| 1. |
- Jansson, Robert, et al.
(författare)
-
Reduction of fire spalling of concrete with small doses of polypropylene fibers
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The addition of polypropylene fibers has been shown to reduce the fire spalling propensity of concrete. This has been proven in many fire tests; but, very few large scale tests exist showing the function of polypropylene fibers at low dosages. In this study results on polypropylene fibers included in w/c 0.40 mixes typical used in tunnel construction that is spalling sensitive without fibers shows that an amount of only 0.6 kg/m3 (1.01 lb/yd3) has a significant effect on the spalling propensity and that even lower amounts reduce the spalling although they do not eliminate it entirely. During one of the fire tests on large slabs loaded in compression, unloaded cubes of the same mixes were also included in the furnace. None of the small specimens spalled whereas some of the corresponding large slabs spalled beyond the layer of reinforcement. This showed that the cube test method is not conservative.
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| 2. |
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| 3. |
- Silfwerbrand, Johan, et al.
(författare)
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New Swedish Design Method for Concrete Pavements
- 2008
-
Ingår i: 9th International Conference on Concrete Pavements.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A new concrete pavement design method is currently introduced in Sweden. It consists of two parts: (i) computations of subgrade and base distresses and (ii) computations of concrete pavement distresses. To eliminate the difference between concrete and asphalt pavement design, the first part is carried out with equal requirements, in the same manner, and with the very same computer program. The computer run also provides a coefficient of subgrade reaction that is used as input in the second part. For this part, the American FE program ISLAB2000 is used to compute stresses - both traffic and thermal stresses, simultaneously - in various locations of the concrete pavement slab. Contrary to previous Swedish tradition, both bottom-up and top-down cracking are considered in the analysis of the computations. For the pavement designer, the division into two parts will not be visible. She will use the same user-friendly computer program (that previously has only been used for flexible pavement design) for both pavement alternatives. It is the authors' hope that the selection of pavement solution for a certain case will be dependent solely on technical and economical factors and not on tradition and intensive advertising. The new design method includes a novelty concerning safety philosophy. The safety margin should be obvious and transparent and determined by the client in co-operation with the designer by selecting an appropriate safety class that is dependent on the economical consequences of a pavement failure but independent of material in the wear layer.
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| 4. |
- Söderqvist, Johan, et al.
(författare)
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Design criteria for lean concrete
- 2006
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Ingår i: Proceedings, 6th Int. DUT-Workshop on Fundamental Modelling of Design and Performance of Concrete Pavements, Old-Turnhout, Belgium, September 15-16, 2006.
-
Konferensbidrag (refereegranskat)
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| 5. |
- Söderqvist, Johan
(författare)
-
Design of concrete pavements : design criteria for plain and lean concrete
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- New road infrastructure projects are important and constitute of large investments that have to serve the society for a long time. The investments have to be durable at the lowest life cycle cost and the pavements have to sustain loads from increasing traffic intensity and heavy traffic loads. In Sweden less than 1 ‰ of the national road network consists of concrete pavements. In parts of Europe and in the U.S., on the other hand, concrete roads are used to a large extent for highways as well as rural roads. To encourage the competition between different road materials in Sweden, the tools for designing robust concrete pavements have to be brought forward. In order to emphasize plain concrete pavements as an alternative in road construction, the design must also be competitive. The current Swedish design method for concrete pavements is straightforward but offers no flexibility when designing roads with, for instance higher traffic loads. The method calculates concrete thicknesses on the conservative side since only a limited number of parameters are treated. Modern methods that take into account many more parameters in the design are being developed internationally. For a new Swedish design method, these parameters have to be established for actual conditions in Sweden. Also, the design has to be flexible and meet the demands from contractors and clients for a wider use. The aim of this project is to develop a new design method for plain concrete pavements that is more flexible than today. A new design method is also intended for the Swedish Road Administrations’ (SRA) computer based public design guide, PMS Objekt. Information for a new design method has been assembled mainly by investigating two newly developed design methods, VENCON2.0 in the Netherlands, and the Mechanistic-Empirical Pavement Design Guide (MEPDG) in the USA. Comparative calculations between the Swedish design method and the MEPDG are presented. The comparison is made on the level of input parameters and highlights the advantageous aspects of a semi-mechanistic design procedure where the functional properties of a concrete pavement are calculated incrementally over the design period. Plain and lean concrete, separately, but also the in composite beams, have been studied in flexural fatigue testing. The results show that Tepfers’ fatigue criterion is valid for both plain and lean concrete when subjected to flexural fatigue loading. The results also show that the fatigue strength of composite beams of plain and lean concrete is mainly dependent on the strength of the lean concrete but that Tepfers’ fatigue criterion is applicable. The bond between plain in lean concrete is found to be strong and fatigue resistant, making the composite section able to accommodate higher stresses. The bond nevertheless contributes to the risk for reflection cracks in the plain concrete wear layer and a recommendation to focus on stresses in the bottom of the lean concrete is formulated. Also, well distributed expansion joints in the lean concrete are necessary. A new project for measuring temperature gradients for use in concrete pavement design is also presented. This is done with means of concrete prisms placed in the pavement and are done in order to establish actual temperature gradients for various locations in Sweden. Also, the nonlinear gradients that act in the pavement as well as the negative temperature gradients will be analysed for the use in the design. Finally, the thesis outlines a new design method for Swedish conditions. The method is possible to develop gradually and is based on FE-analysis for fast computations. In the design, stresses from traffic and temperature loads are calculated simultaneously in a number of critical locations in the concrete slab. The method will also make it possible to alter design features as slab lengths and widths, with various connections between the slabs.
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| 6. |
- Söderqvist, Johan, et al.
(författare)
-
Design of concrete pavements : a comparison between Swedish an U.S. methods
- 2005
-
Ingår i: Proceedings - 8th International Conference on Concrete Pavements: Innovations for Concrete Pavement: Technology Transfer for the Next Generation. - 9780984065820 ; , s. 1-20
-
Konferensbidrag (refereegranskat)abstract
- The Swedish regulations for roads have now been converted into a computerised design guide that will provide engineers with the necessary, up to date, tool for the design of roads, no matter the surfacing material. The design of concrete roads is, however, based on old tables that offer little change in the concrete thickness when altering parameters like climate, traffic, and material properties. In an ongoing project a new computer-based design method for concrete roads is being developed. The aim of the project is to facilitate the design method and establish a method that treats the concrete pavement with the same ease, accuracy and safety level as current asphalt pavement design methods. In the Ph. D. project an inventory of various design methods is conducted. The project has a focus on investigating and comparing the mechanistic-based design procedure available in the United States to the current Swedish aspects of design.
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| 7. |
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| 8. |
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| 9. |
- af Klintberg, Tord, 1951-, et al.
