Field and theoretical evaluation of thermal fatigue cracking in flexible pavements

Thermal cracking in flexible pavement occurs when the tensile stress exceeds the tensile strength of hot-mix asphalt at a given temperature or when fluctuating stresses and strains caused by temperature variation lead to a buildup of irrecoverable deformations over time. The objective of this study was twofold: (a) to quantify the measured strain magnitude associated with thermal fatigue through field measurements and (b) to present a three-dimensional, finite element (FE) model that accurately simulated thermal fatigue in flexible pavement. Results of the experimental program indicated that pavement response to thermal loading was associated with a high strain range, reaching a maximum recorded value of 350 μm/m. This finding confirms the hypothesis that the criticality of thermal fatigue arises from the high stress-strain level exhibited in each cycle rather than its frequency, which is usually the critical factor in load-associated fatigue cracking. Moreover, the developed FE model accurately simulated pavement response to thermal loading by conducting a sequential coupled heat transfer analysis. Results of the developed FE model were in agreement with field measurements and demonstrated the model\u27s capability to simulate both the temperature and stress fields associated with thermal loading. This model may be used to evaluate pavement performance against transverse cracking induced by thermal fatigue

Heterogeneous finite-element modeling of the dynamic complex modulus test of asphalt mixture using X-ray computed tomography

Asphalt mixture is a heterogeneous, composite material consisting of aggregate, mastic, and air voids. Analysis of laboratory tests such as the dynamic complex modulus assumes that this material can be dealt with as a homogeneous material while overlooking the particulate nature of this composite. Because of the limitations of the elastic continuum theory, pavement engineers have recently paid considerable attention to the use of advanced modeling techniques for simulating the realistic behavior of asphalt mixtures. The objective of this study is to develop a three-dimensional (3D), heterogeneous model to describe the response of asphalt mixtures in the dynamic complex modulus test using an X-ray computed tomography image-based finite-element (FE)-modeling approach. Experimental testing results for two superpave mixtures, including one conventional hot-mix asphalt and one warm-mix asphalt, were used to validate and calibrate the developed FE models. Acceptable agreement between laboratory-measured and model-predicted dynamic modulus test results was achieved. Results of the developed FE models at different temperatures indicated that most of the deformations during the dynamic modulus test are derived from the mastic. In addition, the asphalt mastic had more influence than the aggregates on the results of the dynamic complex modulus test

Measurement of pavement surface reflectance for a balloon lighting system

Nighttime construction offers many advantages to the public and to state agencies. Under these conditions, traffic is minimal and construction operations can be conducted effectively and quickly. In addition, cooler temperatures are favorable for the equipment and the material being installed. Despite these advantages, controlling glare is a critical and important issue in adequately lighting highway work zones. One of the controlling parameters in glare calculation is the pavement luminance, which is a quantitative measure of the surface brightness. Pavement luminance is based on predefined parameters known as r values provided by the Illuminating Engineering Society of North America (IESNA) for four standard pavement surfaces in the r tables. With the recent introduction of balloon lighting system for construction applications, the objective of this study was to measure pavement reflectance characteristics for this system in the laboratory and to compare the results to the standard r tables. For this purpose, a laboratory experimental setup was developed. On average, measured r values were 20% greater than the IESNA standard values for concrete surfaces (R1), 84% greater for R2 standard surfaces, and 95% greater for R3 standard surfaces. An analysis of variance statistical analysis indicated that the differences between the measured r values and standard r tables were not significant for concrete surfaces but were statistically significant for asphalt road surfaces. This was attributed to the weathering of the road samples used in this study, to the shorter towers used with balloon lights, and to major changes in asphalt construction practices and mix ingredients in the past 30 years. Recommendations based on the results of this study are presented. © 2008 ASCE

