Tire-pavement Contact Pressure Research Articles

Finite Element Modeling of Direct Transition from Concrete Pavement to Asphalt Pavement

The origin of premature distress in direct transitions from Portland cement concrete pavement (PCCP) to asphalt concrete pavement (ACP) constructed as part of TransMilenio pavement repairs has not been investigated and the related literature is limited, therefore, a three-dimensional finite element (FE) model was used to determine the mechanical responses of a direct ACP-PCCP transition under moving vehicular loading in order to identify failure mechanisms. In this sense, a PCCP model was validated with a falling-weight deflectometer (FWD) test, field measurements, and analytical solutions, then a concrete slab (CS) was replaced with flowable fill and asphalt concrete (AC) to create the direct ACP-PCCP transition. The direct transition model considered: 1) the viscoelastic nature of the AC; 2) non-uniform tire-pavement contact pressure; and 3) the bonding variation of the AC-concrete interface of the transition joint using different coefficients of friction (COF) and the Coulomb-type friction model. The results showed 1) relatively high near-surface shear strain of the AC, primarily at the joint and extending 122 mm from the joint; 2) relatively high compressive vertical strain on the subgrade top; and 3) high vertical differential displacement of the joint surface. It is concluded that the AC may prematurely experience near-surface cracking at the vicinity of the joint and rutting from the subgrade, however, increasing the AC-concrete interface bonding may be conservative for fatigue cracking and vertical differential displacement.

Viscoelastic modelling of an asphalt pavement based on actual tire-pavement contact pressure

A three-dimensional finite element (3-D FE) modelling was conducted based on non-uniform distributed tire-pavement contact pressure, full interfacial layer bonding conditions, and viscoelastic characterisation of the asphalt layers. In general, high temperatures were observed to be beneficial to the bottom of the asphalt layer – both the tensile and shear stresses decreased as the temperature was increased. By contrast, the shear stresses increased on the surface of the asphalt layer with an increase in temperature – thus, increasing the propensity to surface shear failure as the temperature increased. Overall, the results indicated that under elastic modelling assumptions, there is a high propensity for failure at the bottom of the asphalt and/or base layer due to high tensile stresses. With viscoelastic modelling assumption, however, the asphalt layer is more likely to suffer from surface shear failure due to high shear stresses on the surface.

Evaluation of factors that affect rutting resistance of asphalt mixes by orthogonal experiment design

Rutting has been one of the major distresses observed on asphalt pavement in China, due to increasing traffic volume, heavy axle load, continuous hot weather, etc., especially in long-steep-slope section, bus stops, etc. Many factors would affect rutting resistance of asphalt pavement, including material properties, climatic condition, traffic volumes, speed, and axle types, and construction quality.The orthogonal experimental design method was used in this study to reduce the number of tests required, without comprising the validity of the test results. The testing variables and their levels were selected according to investigations and field test results. Effects of various factors on asphalt pavement rutting performance were evaluated, including the asphalt binders, mixture type (aggregate gradation), axle load, vehicle speed and temperature.In this study, the wheel tracking test was used to evaluate rutting performance, as represented by the parameter Dynamic Stability (DS), of the various asphalt mixes. Test results were analyzed using range analysis and analysis of variance (ANOVA). All four factors evaluated in this study had significant effects on pavement rutting performance. The ranking of the significance was asphalt mixture type, temperature, loading frequency, and tire-pavement contact pressure. Asphalt mixture type was the most important factor that affects rutting resistance. Within the asphalt mixtures, asphalt binder had significant effects on rutting performance of mixes more than aggregate gradation. Rutting resistance of SBS modified asphalt mixes was significantly better than neat asphalt mixes, and skeleton dense structure mixes were better than suspended dense structure mixes.

Combined Effect of Three-Dimensional Contact Load and Thermal Gradients on the Cracking Performance of Heavy-Duty Asphalt Pavements

Top-down cracking is well recognized as a major distress for heavy-duty asphalt pavements, yet the mechanism is not fully understood. Studies have indicated that nonuniform tire–pavement contact stress may play a significant role in the initiation of top-down cracking, and thermal stress caused by the temperature gradient may contribute to the initiation and development of top-down cracking. These relevant factors were evaluated with a sophisticated three-dimensional viscoelastic finite element model that was developed for studying the cracking performance of heavy-duty flexible pavements under combined three-dimensional tire–pavement contact stress and thermal stress induced by the temperature gradient. It was found that the stress distribution in asphalt concrete layers continuously changed as the pavement was loaded because of the rheological behavior of the asphalt concrete. Significant maximum principal tensile stresses are present at the tire edge at the asphalt concrete surface, which may result in an accumulation of dissipated creep strain energy over time (or with a cumulative number of loads) and may eventually lead to crack initiation. Additionally, near-surface pavement responses associated with top-down cracking under three-dimensional tire–pavement contact pressure are found to be more severe than those from uniform contact pressure. In a comparison with pavements without thermal effect, the negative temperature gradient increases the potential for top-down cracking, and the positive temperature gradient increases the potential for bottom-up cracking. The study provides insight into crack mechanisms, which may improve current heavy-duty asphalt pavement design procedures.

