6 research outputs found

    Development of a phenomenological constitutive model for fracture resistance degradation of asphalt concrete with damage growth due to repeated loading

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    Discontinuous areas under the asphalt concrete (AC) layer, such as joints and cracks in an underlying layer, induce higher stress concentration than the designed strength. Stress concentration in the vicinity of discontinuities accelerates distress on the AC layer. Repeated traffic and environmental loading applied to the AC layer also induce degradation of the layer’s strength as microcracks grow at stress levels lower than the layer’s designed strength. In addition, this could be magnified when combined with low temperature cracking, one of the main distresses in AC pavements resulting from extreme temperature changes. When loading is applied near the joints or discontinuity, it amplifies the tensile stress at the bottom of the AC layer as well as the shear stress when the Portland cement concrete (PCC) slab or discontinuity moves vertically. Repetitive traffic loading and environmental changes cause continuous damage accumulations which consequently results in the acceleration of movement in the AC layer at the localized area close to the discontinuity region, thus leading to mechanical degradation of the AC materials which become less resistant to fracture. Even a small load can result in fracture failure of AC pavements when the loss of strength in AC pavements progresses significantly through repeated loading. The current approach to determine the critical properties of AC materials is to conduct laboratory testing under monotonic loading and cyclic loading separately. The fatigue testing under cyclic loading can only provide bulk material properties without consideration to any discontinuities, such as cracks in underlying pavement or joints. On the other hand, the current fracture tests conducted under monotonic loading fail to capture the loss of material strength as repeated loading is applied on pavements. For an accurate estimation of pavement life, it is essential to consider the effect of repeated traffic and thermal loading on the fracture resistance of the AC materials. This study investigates the degradation of the fracture resistance of AC materials as a result of the progressive damages caused by repeated loading application. The study develops the phenomenological constitutive model for fracture resistance degradation with damage growth caused by repeated loading. An experimental program was designed to apply monotonic and cyclic loading to the same test geometry and to examine the degradation of fracture properties with damage growth at the crack tip. Fracture and fatigue tests were implemented using semi-circular bending (SCB) test geometry with notched specimens at various temperatures, loading frequencies, and loading amplitudes. It is observed that damage functions and proposed parameters reflect the degradation rate of fracture resistance with respect to damage growth at the notch tip region. A presented constitutive model accurately predicts the remaining service life of existing pavements. It is further observed that the model coefficient distinguishes AC materials in terms of sensitivity to cracking resistance under both monotonic and cyclic loading.U of I OnlyGraduate College 2-year Extension For

    Development of a phenomenological constitutive model for fracture resistance degradation of asphalt concrete with damage growth due to repeated loading

    No full text
    Discontinuous areas under the asphalt concrete (AC) layer, such as joints and cracks in an underlying layer, induce higher stress concentration than the designed strength. Stress concentration in the vicinity of discontinuities accelerates distress on the AC layer. Repeated traffic and environmental loading applied to the AC layer also induce degradation of the layer’s strength as microcracks grow at stress levels lower than the layer’s designed strength. In addition, this could be magnified when combined with low temperature cracking, one of the main distresses in AC pavements resulting from extreme temperature changes. When loading is applied near the joints or discontinuity, it amplifies the tensile stress at the bottom of the AC layer as well as the shear stress when the Portland cement concrete (PCC) slab or discontinuity moves vertically. Repetitive traffic loading and environmental changes cause continuous damage accumulations which consequently results in the acceleration of movement in the AC layer at the localized area close to the discontinuity region, thus leading to mechanical degradation of the AC materials which become less resistant to fracture. Even a small load can result in fracture failure of AC pavements when the loss of strength in AC pavements progresses significantly through repeated loading. The current approach to determine the critical properties of AC materials is to conduct laboratory testing under monotonic loading and cyclic loading separately. The fatigue testing under cyclic loading can only provide bulk material properties without consideration to any discontinuities, such as cracks in underlying pavement or joints. On the other hand, the current fracture tests conducted under monotonic loading fail to capture the loss of material strength as repeated loading is applied on pavements. For an accurate estimation of pavement life, it is essential to consider the effect of repeated traffic and thermal loading on the fracture resistance of the AC materials. This study investigates the degradation of the fracture resistance of AC materials as a result of the progressive damages caused by repeated loading application. The study develops the phenomenological constitutive model for fracture resistance degradation with damage growth caused by repeated loading. An experimental program was designed to apply monotonic and cyclic loading to the same test geometry and to examine the degradation of fracture properties with damage growth at the crack tip. Fracture and fatigue tests were implemented using semi-circular bending (SCB) test geometry with notched specimens at various temperatures, loading frequencies, and loading amplitudes. It is observed that damage functions and proposed parameters reflect the degradation rate of fracture resistance with respect to damage growth at the notch tip region. A presented constitutive model accurately predicts the remaining service life of existing pavements. It is further observed that the model coefficient distinguishes AC materials in terms of sensitivity to cracking resistance under both monotonic and cyclic loading.U of I OnlyAuthor submitted an U of I Access for 2 Years extension request, which was approved by the Graduate College Thesis Office