(författare)
-
System för personlig meritering och certifiering för ingenjörer inom den svenska byggsektorn
- 2018
-
Rapport (populärvet., debatt m.m.)abstract
- SammanfattningIncitament till systematisk personlig kompetensutveckling för ingenjörer inom byggbranschen saknas. Detta leder till att vi har svårt att upprätthålla tillräckligt hög kompetens och utvecklingstakt i branschen.Frågan är om ett system för meritering kan underlätta och ge större incitament för kontinuerlig kompetensutveckling än vad som finns idag. I ansökningstexten till detta projekt nämns bland annat att: Det är dock väsentligt att ett sådant system är utformat på ett sätt som gör att branschens aktörer finner det relevant och behövligt, samt att det verkligen stärker ingenjörens roll och bidrar till att kompetens bibehålls och utvecklas. I projektet ingår också att beakta ekonomiska och legala aspekter.Arbetet rör först och främst konstruktörer även om slutsatserna kan tillämpas på stora delar av ingenjörskollektivet. Det förefaller finnas brist på kompetenta ingenjörer för centrala positioner i stora projekt med förmåga att upprätthålla kontroll och kommunikation med projektets ingående parter, som byggherre, installationsföretag etc.Ett flertal intervjupersoner hävdar att många stora bygg- och anläggningsprojekt är fragmentiserade med bristande intern kommunikation och att de lider av höga merkostnader. Intervjuade personer inom Trafikverket, med inblick i den egna verksamheten, menar att det kan finnas höga merkostnader även inom de egna projekten. Trafikverket är dock en mycket kompetent byggherre. Det är troligt att mindre byggherrar med lägre kompetens kan ha en värre situation avseende denna typ av kostnader. Många merkostnader skulle kunna begränsas eller undvikas om kompetensnivån höjs inom ingenjörssektorn.Ett meriteringssystem med vidareutbildning, mentorskap mellan seniorer och juniorer, fokuserat på bland annat personlig utveckling skulle kunna höja kompetensnivån bland ingenjörer. Ett meriteringssystem skulle göra konstruktörsyrket mer attraktivt, om det blir tydligt att en oerfaren konstruktör har en karriärväg mot högre expertkompetens.Förbättrade meriter kan valideras genom ett certifieringssystem, som bör fokusera på ingenjörskunskaper såsom konceptuell förståelse och bedömning av bärförmåga och konstruktioners verkningssätt. Systemet ska ha en kontroll- och reklamationsfunktion, som hanterar eventuella kvalitetsproblem hos den certifierade personen. Ett certifieringssystem dokumenterar kompetensnivån för en certifierad och kan därigenom göra det lättare för byggherrar att säkerställa kvalitet i sina beställda projekt.Beträffande värdet av certifiering påvisas i en brittisk rapport att certifiering för testlaboratorier är lönsamt för ingående parter, alltså både för de certifierade och för beställarna. Rapportens slutsats är att det är samhällsekonomiskt lönsamt med certifiering, då den bygger upp förtroende samt minskar risker.Regeringen skulle kunna ge en eller flera myndigheter, exempelvis Transportstyrelsen och/eller Boverket ansvar för personlig kompetensutveckling inom väg och vattenbyggnadssektorn. Denna myndighet skulle alltså få ett liknande ansvar som Socialstyrelsens, som under ett flertal år har medverkat till att utveckla medicinsektorn, med en höjd personlig expertis som resultat. Socialstyrelsens verktyg har här varit personcertifiering (läkarlegitimation). Dessutom ges vidareutbildning, samt handledar- och mentorskap inom medicinsektorn.Trafikverket skulle eventuellt kunna undersöka möjligheten att upphandla certifiering för nyckelkompetenser samt definiera dessa kompetenser i sina egna projekt. Ett liknande förfarande finns hos Stockholms Exploateringskontor när det gäller upphandling av nyckelkompetenser. Om Trafikverket skulle avisera att det skulle ställa särskilda krav på certifiering vid cirka 20 upphandlingar år 2021, så skulle det ge konsultbolagen tid att etablera ett antal certifierade ingenjörer. Dessa projekt kan då jämföras med projekt utan certifiering.Det är förmodligen kostsamt att bygga upp ett svenskt system för personlig certifiering liknande medicinsektorns legitimationssystem. Författarnas förslag är därför att branschen kan börja använda internationella certifieringssystem, exempelvis ”Institution of Civil Engineers” (ICE) och ”Institution of Structural Engineers” (IStructE). ICE är ett bredare system för väg och vattenbyggnadsingenjörer i allmänhet och IStructE certifierar konstruktörer. ICE och IStructE fokuserar på ingenjörs- och marknadskompetens, personlig utveckling och har en kontroll- och reklamationsfunktion samt olika grader avseende medlemmarnas kompetens.De svenska konsult- och entreprenadföretagen har i denna rapports intervjuundersökning visat stort intresse för att låta meritera och certifiera sina konstruktörer, särskilt om stora beställare kommer att efterfråga meriterade konstruktörer. Om internationella certifieringssystem (ICE och IStructE) används, kommer förmodligen svenska konsult- och entreprenörföretag att stärkas på en internationell marknad. Under en övergångstid behövs ett register över befintliga svenska kompetenta ingenjörer så att dessa inte stängs ute från marknaden.Det kommer att ta tid att införa utökad meritering, mentorskap och certifiering. Det är fråga om en kulturförändring i ingenjörssektorn och det behövs då en uthållighet hos branschen, framför allt hos byggherrar. Systemet kommer inledningsvis att medföra ökade kostnader, medan besparingar och vinster kommer i ett senare skede.
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| 10. |
- Ahmed, Lamis, et al.
(författare)
-
Dynamic Measurements for Determining Poisson’s Ratio of Young Concrete
- 2018
-
Ingår i: Nordic Concrete Research. - 0800-6377. ; :58, s. 95-105
-
Tidskriftsartikel (refereegranskat)abstract
- Knowledge of the elastic properties of concrete at early age is often a pre-requisite for numerical calculations. This paper discusses the use of a laboratory technique for determining Poisson’s ratio at early concrete age. A non-destructive test set-up using the impact resonance method has been tested and evaluated. With the method, it has been possible to obtain results already at 7 hours of concrete age. Poisson's ratio is found to decrease sharply during the first 24 hours to reach a value of 0.08 and then increase to approximately 0.15 after seven days.
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| 11. |
- Albrektsson, Joakim, et al.
(författare)
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Assessment of fire exposed concrete structures
- 2012
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Ingår i: fib Symposium 2012: Concrete Structures for Sustainable Community. - 9789198009811 ; , s. 619-622, s. 619-622
-
Konferensbidrag (refereegranskat)abstract
- Annually, several concrete structures, such as buildings, bridges, parking garages and tunnels are exposed to fires. An assessment is then necessary to decide whether the structure can be repaired or needs to be replaced. In a recent research project, recommendations for assessments of fire exposed concrete structures have been developed. The recommendations are based on a literature survey, results from an experimental study, where ultrasonic measurements, microscopy, Digital Image Correlation (DIC) measurement on loaded core samples were used and practical experience of real post-fire structural assessments. A refined assessment of the fire damage is obtained by combining these test methods.
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| 12. |
- Albrektsson, Joakim, 1981-
(författare)
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Durability of fire exposed concrete : Experimental Studies Focusing on Sti„ffness & Transport Properties
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Road and rail tunnels are important parts of the modern infrastructure. High strength concrete (HSC) is commonly used for tunnels and other civil engineering structures, since it allows high load carrying capacity and long service life. In general, Swedish road and rail tunnels should be designed for a service life of 120 years. However, HSC has shown to be sensitive to severe fires in the moist tunnel environment, i.e., fire spalling may occur. Extensive research shows that addition of polypropylene (PP) fibres in the fresh concrete mix significantly reduces the risk of fire spalling. The durability of a concrete structure is mainly governed by the transport properties. Further, experimental studies aimed at understanding the protective mechanism of PP fibres indicate that fluid transport increases in connection with the melting temperature of such fibres. This might reduce the durability of fire exposed concrete with addition of PP fibres. This study aims to investigate whether the use of PP fibres has any significant effect on the durability of moderate fire exposed concrete structures.The experimental study focused on transport properties related to durability and stiffness reduction of fire exposed civil engineering concrete with and without addition of PP fibres. The study consists of three parts; (i) unilateral fire exposure in accordance with the standard time-temperature curve (Std) and a slow heating curve (SH), (ii) uniformly heating of non-restrained samples to 250oC, and (iii) moderate unilateral fire exposure, 350oC, of restrained samples. Changes in material properties caused by the fire exposure were studied by means of ultrasonic pulse velocity, full field-strain measurements during uniaxial compression core tests, polarization and fluorescence microscopy (PFM), water absorption and non-steady state chloride migration.The study shows that fire exposure influences different properties of importance for load carrying capacity and durability. To get a clear image of the fire damage one has to combine different test methods during damage assessments. Transport properties of concrete both with and without addition of PP fibres were considerably affected even at moderate fire exposure. Hence, the service life might be reduced. All series with addition of PP fibres exhibited higher water absorption compared to the series without PP fibres. The practical importance of this might, however, be small since also the water absorption of concrete without PP fibres was considerably affected for the fire scenarios considered in this study. Behind the fire exposed surface, i.e., between 30 and 60 mm, no change in water absorption was observed for concrete without PP fibres. However, higher water absorption of the series with addition of PP fibres was observed.Indicative fire tests aimed to evaluate the resistance to fire spalling during a subsequent severe fire was also conducted. The concretes with addition of PP fibres showed no signs of fire spalling, while progressive spalling was observed for the concrete without PP fibres.
