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  • 1.
    Ahmed, Abubeker W
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Rahman, Mohammad Shafiqur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Impact of longer and heavier vehicles on the performance of asphalt pavements: A laboratory study2018In: Bearing Capacity of Roads, Railways and Airfields - Proceedings of the 10th International Conference on the Bearing Capacity of Roads, Railways and Airfields, BCRRA 2017, CRC Press/Balkema , 2018, p. 483-490Conference paper (Refereed)
    Abstract [en]

    Historically, Longer and Heavier Vehicles (LHVs) have been permitted to operate in Sweden. Since 1996 and as of the beginning of 2015, the maximum gross vehicle weight of 60 tons and a length of up to 25.25 m have been permitted. The Swedish Transport Administration has decided to further increase the maximum gross vehicle weight to 74 tons and studies are undergoing to evaluate the impact of the proposed LHVs on existing transport infrastructure. To this end, repeated load triaxial tests and indirect tensile fatigue tests were conducted on selected conventional asphalt mixtures to investigate and quantify the impact of single, tandem and tridem axle configurations on permanent deformation and fatigue performances of conventional asphalt pavements. In addition, fatigue tests for selected LHV scenarios were conducted. This paper presents the results of the laboratory tests and simulations conducted. The test results have clearly demonstrated the impact of the different axle configurations on the rutting and fatigue performances of the mixture. Furthermore, such results can explain the significance of axle configuration on modelling the rutting and fatigue performances of asphalt pavements.

  • 2.
    Ahmed, Abubeker W
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Rahman, Mohammad Shafiqur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Impact of tire types and configurations on responses of a thin pavement structure2018In: Advances in Materials and Pavement Performance Prediction: Proceedings of the International AM3P Conference, 2018, London: CRC Press , 2018, p. 271-274Conference paper (Refereed)
    Abstract [en]

    The objective of this study was to assess the impact of tire and tire configurations on the responses of a thin asphalt pavement structure by means of full-scale tests using a Heavy Vehicle Simulator (HVS). A total of six different types of tires, four single and two dual tire configurations, were investigated. The structure was instrumented to measure tensile strains at the bottom of the asphalt layer and vertical stresses and strains in the unbound base, subbase and subgrade layers. The results indicated that, in general, single tire configurations produced higher tensile strain at the bottom of the asphalt layer and higher vertical stresses and strains in unbound base, subbase and subgrade layers.

  • 3.
    Erlingsson, Sigurdur
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Rahman, Mohammad Shafiqur
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Evaluation of Permanent Deformation Characteristics of Unbound Granular Materials by Means of Multistage Repeated-Load Triaxial Tests2013In: Transportation Research Record, ISSN 0361-1981, E-ISSN 2169-4052, no 2369, p. 11-19Article in journal (Refereed)
    Abstract [en]

    Rutting in flexible pavements is often associated with permanent deformation of the unbound granular layer. The current permanent deformation models are applicable only to a single stress path in repeated-load triaxial (RLT) tests, in which the load pulses are of constant amplitude. In this paper, a general approach using the time-hardening concept was introduced to model the permanent deformation of unbound granular materials (UGMs) continuously in multistage (MS) RLT tests, in which load pulses of a range of different amplitudes are applied, to represent field conditions realistically. With this formulation, three existing permanent deformation models were reconstructed, and one of the models was slightly modified, to suit MS loading conditions better. The material parameters of these models were then optimized for three UGMs used in pavement construction with data from MS RLT tests and application of a least squares curve-fitting method to the test data. The goodness-of-fit statistics were computed to evaluate and compare the quality of fit achieved with these models. The shakedown ranges were also calculated for each stress path of the MS RLT tests to compare these models in simulating these ranges. Generally, the time-hardening approach, for which the quality of fit is dependent on the chosen model, was found to work successfully. In this study, the selected models performed quite well, with the modified model showing the closest agreement to the test data. Thus, this approach has the potential to be applied for better modeling and prediction of pavement performance.