    Development of an Economical Thin, Quiet, Long-Lasting, High Friction Surface Layer for Economical Use in Illinois, Volume 2: Field Construction, Field Testing, and Engineering Benefit Analysis

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    This project provides techniques to improve hot-mix asphalt (HMA) overlays specifically through the use of special additives and innovative surfacing technologies with aggregates that are locally available in Illinois. The ultimate goal is to improve pavement performance through optimized materials while also controlling cost by efficiently using local materials. Therefore, the proposed new mixes use locally available aggregates when possible. The project also considered the use of alternative aggregates such as steel slag to increase the friction quality of the HMA and therefore improve pavement performance. To evaluate the newly developed wearing course mixtures and evaluate their performance under actual traffic loading, test pavements were constructed, including control mixtures, between August and November 2010 in northern Illinois. The newly proposed mixtures include fine dense-graded HMA and stone matrix asphalt (SMA). The fine dense-graded HMA was designed using the Bailey method and developed with the hope of improved compactability for thinner asphalt layers. The SMA contained a 4.75-mm nominal maximum aggregate size (NMAS) that allows for layers as thin as 0.75 in. On-site performance tests were conducted at 4-month intervals following construction; the tests include noise, friction, rutting, and texture profiling. An engineering benefit analysis was performed to evaluate the new mixes’ cost effectiveness. New HMAs are proposed, along with alternative cross-sections that improve pavement performance while controlling costs.Illinois Department of Transportation R27-42published or submitted for publicationnot peer reviewe

    Development of an Economical, Thin, Quiet, Long-Lasting, High Friction Surface Layer, Volume 1: Mix Design and Lab Performance Testing

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    This project developed and evaluated four new asphalt concrete (AC) mixtures that use locally available aggregates whenever possible with the ultimate goal of a cost-effective mixture that also improves pavement performance. Although numerous tactics have previously been introduced to improve the performance of asphalt pavement, these improvements often add expenses because they use unnecessarily large amounts of high quality aggregates and highly modified binder. The Illinois Department of Transportation initiated a program to develop sustainable asphalt pavements that use locally available aggregates as much as possible to reduce the material cost while also improving performance. These new mixtures were developed using the Bailey method to provide a promising aggregate structure that makes it possible to ensure compactability at thinner layers. The newly developed mixes use locally available natural aggregates such as dolomite, and including smaller amounts of imported materials such as quartzite, steel slag, and fibers to improve their performance in terms of durability, rut resistance, moisture susceptibility, fracture, and complex modulus. To evaluate the performance of each new mixture, five laboratory tests were conducted at the Advanced Transportation and Research Engineering Laboratory (ATREL), and the results suggest a preferred mixture.Illinois Department of Transportation R27-42published or submitted for publicationnot peer reviewe
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