of dynamic loads on the development of rutting in asphalt concrete pavements, and the development of new suspension concepts to reduce dynamic load variations with pavement roughness. Also included are recommendations for field measurement procedures to truly identify dynamic load spectra, methods to identify pavement profiles to reflect the effects of such profiles on truck suspension performance, and measurements to evaluate the methodology developed within the proposed framework.