| 1. |
- Ademuyiwa, Adesoji O., et al.
(författare)
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Determinants of morbidity and mortality following emergency abdominal surgery in children in low-income and middle-income countries
- 2016
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Ingår i: BMJ Global Health. - : BMJ Publishing Group Ltd. - 2059-7908. ; 1:4
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Tidskriftsartikel (refereegranskat)abstract
- Background: Child health is a key priority on the global health agenda, yet the provision of essential and emergency surgery in children is patchy in resource-poor regions. This study was aimed to determine the mortality risk for emergency abdominal paediatric surgery in low-income countries globally.Methods: Multicentre, international, prospective, cohort study. Self-selected surgical units performing emergency abdominal surgery submitted prespecified data for consecutive children aged <16 years during a 2-week period between July and December 2014. The United Nation's Human Development Index (HDI) was used to stratify countries. The main outcome measure was 30-day postoperative mortality, analysed by multilevel logistic regression.Results: This study included 1409 patients from 253 centres in 43 countries; 282 children were under 2 years of age. Among them, 265 (18.8%) were from low-HDI, 450 (31.9%) from middle-HDI and 694 (49.3%) from high-HDI countries. The most common operations performed were appendectomy, small bowel resection, pyloromyotomy and correction of intussusception. After adjustment for patient and hospital risk factors, child mortality at 30 days was significantly higher in low-HDI (adjusted OR 7.14 (95% CI 2.52 to 20.23), p<0.001) and middle-HDI (4.42 (1.44 to 13.56), p=0.009) countries compared with high-HDI countries, translating to 40 excess deaths per 1000 procedures performed.Conclusions: Adjusted mortality in children following emergency abdominal surgery may be as high as 7 times greater in low-HDI and middle-HDI countries compared with high-HDI countries. Effective provision of emergency essential surgery should be a key priority for global child health agendas.
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| 2. |
- Ahmed, Abubeker W, 1981-, et al.
(författare)
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Pavement performance follow-up and evaluation of polymer-modified test sections
- 2019
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Ingår i: The international journal of pavement engineering. - : Taylor and Francis Ltd.. - 1029-8436 .- 1477-268X. ; 20:12, s. 1474-1487
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Tidskriftsartikel (refereegranskat)abstract
- Between 2003 and 2006, a test road consisting of several conventional and polymer-modified structures was built on a motorway. Different combinations of styrene–butadiene–styrene (SBS) and ethyl vinyl acetate (EVA) polymer-modified binders were used. The test structures have been in service since then and have been monitored for over 9 years. The resistance of the different types of asphalt concrete mixes to rutting and cracking was measured and predicted. The impact of ageing on the mixes was also evaluated. Although all the sections are in good condition after 9 years of traffic, the predicted differences between the test sections based on the PEDRO (Permanent Deformation of asphalt concrete layers for Roads) approach and laboratory evaluations are noticeable. Lateral wander and transverse profile measurements indicated that studded winter tyre wear contributed to most of the rutting compared to permanent deformation due to heavy traffic. The unmodified mixes exhibited considerable ageing and the SBS-modified mixes were least affected by ageing. Furthermore, the SBS-modified base mix produced significantly better fatigue resistance than the conventional base mix. However, further investigations of the relationships between bitumen and mix properties and further follow-ups of the test sections are recommended to validate the findings.
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| 3. |
- Ahmed, Abubeker W, 1981-, et al.
(författare)
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Utilizing GPR and FWD for Pavement Structural Assessment and Moisture Detection
- 2024
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Tillståndet hos vägöverbyggnader påverkas bland annat av förekomsten av vatten och fukt i vägkonstruktionen. Förekomst av vatten accelererar nedbrytningen av vägen och leder till dyra underhållskostnader. Forskningen har visat att betydande vägandelar behöver tidigarelägga underhållsåtgärder, oavsett trafikvolymen på grund av fuktrelaterade skador. Övervakning av fuktförhållanden i synnerhet med icke-förstörande och kontinuerliga metoder är därför bra att ha vid val av lämplig underhållsåtgärd. Dessutom är det värdefullt att känna till fukttillståndet i vägen för en mer korrekt bedömning av bärighetsmätningar med FWD (fallviktapparat) eller TSD (Traffic Speed Deflectometer), särskild under våren (upptiningsperiod).I denna studie används en flermottagande markradar (GPR) och en fallviktsdeflektometer för bedömning av fuktnivåer och strukturellt tillstånd för en fullskalig vägkonstruktion inomhus. Grundvattennivåer i vägkonstruktionen varierades genom tillförsel av vatten i testkonstruktionen. GPR-mätningarna rapporterar en relativ vattenhalt i testkonstruktionen. Resultaten visade en uppenbar korrelation mellan fallviktsmätningarna och de genomsnittliga GPR-hastighetsmätningarna för de undersökta testerna. Vidare forskning av andra GPR-parametrar, såsom frekvens, magnitud och amplitud för GPR-signalen, rekommenderas.
