| 1. |
- Lindvall, Anders, 1971
(författare)
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Chloride ingress data from field exposure, at twelve different marine exposure locations, and laboratory exposure
- 2003
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Concrete specimens, made from one single concrete composition and under identical conditions, have been exposed at different exposure sites around the world. The exposure has mainly been made in marine submerged conditions, i.e. below the surface of the water, to get well-defined exposure conditions. Specimens have also been exposed in marine tidal conditions and along a thaw-salted road. Parallel with the field exposure specimens have been exposed in salt-solutions, with different chloride concentrations and temperatures, in the laboratory. Four or five specimens have been exposed on each site to get a measure of the scatter in chloride ingress. The duration of all exposures has been approximately one year.After finalised exposure the specimens have been analysed for chloride and calcium content (acid-soluble) in depth intervals from the surface. The analyses have been made on dust-samples achieved by means of profile grinding of cores drilled from the specimens. The chloride ingress has been measured as chloride ingress profiles, where the quotient between chloride and binder content is given in depth-intervals. The binder content has been estimated from the analysed calcium content, since the content of acid soluble calcium in the aggregates in the exposed concrete composition is negligible. Additionally chloride-binding isotherms (as free-bound and free-total chloride content) have been determined for the concrete composition used in the exposure programme.The measured chloride ingress profiles have been evaluated with the error-function solution of Ficks second law to derive apparent chloride diffusion coefficients, DF2, and surface chloride contents, Csa. Two additional parameters have been collected to describe non-Fickian behaviour of the profiles, thicknesses of the convection-zones (where the profiles do not fit to the error-function), xc, and surface chloride contents for the diffusion-zones, Csc. Additionally the areas below the chloride ingress profiles have been determined to get an estimate of the amount of chlorides that have penetrated into the concrete.In this report the exposure programme is summarised. The concrete specimens (concrete composition and dimensions) and the exposure locations (geographical locations and exposure conditions) are described. The measurement techniques are briefly described and the results are presented as chloride ingress profiles. Furthermore parameters evaluated from and areas below the profiles are presented. The parameters and areas have also been statistically analysed to get mean values and standard deviations.
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| 2. |
- Lindvall, Anders, 1971
(författare)
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Chloride Ingress in a Swedish Road Environment
- 2002
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Concrete blocks have been exposed up to five winters at a field station along the motorway Rv40 west of Borås, some 60 km from the Swedish west coast. The concrete mixes are made from a number of Nordic cements and other types of binders (fly ash, silica fume and blast furnace slag) and admixtures. The concrete blocks have been periodically investigated for chloride ingress, frost and salt attack, moisture content and reinforcement corrosion. In this report the chloride ingress measured for three of the exposed concrete mixes, with w/b=0.40 and 0.75 and with an addition of silica fume, is presented. The exposure environment has been documented with data from a meteorological station at the field station together with information about spread of de-icing salt and records of water, snow and ice around the blocks.The chloride ingress is measured as chloride ingress profiles, where the quotient between the chloride and calcium content is given in depth-intervals from the surface. The results show the following:Chloride ingress during a year. There is a build up of chlorides in the concrete during a winter. The build up seems to be more rapid for vertical surfaces but the maximum ingress depths are higher for horizontal surfaces. During the summer there is a redistribution of chlorides, with a transport into the concrete and a decrease of the surface chloride content.Effect of age at the first exposure to chlorides. The age of the concrete at first exposure to chlorides seems to have a decisive effect on the achieved chloride ingress. If the concrete is young at the first exposure to chlorides the result will be a comparable higher chloride ingress, while a lower chloride ingress is achieved if the concrete is older at the first exposure to chlorides. The reason for this is probably that the pore-structure of the concrete is not fully densified, since the cement hydration has not reached its final level. The results indicate that a difference in age of one to two weeks at the first exposure to chlorides may give a significant different chloride ingress.Development in time for chloride ingress. The major part of the chloride ingress takes place during the first winter. After that only a slow increase in the chloride ingress has been observed. If an apparent diffusion coefficient, DF2, is determined special attention should be paid to the definition of the exposure time (total time or time of exposure to chlorides?).Effect of surface orientation on chloride ingress. The surface orientation (horizontal/vertical) does not seem to have any significance on the chloride ingress into concrete with low w/b (w/b=0.40). However, for concrete with high w/b (w/b=0.75) the chloride ingress and the penetration depths are higher for vertical surfaces.Effect of concrete composition. The concrete composition has a significant influence on the achieved chloride ingress, where, as expected, the w/b is the dominating factor. A low w/b gives a low chloride ingress and vice-versa. However, the effect on chloride ingress from use of silica-fume in the concrete is unclear sometimes silica-fume concrete has lower and sometimes higher chloride ingress compared to Portland cement concrete. Probable explanations could be the slower degree of reaction and lower chloride binding in silica-fume concrete compared to Portland cement concrete, which means that the age of the concrete at first exposure to chlorides is important. It is obvious that more research is needed to better explain the effect of silica-fume in concrete.
