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Flow behavior of asphalt mixtures under compaction
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.ORCID iD: 0000-0002-5526-5896
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Asphalt compaction is one of the most important phases of road construction, being the decisive phase when the structure of the asphalt pavement layer is formed. In spite of its importance, the knowledge about this construction phase is still based on empirical and technological background and therefore surprisingly limited. This lack of knowledge is also due to the fact that the existing laboratory scale compaction devices for mix design are not fully capable of simulating the field compaction. The simulation of asphalt compaction in the laboratory is normally focused on the vertical rearrangements of asphalt particles whereas the flow behavior of these particles in other directions is mostly neglected. However, existing literature suggests that the neglected flow is one of the most important factors for the quality of the road construction, particularly in special cases such as asphalt joints. Therefore, building up a better understanding of the flow behavior of asphalt mixtures subjected to compaction loads is needed for improving the quality of the pavements.

In this study, a new test setup, the so called Compaction Flow Test (CFT), was developed to simulate the flow behavior of asphalt mixtures at early stages of compaction. In the first step, feasibility tests were performed, substituting asphalt mixtures by model materials with simple geometries and less complex properties. X-ray Computed Tomography (CT) was utilized for capturing 2D radiography images of the flow patterns in the model material during the test. Results of the CFT showed the capability of the new test setup to clearly distinguish between model mixtures with different characteristics. Hence, in the next step, the CFT was applied to real asphalt mixtures and the obtained results were found to support the findings of the feasibility tests with the model materials.

The results from the feasibility tests encouraged examining the possible use of an ultrasonic sensor as alternative to the complex and costly X-ray imaging for flow measurements during the CFT. Hence, the CFT was used along with a distance measuring ultrasonic sensor for testing asphalt mixtures with different characteristics. The test results confirmed that an ultrasonic sensor could be effective for capturing the differences of the flow behavior of asphalt mixtures tested by the CFT. 

In addition, a parametric study with the X-ray setup was carried out to examine the capability of the CFT in reflecting the possible changes of the flow behavior in asphalt mixtures due to the change of construction parameters such as lift thickness, bottom roughness and compaction modes. The results obtained also confirmed the capability of the CFT in showing the possible differences in the flow behavior of the mixtures under the chosen conditions.

The encouraging results suggested that the CFT may have potential to become a simple but effective tool for assessing compactability of the mixtures on-site, right after production in an asphalt plant or before placing the mixture on the road. Hence, discrete element method (DEM) was utilized to understand both the influence of selected boundaries of the CFT and the effect of its design on the results.

As one specific example of application, an investigation was carried out using the CFT to find the most suitable tracking method for flow measurements in the field. Based on the literature review and feasibility tests, a tracking method with the highest potential for conducting flow measurements during field compaction was introduced. X-ray radiography confirmed the validity of the results obtained with the suggested method.

The overall results obtained from this study suggest that the recommended CFT along with the suggested field tracking method may be helpful in building up a comprehensive basis of knowledge on the flow and compaction behavior of asphalt mixtures thus helping to close the gap between the field and laboratory.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017. , p. 59
Series
TRITA-BYMA, ISSN 0349-5752 ; 2017:07
National Category
Infrastructure Engineering
Research subject
Transport Science
Identifiers
URN: urn:nbn:se:kth:diva-219857ISBN: 978-91-7729-635-5 (print)OAI: oai:DiVA.org:kth-219857DiVA, id: diva2:1165645
Public defence
2018-01-25, Teknikringen 56, Kemi, våningsplan 3, Stockholm, 13:00 (English)
Supervisors
Note

QC 20171214

Available from: 2017-12-14 Created: 2017-12-13 Last updated: 2017-12-14Bibliographically approved
List of papers
1. Particle Flow during Compaction of Asphalt Model Materials
Open this publication in new window or tab >>Particle Flow during Compaction of Asphalt Model Materials
2015 (English)In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 100, no 15, p. 273-284Article in journal (Refereed) Published
Abstract [en]

Compaction is one of the key phases of the pavement construction and has been subject of research for a long time. However, very little is known regarding what really happens during compaction and how the pavement structure and the aggregate skeleton of the asphaltic layer are formed. Studies on that matter are of special practical importance since they may contribute to reduce the possibility of over-compaction and aggregate crushing. In this study, a new test method (Flow Test) was developed to simulate the material flow during compaction. Initially, asphalt materials were substituted by model materials to lower the level of complexity for checking the feasibility of the new test method as well as modeling purposes. Geometrically simple materials with densest possible combinations were tested for both dry and coated mixtures. X-ray radiography images were used for evaluating the material flow during compaction for different model mixtures. Results showed the capability of the test method to clearly distinguish mixtures with different properties from one another and also the potential of such a method to be used as an evaluating tool in the field. In addition, a simple discrete element model was applied for better understanding the flow of the model material during compaction as a basis for further improvement when moving from the asphalt model material to real mixtures. Therefore, real mixtures were prepared and tested under the same test configuration as for the model materials. The overall results of the real mixtures were found to support the model material test results.