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| 4. |
- Bekele, Abiy, 1983-
(författare)
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Application of Automated Non-contact Resonance Testing for Low Temperature Behavior of Asphalt Concrete
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Impact resonance testing is a well-documented non-destructive testing method and its applications on asphalt concrete have also been implemented successfully. The test is carried out manually by inducing an impact in order to excite the test specimen and taking measurements of the vibrational response. In an effort to improve the manual procedure of impact resonance testing, an automated non-contact methodology is developed and its applicability with regards to low temperature behaviors of asphalt concrete is investigated. Results from this work show that repeatable fundamental resonance frequency measurements can be performed on a disc shaped specimen in an automated manner without the need to open the thermal chamber. The measurements obtained from the new method have been verified by taking similar resonance frequency measurements using an instrumented impact hammer. It has also been shown in this work that the proposed method is suitable to investigate the lone effects of cyclic thermal conditioning on asphalt concrete without any other possible biasing effects associated with contact in the conventional testing. A hysteretic behavior of stiffness modulus is obtained on three different asphalt concrete specimens subjected to repeated low temperature cyclic conditioning. Reduced modulus values at each temperature are obtained in all the tested specimens after a low temperature stepwise conditioning at temperatures from 0oC to -40 oC. This observed behavior shows that the dynamic modulus of the tested specimens is affected by low temperature conditioning. The norm of the complex modulus decreases and the phase angle or damping ratio increases after low temperature conditioning. Hence, valuable and practical low temperature characteristics of different asphalt concrete mixtures can possibly be obtained by using the proposed methodology.
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| 5. |
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| 6. |
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| 7. |
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| 8. |
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| 9. |
- Erlingsson, Sigurdur, et al.
(författare)
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Influence of heavy traffic lateral wander on pavement deterioration
- 2012
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Ingår i: EPAM 2012. - Linköping : Statens väg- och transportforskningsinstitut. - 9789163714320
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Lateral wander of the traffic has an impact on the degradation development of pavements. This is usually not accounted for in the structural design process. Facilities with wide carriageways and broad shoulders tends to have relatively large lateral spreading while narrow road facilities lacking any shoulders can have highly channelized traffic pattern. In this research lateral wander characteristics have been measured for different road facilities. They can be assumed follow a normal distribution where the standard deviation describes their lateral spreading. Rut depth has thereafter been estimated according to two new rutting calculation scheme where lateral wander characteristics has been taken into account. The first approach is based on a two step mechanistic empirical (M-E) evaluation of the permanent strain in all layer of the structure and using a time hardening approach to sum up for all wander locations. This has thereafter been used to estimate the difference in rutting development as a function of the standard deviation. The second approach concentrates on calculating the permanent strain visco-elastically in the bound layers of the structure. Both procedures can be used to estimate the rate of relative deterioration for different road facilities. Based on the same structure the first approach give around 6 % increase in the surface rut as the standard deviation of the lateral wander increases from 10 to 20 cm. The second approach estimates this difference to be around 20 %. The difference between the two approaches are partly explained due to that the first approach estimates the rut based on all layers but the second approach from the bound layers only.
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| 10. |
- Fadil, Hassan
(författare)
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Spherical Indentation Technique for Multiscale Characterisation of Asphalt Mixtures
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The viscoelastic properties of asphalt mixtures strongly influence the performance of flexible pavements with respect to their resistance to several common distress modes. Therefore, accurate measurement of these properties and their change during the service life is an important area of ongoing research. Despite considerable progress in this field, certain questions are still not fully resolved. In particular, commonly used experimental methods cannot be applied for the viscoelastic characterisation of thin asphalt layers and asphalt overlays. Moreover, measuring the viscoelastic properties of the downscaled sub-phases of asphalt mixtures, such as mastic or mortar, in the field remains a challenge. Understanding the viscoelastic properties of those sub-phases is crucial for gaining fundamental insight into the mixture performance. In this context, advanced and computationally efficient micromechanical models are also needed in order to establish the quantitative link between the viscoelastic properties of asphalt mixtures and of their sub-phases. This thesis aims to contribute to this important area through the development of new experimental and modelling tools for the multiscale characterisation of asphalt mixtures. In this thesis, a new micromechanical modelling approach for bitumen-aggregate composites is proposed and used to investigate the mechanical behaviour of mastic, mortar and asphalt mixtures. To achieve computational efficiency, the proposed approach is based on a simplified, computer-generated representation of materials internal structure and utilises periodic boundary conditions to reduce the representative volume element size. Based on the Dynamic Shear Rheometer (DSR) measurements, it is shown that the proposed model can capture the measured viscoelastic behaviour of mastics for the range of loading, temperature and material parameters examined. For the modelling of mortar and asphalt mixtures, the multiscale approach is applied in order to improve computational efficiency. Obtained computational results indicate that the developed approach is capable of capturing the mixtures’ macro-scale viscoelastic properties with reasonable accuracy. An instrumented indentation test for the viscoelastic characterisation of bitumen and bitumen-aggregate composites, such as mastic, mortar and asphalt mixtures is proposed in this thesis as a new alternative to existing techniques. A new methodology for the indentation testing of linear viscoelastic materials is developed, allowing their characterisation at arbitrary non-decreasing loading. In order to extend the developed method to the multiscale characterisation of bitumen-aggregate composites, the spherical indentation on different types of asphalt mixtures, such as asphalt mortar, mastic asphalt (MA) and asphalt concrete (AC), has been investigated experimentally and through micromechanical modelling. The effect of the indentation test parameters on the measured apparent viscoelastic properties of bitumen-aggregate composites has been evaluated. A particular emphasis is put on the identification of test parameters corresponding to the characterisation of binder-aggregate composites on the macroscale as well as on the individual component scale. The experimental results demonstrate that the developed indentation test can capture the macroscale properties of materials reasonably well, and the obtained results correlate linearly with the properties measured with established test methods. Furthermore, in order to gain better insight into mastic phase properties from the indentation tests performed on MA and AC, a new statistical analysis procedure has been developed for the evaluation of a series of indentation tests. The developed procedure allows identifying clusters of measurements capturing the mastic- and aggregate-dominated responses of the asphalt mixture. The indentation measurements attributed to mastic-dominated response are found to be more sensitive to the temperature and mastic properties as compared to the mean measurements of the indentation test series. The obtained results indicate that the developed indentation test is a viable alternative to existing viscoelastic characterisation methods, in particular as the test is quasi-non-destructive and can be used to characterise thin asphalt layers. Furthermore, combined with the developed statistical analysis procedure, indentation testing is a promising tool to monitor the changes in the mastic phase of the materials due to ageing, moisture damage or fatigue from the measurements on asphalt mixtures without extracting the binder. The developed micromechanical model can also be used to quantify the effect of changing mastic properties on the asphalt mixture performance. This is particularly true for the strain localisations in the mastic phase and thus the mixture’s damage resistance.