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| 3. |
- Lindvall, Anders, 1971
(författare)
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Environmental Actions and Response - Reinforced Concrete Structures exposed in Road and Marine Environments
- 2001
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The expenses for repair, maintenance and remediation of existing concrete structures have significantly increased. A large proportion of these expenses are due to problems related to a lacking durability of the structure. Thus, to reduce these expenses it is required to make a design of the service life of the structure in which the service life is explicitly specified.In this Licentiate thesis it is described how the service life of concrete structures can be determined. The factors that have an influence on the service life of a concrete structure are described. Furthermore it is described how the service life can be mathematically modelled and which techniques that can be used to determine the service life. Three principal factors that influence the service life of a concrete structure have been identified: (1) Material properties, (2) Execution during construction and (3) Environmental actions. Lots of efforts have been made to get a better understanding of how the material properties and to some extent the execution during construction influence the service life. However, very little has been made to clarify, which influence the environmental actions has on the service life.The deterioration of concrete can be predicted with two principal types of mathematical models namely physical models, which are based on theories of transport in porous materials, and empirical models, which are based on observations from structures. A few examples of different prediction models dealing with chloride penetration, carbonation and corrosion of the reinforcement are shown. It is also briefly described how a prediction of the service life can be made, with a performance based design methodology and probabilistic methods. To achieve reliable results with these prediction models it is required to have knowledge about boundary and initial conditions, e.g. how the environmental conditions vary inside and at the surface of the structure.Predictions of the service life can be made with two different methodologies: deem-to-satisfy rules, based on rules of thumb, and performance-based design. Usually probabilistic methods are used to predict the service life in a performance based design. However these kinds of predictions require extensive statistical quantifications of the parameters in the mathematical models. These statistical quantifications require good knowledge about which parameters that influence the deterioration of concrete, e.g. concrete composition, environmental actions at the surface of the structure and/or the response from the concrete.The environmental actions on a concrete structure have a decisive influence on the service life of the structure. The description of the environmental actions can be divided into four different levels depending on the dimensional scale. The objective is to determine the environmental actions at the surface of the concrete structure in terms of temperature, humidity and chloride conditions and the concentration of carbon dioxide. Furthermore the response from the material is of interest, e.g. how moisture and temperature distributions are distributed in a concrete structure. It is described how the environmental actions at the surface of concrete structure can be derived and what the response from the concrete is described.Finally a study of the response concrete structures exposed in road environments is presented. Seven bridges in and around Göteborg, around 30 years old, have been examined to determine the chloride penetration, moisture conditions and resistance against freeze/thaw actions. The analyses have been made on cores taken from selected positions on the bridges. The results from the study show large variations in chloride penetration between the examined bridges and even on a single part of a bridge, e.g. a column. A large part of these variations are assumed to arise due to variations in environmental actions at the surface of the bridges.