  • 4.
    Erlingsson, Sigurdur
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Rahman, Mohammad Shafiqur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology. KTH.
    Evaluation of permanent deformation characteristics of unbound granular materials from multi-stage repeated load triaxial test2013In: Transportation Research Record, ISSN 0361-1981, E-ISSN 2169-4052, no 2369, p. 17p. 11-19Article in journal (Refereed)
    Abstract [en]

    Rutting in flexible pavements is often associated with permanent deformation of the unbound granular layer. The current permanent deformation models are only applicable to a single stress path in repeated load triaxial (RLT) tests. In this paper, a simple approach using the time hardening concept was introduced to continuously model the permanent deformation of unbound granular materials (UGM) in multi-stage (MS) repeated load triaxial (RLT) tests. Three existing permanent deformation models were reconstructed to be implemented with this method and one model was slightly modified to better suit this approach. This approach was validated by calibrating these reconstructed models using data from MS RLT tests on three different UGM used in base layers of flexible pavement structures. The calibrations were done by optimizing the material parameters of the models using least square curve fitting method. The shakedown ranges were also calculated for each stress path of the MS RLT tests to compare these models in simulating these ranges. Generally, very good fits were obtained for these models where the modified model showed the best agreement.

  • 5.
    Erlingsson, Sigurdur
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology. University of Iceland.
    Rahman, Mohammad Shafiqur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Salour, Farhad
    Trafikverket.
    Characteristic of unbound granular materials and subgrades based on multi stage RLT testing2017In: Transportation Geotechnics, ISSN 2214-3912, Vol. 13, p. 28-42Article in journal (Refereed)
    Abstract [en]

    The unbound granular layers (UGM's) and the subgrade of a pavement structure provide a significant support for the structure as a whole. Hence the mechanical properties of these materials are important for the overall performance of the structure. These materials exhibit both non-linear stress dependency and their mechanical properties are highly affected by their moisture content. This paper describes two of the most important material properties of the unbound layers of the pavements, i.e. the resilient and the permanent deformation properties. The stress dependency of UGMs can be captured by the universal model or the enhanced model by Cary and Zapata (2011) for materials with high fine content. The Bishop's effective stress approach can be used for high fine content materials for estimating the effect of suction. UGMs and subgrade materials are further highly dependent on moisture content. Either the AASHTO sigmoidal model can be used to describe the moisture dependency or the simple exponential model described in this paper. The paper further discusses four models to characterize the accumulation of permanent deformation with the number of load repetitions in repeated load triaxial (RLT) testing. The models are all developed to fit single stage (SS) RLT test results but have been extended to fit multi-stage (MS) RLT test results with the aid of the time hardening scheme. The advantage of the MS RLT tests over the SS RLT tests is that it applies a range of stress paths on a single specimen, thus taking into account the effect of stress history and reducing the time and effort required to test a separate specimen for each stress path.

  • 6.
    Rahman, Mohammad Shafiqur
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Characterising the Deformation Behaviour of Unbound Granular Materials in Pavement Structures2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Unbound granular materials (UGMs) used in the base and sub-base layers of flexible pavements play a significant role in the overall performance of the structure. Proper understanding and characterization of the deformation behaviour of UGMs in pavement structures are, therefore, vital for the design and maintenance of flexible pavements. In this study, the resilient deformation (RD) and the permanent deformation (PD) behaviour of UGMs were investigated for the better understanding and improved modelling of these deformation characteristics. The study is based on a series of repeated-load triaxial (RLT) tests carried out on several UGMs commonly used in pavement structures. Here, the influences of stress level and moisture content - two of the most significant factors affecting the deformation behaviour of UGMs - were analysed. The effects of the grain size distribution and the degree of compaction were also considered.