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| 13. |
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| 14. |
- Andersson, Louise
(författare)
-
Continuous Preventive Bridge Maintenance : Effect of High Pressure Washing on Concrete Bridges
- 2022
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In Sweden, as in many other countries, preventive maintenance of structures andbridges is considered important. It provides several benefits such as prolonged lifespan or service life, less need for repair, and hopefully reduced costs and lowerenvironmental impact.A large part of Sweden’s bridge stock is getting quite old. The idea that small actionscan improve and/or prolong the status of the bridge and postpone needs for repairor prevent damage with a reduction in life cycle cost is generally in the owner’sinterest. One such preventive maintenance measure is the annual washing ofbridges. While clear positive effects have been observed on the expansion joints,drainage system, and the bridge’s visual appearance, an important question is howthe washing affects chloride ingress, mainly from de-icing salts, in reinforcedconcrete bridge members. The hypothesis is that the high-pressure washing cleansaway the contaminants on the surface and in the long run reduces the chloridecontent. While the practical experience has been positive in Sweden, no research hasyet been done concerning the effect of high-pressure washing on chloride ingress inconcrete bridges.A study has been conducted on the preventive bridge maintenance practice of theSwedish Transport Administration (STA) and Swedish municipalities. This work hasbeen based on a literature review, a survey of municipalities’ bridge maintenance,and practical participation with contractors during annual maintenance. Field andlaboratory tests were carried out on the effect of washing on chloride ingress in twotypes of concrete. A field station was installed on an edge beam of a bridge and wasfollowed over three years’ exposure including winter seasons, winter maintenance,and annual washing in June. Also, an accelerated test method was developed in thelaboratory to simulate the yearly exposure and test the effect of high- pressurewashing in a long-term simulation over just a few weeks.The practical aspects of bridge maintenance seem to be quite similar betweenSweden and in other countries. However, in terms of descriptions of and availablemeans for maintenance and repairs, there seem to be larger differences. For the fieldstation, the results after one year’s exposure do not show anything more than theanticipated difference in chloride ingress between the two concrete types understudy. For year two, a slight difference indicated that washed samples had a reducedchloride content. For year three, however, there was no distinct difference betweenivwashed and unwashed samples. The reasons for this need to be further investigatedand examined. This will be done in the continuous tests of field exposure.The laboratory test method has been developed and successively improved. The shape and levels of chloride ingress are reasonable and comparable with fieldsamples. However, there is a need to examine the effect of natural rain exposurewhich might have the same or greater effect of diluting the chloride content aswashing the surface once a year. Other factors also need to be considered, such aswhen and how often the maintenance is performed. A first step to be able to examinethis has been completed through the development of the accelerated test method.
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| 15. |
- Andersson, Louise, et al.
(författare)
-
Continuous preventive bridge maintenance in Sweden - Field experiment on the effect of washing on concrete bridges
- 2019
-
Ingår i: Proceedings of the fib Symposium 2019. - : International Federation for Structural Concrete. - 9782940643004 ; , s. 1135-1141, s. 1135-1141
-
Konferensbidrag (refereegranskat)abstract
- Bridges are an important part of the infrastructure. For the bridges to have the longest possible service life with minimum repairs, the maintenance is of great importance. One type of bridge maintenance that is rarely researched is the continuous preventive maintenance. The continuous preventive maintenance consists of removal of vegetation, cleaning of bridge joints and drainage systems as well as high-pressure washing of the structure. The effects of washing is heavily discussed but not properly researched. A study on the effectiveness of washing concrete is therefore being conducted. A field experiment has been initiated where concrete specimens are installed on an edge beam of a road bridge. The specimens are of two recipes where one represents an old bridge with rather high water-cement ratio and the other one represents a new bridge with a low water-cement ratio. 50% of the specimens are washed annually, while the others are not. Each year samples are collected and tested for a chloride profile. The results for the first year of exposure have been determined. They are promising but are still only very preliminary. The effect of washing, if any, will be visible after a longer exposure.
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| 16. |
- Andersson, Louise, et al.
(författare)
-
Continuous Preventive Bridge Maintenance of Swedish Municipalities : A Survey on Common Practice
- 2018
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Ingår i: Nordic Concrete Research. - Oslo : Walter de Gruyter GmbH. - 2545-2819 .- 0800-6377. ; 58
-
Tidskriftsartikel (refereegranskat)abstract
- As part of a report [1] on continuous preventive bridge maintenance, a survey was conducted with Swedish municipalities. The survey’s focus was on bridges and preventive maintenance, as well as the demands and performance control stated by the municipalities. The preventive maintenance the survey focused on was the annual maintenance concerning washing, cleaning of drainage system and removal of vegetation. The survey showed both similarities and differences within the municipalities but also in comparison with Swedish Transport Agency (STA).
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| 17. |
- Andersson, Louise, et al.
(författare)
-
Effect of High Pressure Washing on Chloride Ingress in Concrete : Development of an accelerated test method
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Bridges constitute an important part of the infrastructure. For the bridges to have the longest possible service life with minimum repairs, the maintenance is of great importance. One type of bridge maintenance that is rarely researched is the continuous preventive maintenance. The continuous preventive maintenance consists of removal of vegetation, cleaning of bridge joints and drainage systems as well as high-pressure washing of the structure. The effects of washing is discussed but not properly researched. A study on the effectiveness of washing concrete is therefore being conducted. An accelerated method is being developed to mimic field testing. The method has been developed through tests on small concrete specimens subjected to fluctuating temperature, fluctuating moisture, and repeatable exposure to de-icing salt in cycles. The specimens are of two recipes where one represents an old bridge with rather high water-cement ratio (0.6) and the other one represents a new bridge with a low water-cement ratio (0.4). The first two versions of the method are described. The second version shows promising results, but the method needs further development to incorporate additional factors.
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| 18. |
- Andersson, Louise, et al.
(författare)
-
Effect of High-Pressure Washing on Chloride Ingress in Concrete : Development of an Accelerated Test Method
- 2022
-
Ingår i: Nordic Concrete Research. - : Walter de Gruyter GmbH. - 0800-6377 .- 2545-2819. ; 67:2, s. 35-50
-
Tidskriftsartikel (refereegranskat)abstract
- Bridges constitute an important part of the infrastructure. For bridges to have the longest possible service life with minimum repairs, the maintenance is of great importance. One type of bridge maintenance that is rarely researched is the continuous preventive maintenance. The continuous preventive maintenance consists of removal of vegetation, cleaning of bridge joints and drainage systems as well as high-pressure washing of the structure. The effect of washing is discussed but not properly researched. A study on the effectiveness of high-pressure washing on concrete is therefore being conducted. An accelerated test method is being developed to mimic field testing. The method has been developed through tests on small concrete specimens subjected to fluctuating temperature, fluctuating moisture, and repeatable exposure to de-icing salt during several cycles. The specimens are of two recipes where one represents an old concrete bridge with rather high water-cement ratio (0.6) and the other one represents a new concrete bridge with a low water-cement ratio (0.4). The first two versions of the method are described. The second version shows promising results, but the method needs further development to incorporate additional factors.