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| 4. |
- Lindvall, Anders, 1971
(författare)
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Environmental actions on concrete exposed in marine and road environments and its response - Consequences for the initiation of chloride induced reinforcement corrosion
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The object of the study presented here has been to describe, further explain and model the influence of the exposure conditions on reinforced concrete structures and the consequences on their expected service life. The focus has been on investigating and quantifying the exposure conditions for structures in marine and road conditions exposed to chloride ions. This has been done by literature studies complemented by field studies, where data on the behaviour of concrete have been gathered and analysed. The literature study has shown that the exposure conditions have a large influence, e.g. due to variations in the severity of exposure to chlorides. Field studies have been made in both marine and road conditions, where the influence of the exposure conditions has been measured as the environmental response of concrete and mortar. In marine conditions identical concrete specimens, exposed at different submerged locations, have been investigated. The results show that the temperature of the seawater has a large influence on chloride ingress. In road conditions both existing structures and specimens have been investigated. The results show that the exposure to chlorides and the chloride ingress into concrete depend on several factors, e.g. height above and distance to the road and surface orientation towards traffic. Service life predictions have been made for structures in marine and road conditions, to exemplify the effect of the exposure conditions. The results of the predictions show that the exposure conditions have a large influence on the expected service life. The predictions also showed that the level of the chloride threshold level, Ccrit, has a large influence on the predicted service life. The environmental actions, and their variations, have been found to have a large influence on the chloride ingress into and the service life of reinforced concrete structures. Therefore it is not enough to describe these by rough divisions into exposure classes, but instead the true exposure conditions should be taken into account. Preferably each structure should be treated separately, but this is usually not possible. For these structures the methodology described in this thesis can be used to describe and model the environmental actions.
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| 5. |
- Lindvall, Anders, 1971
(författare)
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Mapping of the chloride load around two Swedish reinforced concrete bridges
- 2002
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this report a study of the road environment around two motorway-bridges around Göteborg is presented. The study is a completion of an earlier study, made during theautumns of 1998 and 1999, where seven concrete motorway-bridges around Göteborg have been studied regarding moisture conditions, chloride penetration, frost damage andreinforcement corrosion. The results from this study show on large variations, especially in chloride penetration, both between different bridges, but also on one single bridge. The new study has been initiated to confirm and further investigate the results from this earlierstudy. The study has been carried out by exposing specimens made from mortar on bridgecolumns.The specimens are manufactured at one occasion with the same mortar composition to minimise variations in the results due to the execution and the material composition. The specimens have been exposed on two of the bridges investigated in the earlier study. Two bridges are bridge O 951, which is situated along the motorway E6 some 20 km south of Göteborg, and bridge O 978, which is situated along the motorway Rv40 some 15 km east of Göteborg. The exposure, made at different heights over the roadways and orientations towards the traffic, was started in the middle of February 2001, and was finished in the middle of May 2001. After finalising the exposure, the chloride penetration into each specimen has been determined by profile grinding in depth intervals and wet chemical analysis of the powder samples to determine the chloride and calcium content. The chloride penetration is presented as chloride penetration profiles where the quotient between the chloride and calcium content at different depths is presented.The results from the study show that the exposure for chlorides varies a lot depending on the height over the roadway and the orientation towards the traffic. The exposure for chloride was found to be largest for surfaces orientated towards the traffic on the same level as the roadway. Since de-icing salt normally is spread during the night or early in the morning, this means that surfaces that faces towards the morning traffic has the highest exposure to chlorides. This effect can be observed on bridge O 951, with marked commuter traffic to and from Göteborg, where the surface that faces towards the traffictowards Göteborg has significantly higher exposure for chlorides compared to the other surfaces. On bridge O 978, with less commuter traffic, this variation in exposure tochlorides cannot be observed. Furthermore, large chloride penetration was observed up to two meters above the roadway on bridge O 978. A possible explanation for this is adeposition of airborne chlorides at certain wind-directions on the lee-side of the column. This surface is not exposed to rain, that will wash the chlorides away, which means thatthe chlorides will be accumulated in the concrete. These results confirm the results from the study made during the autumns of 1998 and 1999.