    The study on the RD behaviour indicated that the resilient stiffness (MR)of UGMs increases with the increased bulk stress level, which can be satisfactorily described by the k-θ model. Moisture was found to negatively impact the MR as long as the deformation was mostly resilient with a negligible amount of accumulated PD. Analysis of the influence of moisture on the parameters k1 and k2 of the k-θ model showed that k1 decreases with increased moisture and k2 is relatively insensitive to moisture. Based on these observations, a simple model was developed for the impact of moisture on MR. The performance of this model was comparable to an existing moisture dependent MR model. In contrast, it was further observed that at the later stages of the RLT tests, after a relatively large number of load applications, the MR increased with increased moisture up to the optimum moisture content. This occurred when the RD was accompanied by a significant amount of PD. Further investigation suggested that moisture aided the post-compaction (PC) and possible particle rearrangement that resulted in the increased PD and increased MR. In this case k1 decreased, whereas k2 increased, with increased moisture. The existing MR-moisture model did not work for this behaviour. This suggests that the effect of PC on MRshould be considered in modelling. However, although not explored in this study, it may be possible to simulate this effect of increase in MR with increased moisture due to PC using the proposed model if k2 is expressed as a function of moisture.

    The PD characteristics of UGMs were investigated based on the multistage (MS) RLT test. In contrast with the single stage (SS) RLT test, the MS RLT test accounts for the effect of stress history and enables a comprehensive study of the material behaviour under cyclic stresses of various magnitudes. Since the existing PD models cannot be directly applied for the MS loading procedure, a general formulation based on the time hardening concept was derived that can be used to extend the models for the MS loading conditions. Based on this formulation, some of the current models were calibrated and their performance in predicting the PD behaviour in MS RLT tests was compared. The investigation regarding the impact of moisture on PD showed that moisture significantly increases the accumulation of PD. Generally, materials with finer grading showed more sensitivity to moisture with regards to both PD and RD. To characterize the impact of moisture, moisture sensitivity of different grain size distributions and the impact of the degree of compaction on PD with reduced effort, a simple model was proposed. Unlike some of the well-performing existing models, this model can be calibrated using a single MS RLT test without requiring any separate static failure triaxial tests. This model was validated using the MS RLT test data with satisfactory results. The sensitivity of the parameters of this model was studied with respect to moisture content, degree of compaction and grain size distribution. Some reasonable trends for the sensitivity of the parameters to these influential factors were obtained, which suggests that these may be further developed to incorporate into the model.

  • 7.
    Rahman, Mohammad Shafiqur
    et al.
    KTH.
    Erlingsson, S.
    Influence of moisture on Resilient Deformation behaviour of Unbound Granular Materials2014In: Asphalt Pavements - Proceedings of the International Conference on Asphalt Pavements, ISAP 2014, 2014, p. 571-580Conference paper (Refereed)
    Abstract [en]

    This study investigated the influence of moisture on the Resilient Deformation (RD) properties of Unbound Granular Materials (UGMs). A typical UGM used in pavement constructions with three different grain size distributions were tested with a range of moisture contents using Repeated Load Triaxial tests (RLTTs). From the European standard, the procedure for the study of the RD behaviour was used where each stress path is applied for 100 cycles. Additionally, the Multi-Stage (MS) loading procedure for the study of the permanent deformation behaviour were used where each stress path is applied for 10,000 cycles, to compare the results using the two test procedures. Results showed that resilient modulus (MR) generally decreased with increase in moisture, where the finer grading was more affected. However, for the MS RLTTs, after a large number of load applications, some increase in MR with increasing moisture was observed. This happened when the moisture content increased up to close to the optimum; above the optimum, MR always decreased. This may be due to Post-Compaction (PC) aided by moisture in MS RLTTs where a large number of load cycles were applied.

  • 8.
    Rahman, Mohammad Shafiqur
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology. Kungliga Tekniska Högskolan.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology. University of Iceland.
    A model for predicting permanent deformation of unbound granular materials2015In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 16, no 3, p. 653-673Article in journal (Refereed)
    Abstract [en]

    A simple model has been proposed to characterise the accumulation of permanent deformation (PD) in unbound granular materials (UGMs) under cyclic loading of variable magnitudes. The model was developed based on multi-stage (MS) repeated-load triaxial (RLT) tests. The material parameters of this model can be evaluated using an MS RLT test. The model was validated by calibrating it for a few UGMs with a range of grain size distributions, moisture contents and degrees of compaction.

    The calibrated model was further validated by predicting the PD behaviour of some of these UGMs for different stress conditions. Generally, quite satisfactory predictions were obtained with this model with the advantage of reduced effort required for its calibration compared to some existing models. Additionally, the sensitivity of the parameters of this model to moisture, degree of compaction and grain size distribution was investigated with the aim of incorporating them into the model in future.