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| 19. |
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| 20. |
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| 21. |
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| 22. |
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| 23. |
- Ansell, Anders, et al.
(författare)
-
The vibration resistance of young and early age concrete
- 2003
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Ingår i: Structural Concrete. - 1464-4177 .- 1751-7648. ; 4, s. 125-134
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Tidskriftsartikel (refereegranskat)abstract
- During early age, concrete is vulnerable to disturbance from vibrations of large magnitudes. Today, conservative vibration limits are used as standards, and guidelines provide little information. The literature cited in this study contains experiences and results from the construction and civil engineering field, in-situ testing, laboratory testing and computer modelling. On the basis of the reviewed literature, recommended maximum vibration levels for young and early-age concrete are given.
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| 24. |
- Ask, Maria, et al.
(författare)
-
Tio år med Sveriges bygguniversitet
- 2021
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Ingår i: Samhällsbyggaren. - : Samhällsbyggarna. - 2002-956X.
-
Tidskriftsartikel (populärvet., debatt m.m.)
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| 25. |
- Billberg, Peter
(författare)
-
Form pressure generated by self-compacting concrete : influence of thixotropy and structural behaviour at rest
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Self-compacting concrete (SCC) offers rational and fast casting process since it merely has to be poured, or pumped, into the formwork without any compaction work needed. But this can be at the cost of high form pressure. However, reported results show that SCC can act thixotropically, i.e., build up a structure at rest, and this can reduce the form pressure considerably. Thus, in order to utilise the favourable possibilities to increase effectiveness without risking form collapses, the need arises for deeper and broader understanding of the mechanisms behind this thixotropic behaviour. Methodologies have been developed for the characterisation and measurement of the structural build-up at rest, both for the fluid (micro mortar) phase and the concrete itself. Hypotheses state that thixotropic mechanisms originate within the colloidal domain and, thus, motivate studies on the fluid phase comprising this domain. The stress-strain methodology is based on the hypothesis stating that the magnitude of the structure is represented by the maximum elastic stress the fresh material can withstand before the structure breaks. An instrumented steel tube is used to simulate various casting heights and rates. Results show that both micro mortar and SCC are thixotropic and this behaviour is influenced by every measure taken influencing the interparticle colloidal forces. The time-dependent structural build-up of SCC is a function of an irreversible structure (slump-loss) and a reversible, thixotropic structure. There is apparently a threshold value of the structural build-up necessary to reach before obtaining any significant form pressure reduction. Housing SCC´s, with W/C = 0.58, show low degree of structural build-up and pressure decrease while civil engineering SCC´s can show the opposite, but this often at the cost of slump-loss. Recommendations are presented and for the nearest future, suggesting a conservatism regarding design of formwork systems when SCC is used. If the behaviour of a SCC is known it should be used to optimise the formwork. If not, calculating with hydrostatic pressure should be done or the knowledge missing should be gained by using this methodology. A third option is given and this is to monitor the form pressure in real time using sensors.
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| 26. |
- Billberg, Peter, et al.
(författare)
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Form Pressures Generated by Self-Consolidating Concrete
- 2005
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Ingår i: Concrete International. - 0162-4075 .- 1944-7388. ; 27:10, s. 35-42
-
Tidskriftsartikel (refereegranskat)abstract
- Since its development, it has been generally assumed that self-consolidating concrete (SCC) would generate hydrostatic formwork pressure due to the rate at which it can be cast and the long time before it starts to set. However, in 1998 when the first bridges were cast using SCC in Sweden, measured form pressures were even lower than the design values for conventional concrete. To investigate the need for special formwork design considerations when using SCC, a series of eight wall specimens were cast, and the resulting form pressures were monitored.
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| 27. |
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| 28. |
- Bissonnette, B., et al.
(författare)
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Recommendations for the repair, the lining or the strengthening of concrete slabs or pavements with bonded cement-based material overlays
- 2013
-
Ingår i: Materials and Structures. - : Springer. - 1359-5997 .- 1871-6873. ; 46:3, s. 481-494
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Tidskriftsartikel (refereegranskat)abstract
- The recommendations presented in this publication are inspired by the State of the Art Report edited by the RILEM Technical Committee TC 193 RLS Bonded cement-based material overlays for the repair, the lining or the strengthening of slabs and pavements. The objective is to lay out all the practical aspects to be considered in the design of concrete overlay.bonded concrete overlay process, assessment of the existing structure, surface preparation, overlay materials, design methods, construction procedure and quality control/assurance system, and maintenance.
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| 29. |
- Bröchner, Jan, 1948, et al.
(författare)
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Performance of performance specifications in design-build highway projects
- 2019
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Ingår i: Australasian Journal of Construction Economics and Building. - : UNIV TECHNOLOGY, SYDNEY-UTS EPRESS. - 1835-6354 .- 1837-9133. ; 19:2, s. 111-125
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Tidskriftsartikel (refereegranskat)abstract
- Design-build contracts with performance-based specifications are believed to raise productivity and the innovation rate. Such specifications for highway and bridge contracts may create risks, be too detailed or difficult to verify. The purpose has been to analyse how performance-based requirements are used in Swedish design-build contracts for highway projects. How contractors are encouraged to provide innovative technologies is emphasized. Generic documents from the Swedish Transport Administration for design-build contracts have been studied, and case studies of six design-build contracts with performance-based requirements have been made. Technical specifications for these contracts have been analysed and interviews held with both client and contractor project managers. Results include that it is along the time axis that major obstacles to innovation arise. Before the contractor is able to develop innovative solutions, the initial design plan restricts the highway geometry. During construction, a mix of performance and prescriptive requirement formulations is more of a challenge than clashes between performance requirements. The client may avoid performance language, more so for bridges than road surfaces, because of concerns with efficient maintenance in the future. It is recommended that performance-based specifications should be less detailed and that a life cycle view of highway projects should support innovative technologies.
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| 30. |
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| 31. |
- de Frias Lopez, Ricardo, et al.
(författare)
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A discrete element material model including particle degradation suitable for rockfill embankments
- 2019
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Ingår i: Computers and geotechnics. - : Elsevier. - 0266-352X .- 1873-7633. ; 115
-
Tidskriftsartikel (refereegranskat)abstract
- A material model for future implementation in high rockfill embankments has been developed using discrete elements. Compared to previous modelling of railway ballast representing particles as clumps of spheres with bonded asperities, much simpler breakable clumps are used. This allows considering not only corner breakage but also particle splitting without a prohibitive computational time, something unique when modelling three-dimensional assemblies of particles. Moreover, breakage is controlled by values of contact forces and particle loading configuration, resulting in significantly fewer parameters and with a much clearer physical meaning. All in all, it results in a more computationally efficient and robust model suitable for implementation in rockfill embankments. Numerical monotonic and cyclic triaxial tests are performed under a range of low deviatoric to confinement stress ratios, as anticipated for railway embankments. A comparable degree of resemblance to empirical results as the previous modelling efforts with bonded asperities is observed when including degradation. Results at particle level proved useful to partially explain the observed macroscopic responses; however, these were substantially affected by breakage and none of the studied variables could, on its own, satisfactorily fully explain the observed behaviour. As a matter of fact, a complex interdependency of different factors, both at particle and macroscopic level, was identified that ultimately explained the macroscopic response. The key contribution is thus presenting an efficient and realistic material model specifically aimed at modelling high rockfill embankments including degradation, something not attempted to date.