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| 6. |
- Lindvall, Anders, 1971
(författare)
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Mapping the chloride load around two Swedish reinforced concrete bridges - second season
- 2004
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this report a study of the road environment around two motorway bridges situated outside Göteborg is presented. The road environment has, in this study, been described in terms of exposure to chlorides on the examined bridge structures. The study is a follow-up of two earlier studies, where both the exposure to chlorides on structures and the chloride ingress into concrete have been studied. The results from these earlier studies show on large variations in both the exposure to chlorides on the structures and chloride ingress into the concrete. Therefore this new study has been initiated to further investigate the exposure conditions for the examined motorway bridges.The exposure to chlorides on a specific structure is influenced by several factors, e.g. height over and distance to the roadway, surface orientation towards traffic, weather conditions and characteristics of road, spread of de-icing salt and traffic etc. In this study, however, the focus has been on the significance of the height over the roadway and the orientation towards traffic together with the characteristics of the traffic and spread of de-icing salt.The study has been carried out by exposing mortar specimens, with similar mortar composition, on selected positions on bridge columns. The examined bridges have been bridge O 951, situated along the motorway E6 some 20 km south of Göteborg, and bridge O 978, situated along the motorway Rv40 some 15 km east of Göteborg. The mortar specimens have been exposed on different heights above the roadway and orientations towards the traffic. The exposure started in the beginning of December 2001 and ended in the middle of April 2002. After finalised exposure the mortar specimens have been analysed for chloride ingress in depth intervals.The results from study show that the exposure to chlorides on a structure depends both on the height over the roadway and orientation towards the traffic. Fairly large variations in exposure to chlorides on a structure were, however, observed both between the bridges but also within one single bridge. The exposure to chlorides on structures generally decreases with increasing height over the roadway. This effect, however, was only observed on one of the examined bridges, while no effect was observed on the other. The exposure to chlorides has also been found to depend on the orientation towards the traffic, where surfaces facing towards the traffic have more severe exposure than surfaces facing from the traffic. The effect from orientation towards the traffic has been observed up to 3 meters above the roadway.The exposure to chlorides on structures, measured in this study, has been compared with similar measurements made on the same bridges but during another winter season. This comparison shows that it seems not possible to directly compare severities in exposure to chlorides, measured during different winter seasons. The exposure to chlorides on structures has also been compared with chloride ingress measured in the concrete. This comparison shows large deviations between the exposure to chlorides on structures and the actual chloride ingress into concrete, e.g. that spots with severe exposure to chlorides have small chloride ingress and vice versa. The reasons for these observations are not known, but anyhow they show that it is difficult to correlate data on the exposure to chlorides, measured after exposure during only one winter season, with data on the actual chloride penetration into the concrete, following from exposure during several years. The comparison indicates that there are also other factors, which have significant influence on the exposure to chlorides on the structure, e.g. direction of commuter traffic and airstreams around the structures. Thus, it is not trivial to describe and quantify the exposure conditions for bridges situated along thaw-salted roads. The overall conclusion from the study is therefore that preferably each bridge should be treated separately when the exposure conditions are described and quantified.
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| 7. |
- Lindvall, Anders, 1971, et al.
(författare)
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Undersökning av kloridinträngning, armeringskorrosion, frysning och fukttillstånd på sju brokonstruktioner exponerade för tösalter
- 2000