  • 9.
    Rahman, Mohammad Shafiqur
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. Swedish National Road and Transport Research Institute (VTI).
    Erlingsson, Sigurdur
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. Swedish National Road and Transport Research Institute (VTI).
    A Model for Predicting Permanent Deformation of Unbound Granular Materials2015In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 16, no 3, p. 653-673Article in journal (Refereed)
    Abstract [en]

    A simple model has been proposed to characterize the accumulation of permanent deformation (PD) in Unbound Granular Materials (UGMs) under cyclic loading of variable magnitudes. The model was developed based on Multi-Stage (MS) Repeated-Load Triaxial (RLT) tests. The material parameters of this model can be evaluated using an MS RLT test. The model was validated by calibrating it for a few UGMs with a range of grain size distributions, moisture contents and degrees of compaction. The calibrated model was further validated by predicting the PD behaviour of some of these UGMs for different stress conditions. Generally, quite satisfactory predictions were obtained with this model with the advantage of reduced effort required for its calibration compared to some existing models. Additionally, the sensitivity of the parameters of this model to moisture, degree of compaction and grain size distribution was investigated with the aim of incorporating them into the model in future.

  • 10.
    Rahman, Mohammad Shafiqur
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. Swedish National Road and Transport Research Institute (VTI).
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute (VTI).
    Characterizing the Impact of Moisture on the Permanent Deformation Behavior of Unbound Granular Materials2015In: Compendium of Papers of the 94th Annual Meeting of the Transportation Research Board, Washington, D.C., 2015Conference paper (Refereed)
    Abstract [en]

    The influence of moisture on the permanent deformation (PD) behavior of several Unbound Granular Materials (UGMs) was investigated through Multi-stage (MS) Repeated-load Triaxial (RLT) tests. Results showed that the accumulation of PD with the number of load applications increased with increased moisture content for all the UGMs. The UGMs with the finer grain size distributions showed greater sensitivity to moisture variations. A simple model was developed to characterize the PD behavior of UGMs under cyclic loading of varying magnitudes. The model was calibrated for the UGMs using the experimental data. Using the model, reasonably good quality of fit was obtained for the UGMs within the range of moisture content used for the tests. Then the material parameters of the model were studied for their sensitivity to moisture. It was found that one parameter varied linearly with the moisture content while the others remained fairly constant. Thus the proposed model with one of its parameters as a linear function of moisture content can be used for predicting the PD behavior of UGMs with variation in moisture.

  • 11.
    Rahman, Mohammad Shafiqur
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. Swedish National Road and Transport Research Institute (VTI).
    Erlingsson, Sigurdur
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. Swedish National Road and Transport Research Institute (VTI).
    Characterizing the Impact of Moistureon the Permanent Deformation Behaviour of Unbound Gronular Materials2014Manuscript (preprint) (Other academic)
  • 12.
    Rahman, Mohammad Shafiqur
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology. Kungliga Tekniska Högskolan.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology. University of Iceland.
    Influence of moisture on Resilient Deformation behaviour of Unbound Granular Materials2014In: Asphalt Pavements: Proceedings of the International Conference on Asphalt Pavements, ISAP 2014, 2014, p. 571-580Conference paper (Refereed)
    Abstract [en]

    This study investigated the influence of moisture on the Resilient Deformation (RD) properties of Unbound Granular Materials (UGMs). A typical UGM used in pavement constructions with three different grain size distributions were tested with a range of moisture contents using Repeated Load Triaxial tests (RLTTs). From the European standard, the procedure for the study of the RD behaviour was used where each stress path is applied for 100 cycles. Additionally, the Multi-Stage (MS) loading procedure for the study of the permanent deformation behaviour were used where each stress path is applied for 10,000 cycles, to compare the results using the two test procedures. Results showed that resilient modulus (MR) generally decreased with increase in moisture, where the finer grading was more affected. However, for the MS RLTTs, after a large number of load applications, some increase in MR with increasing moisture was observed. This happened when the moisture content increased up to close to the optimum; above the optimum, MR always decreased. This may be due to Post-Compaction (PC) aided by moisture in MS RLTTs where a large number of load cycles were applied.