Modeling mechanistic responses in asphalt pavements under three-dimensional tire-pavement contact pressure

A three dimensional finite element program incorporating actually measured vertical tire-pavement contact pressure (TPCP) was utilized for modeling the mechanistic responses in asphalt concrete (AC) layers by simulating various vehicle motions: stationary and non-stationary (i.e. in acceleration or deceleration mode). Analysis of the results indicated the following items. 1) It is critical to use the vertical TPCP as the design control criteria for the tensile strains at the bottom of the AC layer when the base layer modulus is lower in magnitude (e.g. ≤400 MPa); however, when the base layer modulus is higher in magnitude (e.g. ≥7 000 MPa), the horizontal TPCP and the tensile strains in the X-direction at the surface of the AC layer should also be considered as part of the design response criteria. 2) The definition of “overload” needs to be revised to include tire pressure over-inflation, i.e., a vehicle should be considered to be overloaded if the wheel load exceeds the specification and/or the tire inflation pressure is higher than the specification. 3) Light trucks have more structural impact on the strain responses and pavement design when the thickness of the surfacing AC layer is thinner (e.g. ≤50 mm). 4) The acceleration of a vehicle does not significantly impact the AC surface distresses such as rutting at the top of the upgrade slopes or intersections; however, vehicle deceleration can dramatically induce horizontal shear strains and consequently, aggravate shoving and rutting problems at the highway intersections. Evidently, these factors should be taken into account during mechanistic stress-strain modeling and structural design of asphalt pavements.

Impacts of Reduced Tire Pressure on Strain Response of Thaw-Weakened, Low-Volume Roads in Manitoba, Canada

The spring thaw period significantly reduces the bearing capacity of low-volume asphalt roads. To compensate for the reduced bearing capacity, highway agencies apply spring load restrictions (SLR) to limit the damage caused by heavy loads during the period when the road is weakened by thaw. Although the imposition of SLR may reduce road damage, it has a major impact on truck productivity. An alternative to reducing truck loads during the spring is the reduction of truck tire pressure. The reduced tire pressure lowers the tire–pavement contact pressure and the associated damage during the spring period. In 2008, asphalt strain gauges were installed in a section of a low-volume haul road in Manitoba, Canada. Field testing was conducted in the spring and fall of 2009 with a double semitrailer or B-Train equipped with a semiautomated tire pressure control system. The tests were conducted at various loads and speeds and at normal and reduced tire pressures. The results of the field testing showed that when the tire pressure was reduced by 50%, the measured maximum tensile strain at the bottom of the asphalt layer decreased by an average of 15% to 20%. The effects of gauge orientation, truck speed, and tire offset from the strain gauge were analyzed and are presented.

Effects of Layer Interfacial Bonding Conditions on the Mechanistic Responses in Asphalt Pavements

The bonding condition between pavement layers plays an important role in the performance of pavement structures. In this paper, a three dimensional finite-element (3D-FE) program was used for modeling the mechanistic responses (stresses and strains) in the asphalt concrete (AC) layers by simulating two layer interfacial bonding conditions, namely fully bonded and debonded (i.e., the layer separated but still considering friction). The 3D-FE modeling incorporated actual measured vertical tire-pavement contact pressure (TPCP) and assumed horizontal TPCP, including investigating the effects of vehicle acceleration and deceleration. The results of these computational modeling are presented in this paper and indicated that the layer interfacial bonding condition has a significant effect on some pavement mechanistic responses such as the tensile, compressive, and shear stresses/strains in AC pavement structures. In general, layer interface debonding (or separation) was analytically found to indirectly exacerbate pavement distresses such as slippage cracking, fatigue cracking, shoving, shear deformation, and rutting, which is undesirable.

Laboratory Measurement of the Actual Tire-Pavement Contact Pressure Using a Static Test Device

Abstract It is well-known that the tire-pavement contact pressure (TPCP) is hardly circular or uniformly distributed as often assumed. In this study, using a simple but effective static test set-up, numerous actual TPCPs between a loaded wheel-tire and the surface of an asphalt-mix slab were measured in the laboratory. Various TPCP loading conditions were investigated, including varying the tire inflation pressures, varying the load levels, and using different tire types, different tire tread patterns, and tire ages. Analysis of the results indicated that a linear proportional relationship existed between the following variables: (a) Tire inflation pressure and TPCP, (b) load level and the effective tire-pavement contact area, and (c) load level and TPCP. At a fixed constant tire inflation pressure, an increment in the load level significantly impacted the tire edges compared to the middle zone, and at a constant wheel loading, an increase in the tire inflation pressure will result in possibly a 1.5 times increase in the TPCP. This is detrimental to pavements and is undesirable. Furthermore, the TPCP under new tires was observed to be closer to being uniformly distributed than that under the old tires. In other words, in terms of distresses, if all other factors are equal, an old tire will likely cause more damage to an asphalt pavement than a new tire.