Place, publisher, year, edition, pages
Elsevier, 2015
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-176318 (URN)10.1016/j.conbuildmat.2015.09.061 (DOI)000364608000029 ()2-s2.0-84944346091 (Scopus ID)
Note

Updated from Accepted to Published. QC 20160210

Available from: 2015-11-03 Created: 2015-11-03 Last updated: 2017-12-13Bibliographically approved
2. A new test to study the flow of mixtures at early stages of compaction
Open this publication in new window or tab >>A new test to study the flow of mixtures at early stages of compaction
2016 (English)In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 49, no 9, p. 3547-3558Article in journal (Refereed) Published
Abstract [en]

Workability is one of the most commonly used indicators for the capability of asphalt mixtures tobe placed and compacted on the roads with long lasting quality and minimum maintenancethroughout its service life. Despite of valuable previous efforts for measuring and characterizingworkability, none of them has proven successful in representing the field conditions of roadconstructions. This paper is an attempt towards developing a systematic workability test methodfocusing on compaction, the so-called Compaction Flow Test (CFT), by simulating fieldcompaction at early stages and at laboratory scale with the main focus on mixture flow. The CFTwas applied for different mixtures in order to identify the parameters with highest impact on theasphalt particle movements under compaction forces. A new setting inside X-ray ComputationalTomography (CT) allowed tracing asphalt particles during the CFT and acquiring CT imagesunderlining the reliability of the CFT results. In addition, simple Discrete Element Models (DEM)were successfully generated to justify some of the CFT results.

Place, publisher, year, edition, pages
Kluwer Academic Publishers, 2016
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-176317 (URN)10.1617/s11527-015-0738-8 (DOI)000379590900005 ()2-s2.0-84945556719 (Scopus ID)
Note

QC 20160818

Available from: 2015-11-03 Created: 2015-11-03 Last updated: 2017-12-13Bibliographically approved
3. Modelling the flow behavior of asphalt under simulated compaction using discrete element
Open this publication in new window or tab >>Modelling the flow behavior of asphalt under simulated compaction using discrete element
(English)In: Materials and DesignArticle in journal (Refereed) Submitted
Abstract [en]

The flow differences between the particles of asphalt mixtures compacted in the laboratory and in the field have been identified as one of the reasons for the discrepancies between laboratory and field results. In previous studies, the authors developed a simplified test method, the so-called compaction flow test (CFT), for roughly simulating the flow of particles in asphalt mixtures under compacting loads under laboratory conditions. The CFT was used in different studies to examine its capability of revealing the differences between the flow behavior of different asphalt mixtures under different loading modes. The promising results encouraged further development of the CFT by investigating the impact of simplifications and boundary conditions on the results of the test. For this reason, discrete element method (DEM) was utilized and the possible impacts of the mold size as well as the shape of the loading strip on the results of the CFT were simulated for a mixture with extreme idealized aggregate structure. The results indicate that in case of wearing course layers with a single size gradation of 11mm spheres, the length of the CFT mold can be increased from 150mm to 200-250mm for reducing disturbances from walls of the mold. However, since the majority of the flow is expected to take place within the first 100-150mm length of the mold, reasonable results are obtained even without changing the size of the CFT mold. Moreover, comparing results with different loading strip geometries and loading rates indicates that the current CFT setup still appears to provide consistent results.    

National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-219870 (URN)
Note

QC 20171214

Available from: 2017-12-13 Created: 2017-12-13 Last updated: 2017-12-14Bibliographically approved
4. Introducing a new method for studying the field compaction
Open this publication in new window or tab >>Introducing a new method for studying the field compaction
2017 (English)In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 18, p. 26-38Article in journal (Refereed) Published
Abstract [en]

The flow of particles during compaction may have a prominent influence on the difference of field and laboratory results as recently demonstrated by the authors with their newly developed compaction flow test (CFT). This test with a simple compaction simulator was used for studying the flow behaviour and rearrangement of particles for mixtures with different structures and thicknesses. However, validating the CFT results for practical purposes requires field measurements that provide more insight into the compaction process and eventually allowing to adjust the CFT for further use as an evaluating in-site tool. This study presents a new method for conducting such measurements during field compaction. In this method, some representative particles are tracked inside asphalt specimens and the accuracy of the results is examined by X-ray computed tomography. The results of the feasibility tests show that this method has potential for further use in the field and for building up a comprehensive basis of knowledge on field compaction towards closing the gap between the field and laboratory results.

Place, publisher, year, edition, pages
TAYLOR & FRANCIS LTD, 2017
Keywords
asphalt compaction, CFT, magnetic field, X-ray computed tomography
National Category
Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-208735 (URN)10.1080/14680629.2017.1304245 (DOI)000402301700004 ()2-s2.0-85016113084 (Scopus ID)
Note

QC 2017-06-13

Available from: 2017-06-13 Created: 2017-06-13 Last updated: 2017-12-13Bibliographically approved

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