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| 32. |
- de Frias Lopez, Ricardo, et al.
(författare)
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A Numerical Study on the Permanent Deformation of Gap-Graded Granular Mixtures
- 2016
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Ingår i: Proceedings of the Third International Conference on Railway Technology. - Stirlingshire, UK : Civil-Comp Press.
-
Konferensbidrag (refereegranskat)abstract
- Permanent deformation accumulation of unbound granular layers under traffic plays a critical role in the performance and need for maintenance of pavements and railway structures. In this paper, the discrete element method is used to study the permanent strain behaviour of binary mixtures of elastic spheres, as an idealization of gap-graded mixtures, under triaxial monotonic loading. The effects of stress level and soil fabric structure, based on a recently proposed classification system founded on micromechanical considerations, are assessed by subjecting mixtures with varying fines contents to different stress levels. Additionally, mixtures are loaded to static failure to study the dependency of the permanent strains on the closeness of the applied stress to failure stress, in accordance with existing empirical models. Numerical results are also compared with the experimentally determined behaviour of granular materials. The findings indicate that numerical mixtures are able to reproduce some of the most significant features observed in laboratory tests on granular materials, further encouraging the use of numerical simulations to enhance the understanding of granular media behaviour. Additionally, a good correlation between fabric structure and performance is obtained, giving additional support to the use of the studied fabric classification system for performance characterization.
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| 33. |
- de Frias Lopez, Ricardo
(författare)
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DEM Modelling of Unbound Granular Materials for Transport Infrastructures : On soil fabric and rockfill embankments
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Unbound granular materials (UGM) are widely used as load-bearing layers and for embankment construction within transport infrastructures. These play a significant role on operation and maintenance of transportation systems. However, pavement and railway engineering still today rely heavily on empirical models based on macroscopic observations. This approach results in limited knowledge on the fundamentals at particle scale dictating the macroscopic response of the material. In this sense, the discrete element method (DEM) presents a numerical alternative to study the behaviour of discrete systems with explicit consideration of processes at particulate level. Additionally, it allows obtaining information at particulate level in a way that cannot be matched by traditional laboratory testing. All of this, in turn, can result in greater micromechanical insight.This thesis aims at contributing to the body of knowledge of the fundamentals of granular matter. UGM for transport infrastructures are studied by means of DEM in order to gain insight on their response under cyclic loading. Two main issues are considered: (1) soil fabric and its effect on the performance of coarse-fine mixtures and (2) modelling of high rockfill railway embankments. Among the main contributions of this research there is the establishing of a unified soil fabric classification system based exclusively on force transmission considerations that furthermore correlates with performance. In particular, fabrics characterized by a strong interaction between the coarse and fine fractions resulted in improved performance. A soil fabric type with a potential for instability was also identified. Regarding embankments, DEM modelling shows that traffic induced settlements accumulate on the top layers and therefore seem to be unaffected by embankment height above a certain value. A marked influence of degradation, even considering its nearly negligible magnitude, was observed, largely resulting in increased settlements.
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| 34. |
- de Frias Lopez, Ricardo, et al.
(författare)
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Discrete element modelling of rockfill railway embankments
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Uncertainty on the development of settlements due to traffic loading exists within railway embankments, playing a potentially critical role in maintenance for slab-track configurations. A previously developed model for large constructions of unbound stone-based materials has been implemented for modelling rockfill embankments. Particles are represented by simple breakable tetrahedral clumps of spheres with four asperities each. Both corner breakage and particle splitting are allowed and differentiated depending on contact geometry. Embankments with heights ranging between 2 to 10 m are generated by successive dumping and compaction of layers of clumps on top of each other, mimicking the construction of real embankments. Cyclic loading of the embankments representing railway traffic, for both breakable and unbreakable assemblies, was carried out. No clear influence of embankment height on settlements was observed, as these accumulate on the top layers independently of the number of layers below. A clear effect of degradation was observed, largely resulting in increased settlements. Regarding the resilient response, a linear stiffening effect of embankment height was observed with a minor influence of breakage. Results at particle level were proven useful in explaining the observed behaviour. The key contribution is showing that it is possible to model high rockfill embankments under a large number of loading cycles and furthermore including degradation, something not attempted to date.
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| 35. |
- de Frias Lopez, Ricardo, et al.
(författare)
-
Discrete element modelling of rockfill railway embankments
- 2021
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Ingår i: Granular Matter. - : SPRINGER. - 1434-5021 .- 1434-7636. ; 23:3
-
Tidskriftsartikel (refereegranskat)abstract
- There is a need of reducing the uncertainty in traffic loading-induced settlements within railway embankments. A previously developed model for unbound stone-based materials has been implemented for modelling rockfill embankments. Particles were represented by simple breakable tetrahedral clumps of spheres with four asperities each. Both corner breakage and particle splitting were allowed. Embankments with heights between 2 and 10 m were generated by successive dumping and compaction of layers of clumps on top of each other, mimicking the construction of real embankments. Cyclic loading of the embankments representing railway traffic, for both breakable and unbreakable assemblies, was carried out. Results show that the mechanical response is marked by a substantial degree of uncertainty exacerbated by particle degradation, especially for intermediate to high embankments. An analysis of particle rotation showed that particle rearrangement mostly accumulates in the top layers, resulting in a lack of influence of embankment height on settlements. Breakage, even being of (very) limited magnitude, had a statistically significant effect. Good agreement with common geostatic theories predicting horizontal pressures was also observed. Regarding resilient response, linear stiffening with embankment height is observed with a minor influence of breakage. All in all, it is shown that the specific scale, boundary and stress conditions of embankments results in a behaviour deviating from that observed under triaxial conditions. Therefore, the key contribution is showing that it is possible to realistically model high rockfill embankments under a large number of loading cycles and furthermore including degradation, something not attempted to date. Graphic abstract
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| 36. |
- de Frias Lopez, Ricardo, et al.
(författare)
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Force transmission and soil fabric of binary granular mixtures
- 2016
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Ingår i: Geotechnique. - : ICE Publishing. - 0016-8505 .- 1751-7656. ; 66:7, s. 578-583
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Tidskriftsartikel (refereegranskat)abstract
- The effect of fines content on force transmission and fabric development of gap-graded mixtures under triaxial compression has been studied using the discrete-element method. Results were used to define load-bearing soil fabrics where the relative contributions of coarse and fine components are explicitly quantified in terms of force transmission. Comparison with previous findings suggests that lower particle size ratios result in higher interaction between components. A potential for instability was detected for underfilled fabrics in agreement with recent findings. It was also found that the threshold fines content provides an accurate macroscopic estimation of the transition between underfilled and overfilled fabrics.