  • 13.
    Rahman, Mohammad Shafiqur
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Influence of post compaction on the moisture sensitive resilient modulus of unbound granular materials2016In: Procedia Engineering, Elsevier, 2016, p. 929-936Conference paper (Refereed)
    Abstract [en]

    The impact of moisture on the resilient modulus (MR) of unbound granular materials (UGMs) was investigated based on repeated load triaxial (RLT) tests and considering the effect of post compaction (PC) from cyclic loading. Results showed that although MR decreases with increased moisture, it may appear to increase with increased moisture if the PC process is aided by moisture for a relatively large number of load applications. When limited PC was involved, the parameter k1 of the k-θ model decreased with increased moisture while the parameter k2 was unaffected. On the other hand, when significant amount of PC took place, k2 increased with increased moisture.

    The mechanistic-empirical pavement design guide (MEPDG) model worked well to capture the influence of moisture on the stiffness when MR decreased with increased moisture. However, it did not work when MR increased with increased moisture due to the PC effect. On the other hand, an alternative approach expressing k1 and k2 as functions of moisture worked well for both situations. Generally, this study suggested that the effect of PC should be considered in modelling the impact of moisture on MR for better accuracy.

  • 14.
    Rahman, Mohammad Shafiqur
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Modelling the moisture dependent permanent deformation behavior of unbound granular materials2016In: Procedia Engineering, Elsevier, 2016, p. 921-928Conference paper (Refereed)
    Abstract [en]

    The impact of moisture on the permanent deformation (PD) behavior of unbound granular materials (UGMs) was investigated based on multistage (MS) repeated load triaxial (RLT) tests. Two UGMs with different particle size distributions were tested for a range of moisture contents and the accumulation of permanent strains for the different moisture contents were modelled using a simple predictive model.

    Moisture was found to increase the accumulation of PD in the materials. Analyses of the variation of the parameters of the model with respect to moisture showed that it is possible to capture the moisture dependent PD behavior of the materials assuming a simple linear relationship between one of the parameters of the model and the moisture content.

  • 15.
    Rahman, Mohammad Shafiqur
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology. Kungliga Tekniska Högskolan.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology. University of Iceland.
    Moisture influence on the resilient deformation behaviour of unbound granular materials2015In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268XArticle in journal (Refereed)
    Abstract [en]

    The influence of moisture on the resilient deformation properties of unbound granular materials was investigated based on repeated load triaxial tests. Results showed that the resilient modulus (MR) decreased with increasing moisture for a relatively low number of load cycles (N) where the deformation behaviour was mostly resilient with a negligible amount of associated accumulated permanent deformation (PD). Modelling attempts on this behaviour were quite satisfactory.

    Furthermore, the MR showed an increasing trend with increasing moisture, up to the optimum, when the N was relatively large with a significant amount of accumulated PD. Above the optimum, the MR generally decreased. Further investigation suggested that moisture aided the post-compaction (PC) and possible particle rearrangement that resulted in the increased PD and increased MR. The existing model did not work in this case indicating that the effect of PC on MR should be considered in modelling.

  • 16.
    Rahman, Mohammad Shafiqur
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. Swedish National Road and Transport Research Institute (VTI).
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute (VTI).
    Moisture Influence on the Resilient Deformation Behaviour of Unbound Granular Materials2016In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 17, no 9, p. 763-775Article in journal (Refereed)
    Abstract [en]

    The influence of moisture on the resilient deformation (RD) properties of unbound granular materials (UGMs) was investigated based on repeated load triaxial (RLT) tests. Results showed that the resilient modulus (MR) decreased with increasing moisture for a relatively low number of load cycles (N) where the deformation behaviour was mostly resilient with a negligible amount of associated accumulated permanent deformation (PD). Modelling attempts on this behaviour were quite satisfactory. Furthermore, the MR showed an increasing trend with increasing moisture, up to the optimum, when the N was relatively large with a significant amount of accumulated PD. Above the optimum, the MR generally decreased. Further investigation suggested that moisture aided the post-compaction (PC) and possible particle rearrangement that resulted in the increased PD and increased MR. The existing model did not work in this case indicating that the effect of PC on MR should be considered in modelling.