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| 11. |
- Gustafson, Kent, 1951-, et al.
(författare)
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Bearing capacity of flexible road structures reinforced with steel fabrics
- 2002
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Ingår i: Bearing Capacity Of Roads, Railways and Airfields. - London : CRC Press. - 9781000108101 - 9789058093967 ; , s. 423-432
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The EU-project REFLEX, "Reinforcement of Flexible Road Structures with Steel Fabrics to Prolong Service Life" is a three-year study (1999-2002) with the main objective to develop a new methodology of road construction and rehabilitation with the use of steel reinforcement fabrics. The result will be gained through a mix of work comprising experimental as well as theoretical work. Of great importance is accelerated pavement testing and test roads to verify the results of the laboratory work and to validate and calibrate theoretical models. Accelerated tests were carried out with the Heavy Vehicle Simulator HVS-NORDIC. Further within the frame of the project a number of test roads, some already existing and some built during the project, were investigated. This paper presents the performance and results from some of the full-scale tests.
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| 12. |
- Hakim, Hassan, et al.
(författare)
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Glimmer i bitumenbundna beläggningar : inverkan av fina, fria glimmerkorn
- 2002
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- På senare tid har man på sina håll observerat en del skador på vägarna vilketman tror beror på ökad halt av glimmer i finandelen. Mot den bakgrunden harVTI på uppdrag av Vägverket undersökt effekten av glimmerhalt i en massaunder simulerade vinterförhållande. Syftet med det här arbetet är att belysaeffekten av förekomst av fina glimmerkorn i bergkrossmaterial påmassabeläggningars egenskaper och eventuellt också ta fram rekommendationerför gränsvärden på glimmerhalt hos asfaltmassor. Fyra serier av asfaltprovhar tillverkats innehållande varierande halter av glimmerkorn. Seriernaundersöks och utvärderas med hänsyn till styvhetsmodul, svällning och ev.indirekt draghållfasthet. Proverna har konditionerats under inverkan avsaltlösning och vatten samt frys-töcykler. Rena glimmerpartiklar sommarknadsförs kommersiellt används i massan för att få bättre kontroll avglimmerhalten tillsammans med en bergart som icke är särskilt känslig fördålig vidhäftning.
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| 13. |
- Hakim, Hassan, 1955-, et al.
(författare)
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Utveckling av provningsmetod för bestämning av styvhetsmodul
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- There is a great variation between the laboratories when determining the stiffness modulus of bituminous pavements. This is a problem in connection with the evaluation and control of the stiffness modulus of bituminous pavements performed by different laboratories. It is also an obstacle with reference to the stiffness modulus of bituminous pavements in connection with performance based contracts. Stiffness modulus is also an important parameter when designing road structures. Inaccuracy about the measured stiffness modulus can lead to unreasonable thicknesses of pavement layers. In an earlier study concerning the determination of stiffness modulus, it was stated that the comparative tests showed that there is a great variation both within and in-between the results of different laboratories. The aim is to refine the test method for determining the stiffness modulus in a way that partly leads to less variation between stiffness modulus measurements performed by different laboratories, partly to increased knowledge of different apparatuses used in Sweden. This is done by controlling and comparing the load pulse and the resulting deformation pulse when using variable loading. Force and deformation were registered by different systems (additional stress and strain gauges). Dummy specimens, with more stable characteristics than bituminous test specimens, were used as a completion to the calibration and for the analysis of stress, deformation, loading time and pulse of different apparatuses.
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| 14. |
- Höbeda, Peet, et al.
(författare)
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Funktionsegenskaper hos dränbeläggning : Undersökning av borrkärnor från väg E20 vid Skara
- 1994
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- En vägsträcka, 4600 meter lång, bestående av dränbeläggning på väg E20 är objekt för rehabilitering. Frågan är om man kan lägga ett nytt slitlager på den befintliga dränbeläggningen utan störrerisk för allt för tidiga deformationer i lagren. Alternativt finns det möjlighet för remixing av denbefintliga dränbeläggningen.Vid påläggning av nytt slitlager kommer det dränerade lagret att vara mellan två täta beläggningaroch några centimeter under vägytan. Risken för vattenansamling och plastiska deformationerökar i dränbeläggningen, varför vattenkänslighet och stabilitetsegenskaper har undersöktshos borrkämor från dränbeläggningen. Slutsatsen är att aktuell beläggning inte bör byggas inmellan täta asfaltlager p g a potentiell vattenkänslighet och därefter ökad risk för deformationer.Remixing av beläggningen har visat sig vara ett bra alternativ i det här fallet.
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| 15. |
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| 16. |
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| 17. |
- Jacobson, Torbjörn, et al.