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| 37. |
- de Frias Lopez, Ricardo
(författare)
-
Granular Materials for Transport Infrastructures : Mechanical performance of coarse–fine mixtures for unbound layers through DEM analysis
- 2016
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Granular materials are widely used as unbound layers within the infrastructure system playing a significant role on performance and maintenance. However, fields like pavement and railway engineering still heavily rely on empirically-based models owing to the complex behaviour of these materials, which partly stems from their discrete nature. In this sense, the discrete element method (DEM) presents a numerical alternative to study the behaviour of discrete systems with explicit consideration of the processes at particulate level governing the macroscopic response. This thesis aims at providing micromechanical insight into the effect of different particle sizes on the load-bearing structure of granular materials and its influence on the resilient modulus and permanent deformation response, both of which are greatly influenced by the stress level. In order to accomplish this, binary mixtures of elastic spheres under axisymmetric stress are studied using DEM as the simplest expression for gap-graded materials, which in turn also can be seen as a simplification of more complex mixtures.First, the effect of the fines content on the force transmission at contact level was studied. Results were used to define a soil fabric classification system where the roles of the coarse and fine fractions were defined and quantified in terms of force transmission.A behavioural correspondence between numerical mixtures and granular materials was established, where the mixtures were able to reproduce some of the most significant features regarding the resilient modulus and permanent strain dependency on stress level for granular materials.A good correlation between soil fabric and performance was also found. Generally, higher resilient modulus and lower deformation values were observed for interactive fabrics, whereas the opposite held for instable fabrics.Mixtures of elastic spheres are far from granular materials, where numerous additional factors should be considered. Nevertheless, it is the author’s belief that this work provides insight into the soil fabric structure and its effect on the macroscopic response of granular materials.
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| 38. |
- de Frias Lopez, Ricardo, et al.
(författare)
-
Resilient properties of binary granular mixtures: A numerical investigatio
- 2016
-
Ingår i: Computers and geotechnics. - : Elsevier. - 0266-352X .- 1873-7633. ; 76, s. 222-233
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of stress level on the resilient modulus for binary mixtures of elastic spheres under triaxial loading is investigated using the discrete element method. The secant modulus during the first cycle of unloading is used as an estimate of the modulus after several load cycles due to computational time restrains. Later in the paper, its adequacy as an accurate and efficient estimator is shown. Numerical results are statistically compared with existing relations characterizing the stress dependency of the resilient modulus for real granular materials. It is concluded that the modulus prediction is significantly improved considering the effect of the deviator stress in addition to the confinement stress, obtaining a good correlation between the modulus and the confinement to deviator stress ratio for the numerical mixtures. The stress dependency of a recently proposed soil fabric classification system, based on force transmission considerations at particulate level, is also studied and its correlation with performance investigated. It is found that the relative load-bearing role of coarse and fine components is governed by the deviator to confinement stress ratio. However, the implemented fabric classification is fairly insensitive to changes in this ratio. Regarding resilient performance, interactive fabrics show the stiffest response whereas underfilled fabrics should be avoided due to a potential for instability.
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| 39. |
- Destrée, Xavier, et al.
(författare)
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Steel fibre reinforced concrete in free suspended slabs : Case study of the Swedbank Arena in stockholm
- 2012
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Ingår i: fib Symposium 2012. - 9789198009811 ; , s. 97-100
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Konferensbidrag (refereegranskat)abstract
- The total replacement of traditional rebars with steel fibres is now completely routine for 19 years in applications such as industrial and commercial suspended slabs resting on pile grids. In Stockholm, the Swedbank Arena foundation slabs have been completed according to that long successful experience. Its foundation slabs span from 3 m to 5 m each way, with span to depth ratios from 10 to 20. The foundation slab was designed according to Belgian praxis but has been compared with Swedish praxis. The steel fibre reinforced concrete (SFRC) mixes, which contain up to 50 kg/m3 of steel fibres, were also fully pumpable and did not need any poker vibrating. Significant time and material cost savings were then achieved compared with traditional reinforced concrete. Therefore SFRC enables a lean design with a better carbon footprint.
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| 40. |
- Dolk, Ellen, 1984-, et al.
(författare)
-
Concrete pavement Falkenberg, Sweden : a 20 year review
- 2016
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Konferensbidrag (refereegranskat)abstract
- The majority of the road network in Sweden consists of flexible pavements. Only a small fraction is rigid pavements and the most recent concrete structure was built ten years ago. This creates a problem as the national experience and knowledge in terms of design and maintenance of rigid pavements is not maintained. It is therefore important to gather and adequately document the performance of existing concrete structures.One such structure is along the motorway E6 close to Falkenberg on the southwest coast of Sweden built in 1993-1996. The structure is a 28 km long Jointed Plain Concrete Pavement (JPCP) resting on a cement-treated base. The climate in the area consists of a typical coastal climate with high precipitation and short, relatively warm summers and relatively cold winters with a high number of zero degree changes. Studded tire wear, normally contributing to a large extent to the total rut on the Swedish road network, is only 5 mm after these 20 years. However, the structure is suffering from longitudinal cracking along the outer wheel track that is thought to have been caused by the combined effects of erosion within the cement-treated base, resulting in cavities under the concrete slabs and the fact that the dowel bars are placed too low and thus reducing the load transfer mechanism between the slabs and acting as crack inducers.
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| 41. |
- Döse, Magnus, 1970-, et al.
(författare)
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Effect of Carbonation on Radon Exhalation Rate in Concrete
- 2022
-
Ingår i: ACI Materials Journal. - USA : American Concrete Institute. - 0889-325X .- 1944-737X. ; 119:03, s. 67-78
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Tidskriftsartikel (refereegranskat)abstract
- Crushed rock aggregates may lead to unhealthy concentrations of radon gas in concrete buildings. The radon exhalation rate isdependent not only on the concrete mixture but also on its microstructure. Carbonation changes the microstructure, and it also influences the radon exhalation rate. With the guidance of the standard carbonation test, EN 12390-3:2019, and radon exhalation rate tests as specified in ISO-EN1165-7, it is found that carbonation has a significant effect on the radon exhalation rate, being reduced by approximately 25% for ordinary portland cement (OPC) after carbonation. In concretes with a substitution of supplementary cementitious materials(SCMs), the radon exhalation rate increased by approximately 30% after carbonation. Conclusively, concretes containing OPC and concretes containing SCMs (fly ash and slag) showed opposite trends as a result of increased carbonation ingress into the concrete mixtures. Diffusion measurements of OPC concrete and concrete containing slag (SCM) support this hypothesis.
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| 42. |
- Döse, Magnus, et al.
(författare)
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Effect on Radon Exhalation Rate Due to Cracks in Concrete
- 2019
-
Ingår i: Nordic Concrete Research. - : NORDIC CONCRETE FEDERAT. - 0800-6377 .- 2545-2819. ; 61:2, s. 79-90
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Tidskriftsartikel (refereegranskat)abstract
- The second largest cause of lung cancer in the World is related to radon (Rn-222) and its progenies in our environment. Building materials, such as concrete, contribute to the production of radon gas through the natural decay of U-238 from its constituents. The Swedish Cement and Concrete Research Institute (CBI), part of RISE (Research Institute of Sweden AB), has examined the effects of cracks in concrete on two different concrete recipes where an Ordinary Portland Cement, OPC-CEM-I concrete (REF) and an OPC concrete including a hydrophobic additive (ADD) were addressed. Two concrete prisms from each concrete recipe were examined. The radon exhalation rate was measured in the pristine state and after concrete cracks had been induced into the concrete prisms. Measurements were performed with an ATMOS 33 ionizing pulsation chamber. The results indicate a strong influence of cracks on the radon exhalation rate. An increase in radon exhalation rate was calculated for every test prism. The increase in radon exhalation rate varied between 80 and 260 %. The crack apertures may play a significant role on the exhalation rate. The concrete prisms with the largest apertures (ADD) also generated the highest radon exhalation rates. The results imply that there could be a substantial variation in the exhalation rate, due to numerous factors, but nonetheless, the results should, raise the awareness of the impact cracks in concrete structures, may have on the final exhalation rate of radon. The exhalation rate of the recipe with an additive (ADD) also showed a lower exhalation rate than for the reference recipe (REF), when compared in a pristine state. This was in part expected. However, the effect of induced cracks and its aperture, seemingly trumps the effect that an additive may play on the radon exhalation rate, when cracks are induced.The hypothesis is in part verified in view of the results of the prism for the ordinary Portland recipe (REF-prisms), were an increase of approximately 100 % would be expected due to the total surface increase. The results also indicate this. The major increase in the radon exhalation rate of the ordinary Portland recipe including an additive, implies however other factors, such as minor internal cracks, that may substantially contribute to the final exhalation rate.
