| 1. |
- Fladvad, M., et al.
(författare)
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Unbound pavement materials' response to varying groundwater table analysed by falling weight deflectometer
- 2021
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Ingår i: Eleventh International Conference on the Bearing Capacity of Roads, Railways and Airfields. - London : CRC Press. - 9781003222880 ; , s. 409-418
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Expected climate changes will in many areas represent a shift towards increased precipitation and more intense rainfall events. This may lead to increased moisture within road structures and possible overloading of road drainage systems. Pavement design methods must therefore be able to predict the behaviour of pavement materials at increased moisture levels. An instrumented accelerated pavement test (APT) has been conducted on two thin flexible pavement structures with coarse-grained unbound base course and subbase materials using a heavy vehicle simulator (HVS). The two pavement structures were identical except for the particle size distribution (PSD) of the subbase materials, where one had a dense 0/90 mm curve with a controlled fines content, and the other had an open-graded 22/90 mm curve. The APT was conducted using constant dual wheel loading, and three different ground- water levels were induced in order to change the moisture content in the structures. Falling weight deflectometer (FWD) measurements were conducted at each groundwater level during the APT. Additional FWD measurements were conducted as the groundwater was lowered after the APT loading was finished. The moisture content in the unbound materials was con- tinuously measured throughout the test. The analysis is focussed on the response of the unbound aggregate layers to varying moisture levels in the pavement structures. Analysis results show how the dense- and open-graded materials respond to the moving groundwater table, and how this affects the deflection of the full structures.
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| 2. |
- Rahman, Mohammad Shafiqur, 1978-, et al.
(författare)
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A model for the permanent deformation behavior of the unbound layers of pavements
- 2021
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Ingår i: Proceedings Eleventh International Conference on the Bearing Capacity of Roads, Railways and Airfields. - London : CRC Press. - 9781003222880 ; , s. 277-287
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This article presents a model for the permanent deformation (PD) behavior of unbound granular materials (UGMs) used in the base and subbase layers of pavement struc- tures. The model was developed based on multistage (MS) repeated load triaxial (RLT) test- ing. This is essentially a modified version of a previously developed model to better suit to field conditions in a simple and effective manner. The model was calibrated for eight com- monly used UGMs using MSRLT tests with a range of moisture contents. For validation, the calibrated models were used to predict the PD behavior of three of the UGMs in MSRLT tests with stress levels and moisture contents different from those used during the calibrations. This model showed better quality of fit when compared with another widely used PD model. The model was further tested successfully for field conditions by capturing the PD behavior of an instrumented pavement test section in a controlled environment using a heavy vehicle simu- lator (HVS) based accelerated pavement testing (APT). Inputs for calibrating the model were based on the readings from the instrumentations. The parameters of the model were adjusted to match the measured data with the predictions. Based on these results for various design conditions, some ranges of values of the material parameters of the model were suggested.
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| 3. |
- Rahman, Mohammad Shafiqur, 1978-, et al.
(författare)
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Impact of introducing longer and heavier vehicles on the bearing capacity of pavement subgrades
- 2021
-
Ingår i: Proceedings Eleventh International Conference on the Bearing Capacity of Roads, Railways and Airfields. - London : CRC Press. - 9781003222880 ; , s. 239-249
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Increasing the maximum permissible gross weight of vehicles from 64 tons to 74 tons on Swedish highways may significantly increase deformation in subgrades requiring extensive and expensive measures for maintenance deep down in the structures. Even though the individual axle load remains the same, longer and heavier vehicles will contain higher pro- portions of tandem and tridem axles and the total load will be superposed on to the subgrade resulting in higher deformations. In this study, the relative impact of single, tandem and tridem axles on subgrade deformation was analyzed based on calculations in a pavement design software called ERAPave. Three structures with different layer thicknesses and varying material properties during the spring-thaw and summer period were analyzed. In general, it was observed that the relative impact is dependent on the thicknesses and material properties of the pavement structure and the subgrade. Weaker subgrade is more affected by the tridem axle followed by tandem and single axle. The tridem axle is more damaging to the sub-grade for thicker and stiffer structures. In certain cases, the single axle showed more impact on the top of the subgrade. The tridem axle showed more vertical deflection in all cases that may induce increased fatigue cracking of the asphalt concrete (AC) layer. Duration of loading was higher for the tridem axle which has more damage potential. Thus, for the whole vehicle, con- taining more tridem axles, the effects may be superposed resulting in greater damage. On the other hand, the higher load carrying capacity of the tandem and tridem axle configurations will reduce the number of trips required to carry the same amount of goods. This may compensate for the increased damage to the subgrade and the impact on the life cycle of the pavement.
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| 4. |
- Vieira, Tiago, 1984-, et al.
(författare)
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Evaluation air void content of drilled porous asphalt mixture cores using non-destructive X-ray computed tomography
- 2021
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Ingår i: Proceedings Eleventh International Conference on the Bearing Capacity of Roads, Railways and Airfields. - London : CRC Press. - 9781003222880 ; , s. 48-58
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Tomography technology is not usual when investigating drilled asphalt cores properties. Currently, there is no internationally recognised standard tomography method for asphalt pavements. Tomography provides, however, a non-destructive alternative to traditional, usually destructive, testing of drilled cores. Furthermore, tomography offers possibilities, which traditional laboratory analyses do not. It is not straightforward to distinguish mastic and aggre- gates in tomography results while air void content is less difficult to assess. To have a more reliable assessment of drilled cores properties found by tomography, the method must be carefully planned, executed, and the results compared to those of traditional laboratory methods. In this work, analysis was carried out using six in-situ drilled cores from a double layered porous asphalt pavement. This allowed a comparison of tomography and a standardised conventional laboratory air void measurement on the exact same samples. Comparisons of the air voids found by tomography in all three directions were also carried out, estimating how anisotropic and heterogeneous the samples are, which is not possible using traditional laboratory tests. As few as four tomography slices can give enough precision in the determination of air void content for the porous layers. No more than eight slices per sample were needed in the suggested tomog- raphy method. The statistical results did not indicate that the air void content determined by tomography is different from the laboratory results.
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| 5. |
- Winter, M., et al.
(författare)
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Validation of national empirical pavement design approaches for cold recycled asphalt bases
- 2021
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Ingår i: Eleventh International Conference on the Bearing Capacity of Roads, Railways and Airfields. - London : CRC Press. - 9781003222880 ; , s. 87-95
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The applied pavement design procedures differ from country to country within Europe. Especially the use of cold recycling materials which is handled similar to hot-mix asphalt (HMA) in the most available guidelines isn’t sufficient researched. To verify developed procedures, practical trial sections are indispensable. Within this study cold recycled asphalt base layers (CRAB) were assessed according to the German procedure for monitoring and evaluation of road surface conditions. It can be concluded, that the general applied empirical design approach, in which the CRAB layer thickness is increased by 50 % compared to a HMA base will result in a feasible pavement structure. In general, the re-designing of the sections according to various national empirical pavement design approaches partly results in high differences for same layer types.
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