(författare)
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Undersökning av mekaniska egenskaper hos tunna beläggningar av MJAB : etapp 1
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Tunna asfaltbeläggningar har använts till lågtrafikerade vägar i många år. I delar av Norrland har mjukgjord asfaltbetong och mjukbitumenbundet grus (MJAB och MJOG) ersatt oljegruset under senare år. Beläggningar med god flexibilitet och mjuka bindemedel är en förutsättning för att vägarna i denna del av landet skall klara ojämna tjällyftningar, svag bärighet eller låga temperaturer utan att spricka sönder. Beläggningen måste samtidigt vara tillräckligt stabil för att klara påkänningarna från den tunga trafiken (timmerbilar) under sommaren utan att deformationer uppstår. I ATB VÄG saknas funktionskrav på tunna eller mjukgjorda beläggningar. Därför har VTI på uppdrag av Vägverket undersökt ett antal borrkärnor från några vägobjekt i norra Norrland. Beläggningstyperna bestod av MJAB- och MJOG-massorna. Proven har undersökts med avseende på funktionsegenskaper och parametrar som behövs vid dimensionering av överbyggnader. Ett begränsat antal prover undersöktes med avseende på sammansättning för helhetsbedömning och verifiering av analysresultat.
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| 18. |
- Jansson, Håkan, et al.
(författare)
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Töjningskriterier tunna beläggningar
- 2001
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Beläggningens utmattningsegenskaper är avgörande för uppkomsten av sprickor. Hur dessa egenskaper uttrycks i form av dimensioneringskriterier är också avgörande för den trafikbelastning som en konstruktion beräknas klara. Det kriterium som återfinns i VÄG 94 är grundat på erfarenheter från vägar med bärlager av typ AG med bindemedel av typ B 180. Kriteriet anges gälla enbart för denna typ av material och för vägöverbyggnad med en sammanlagd nominell tjocklek på bitumenbundna lager på minst 75 mm. Vid beräkning av horisontell dragtöjning i underkant av en tunnare beläggning kan för en given last och konstruktion töjningen öka med ökad beläggningstjocklek upp till en viss gräns, varefter töjningen minskar med ökad tjocklek. Fenomenet med ökad töjning med ökad beläggningstjocklek kan med nuvarande standardaxel inträffa under perioder med hög temperatur i beläggningen, då beläggningen har låg styvhet. Perioder med hög temperatur i beläggningen är dock inte kritiska med det angivna kriteriet. Ett förslag är att begränsningen i tjocklek vid användning av kriteriet slopas. Vid en beläggningstjocklek understigande 75 mm (>40 mm) görs en kontroll av att detta inte leder till oönskade konsekvenser i form av att en alltför tunn beläggning kan beräknas klara en trafik som överstiger den som motsvarande konstruktion med en tjockare beläggning kan klara. Då endast en tunn beläggning behövs kan det bundna bärlagret slopas och enbart slitlager läggas. Om ett sådant ska dimensioneras saknas sålunda ett kriterium för detta.Ett alternativt kriterium har tagits fram baserat på fältstudier av nybyggda svenska vägar. Även detta förutsätter ett bundet bärlagret av typ AG, men skiljer sig i några avseenden från kriteriet i VÄG 94. Massans sammansättning påverkar såväl styvhet som utmattningsegenskaper och bör beaktas vid dimensionering av en flexibel vägkonstruktion. Formler för beräkning av beläggningens styvhet utifrån massans sammansättning presenteras liksom laboratoriebaserade utmattningssamband.
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| 19. |
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| 20. |
- Jelagin, Denis, Docent, 1979-, et al.
(författare)
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Asphalt layer rutting performance prediction tools
- 2018
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Flexible pavement rutting due to permanent deformation accumulation in asphalt layers is one of the most common modes of road failures. In addition to creating high maintenance costs, rutting is a major concern for traffic safety, as the rut development increases the risk of hydroplaning and introduce difficulties in vehicle steering. In this context, accurate methodologies for pavement rutting performance prediction are crucial for decision support in pavement design and rehabilitation. In particular, better rutting performance models are needed to evaluate, new asphalt materials as well as to evaluate the impact of different vehicle types on roads’ service life.The main goal of this report is to present a summary of the existing asphalt rutting performance prediction tools. The present review is limited to available and/or frequently referred to tests and models with an established link to field rutting performance. Accordingly, models focusing solely on permanent deformation on the material level are beyond the framework of the present study.Road structure and its materials, heavy vehicle parameters and climate affecting rutting accumulation in the field are identified. Their significance has been evaluated based on the experimental and numerical findings reported in the literature. Several rutting performance prediction models recently proposed in the literature are summarized along with the material characterization tests used in the models. The reviewed models’ capability to quantify the influence of various structural, material and traffic parameters on the pavement’s rutting performance is examined.It is concluded that implementation of rutting performance models incorporating experimentally measured viscoelastic and permanent deformation properties of asphalt mixtures is a promising way to improve the accuracy of pavement performance predictions. In particular since they allow the effect of novel materials, e.g. polymer-modified, on the pavement’s rutting performance to be quantified.
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| 21. |
- Kalman, Björn, 1961-, et al.
(författare)
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Beständighet hos asfaltbeläggningar : utmattning av asfaltlager som utsätts för upprepade belastningar i närvaro av vatten
- 2005
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Brister i asfaltlagers beständighet kan antas orsaka stora kostnader för samhället. För att förbättra beständigheten på asfaltbeläggningar har vattenkänsligheten undersökts på bitumenbundet bärlager. Av speciell betydelse för bärlager är dess förmåga att motstå utmattning. Samband mellan töjningsnivån i underkant av bärlagret och förmågan att motstå utmattning är av vikt vid dimensionering av bitumenbundna lager. Hur vatten påverkar dessa samband är därför av stor betydelse för att kunna göra en lägesspecifik dimensionering eftersom olika vägkonstruktioner i olika klimat utsätts för mer eller mindre vatten.Två bärlagerbeläggningar, AG16, undersöktes med en speciell försöksuppställning i VTI:s wheeltracking-utrustning, med syftet att studera sprickinitiering och sprickpropagering i konstruktionerna under torra respektive våta förhållanden. De två beläggningarnas styvhetsmoduler och hur dessa påverkades av s.k. vinterkonditionering studerades parallellt med utmattningsprovningen.Sambandet mellan töjningsnivån i utmattningsförsöken och antalet belastningar till sprickinitiering var likvärdigt för de två bärlagren samt relativt oberoende av om bärlagren testades under torra eller våta förhållanden. Likaså var sprickpropageringen, dvs. antalet belastningar mellan det att en spricka bildats i underkanten i beläggningen och till dess sprickan är genomgående, likvärdiga för de två beläggningarna under torra förhållanden. Undersökningarna visar däremot att sprickpropageringen gick markant snabbare för ett av materialen vid närvaro av vatten. Detta material uppvisade också större sänkning av styvhetsmodulen vid vinterkonditionering.