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| 43. |
- Döse, Magnus, et al.
(författare)
-
Evaluation of the I-index by use of a portable hand-held spectrometer and laboratory methods: a risk assessment of Swedish concrete by use of different crushed aggregates
- 2014
-
Ingår i: Mineralproduksjon. - 1893-1057 .- 1893-1170. ; :5, s. A35-A52
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The recommended levels of ionizing radiation from construction materials in effective dose is set to a maximum of 1 mSv/year, EC (1996, 1999, 2013), ICRP (2007), IAEA (2011). By using a theoretical model proposed by the European Union (1999), this is equivalent to I-index 1. By using of concrete slabs with dimensions of 1.5 m × 1.5 m × 0.15 m, an empirical approach is suggested for the calculation of the I-index of naturally occurring ionizing radiation from construction materials. Measurements of 40K, 226Ra, 232Th and the total gamma radiation were conducted and the I-index values were calculated for each concrete mix. A good linear relationship could be established between measurements performed by the Swedish Cement and Research Institute (CBI) and the laboratory results acquired from the Radiation and Nuclear Safety Authority of Finland (STUK) and Centre de Recherches Pétrographique et Géochimiques/ Le Centre National de la Recherche Scientifique (CRPG/CNRS). The results indicate that 60 % of the investigated construction materials are in agreement with the stipulated levels set out by the EC (1999, 2013). The cause for the higher levels of ionizing radiation is often elevated concentrations of all the radioactive elements measured. Regarding the concrete samples yielding values of I-index > 1, 232Th makes the largest contribution.
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| 44. |
- Döse, Magnus, 1970-
(författare)
-
Ionizing Radiation in Concrete and Concrete Buildings : Empirical Assessments
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- One of the major issues with radiation from the natural isotopes 40K, 226Ra (238U) and 232Th and their decay products is the forthcoming legislation from the European Commission in relation to its Basic Safety Directive (2014). The European legislation is mandatory and could not be overthrown by national legislation. Hence, even though the BSS is still a directive it is foreseen as becoming a regulation in due time.The reference value of the natural isotopes, from a radiation point of view, set for building materials is 1 mSv per year (EC, 2014). Earlier recommendations (The Radiation Protection Authorities in Denmark, Finland, Iceland, Norway and Sweden, 2000) within the Nordic countries set an upper limit at 2 mSv per year of radiation from building materials.The main objective within the frame of the thesis was to investigate gamma radiation in relation to Swedish aggregates and their use as final construction products and the applicability and use of a model (EC, 1999) for building materials to calculate the effective dose within a pre-defined room. Part of the thesis also investigates different methodologies that can be used to assess the radiation in a construction material made up of several constituents (building materials) and aims to show that for some purposes as for the construction industries (precast concrete), that a hand-held spectrometer can be used with good accuracy, even though the object is limited in thickness and size. Secondly, the author proposes a simplified way of assessing the radiation in a construction material by use of correlation coefficient of a specified recipe by use of a hand-held spectrometer. Moreover, an understanding of the different building materials´ contribution to the finalized construction product, e.g. concrete is demonstrated, and how to achieve a good control of the radiation levels in the concrete building.
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| 45. |
- Döse, Magnus, et al.
(författare)
-
Naturally occurring radioactivity in some Swedish concretes and their constituents - Assessment by using I-index and dose-model
- 2016
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Ingår i: Journal of Environmental Radioactivity. - : Elsevier. - 0265-931X .- 1879-1700. ; 155-156, s. 105-111
-
Tidskriftsartikel (refereegranskat)abstract
- The reference level for effective dose due to gamma radiation from building materials and construction products used for dwellings is set to 1 mSv per year (EC, 1996, 1999), (CE, 2014). Given the specific conditions presented by the EC in report 112 (1999) considering building and construction materials, an I-index of 1 may generate an effective dose of 1 mSv per year. This paper presents a comparison of the activity concentrations of 4 0K, 226Ra and 232Th of aggregates and when these aggregates constitute a part of concrete. The activity concentration assessment tool for building and construction materials, the I-index, introduced by the EC in 1996, is used in the comparison. A comparison of the I-indices values are also made with a recently presented dose model by Hoffman (2014), where density variations of the construction material and thickness of the construction walls within the building are considered. There was a ~16-19% lower activity index in concretes than in the corresponding aggregates. The model by Hoffman further implies that the differences between the I-indices of aggregates and the concretes' final effective doses are even larger. The difference is due, mainly to a dilution effect of the added cement with low levels of natural radioisotopes, but also to a different and slightly higher subtracted background value (terrestrial value) used in the modeled calculation of the revised I-index by Hoffman (2014). Only very minimal contributions to the annual dose could be related to the water and additives used, due to their very low content of radionuclides reported.
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| 46. |
- Döse, Magnus, 1970-
(författare)
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Reducing Radon Gas Emissions in Concrete
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Several compulsory regulations and recommendations regarding ionising radiation for building products have been introduced in recent years. Furthermore, industry-affiliated aggregate and concrete companies strive to implement environmental goals that should be fulfilled regarding building materials. In Sweden, a certification system for high-level environmental quality assurance has beendesigned by the Green Building Council (Miljöbyggnad 3.0). The certification system is used in procurements of house constructions to achieve a high standard and good quality environment for habitants inside new buildings. One of these environmental goals, as part of this certification system,concerns acceptable levels of radon within the indoor environment. In recent decades it has become increasingly common for the concrete industry to use combinations of different Supplementary Cementitious Materials (SCMs) in concrete to reduce the carbon dioxide emissions of cement production. Additions of SCMs and different admixtures can also improve the properties of concrete, such as increased strength and durability. However, knowledge of ionising radiation and radon is still limited. How do SCMs and hydrophobic admixtures contribute regarding properties such as radon gas exhalation from concrete? Are there any advantages? Disadvantages? Can one make use of specific properties in specific indoor climate environments? What is the effect of moisture?The main part of the thesis embraces these concerns. Twelve different concrete recipes were cast to investigate the 222Rn radon exhalation rate of these concrete mixtures in relation to their relative humidity (RH). Ten recipes consisted of different mixes of binders and hydrophobic admixtures containing crushed rock with a slightly enhanced 226Ra-activity concentration (Bq/kg), while two other recipes included crushed rock with low levels of radioactivity. As a reference cement, a CEM I, 52.5 Rproduced by Cementa AB/HeidelbergCement Group (Skövde cement factory) was used. The concretes´ composition had a water binder ratio (w/b) of 0.55.For radon gas analysis and radon diffusion measurements, a method using the decay rate of alpha energies from 222Rn and 218Po was employed. The amount of decay per unit time was calibrated in relation to a well-defined radon gas level. The readings or output from the radon gas monitor were then displayed as 222Rn content in air in the unit Bq/m3. Diffusion measurements included an instrument named RAD 7 from Durridge, Inc. The instrument´s measuring technique uses a solid-statedetector.The results imply that SCMs and hydrophobic admixtures (liquid) have a moderate to fairly large impact on the radon exhalation rate, with a humidity of 75 % and 60 %. The largest impact at a relative humidity of 75 % is shown by micro-silica (SF-30), which reduces the radon exhalation rate by up to 57 %. However, at a relative humidity of 45 %, the radon exhalation of the reference concrete is in line with most other concrete mixes regarding their radon exhalation rates. One needs to separate between radon gas exhalation and radon gas diffusion, although they both affect the radon rate within a building. In the study, the radon gas exhalation rate generally decreased with decreasing relative humidity. The radon gas diffusion, however, increased in general as the relative humidity decreased. Also, the natural process of carbonation affects the radon exhalation rate. The study performed as part of the thesis, relating to carbonation