  • 17.
    Rahman, Mohammad Shafiqur
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology. Kungliga Tekniska Högskolan.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology. University of Iceland.
    Predicting permanent deformation behaviour of unbound granular materials2015In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 16, no 7, p. 587-601Article in journal (Refereed)
    Abstract [en]

    To reliably predict the permanent deformation behaviour of unbound granular materials (UGM) in a pavement structure, the material parameters of the constitutive models used in design should be evaluated using a multi-stage (MS) loading approach. This paper investigated the prediction of the accumulation of permanent strain in UGM using some current models, extended applying the time-hardening approach, based on MS repeated load triaxial tests (RLTTs).

    The material parameters of these models were optimised for five different UGM used in pavement construction using the MS RLTT data with a specific set of stress levels. With these models, the accumulations of permanent strain in the same materials for MS RLTTs with a different set of stress levels were predicted. Using this approach, three out of the four models performed very well, which may be further developed for field conditions for better prediction of rutting.

  • 18.
    Rahman, Mohammad Shafiqur
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science. Swedish National Road and Transport Research Institute (VTI).
    Erlingsson, Sigurdur
    KTH, School of Architecture and the Built Environment (ABE), Transport Science. Swedish National Road and Transport Research Institute (VTI).
    Predicting permanent deformation behaviour of unbound granular materials2015In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 16, no 7, p. 587-601Article in journal (Refereed)
    Abstract [en]

    To reliably predict the permanent deformation behaviour of unbound granular materials (UGM) in a pavement structure, the material parameters of the constitutive models used in design should be evaluated using a multi-stage (MS) loading approach. This paper investigated the prediction of the accumulation of permanent strain in UGM using some current models, extended applying the time-hardening approach, based on MS repeated load triaxial tests (RLTTs). The material parameters of these models were optimised for five different UGM used in pavement construction using the MS RLTT data with a specific set of stress levels. With these models, the accumulations of permanent strain in the same materials for MS RLTTs with a different set of stress levels were predicted. Using this approach, three out of the four models performed very well, which may be further developed for field conditions for better prediction of rutting.

  • 19.
    Rahman, Mohammad Shafiqur
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Hellman, Fredrik
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Stiffness and permanent deformation characteristics of open-graded unbound granular materials2018In: Bearing Capacity of Roads, Railways and Airfields - Proceedings of the 10th International Conference on the Bearing Capacity of Roads, Railways and Airfields, BCRRA 2017, CRC Press/Balkema , 2018, p. 151-157Conference paper (Refereed)
    Abstract [en]

    This paper presents the investigation of the deformation characteristics of two Open-Graded (OG) Unbound Granular Materials (UGMs) that are generally used in permeable pavement structures. Based on multistage Repeated-Load Triaxial (RLT) tests, the stiffness and resistance against Permanent Deformation (PD) of these materials were compared to their well graded (standard) counterparts. The OG UGMs showed similar stiffness characteristics as standard UGMs. On the other hand, the resistance against PD was slightly worse than the standard UGMs in a relatively dry state. However, the OG UGMs showed less sensitivity to moisture variation, yielding similar performance to that of standard materials at higher moisture content. The parameters of a stiffness model and a PD model were evaluated for these materials which may be used for prediction of rutting, estimating bearing capacity and for layer thickness design, using any suitable pavement design software.