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| 22. |
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| 23. |
- Lindelöf, Peter, et al.
(författare)
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Influences of bus traffic loading on asphalt concrete rutting
- 2023
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Ingår i: International Journal of Pavement Engineering. - : Informa UK Limited. - 1029-8436 .- 1477-268X. ; 24:2
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Tidskriftsartikel (refereegranskat)abstract
- Permanent deformation is the primary failure mode for the asphalt concrete (AC) pavement in urban environment. It is mainly caused by a combination of heavy traffic load, low vehicle speed and channelised traffic. A rut prediction model would therefore be a valuable tool for planning maintenance scheduling and selecting an appropriate asphalt material. This study uses the PEDRO (Permanent deformation in asphalt concrete layers for roads) model to evaluate the rutting performance of flexible pavements in dedicated bus lanes and intersections in urban areas. For this purpose, three road sections along a bus lane in Malmö, Sweden, were selected. To achieve this, AC cores from the road sections were tested using a Shear Box Tester to characterise the asphalt mixtures. Traffic data such as axle load, tyre configuration, speed, and lateral wander distribution of vehicles, and climate data were measured for the selected sections. Field measurements were carried out to assess the structural conditions of the pavements and to measure transverse profiles. This study introduced a procedure for the evaluation and local calibration of the PEDRO rutting model. The results revealed that the prediction of the transverse profiles are generally in good agreement with the rut measurements.
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| 24. |
- Lindelöf, Peter, et al.
(författare)
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Poisson’s Ratio of Asphalt Concrete Mixes Using Indirect Tensile Test
- 2019
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Ingår i: Journal of Testing and Evaluation. - : ASME Press. - 0090-3973 .- 1945-7553. ; 47:1, s. 498-510
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Tidskriftsartikel (refereegranskat)abstract
- Increased interest in mechanistic evaluation of flexible pavement structures has brought a demand for accurate and practical methods, models, or both to estimate the mechanical properties of asphalt concrete mixtures. One of these properties is the Poisson’s ratio (ν) of asphalt concrete mixtures, which is often assumed to have a constant value of 0.35 in asphalt concrete evaluations. However, investigations have reported that mixture type, air void content, and temperature produce considerable variation in measured ν-values that could have a significant effect on evaluations of asphalt concrete mixes. The objective of this study was to evaluate the effect of air voids, binder type, and testing conditions on the measured ν-values. Indirect tensile (IDT) tests were conducted to measure ν-values. The study indicated that the Poisson’s ratio of the asphalt concrete mixes, on average, attained a maximum value at a particular level of air void content. Furthermore, when comparing the Poisson’s ratio values in relation to the dynamic modulus, calculated using the Mechanistic Empirical Pavement Design Guide (MEPDG) equation, higher ν-values were attained. This demonstrates the importance of measuring the Poisson’s ratio of a mix type.
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| 25. |
- Loorents, Karl Johan, et al.
(författare)
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On mineralogical composition of filler and performance of asphalt concrete
- 2009
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Ingår i: The international journal of pavement engineering. - : Informa UK Limited. - 1029-8436 .- 1477-268X. ; 10:4, s. 299-309
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that mineral fillers have an important influence on the performance of asphalt mixes. For example, usually micaceous fillers are disregarded in manufacturing asphalt mixes. Substituting the fine fraction in an asphalt mixture with a fine fraction of a noticeably different material with respect to physical-mineralogical properties will change the asphalt mixture properties and its performance in the field, especially under severe winter condition. The effect of the surface area of the fine materials is already known, however, the present paper studies mineralogically related factors of the filler fraction that influences the asphalt concrete resistance against water impact and freeze-thaw cycles. Five fillers derived from common crushed rock aggregates for construction purposes were analysed. The samples have been mineralogically characterised, the specific surface area (SSA) has been determined together with geometrical parameters and surface texture to differentiate between samples. The analysed data confirms a correlation between the SSA and mineralogical composition of fine material and the deterioration of the stiffness modulus of asphalt concrete under severe winter condition. This study indicates the vitality of the mineralogical composition of the fine material for the performance of bituminous layers. This work should give rise to better quality assurance and economise on natural resources in the production of asphalt mixes.
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| 26. |
- Lu, Xiaohu, et al.
(författare)
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Evaluation of test sections with Polymer Modified Bitumens
- 2014
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Ingår i: Asphalt Pavements. - 9781138027121 ; , s. 287-296
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Konferensbidrag (refereegranskat)abstract
- It has been recognized that Polymer Modified Bitumens (PMB) have more potential for use in asphalt paving and can clearly demonstrate the value of their initial higher cost. To further assess sustainable benefits on heavy trafficked roads, test sections using various PMBs were built on highway E6 in Sweden during 2003-2006. The main objective of this paper is to study the aging and rheological properties of the binders used. A large number of cores were drilled and characterized with respect to stiffness, fatigue and permanent deformation. The binders (original, lab aged and recovered) were investigated extensively with rheological and chemical methods. It was found that PMBs, particularly SBS modified, demonstrate better rheological properties as compared to unmodified bitumens, even after several years in the field. These include higher strain recovery and lower non-recoverable compliance at high temperatures, and lower stiffness at low temperatures. For the SBS modified binders, good aging resistance was observed. The high resistance to aging for the SBS modified binders was also evident in the stiffness measurement made on asphalt field cores. Although significant differences have not yet been seen between the test sections (all the sections are in good condition after six years of traffic), the observed improvements for the modified binders are expected to be confirmed by a longer follow-up of the test road.
