Manuel J. C. Minhoto

Predicting Asphalt Pavement Temperature with a Three-Dimensional Finite Element Method

A three-dimensional (3D) finite element (FE) model was developed to calculate the temperature of a pavement located in northeast Portugal. A case study was developed to validate the model. Input data to the model were the hourly values for solar radiation and temperature and mean daily values of wind speed obtained from a meteorological station. The thermal response of a multilayered pavement structure was modeled with a transient thermal analysis for 4 months (December 2003 to April 2004), and the analysis was initiated with the full-depth constant initial temperature obtained from field measurements. During these 4 months, the pavement temperature was measured at a new pavement section, located in IP4 main road, near Braganca, in northern Portugal. At this location, seven thermocouples were installed in the asphalt concrete layers at seven different depths. These pavement data were used to validate this simulation model by a comparison of model calculated data with measured pavement temperatures. The 3D FE analysis proved to be an interesting tool to simulate the transient behavior of asphalt concrete pavements. The suggested simulation model can predict the pavement temperature at different levels of bituminous layers with good accuracy.

Impact of Traffic Overload on Road Pavement Performance

Traffic on a road pavement is characterized by a large number of different vehicle types, and these can be considered in pavement design by using truck factors to transform the damage they apply to the pavement to the damage that would be applied by a standard axle. The truck factors to convert trucks into standard axles or the load equivalent factors to convert axles into standard axles are defined by considering the average loads for each axle. This process includes the vehicles that travel with axle loads above the maximum legal limit. There are also a substantial number of overloaded vehicles in terms of total vehicle weight. These axles/vehicles cause significant damage to the pavements, increasing the pavement construction and rehabilitation cost. Thus, this paper investigates the impact of overloaded vehicles on road pavements by studying the truck factors for different vehicle cases applied to a set of pavements composed of five different asphalt layer thicknesses and five different subgrade stiffness moduli. The study revealed that the presence of overloaded vehicles can increase pavement costs by more than 100% compared to the cost of the same vehicles with legal loads.

The temperature effect on the reflective cracking of asphalt overlays

ABSTRACT This paper presents a study about the influence of temperature on the reflective cracking in a flexible road pavement through the evaluation of the asphalt overlay damage associated to traffic and temperature variations throughout a year. This study was developed from a numerical simulation of the asphalt overlay behaviour based on a three-dimensional finite-element analysis, considering the simultaneous loading of traffic and temperature variations. A mechanistic-based overlay design method was used to predict the reflective cracking overlay life. Climatic temperature variations in pavements lead to an increase of the reflective cracking phenomenon, due to the stress and strain states created by temperature, resulting in the premature distress of the asphalt overlay. This study also intends to establish a comparison between the expected performance of asphalt rubber hot mixes and conventional asphalt overlays.

The Influence of Temperature Variation in the Prediction of the Pavement Overlay Life

ABSTRACT This paper describes a study of the influence of temperature variation in the pavement overlay life, using finite-element methodology to consider the most predominant type of overlay distress observed in the field: reflective cracking. The temperature variation has a significant influence on thermally induced stresses that, in turn, affects the overlay predictive service life. This paper presents a three-dimensional (3D) finite element analysis to predict the pavement overlay life considering a combination of thermal pavement conditions with traffic loads in a pavement overlay modelled on a cracked pavement. The results present the influence of temperature variation in the cracked layer and overlay, as function of the initial pavement temperature. Furthermore, a comparison between the overlay life due to traffic loading and temperature variation in the overlay life is also presented. Finally, the overlay life was predicted using asphalt rubber and conventional mix fatigue laws allowing to conclude that asphalt rubber mixes exhibit more pavement life compared to conventional mixes even when the effects of temperature (temperature variation) are considered in the overlay design.

A model for equivalent axle load factors

Most design methods for road pavements require the design traffic, based on the transformation of the traffic spectrum, to be calculated into a number of equivalent passages of a standard axle using the equivalent axle load factors (EALFs). In general, these factors only consider the type of axle (i.e. single, tandem or tridem), but they do not consider the type of wheel on the axles, i.e. single or dual wheel. The type of wheel has an important influence on the calculation of the design traffic. The existing design methods assume that the EALFs are valid for all pavement structures and do not consider the thickness and stiffness of the pavement layers. This paper presents the results of the development of a model for the calculation of the EALFs considering the type of axle, the type of wheel and the constitution of the pavement. The model was developed based on the tensile strain at the bottom of the asphalt layer that is responsible for bottom-up cracking in asphalt pavement, which is the most widely considered distress mode for flexible road pavements. The work developed in this study also presents the influence of the type of wheel (single and dual) on pavement performance. The results of this work allowed the conclusion that the EALFs for single wheels are approximately 10 times greater than those for a dual wheel. This work also proposes average values for the EALFs. An artificial neural network was developed to calculate the EALFs.

Asphalt Rubber Interlayer Benefits in Minimizing Reflective Cracking of Overlays over Rigid Pavements

This paper provides an overview of the asphalt rubber interlayer benefits on reflective crack retardation in overlays over rigid pavements. These interlayers are known in California as asphalt rubber absorbing membrane interlayers (SAMI-R) or as asphalt rubber aggregate membrane interlayers (ARAM-I) chip seals. The paper focuses on the performance in terms of field project reviews, laboratory performance tests and finite element analysis. SAMI-R has been given a reflective cracking equivalent thickness of 15 mm of asphalt rubber hot mix overlays or 30 mm of dense graded hot mix overlays. The finite element analysis confirms the quantified reflective cracking benefits of SAMI-R and provides optimum design alternatives to conventional dense grades asphalt concrete overlays. The paper concludes that SAMI-R is effective in minimizing reflective cracking distress and in extending pavement life.

Multi-cracks modeling in reflective cracking

Reflective cracking is a major concern for engineers facing the problem of road maintenance and rehabilitation. The problem appears due to the presence of cracks in the old pavement layers that propagate into the pavement overlay layer when traffic load passes over the cracks and due to the temperature variation. The stress concentration in the overlay just above the existing cracks is responsible for the appearance and crack propagation throughout the overlay. The analysis of the reflective cracking phenomenon is usually made by numerical modeling simulating the presence of cracks in the existing pavement and the stress concentration in the crack tip is assessed to predict either the cracking propagation rate or the expected fatigue life of the overlay. Numerical modeling to study reflective cracking is made by simulating one crack in the existing pavement and the loading is usually applied considering the shear mode of crack opening. Sometimes the simulation considers the mode I of crack opening, mainly when temperature effects are predominant. Thus, this paper presents a study where multiple cracks are modeled to assess the reflective cracking phenomenon and to compare to the case of only one crack. The modeling with only one crack was made simulating both mode I and mode II of crack opening taking into account the traffic effects. The influence of multiple cracks was expressed in terms of stress and strain in the zone above existing cracks. One of the conclusions from the current study is that the presence of multiple cracks can lead to a state of stress/strain higher than those obtained with only one crack. Also the position of the crack modeled in the finite elements analysis have a significant influence in the state of stress/strain obtained. However, the consideration of only one crack is sufficient to obtain significant results in the reflective cracking modeling.