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This report examines the feasibility of using the thermal stress restrained specimen test to evaluate low temperature cracking in asphalt pavement mixes. Data were collected from laboratory and field evaluations. Various mixing, aging, and compaction methods were used to prepare test samples with materials obtained from two Wyoming Department of Transportation (WYDOT) highway projects. Field data were obtained from two recently built test sections and compared with laboratory test results. Pavement condition surveys quantified low temperature cracking of both test sections after one winter. Temperature data for the project sites also were collected. Pavement condition and temperature data were compared to results from the thermal stress restrained specimen test. The thermal stress restrained specimen test was effective in testing asphalt pavement mixes. However, test results indicated that lab prepared samples did not closely simulate field samples. Also, comparisons of lab results with field conditions were performed. However, it is recommended that a more comprehensive analysis be performed after test sections have been in service for a few years.
This report describes the thermal stress restrained specimen test (TSRST), which was selected to evaluate the low-temperature cracking resistance of asphalt concrete mixtures. The TSRST system includes a load frame, step-motor-driven load ram, data acquisition hardware and software, temperature controller, and specimen alignment stand. An experiment design that considered a range of mixture and test condition variables was developed to evaluate the suitability of TSRST for characterizing low-temperature cracking resistance of asphalt concrete mixtures. Four asphalts and two aggregates were selected for the experiment. The mixture variables included asphalt type, aggregate type, and air voids content; the test condition variables included specimen size, stress relaxation, aging, and cooling rate.
Low-temperature cracking occurs on some asphalt pavements even though the high-performance grade (PG) binders are applied in asphalt mixtures. It is neither realistic nor economic to solve the problems related to low-temperature cracking on asphalt pavements by purely using high PG binders. Other factors need to be investigated so that this type of distress can be further restrained. This study focuses on investigating the effect of fine aggregates on the low-temperature cracking on asphalt pavements. Low-temperature cracking was monitored and recorded on asphalt pavements in a cold, northeast area of China. Cores were drilled on the spots where low-temperature cracking occurred, and the aggregate gradations of the drilled cores were analyzed in the laboratory. An index called the Fine Aggregate Content Deviation Index (FACDI) was defined as the difference between the actual fine aggregate content and the lower limit of fine aggregate content in the designed aggregate gradation. A positive relation was observed between the FACDI and the cracking index of asphalt pavements. It was demonstrated that the fine aggregate content was another important factor that influences low-temperature cracking of asphalt pavement. The increase of fine aggregate content was found to jeopardize the resistance of asphalt mixture on low-temperature cracking. Based on FACDI, fine aggregate's contents in asphalt mixtures of asphalt layers can be recommended to ensure an asphalt pavement with good low-temperature performance.
This volume highlights the latest advances, innovations, and applications in bituminous materials and structures and asphalt pavement technology, as presented by leading international researchers and engineers at the RILEM International Symposium on Bituminous Materials (ISBM), held in Lyon, France on December 14-16, 2020. The symposium represents a joint effort of three RILEM Technical Committees from Cluster F: 264-RAP “Asphalt Pavement Recycling”, 272-PIM “Phase and Interphase Behaviour of Bituminous Materials”, and 278-CHA “Crack-Healing of Asphalt Pavement Materials”. It covers a diverse range of topics concerning bituminous materials (bitumen, mastics, mixtures) and road, railway and airport pavement structures, including: recycling, phase and interphase behaviour, cracking and healing, modification and innovative materials, durability and environmental aspects, testing and modelling, multi-scale properties, surface characteristics, structure performance, modelling and design, non-destructive testing, back-analysis, and Life Cycle Assessment. The contributions, which were selected by means of a rigorous international peer-review process, present a wealth of exciting ideas that will open novel research directions and foster new multidisciplinary collaborations.
Papers presented at this session include: temperature distributions in asphalt pavements (himeno, k, watanabe, t and maruyama, t); transient effects in low temperature induced failure and fracture initiation in a pavement structure (selvadurai, aps, phang, wa and au, mc); cold climate performance of canadian airport pavements (haas, r, lee, h and meyer, f); applications of a method for evaluation of low temperature tensile properties of asphalt concrete (anderson, ko and leung, sc); evaluation of bearing capacity of asphalt pavement with low-temperature transverse cracking (kasahara, a and yoshida, h); laboratory investigations of low temperature cracking susceptibility of asphalt concrete (janoo, vc and chamberlain, ej); results of laboratory tests on amir compacted asphalt slabs (abd el halim, ao, mshana, g and sithole, v). for the covering abstract of the conference see irrd 807037.
Good fracture properties are an essential requirement for asphalt pavements built in the northern part of the US and in Canada for which the predominant failure mode is cracking due to high thermal stresses that develop at low temperatures. Currently, there is no agreement with respect to what experimental methods and analyses approaches to use to investigate the fracture resistance of asphalt materials and the fracture performance of asphalt pavements. This report presents a comprehensive research effort in which both traditional and new experimental protocols and analyses were applied to a statistically designed set of laboratory prepared specimens and to field samples from pavements with well documented performance to determine the best combination of experimental work and analyses to improve the low temperature fracture resistance of asphalt pavements. The two sets of materials were evaluated using current testing protocols, such as creep and strength for asphalt binders and mixtures as well as newly developed testing protocols, such as the disk compact tension test, single edge notched beam test, and semi circular bend test. Dilatometric measurements were performed on both asphalt binders and mixtures to determine the coefficient of thermal contraction. Discrete fracture and damage tools were utilized to model crack initiation and propagation in pavement systems using the finite element method and TCMODEL was used with the experimental data from the field samples to predict performance and compare it to the field performance data.
In Wisconsin's winter climate, low temperatures can cause asphalt pavements to contract and crack, reducing their ride quality and service lives. To help engineers more accurately determine how well certain pavement designs will fare in such conditions, AASHTO has developed the Mechanistic-Empirical Pavement Design Guide, or MEPDG. Pavement designers can use this manual and accompanying software to predict how pavement distresses will accumulate over time by inputting information about pavement materials, climate and expected traffic levels.
The work detailed in this report represents a continuation of the research performed in phase one of this national pooled fund study. A number of significant contributions were made in phase two of this comprehensive research effort. Two fracture testing methods are proposed and specifications are developed for selecting mixtures based on fracture energy criteria. A draft SCB specification, that received approval by the ETG and has been taken to AASHTO committee of materials, is included in the report. In addition, alternative methods are proposed to obtain mixture creep compliance needed to calculate thermal stresses. Dilatometric measurements performed on asphalt mixtures are used to more accurately predict thermal stresses, and physical hardening effects are evaluated and an improved model is proposed to take these effects into account. In addition, two methods for obtaining asphalt binder fracture properties are summarized and discussed. A new thermal cracking model, called "ILLI-TC," is developed and validated. This model represents a significant step forward in accurately quantifying the cracking mechanism in pavements, compared to the existing TCMODEL. A comprehensive evaluation of the cyclic behavior of asphalt mixtures is presented, that may hold the key to developing cracking resistant mixtures under multiple cycles of temperature.