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| 27. |
- Lu, Xiaohu, et al.
(författare)
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Performance Evaluation of Polymer Modified Bitumens on a Heavily Trafficked Test Road
- 2014
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Ingår i: International Journal of Pavement Research and Technology. - : Chinese Society of Pavement Engineering. - 1997-1400. ; 7:6, s. 381-388
-
Tidskriftsartikel (refereegranskat)abstract
- In asphalt paving, polymer modified bitumens (PMBs) have more potential for use and can clearly demonstrate the value of their initial higher cost. To further assess the sustainable benefits of using PMBs, a test road was constructed on a highway in Sweden. In this paper, the asphalt binders used were investigated extensively using rheological and chemical methods, and asphalt field cores characterized with respect to permanent deformation and fatigue. It was found that the modified binders, particularly with SBS polymers, retain better rheological properties in comparison with conventional ones, even after several years in the field; these include higher strain recovery and lower non-recoverable compliance at high temperatures, and lower stiffness at low temperatures. The SBS modified binders also demonstrate good aging resistance, shown by both laboratory aging tests and field aging. the high resistance to aging for the SBS modified binders was also evident in the stiffness measurement made on asphalt field cores. Moreover, the modified binders with SBS polymers significantly enhance fatigue behaviour.
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| 28. |
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| 29. |
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| 30. |
- Porot, Laurent, et al.
(författare)
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Bituminous binder
- 2018
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Ingår i: Testing and Characterization of Sustainable Innovative Bituminous Materials and Systems. - Cham : Springer Netherlands. ; , s. 15-74
-
Bokkapitel (refereegranskat)abstract
- One of the most important aspects of asphalt pavement deterioration is the ingress of water in pavement which leads to loss of the material characteristics, even material integrity with loss of aggregates. Thus the behaviour of asphalt mixture under moisture conditions is one of the key parameter for specifications. It’s a complex phenomenon which is influenced amongst other things by materials properties with wetting, cohesion and adhesion of bituminous binder and by environmental conditions with temperature, moisture, loading and layer type. It has been a research subject for a very long time and still not precisely described. A large number of test methods is available to estimate the affinity between aggregates and bituminous binders. These test methods can be subdivided in different ways; a first distinction can be based on the presence or absence of water during the test procedure. If water is present, the evaluation is in fact referred to as water sensitivity or moisture damage testing. Another distinction can be based on the type of sample that is evaluated. The test sample can be loose aggregates coated with a bituminous binder or a compacted asphalt mix sample. Lastly the individual components, bitumen and aggregate, can be tested separately through intrinsic properties. Furthermore, test results can also be based on the quantification of the test results, whether this is based on a qualitative or a quantitative evaluation. In RILEM TC 237 SIB, TG1 the main purpose was to evaluate common test methods, used to assess the affinity of bitumen to aggregate surfaces, to determine, if possible, the repeatability and reproducibility and to give recommendations for improvement. In this study both binders and aggregates have been considered. Three bituminous binders, two unmodified from different sources, one polymer modified binder, and four aggregate types, with different mineralogy, have been selected. The test methods considered in the study include the rolling bottle test, the boiling water stripping test and the bitumen bond strength test; also surface energy was investigated. This chapter presents the results of these tests and their accuracy.
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| 31. |
- Prapoorna Biligiri, Krishna, et al.
(författare)
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Prediction of the Remaining Fatigue Life of Flexible Pavements Using Laboratory and Field Correlations
- 2015
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Ingår i: Journal of materials in civil engineering. - : American Society of Civil Engineers (ASCE). - 0899-1561 .- 1943-5533. ; 27:7
-
Tidskriftsartikel (refereegranskat)abstract
- The main objective of this study was to develop comprehensive criteria to evaluate the remaining service life of existing roads as regards their field fatigue cracking characteristics using fracture mechanics principles and associated laboratory performance tests. Two basecourse layers were investigated for their residual fatigue lives: reference and modified stone mastic asphalt mixes. The two pavement systems’material characteristics using the actual field cores were estimated in the laboratory, including moduli, fatigue relationships, and crack propagation parameters. Additionally, field measurements encompassed collection of falling weight deflectometer deflections, temperature variations, and traffic counts. Fatigue lives of the two base course layers were predicted using the developed laboratory-based fatigue and crack propagation parametric relationships during one climatic period. The modified structure presented significantly longer fatigue life than the reference mix. This was indicative of the findings that the laboratory procedure(s) based on asphalt mixture properties’ fracture and fatigue mechanics such as crack initiation, and propagation modeling and relationships are useful for evaluating the pavement mix’s performance in the field as well. Overall, laboratory tests provided reliable information regarding residual life predictions in case it is difficult to actually perform field measurements and estimate the residual life of a pavement system. The criteria developed in this study should serve as guidelines for agencies to comprehend and understand a substantial amount of information regarding asphalt materials’ fatigue characterization so that it can be implemented as one of the quality control tests to assess the pavement design life.