Viscosity determination of hot-poured bituminous sealants

Hot-poured bituminous sealants are typically selected based on standard, but empirical tests such as penetration, resilience, flow, and bond to cement concrete briquettes (ASTM D3405). There is, however, no indication of the pertinence of these standard tests to predict field performance. In an effort to bridge the gap between sealant fundamental properties and field performance, performance-based guidelines for selection of hot-poured crack sealants are currently being developed. A procedure to measure sealant viscosity is proposed as part of that effort. Using a sealant with an appropriate consistency at the recommended installation temperature would provide a better crack filling, and would ensure appropriate bond strength. Therefore, to ensure that sealant-crack wall adhesion is achieved and that the sealant penetrates hot-mix asphalt (HMA) during installation, a testing procedure for bituminous based crack sealant viscosity atinstallation temperature is suggested. This paper proposes the use of a rotational viscometer to measure the viscosity of hot-poured crack sealant materials. Based on the results of this study, the measured viscosity of hot-poured crack sealant using SC4-27 spindle at 60rpm at the recommended installation temperature is reasonably representative of sealant viscosity at shear rates resembling field application. To ensure measurement consistency and stability, a 20min melting time and a 30-s waiting time prior to data collection are recommended. The repeatability of the measurements was acceptable with an average coefficient of variation less than 5%. Variability between operators and variability between sealant samples wereacceptable.Les mat\ue9riaux d'\ue9tanch\ue9it\ue9 bitumineux appliqu\ue9s \ue0 chaud sont g\ue9n\ue9ralement s\ue9lectionn\ue9s au moyen de tests standard mais empiriques, tels que la p\ue9n\ue9tration, la r\ue9sistance, le flux et le liant dans les briquettes de b\ue9ton de ciment (ASTM D3405). Rien ne d\ue9montre toutefois l'efficacit\ue9 de tels tests standard \ue0 pr\ue9voir la performance sur le terrain. Afin de combler l'\ue9cart entre les propri\ue9t\ue9s fondamentales des produits de calfeutrage et la performance sur le terrain, des directives, fond\ue9es sur la performance, quant \ue0 la s\ue9lection des produits de calfeutrage appliqu\ue9s \ue0 chaud sont en cours de r\ue9daction. On y propose entre autres une m\ue9thode de mesure de la viscosit\ue9 des produits de calfeutrage. Un produit dont la consistance est appropri\ue9e, utilis\ue9 \ue0 la temp\ue9rature recommand\ue9e, comblera davantage les fissures et constituera un liant plus efficace. Ainsi, afin d'assurer l'adh\ue9sion du produit de calfeutrage aux parois et sa p\ue9n\ue9tration lors de l'application de l'asphalte m\ue9lang\ue9 \ue0 chaud, on sugg\ue8re une m\ue9thode d'essai de la viscosit\ue9 des produits de calfeutrage \ue0 base de bitume \ue0 la temp\ue9rature ad\ue9quate. Ces m\ueames directives proposent de mesurer la viscosit\ue9 des produits de calfeutrage appliqu\ue9s \ue0 chaud \ue0 l'aide d'un viscosim\ue8tre rotatif. Selon les r\ue9sultats de l'\ue9tude, la viscosit\ue9 des produits de calfeutrage appliqu\ue9s \ue0 chaud \ue0 la temp\ue9rature recommand\ue9e, mesur\ue9e au moyen d'un fuseau SC4-27 \ue0 60 tours/minute, correspond raisonnablement \ue0 la viscosit\ue9 des produits de calfeutrage dont la vitesse de cisaillement s'apparente \ue0 l'application sur le terrain. Afin de maximiser la coh\ue9rence et la stabilit\ue9 de la mesure, on recommande un temps de fusion de 20 minutes et un d\ue9lai de 30 secondes avant la collecte de donn\ue9es. Les r\ue9sultats de la mesure ont r\ue9v\ue9l\ue9 un taux de fid\ue9lit\ue9 acceptable et un coefficient moyen de variation inf\ue9rieur \ue0 5 %. La variabilit\ue9 entre les op\ue9rateurs et celle entre les \ue9chantillons de produits de calfeutrage se sont av\ue9r\ue9es acceptables.Peer reviewed: YesNRC publication: Ye

Characterization of bituminous-sealants utilizing modified bending beam rheometer

Early research showed that the current specification for the selection of crack sealants correlates poorly with field performance. To address this issue and help predict the low temperature properties of hot-poured bituminous sealants, a modified Bending Beam Rheometer (BBR) method is utilized. Eight sealants, with a wide range of rheological behaviors, were tested between ?4 and ?40\ub0C. When the time-temperature superposition principle was used, the stiffness after 240s at a temperature T was equivalent to the stiffness after 5h of creep loading at a temperature of T+10\ub0C. The results indicate that the stiffness of hot-poured sealant at 240s help predict low temperature behavior. In addition, the rate of stiffness change in a log-log scale (m-value) can be used to assess stress relaxation. Two additional parameters are thought toprovide a useful indication of the sealant performance at low temperature: steady-state creep rate, obtained after a 240s loading; and the average creep rate, based on deflection measurements over the 240s.Des recherches pr\ue9liminaires ont d\ue9montr\ue9 une faible corr\ue9lation entre la sp\ue9cification actuelle de la s\ue9lection des produits de calfeutrage et la performance sur le terrain. L'utilisation d'un rh\ue9om\ue8tre de flexion modifi\ue9 a permis de r\ue9gler ce probl\ue8me et de pr\ue9voir plus pr\ue9cis\ue9ment les propri\ue9t\ue9s des mat\ue9riaux d'\ue9tanch\ue9it\ue9 bitumineux appliqu\ue9s \ue0 chaud. Des tests r\ue9alis\ue9s sur huit produits de calfeutrage, entre ?4 et ?40 \ub0C, ont r\ue9v\ue9l\ue9 une gamme \ue9tendue de comportements rh\ue9ologiques. Lors de l'application du principe de superposition temps-temp\ue9rature, la rigidit\ue9 apr\ue8s 240 secondes \ue0 la temp\ue9rature T \ue9quivalait \ue0 la rigidit\ue9 apr\ue8s 5 heures du fluage sous l'action des contraintes m\ue9caniques \ue0 une temp\ue9rature T+10 \ub0C. Les r\ue9sultats ont d\ue9montr\ue9 que la rigidit\ue9 du produit de calfeutrage appliqu\ue9 \ue0 chaud apr\ue8s 240 secondes facilite la pr\ue9vision du comportement \ue0 basse temp\ue9rature. Le degr\ue9 de modification de la rigidit\ue9 selon une \ue9chelle bilogarithmique (valeur M) peut en outre servir \ue0 \ue9valuer la relaxation. Deux autres param\ue8tres seraient des indicateurs utiles de la performance des produits de calfeutrage \ue0 basse temp\ue9rature : le taux uniforme de fluage obtenu apr\ue8s 240 secondes, et le taux moyen de fluage selon la mesure de la d\ue9flexion durant cette p\ue9riode de 240 secondes.Peer reviewed: NoNRC publication: Ye