Modelling Tensile Strain Response in Asphalt Pavements

ABSTRACT Traditionally, HMA pavement designs and modeling methods have historically been based on the fundamental assumption that fatigue cracking generally initiates at the bottom of the HMA layer due to excessive tensile stresses/strains, and then propagates upwards to the surface. However, fatigue cracking can either be bottom-up or top-down initiated depending on the location of the maximum horizontal tensile stresses and strains in the HMA layer. Various factors such as the pavement structure and wheel/tire loading configurations influence both the location and magnitude of the fatigue crack-related tensile strains that are induced in the HMA layer. In this study, the influence of these factors on the tensile strains responses and potential location of fatigue crack initiation in HMA pavements was investigated. To address the non-uniformity distribution of the tire-pavement contact pressure (TPCP), including the vertical tire-pavement contact pressure and horizontal tire-pavement stress, a three-dimensional finite element program was utilized for the computational simulations and numerical analyses. Specifically, the actual TPCP of different tire types and tread patterns measured under variable load levels and tire inflation pressures were utilized to evaluate and analyze the potential locations of maximum tensile strains in terms of fatigue crack initiation. The results showed that the longitudinal and low latitudinal tire-pavement stress hardly influence the maximum tensile strains in the HMA layer; and that the maximum tensile strains can occur either at the top or bottom (or both) of the HMA layer, thus inducing top-down and/or bottom-up fatigue crack initiation. Just like heavy-truck tire loading, the study also demonstrated that light-truck tire loading can induce excessive fatigue crack-related tensile strains in the pavement.

A Simple and Effective Laboratory Test Device for Measuring Tire-Pavement Contact Pressure

Abstract For most mechanistic response analyses of asphalt pavements, the traffic loading between the tire and the pavement is often modeled as a circular contact area with a uniform stress distribution. In reality, the tire-pavement contact pressure is hardly circular or uniformly distributed. In order to more accurately model the pavement responses under traffic loading, it is necessary to measure the actual tire-pavement contact pressure (TPCP) and then use it for pavement mechanistic response analyses. Currently there are a few devices that can be used to measure the TPCP. However, most of these existing devices have some limitations. For example one of the major disadvantages is the fact that the measured data were the pressure between the tire and a steel plate, and not between the tire and the asphalt pavement. For accurate TPCP measurements in this paper, a simple and effective static laboratory test device was developed. One of the features of this device is that the pressure sensors were inserted and suspended within the asphalt slab and the top of the sensors were kept flush with the surface at the interface with the tire. This enabled the true TPCP between the tire and the asphalt surface to be measured. Additionally, the device is relatively easy to set up and conduct the tests. Thus far, the laboratory measured TPCP results with this static test device were reasonably consistent with existing theories and assumptions about modeling the TPCP and pavement mechanistic responses.

Current Status and Variability of In-Service Truck Tire Pressures in Texas

Truck tire pressure is closely related to tire-pavement contact pressure and could be an easy index representing the tire-pavement contact pressure level. To characterize in-service truck tire pressures and truck configurations on Texas highways, a truck survey was conducted on major Texas trucking routes. The survey data demonstrate a significant increase in in-service truck tire pressures in the state of Texas. Analysis of the collected tire-pressure data showed that factors such as axle weight, tire temperature, geographic area, highway class, traveled distance, and axle type are related to the in-service tire-pressure values. In a survey study, a factorial experiment design and a stratified sampling design were used. Analysis of variance, analysis of covariance, and t-tests were used for comparisons of truck tire-pressure data. Laboratory experiments and linear regression were used to identify relationships between the parameters of tire pressure and tire temperature. The survey results for in-service truck tire pressures and the comparisons and analyses of factors differentiating truck tire pressures are presented.

Effects of tire – pavement contact pressure distributions on the response of asphalt concrete pavements

The paper presents the development of a computer program VIEM for the elastic analysis of multilayered elastic pavements under the action of arbitrary tire–pavement contact pressure distributions. The techniques adapted in VIEM primarily involves the use of a two-dimensional numerical integration to integrate point load solutions over the distributed pressure after discretizing the contact area into a finite number of triangular or quadrilateral elements. Values of contact pressure are inputted at the node points of discretized area. Numerical verification of VIEM indicates that numerical solution of high accuracy can be efficiently calculated for the elastic response of multilayered asphalt pavements. As a result, the determination of displacements and stresses (strains) can be achieved using a personal computer. With the use of VIEM, a theoretical investigation is further performed to illustrate the effects of tire–pavement contact pressure distributions on the response of asphalt concrete pavements. An in situ measured tire–pavement contact pressure distribution is utilized in the investigation. The response of asphalt concrete pavements due to the action of this measured contact pressure distribution is examined and compared with that due to the action of a uniform and circular contact pressure distribution by taking into account the influences of moduli and thicknesses of structural layers. The results of this investigation confirm theoretically a general consensus that details of the contact pressure distribution affect stresses and strains near the surface of the pavement, whereas the response in the lower layers depends mainly on the overall load. In particular, the contact pressure distributions have a significant effect on the horizontal tensile strains at the bottom of thin asphalt concrete layer which control the fatigue failure of asphalt pavements. Key words: tire–pavevment interaction, three-dimensional stress analysis, asphalt concrete pavements, numerical integration, multilayered elastic solids, point load solution.