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| 32. |
- Said, Safwat, 1951-
(författare)
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Aging effect on mechanical characteristics of bituminous mixtures
- 2005
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Ingår i: BITUMINOUS BINDERS 2005. - : TRANSPORTATION RESEARCH BOARD NATL RESEARCH COUNCIL. - 0309093724 ; , s. 1-9
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Konferensbidrag (refereegranskat)abstract
- Traditionally, asphalt concrete requirements are based on recipe specifications for bituminous mixtures; these specifications do not consider changes in the mechanical properties of materials over time. A considerable hardening of bitumen occurs with age, a characteristic that must be considered in the evaluation of bituminous materials. In asphalt concrete evaluation work, such as pavement design or end-product contracts, the age of asphalt materials may have a considerable impact on the outcome. This investigation was undertaken to aid the development of a performance specification that is based on the structural functional properties of asphalt concrete. Properties of asphalt concrete cores from various road sections were evaluated with respect to changes in stiffness and creep over several years, with an emphasis on hardening during the early life of the pavement. Relationships between mechanical properties of bituminous mixtures and age have been established. The results make it possible to take into account the effect of aging during pavement evaluation and during characterization of mixes with respect to aging properties. It was shown that stiffness modulus and creep deformation of bituminous layers can change significantly during the early life of the pavement and that this change should be considered in performance specifications and pavement analysis.
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| 33. |
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| 34. |
- Said, Safwat, et al.
(författare)
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Alternativa bitumenbundna bärlager - provsträckor på E18 Köping : lägesrapport
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Nya bitumenbundna bärlagertyper som alternativ till konventionella AG-beläggningar har börjat användas sedan några år. Åtta provsträckor, där 4 olika typer av bitumenbundna bärlager ingår, på E18 Köping har följts upp under ett antal år. Den här lägesrapporten behandlar laboratorieresultat hos borrkärnoroch fältmätningar sedan vägens öppnande 1995.
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| 35. |
- Said, Safwat, et al.
(författare)
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Beläggningslagers temperaturer
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Beläggningars temperatur och dess variation under året har stor effekt på bitumenbundna beläggningars beteende under olika belastningstyper. Beläggningstemperatur varierar också med djupet i en vägkropp. Vid val av beläggning till ett specifikt objekt måste man bl.a. ta hänsyn till förväntade temperaturer i det aktuella lagret. Det geografiska läget för ett vägobjekt och lagrets placering i en vägkonstruktion kan vara avgörande för skadeutveckling av en asfaltbeläggning. Två identiska beläggningar med identiska trafikbelastningar fast med olika geografiska läge kan ha helt olika beteende (t.ex. deformation i asfaltlager) beroende på temperaturen i lagren. Av den anledningen behövs beläggningstemperaturer under sommarperioden för utvärderings- och prognosmodeller med avseende på spårbildning och bestämning av gränsvärde på funktionsegenskaper. Beläggningstemperaturer under vinterperioden behövs med avseende på sprickor vid trafikbelastning och termiska sprickor. Målsättningen är att ta fram indata till modell för stabilitetsspår. Temperaturfördelningen ska kunna användas som dimensionerade temperatur. Mätdata från VVIS-stationer har samlats in från stationer spridda över landet för bearbetning. Dessa data innehåller beläggningens yttemperatur. Temperaturmätare har också monterats vid teststräckor på tre olika djup i beläggningen för validering av beräknade temperaturer i beläggningarna.
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| 36. |
- Said, Safwat, 1951-, et al.
(författare)
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Evaluation of pavement structure reinforced with steel fabrics
- 2002
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Ingår i: Bearing Capacity Of Roads Railways and Airfields. - London : CRC Press. - 9781000108101 - 9789058093967 - 9781003078814 ; , s. 497-504
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- This paper describes the rehabilitation procedure of an old cracked asphalt pavement located at E6 motorway in the West of Sweden. A trial has been made to design the road structure with steel fabric reinforcement in the asphalt concrete. Three full-scale, 100-meter test sections were built. Two test sections were reinforced with steel fabrics and one section without reinforcement as a reference road section. These sections are instrumented with strain gauges. The sections have been tested by deflection measurements with Falling Weight Deflectometer, strain measurements at the bottom surface of the overlays, strain on the steel bars, unevenness and rut depth measurements and manual distress surveys. This work is a part of a co-operation project, called REFLEX, partly financed by the European Commission. The objective is to evaluate the performance of new and rehabilitated road structures reinforced with steel fabric.
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| 37. |
- Said, Safwat F, 1951-
(författare)
-
Alternativa beläggningar – högpresterande : kunskapsöversikt
- 2016
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Det finns kunskaper och erfarenheter av att högpresterande beläggningar, med till exempel polymermodifierat/gummimodifierat bitumen med flera, kan leda till ökade livslängder hos vägar. En ökad livslängd kan innebära en besparing i naturresurser och kostnader. Högprestandabeläggningar skulle därför kunna vara ett sätt för beställare att uppnå de miljömål regering och riksdag har satt upp. Målsättningen med detta projekt var att påvisa nyttan med högprestandabeläggningar ur samhällsekonomiska och miljömässiga synvinklar. Projektet som helhet omfattar dels kunskapsinhämtning inom området, förslag på alternativa konstruktioner och högprestanda-beläggningar, implementering och demonstration samt användning av tillförlitliga nedbrytningsmodeller och funktionsmetoder för dimensionering och tillståndsutveckling av vägar. Generella modeller och metoder skapar gynnsammare förutsättningar för att utvärdera och implementera nyutvecklade produkter. Slutsatserna från denna begränsade kunskapsöversikt är att det finns högpresterande asfaltbeläggningar och teknik som både kan leda till längre livslängd hos vägar och som tar mindre naturresurser i anspråk. Koncepten kan också innebära lägre kostnader och mindre klimatpåverkan.
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| 38. |
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| 39. |
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| 40. |
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| 41. |
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| 42. |
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| 43. |
- Said, Safwat F, et al.