and its influence, generated different results depending on the concrete recipe, but can be summarised as follows: (i) concrete with only CEM I or CEM I combined with an hydrophobic admixture indicated a reduced radon exhalation rate; and (ii) for a concrete recipe containing CEM I as a binder combined with slag or fly ash, the radon exhalation rate increased.Another study, as part of the thesis, embraced induced cracks and their influence upon the radon exhalation rate. The study showed that the influence of cracks can be quite large. In two cases an increase of 200-250 % was calculated compared to the radon exhalation rate of the same concrete without cracks. In the other cases, the increase was proportional to the increase of the concrete surface.iiiSeveral factors influence the final rate of radon being exhaled from a building material. The radon exhalation in the examined building materials can also be addressed as the production rate of radon (exhalation of radon per unit volume) for the investigated concrete mixes. The production rate is mainly governed by the emanation coefficient, the content of radium in the materials and the material´s density (volume and mass) as well as the radon decay constant. Since the investigated concrete mixes have a similar density and radium content, these variables are of less importance when assessing the differences between the concrete mixes’ exhalation rates. Consequently, the influence of the radon emanation becomes a major parameter when comparing the different concrete mixes. The radon emanation has in the ongoing assessments been demonstrated to show substantial variation due to the influence of the relative humidity. Initially, in a water filled system (100 % RH), the water acts as a barrier, and radon are accumulated in the pores (e.g., the recoil theorem). When the moisture level decreases, the initially high radon levels in the pore system are enabled to diffuse into the free air. The initially high concentration of water molecules also acts as a carrier for some of the radon atoms. This promotes the successive reduction of the relative humidity in the concrete samples, and the number of radon atoms that reach the concrete surface is also diminished, which consequently reduces the radon exhalation rate. In other words, the most important factor for differences in the radon exhalation rate can be dedicated to its radon emanation, which refers to the number of radon atoms being released from the material itself into the free air. Therefore, the tightness of the concrete, or its permeability, is very important. This is in part reflected in the diffusion coefficient or radon diffusion length being assessed for the different concrete samples.That the radon gas diffusion increases with a lower relative humidity in the concrete is reasonable since the diffusion rate in water is markedly lower than in air. The diffusion rates in the investigated concrete samples have a subordinate role, however, when one evaluates the final exhalation rate. The high radon exhalation rate in this study is foremost due to (i) the material´s high radium content and (ii) higher emanation coefficient at higher relative humidities. It is of importance to note that the materials´ slightly elevated radium content has a large influence on the high radon exhalation. Comparing concrete recipe C with a recipe replaced with a low radioactive content aggregate (i.e., a low amount of radium), the production rate is very limited, which means a low radon exhalation rate, even though a moderate emanation coefficient can be shown. Conclusively, this implies that the relation between the relative humidity (RH), radon concentration and diffusion within a concrete wall, ceiling or floor is a complicated interaction. In practice, the influence of relative humidity is the dominant factor for the final radon exhalation rate from a building material. Consequently, the radon exhalation rate, in general, decreases over time as the concrete driesout and the relative humidity decreases. Some essential conclusions derived from the thesis are that: SCMs and hydrophobic admixtures can effectively reduce the radon gas exhalation rate, specifically at higher relative humidity levels;fractures in concrete may generate substantial radon concentration increases; and, depending on the choice of binders, the carbonation of concrete may have a positive or negative effect on the radon exhalation rate
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| 47. |
- Döse, Magnus, 1970-, et al.
(författare)
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Reduction of radon gas in concrete – effects and evaluation of effective dose
- 2017
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Ingår i: Nordic Concrete Research. - Oslo, Norway. ; , s. 185-188
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Konferensbidrag (refereegranskat)abstract
- The second largest cause of lung cancer is related to radon (222Rn) and its progenies in our environment. Building materials, such as concrete, contribute to the production of radon gas through the natural decay of 238U from its constituents. The Swedish Cement and Concrete Research Institute (CBI) has examined two identical concrete recipes where only an additive, X1002 Hycrete hydrophobant corrosion inhibitor was added to one of the recipes as a mean to lower the radon exhalation rate. Measurements were performed with an ATMOS 33 ionizing pulsation chamber at four different occasions for each recipe during 12 months. The results indicate a reduction of the exhalation rate by approximately 30-35 %, meaning roughly 2 mSv per year decrease in effective dose to a human.
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| 48. |
- Döse, Magnus, 1970-, et al.
(författare)
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Reduction of Radon Gas in Concrete Using Admixtures and Additives
- 2018
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Ingår i: Nordic Concrete Research. - Oslo. - 0800-6377. ; 58
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Tidskriftsartikel (refereegranskat)abstract
- The second largest cause of lung cancer is related to radon (222Rn) and its progenies in our environment. Building materials, such as concrete, contribute to the production of radon gas through the natural decay of 238U from its constituents. The Swedish Cement and Concrete Research Institute (CBI) has examined three concrete recipes where only an additive as well as fly ash were added as single constituents to a reference recipe and compared to a reference concrete. The inputs of an additive as well as a supplementary cementitious material (fly ash) were made as a mean to investigate their potential influence on the radon exhalation rates of the concrete. Measurements were performed with an ATMOS 33 ionizing pulsation chamber for at least five different occasions for each recipe during a 22 month period. The results indicate a reduction of the exhalation rate by approximately 30-35 % for each altered recipe. This means roughly 1.5-2 mSv per year decrease in effective dose to a human using an additive or a supplementary cementitious material such as fly ash in relation to the investigated standard concrete.
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| 49. |
- Döse, Magnus, 1970-, et al.
(författare)
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Supplementary Cementitious Materials and Additives – Effective Measures to Hinder Radon in Concrete
- 2018
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Konferensbidrag (refereegranskat)abstract
- The second largest cause of lung cancer is related to radon (222Rn) and its progenies in our environment. Building materials, such as concrete, contribute to the production of radon gas through the natural decay of 238U from its constituents. The Swedish Cement and Concrete Research Institute (CBI) has examined ten different concrete recipes containing an additive or Supplementary Cementious Material (SCM), such as fly ash, slag or silica and combinations thereof. The SCM´s were added in small to moderate portions and substituted the reference Portland cement (OPC). The inputs of an additive as well as a supplementary cementitious material were made as a mean to investigate their potential influence on the radon exhalation rates of the concrete as well as the radon gas diffusion length (L) that could be expected from the different recipes. Measurements were performed with an ATMOS 33 ionizing pulsation chamber. The results indicate a reduction of the exhalation rate by approximately 10-55 % depending on recipe at an RH of 75 %. The diffusion coefficients, corrected for background subtraction vary in the interval 1.1 x 10-10 – 7.6 x 10-12 m2/s. The diffusion lengths vary between 2 and 9 mm. In the case where the largest reduction of the exhalation rate is achieved, this roughly correspond to >2 mSv per year decrease in effective dose to a human. Consequently, using an additive or a SCM, as part of the mix, would be an option to effectively lower the radon gas exhalation in their initial stage of production. Secondly, the use of additives and SCM´s will contribute to a lower environmental impact (CO2).
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| 50. |
- Emborg, Mats, et al.
(författare)
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Slitbetong som brobeläggning
- 2019
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Ingår i: Betong. - 1101-9190. ; :1, s. 43-46
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Tidskriftsartikel (populärvet., debatt m.m.)
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