  • 20.
    Rahman, Mohammad Shafiqur
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Hellman, Fredrik
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology. University of Iceland.
    Investigation of the permanent deformation properties of open-graded permeable unbound granular materials2019In: Pavement and Asset Management - Proceedings of the World Conference on Pavement and Asset Management, WCPAM 2017, CRC Press/Balkema , 2019, p. 105-114Conference paper (Refereed)
    Abstract [en]

    Open-Graded (OG) Unbound Granular Materials (UGMs) are generally used in permeable pavement constructions. In this study, the Permanent Deformation (PD) characteristics of two OG UGMs were investigated by means of Multistage (MS) Repeated- Load Triaxial (RLT) tests. The influence of moisture on the PD behavior was also investigated. Compared to a few standard UGMs, these OG UMGs exhibited slightly lower resistance against PD in relatively dry state. On the other hand, these materials were less sensitive to moisture. Therefore, at higher moisture content, the OG UGMs and the standard UGMs showed identical PD behavior. Furthermore, the accumulation of PD was modelled using a simple model which may be used for prediction of rutting, estimating bearing capacity, and for layer thickness design, using a suitable pavement design software.

  • 21.
    Said, Safwat F.
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Lundberg, Thomas
    Swedish National Road and Transport Research Institute, Infrastructure, Infrastructure maintenance.
    Rahman, Shafiqur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Carlsson, Håkan
    Swedish National Road and Transport Research Institute, Infrastructure, Measurement technology and engineering workshop.
    McGarvey, Terence
    Swedish National Road and Transport Research Institute, Infrastructure, Infrastructure maintenance.
    Ahmed, Abubeker
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Enocksson, Carl-Gösta
    Trafikverket.
    Utförandets inverkan på hållbarhet för beläggningslager2019Report (Other academic)
    Abstract [en]

    Non-destructive testing in quantifying the asphalt pavement layers homogeneity can be used for the quality assurance in paving contracts. This paper summarizes the findings from a field study on segregation in bituminous pavement mixes that relates pavement layer surface texture to the homogeneity of the paved bituminous layer by distinguishing mix segregated area. The mean profile depth (MPD) values of paved layer were measured. Based on these values three locations on the road were identified having low, intermediate and high MPD values. Thereafter, cored samples were tested for stiffness modulus before and after moisture conditioning by performing the moisture induced sensitivity test (MIST). Results clearly showed that the samples from the locations with high MPD values were mostly affected by the moisture conditioning for which the stiffness moduli were significantly reduced. The samples with high MPD values had the highest air voids as well. Thus, this study demonstrated that construction quality described by segregation in the paved asphalt mix has a significant impact on the moisture sensitive performance of pavements. A limited number of falling weight deflectometer (FWD) measurements were performed at positions with different degree of separation in the road base layer. There was a tendency for the effect of separation in the road base layer on FWD even though there was a variation in data. The strong correlation between the MPD values and change in stiffness modulus also suggests that the measurements of the MPD values can be a reliable and non-destructive method for evaluating the construction quality of a pavement and in developing the quality assurance criteria based on pavement performance that can be used in paving contracts.

  • 22.
    Salour, Farhad
    et al.
    Trafikverket.
    Rahman, Mohammad Shafiqur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology. University of Iceland.
    Characterizing Permanent Deformation of Silty Sand Subgrades by Using a Model Based on Multistage Repeated-Load Triaxial Testing2016In: Transportation Research Record, ISSN 0361-1981, E-ISSN 2169-4052, no 2578, p. 47-57Article in journal (Refereed)
    Abstract [en]

    A simple model for the prediction of permanent deformation of unbound pavement material was used to characterize the accumulation of permanent deformation of unsaturated silty subgrade soils from multistage repeated-load triaxial (RLT) tests. The model incorporated the time hardening concept; data obtained from RLT tests with cyclic loading of variable magnitudes, conducted on a single specimen, could be used to calibrate the material model parameters. This feature of the model allowed for characterizing the accumulation of permanent deformation of the material under a wide range of stress conditions.

    The tests were carried out on two silty sand subgrades and at different moisture contents with pore suction measurements (matric suction) incorporated into the stress state calculations used in the modeling. The shakedown ranges for the permanent deformations for each stress path were calculated, and the material parameters of the predictive models were optimized with the RLT test data. In general, the models performed satisfactorily in capturing the permanent deformation behavior of the selected subgrade materials.

    The model includes fewer parameters as compared with some existing permanent deformation models and requires reduced testing effort because it is based on results from a multistage RLT test with a single specimen. It can be concluded that the model and the approach have great potential for characterizing and modeling the permanent deformation of subgrade soils.

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