(författare)
-
Evaluering av asfaltkonstruktion : E6 Fastarp-Heberg
- 2008
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Rapport (populärvet., debatt m.m.)abstract
- During the years 1994-1996 a test road was built on E6 near Halmstad. The test road has now been trafficked, and simultaneously studied since 1996. For the present study two test sections were chosen with different bituminous mixes which were to be evaluated concerning damages caused by traffic. One of the constructions is made of the so called FAS-concept, while the other construction is a reference section with conventional roadbase mix (AG22). Wearing course, binder layer and roadbase of the section with FAS-concept is produced by NCC according to their own concept called VIACO, which is based on the idea of using stone mastic asphalt (SMA) principle for all bituminous bound layers. The evaluation is based on laboratory studies of bore cores, an analysis of falling weight measurements, temperature measurements from field stations and theoretical calculations. The main purpose of this project is to evaluate alternative bituminous constructions and to present an evaluation method with relevant criteria concerning the service life related to fatigue cracking. The FAS-concept, which implies that material of good quality is chosen and that the stresses on the construction are diminished, has shown considerable longer fatigue life than the construction with conventional mixes. The fatigue life of the FAS-concept is several times longer that the fatigue life of the reference section. The strains in the lower part of the pavement are small and the risk of fatigue cracks at the bottom of the bituminous bound layer is minimal.
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| 44. |
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| 45. |
- Said, Safwat F
(författare)
-
Fatigue characteristics of asphalt concrete mixtures
- 1988
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report presents the state of the art in investigating fatigue cracking of asphalt mixtures, due to repeated load applications in the laboratory. A review of research relating to bitumen content and type, aggregate, filler, void content, mix stiffness, temperature, and moisture content is presented. The effect of test conditions such as controlied-stress or controlled-strain mode, rest period, and simple or compound loading upon the fatigue response of asphalt concrete is illustrated. Fatigue test apparatus such as two-, three-, and four- point bending test, wheel tracking machine, indirect tensile test, triaxial, direct tension, and push-pull test are reviewed.It is concluded from the comparisons between different apparatus that the test apparatus has a minor effect on fatigue results. Therefore it is reasonable to use the apparatus which is most economical and practical.An acceleration in fatigue testing (for example, testing at high loading speed with large stresses and/or without rest periods) could give unreliable fatigue results if the effect of such variables is not already known. Therefore the test conditions must be chosen with care.Neither the controlled-stress test nor the controlled-strain test can simulate the actual compound loading conditions that occur in the field. Nevertheless, the controlied-stress test is more reliable and practicalthan the controlled-strain test.More attention is desirable concerning the superposition effect of the variables influencing the fatigue resistance of the asphalt materials, which could induce a dramatic change in fatigue life.
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| 46. |
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| 47. |
- Said, Safwat F, 1951-, et al.
(författare)
-
Förstärkning av vägkonstruktion med stålnätsarmering : 12 års uppföljning av väg E6 Ljungskile
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- En sträcka på 800 meter av motorvägen E6 söder om Ljungskile, öppnad för trafik 1991, uppvisade skador i form av längsgående sprickor i hjulspåren redan efter ca 5 års trafikering. Under år 2000 hade vägen omfattande längs- och tvärgående sprickbildning samt visade en omfattande spårbildning med ojämnheter. Sträckan förstärktes genom fräsning och påbyggnad. Inom vägavsnittet anlades tre provsträckor för undersökning av stålnätsarmeringens betydelse för upphöjning och förbättring av bärigheten och motståndet mot sprickor och spår. Teststräckorna instrumenterades med töjningsgivare på den frästa ytan. Syftet är att studera stålnätets förmåga att ge ökad bärighet i vägkroppen och motverka sprickor och spårbildning i beläggningsytan. Denna rapport redovisar resultat från uppföljning efter 12 års trafik. Efter att vägen har trafikerats i 12 år visar referenssträckan omfattande längsgående sprickor i hjulspår. Det förekommer inga tydliga bärighetsrelaterade sprickbildningar på de armerade sträckorna, utom en enstaka fin, längsgående spricka i en av de armerade sträckorna (sträcka 2) och ett par tvärgående, finare sprickor som kan härröra från skarvarna i stålarmeringen i sträcka 3. Det konstateras att armeringen har haft en signifikant effekt (10–15 %) på höjning av bärighet och begränsning av spårutveckling. Omfattande stensläpp på slitlagret har förekommit på alla tre sträckor.
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| 48. |
- Said, Safwat F, 1951-, et al.
(författare)
-
Kalltillverkad asfaltbeläggning
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- En kunskapsöversikt över kalltillverkade asfaltbeläggningar både i Sverige och andra länder presenteras i syfte att vidareutveckla kalltekniken som en miljöanpassad asfaltbeläggning. Kall asfaltteknik har periodvis använts i Sverige under många år, dock endast på lågtrafikerade vägar, både i slit- och bärlagermassor. Under senare år har emulsioner baserade på hårdare bitumen tillverkats för tillverkning av asfaltbeläggningar med högre prestanda. I det här arbetet undersöks kalltillverkade asfaltmassor baserade på hårdare bitumen i bärlagren, på mer högtrafikerade vägar där av tradition varmblandad asfalt används. Uppbyggnaden av flera provsträckor och initial tillståndsutvärdering av provsträckor redovisas. Det konstateras från den här begränsade studien att beläggningar med kallteknik är ett effektivt sätt att minska miljöpåverkan genom lägre koldioxidutsläpp och energiåtgång vid tillverkning och utläggning av kallmassan, dock finns det behov av utvecklingsinsatser för en systematisk användning av kalltillverkad asfalt med bra funktionsegenskaper på högtrafikerade vägar.
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| 49. |
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| 50. |
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