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- I följande rapport presenteras en studie av fukttillstånd, kloridinträngning, frostbeständig-het och tröskelvärden för armeringskorrosion gjord på sju vägbroar belägna i Storgöte-borg.Studien har utförts under hösten 1998 och hösten 1999. De undersökta broarna är mellan 26 och 32 år gamla och både kantbalkar och pelare har undersökts. Broarna har valts ut i samråd med Vägverket och studien har genomförts så att broarna inte skadats, t.ex. har nästan ingen armering borrats av. På broarna som undersökts under hösten 1999 har en eller två pelare på samma bro undersökts på olika höjder över och orienteringsriktningar mot trafiken.Fukttillståndet i de undersökta broarna har bestämts som relativ fuktighet, RF, och kapillär mättnadsgrad, KMG. En betongkonstruktion exponerad i en vägmiljö kan delas in i en torr och en våt zon. I den torra zonen finns de delar av konstruktionen som är skyddade mot nederbörd, t.ex. pelare, och i den våta zonen finns de delar av konstruk-tionen som är oskyddade mot nederbörd, t.ex. kantbalkar. Analysen av fukttillstånden i de undersökta broarna visar att det finns en viss skillnad mellan fukttillståndet i den torra respektive våta zonen. Tillsammans med information om betongens sorptionskurvor kan det konstateras att det i de torra zonerna sker en uppfuktning medan i de våta zonerna sker en uttorkning vid provtagningstillfällena.Analysen av kloridtillståndet visar att det finns stora variationer i kloridinträngning i kantbalkar och pelare både mellan olika broar men också på en enda bro. En stor del av dessa variationer kan förmodligen förklaras med variationer i exponeringsmiljön och betongkvalitet. Variationer i kloridinträngningen beroende på höjd över vägbanan och orienteringsriktning mot trafiken har konstaterats. Resultaten från studien tyder på att det inte finns någon större skillnad i kloridinträngning mellan horisontella och vertikala ytor på kantbalkar. Dock har stora variationer observerats mellan olika broar. Vidare har ingen effekt konstaterats från hastighetsbegränsningen på vägen på kloridinträngning i kant-balkar. Vid en jämförelse mellan en kantbalk och en pelare exponerade längs samma väg observerades att kloridinträngningen var störst på de ytor på pelaren som vetter mot trafiken, därefter kantbalken och slutligen de ytor på pelaren som vetter från trafiken.Frostbeständigheten har undersökts på fyra av broarna enligt SS 13 72 44 (Borås-metoden). Både ytterytor och inre sågade ytor på utborrade kärnor har undersökts. Resultaten visar att frostbeständigheten är god för samtliga uttagna prover utom för den inre delen av betongen på en av broarna.Ett av syftena för den genomförda studien har varit att undersöka tröskelvärden för armeringskorrosion. Om armeringen korroderar eller inte har undersökts visuellt, t.ex. om det finns rostfläckar eller sprickor på betongytan. Armeringskorrosion har inte konstateras på någon av de undersökta pelarna eller kantbalkarna. Endast på undersidan av brobane-plattan på en av broarna (täckskikt på ca 22 mm och kloridkoncentration på ca 1,5 vikt-% av CaO ca 0,9% av cementvikten) har korrosion konstaterats. Exponeringen för klorider har skett genom läckage av kloridhaltigt vatten från vägbanan genom en övergångs-konstruktion mellan två brobaneplattor. I samband med provtag-ningen observerades också skador på översida av pelare och rullager under övergångs-konstruktionen. Läckage av kloridhaltigt vatten genom övergångskonstruktionen är förmodligen orsakat av bristfälligt underhåll av bron. Tröskelvärdet för kloridinitierad armeringskorrosion har konstaterats att ligga mellan ca 1,0 vikt-% (ingen korrosion konstaterad) och 1,5 vikt-% (korrosion konstaterad) av CaO, d v s ca 0,6% till 0,9% av cementvikten.Inverkan av hydrofobering av betongen har studerats på två broar. Resultatet tyder inte på att det finns någon signifikant skillnad på kloridinträngningen mellan betong som är hydrofoberad respektive ej hydrofoberad. Dock kan hydrofobering ha effekt på fukttillståndet i konstruktionen. Detta har inte undersökts i studien.Slutsatser som har dragits av den genomförda studien är att det är svårt att på ett enkelt sätt att systematisera mätningar av kloridinträngning i betongbroar. Stora variationer i kloridinträngning har observerats både mellan olika broar men också på en enda bro. Exponeringsmiljön för konstruktionen har stor inverkan på kloridinträngningen och det är därför viktigt att ha kännedom om denna. Korrosionsskador har observerats endast på konstruktionsdetaljer där dåligt arbetsutförande eller underhåll konstaterats. Tillsammans med arbetsutförande och underhåll har mikroklimatet en avgörande inverkan på hur god beständigheten för betongen blir. Vid en tillståndsbedömning är det alltså viktigt att identifiera de delar av en bro där mikroklimatet är aggressivt och eventuella brister i arbetsutförande samt underhåll kan finnas.Framtida undersökningar som föreslås är att ytterligare utreda vilka effekter avstånd till och höjd över vägbanan samt orienteringsriktning mot trafiken har på kloridinträng-ningen. Ett lämpligt objekt för en sådan studie är en bro som skall rivas, där prover kan tas utan hänsyn till säkerhet för konstruktionen och om givande trafik. Vidare föreslås att ytterligare studier görs av vilken inverkan arbetsutförande och underhåll har på klorid-inträngning och fukttillstånd. Det viktigaste är dock att få ett underlag för att säkrare kunna förutsäga hur stor kvarvarande livslängd en bro har. De undersökta broarna är 26-32 år gamla och kloridinträngningen har ännu inte initierat någon armeringskorrosion i riktigt utförda delar. Det finns idag inte tillräckligt underlag för att förutsäga om armeringskorrosion startar inom t.ex. tio år eller om broarna kanske har 100 års kvarvarande livslängd.
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