A harsh, cold, and icy environment is of no surprise to the conditions of a winter climate, where the wide use of de-icing salts on roads and highways allows for the initiation of chloride-induced corrosion of the reinforcement of concrete structures; a reduced service life, loss of structural integrity, visible damages, and ultimately structural failure are among the many unwanted effects of rebar corrosion. Chloride ingress into concrete has been extensively studied for the last four decades; however, most of the relevant research to date does not take into account the effects of sustained loading on chloride transport properties. Therefore, the objectives of this study were to investigate the influence of sustained compressive and tensile stresses on chloride ingress into concrete, and ultimately to understand what the effect of sustained stress is on chloride penetration depth, on chloride concentration by % weight of concrete, and on apparent diffusion coefficients by comparing results to those of unloaded control specimens. To achieve these objectives, six post-tensioned and four non-reinforced control concrete beams were constructed with different water-to-cement (w/c) ratios and completely submerged in a 4-5% de-icing salt (NaCl) solution for 12 weeks, allowing chloride transfer to be completely governed by continuous diffusion. The effects of supplementary cementing material on chloride ingress are also studied. Concrete beams were post-tensioned to induce variable sustained compressive and tensile stresses along the beam. After 12 weeks of exposure, beams were fractured at specific locations and sprayed with a 0.1N silver nitrate (AgNO3) solution to determine average penetration depths; chloride concentration profiles were obtained from potentiometric titration of grinded powder samples. Apparent chloride diffusion coefficients were then obtained from the results of spraying AgNO3 and titration, the latter by non-linear regression curve-fitting to Fick’s second law of diffusion. A good agreement between results from both methods reveals that the use of AgNO3 in field is acceptable in predicting the rate of chloride ingress in concrete sustaining stress. The chloride diffusivity for each profile, relative to that of the unstressed section, was related to the compressive and tensile stresses in the concrete section. The experimental results indicate the dependence of chloride ingress and concentration on the type and level of sustained stress. An analysis of the results to study the effects of the w/c ratio using colourimetric (silver nitrate spray) and potentiometric titration methods was also completed.

A harsh, cold, and icy environment is of no surprise to the conditions of a winter climate, where the wide use of de-icing salts on roads and highways allows for the initiation of chloride-induced corrosion of the reinforcement of concrete structures; a reduced service life, loss of structural integrity, visible damages, and ultimately structural failure are among the many unwanted effects of rebar corrosion. Chloride ingress into concrete has been extensively studied for the last four decades; however, most of the relevant research to date does not take into account the effects of sustained loading on chloride transport properties. Therefore, the objectives of this study were to investigate the influence of sustained compressive and tensile stresses on chloride ingress into concrete, and ultimately to understand what the effect of sustained stress is on chloride penetration depth, on chloride concentration by % weight of concrete, and on apparent diffusion coefficients by comparing results to those of unloaded control specimens. To achieve these objectives, six post-tensioned and four non-reinforced control concrete beams were constructed with different water-to-cement (w/c) ratios and completely submerged in a 4-5% de-icing salt (NaCl) solution for 12 weeks, allowing chloride transfer to be completely governed by continuous diffusion. The effects of supplementary cementing material on chloride ingress are also studied. Concrete beams were post-tensioned to induce variable sustained compressive and tensile stresses along the beam. After 12 weeks of exposure, beams were fractured at specific locations and sprayed with a 0.1N silver nitrate (AgNO3) solution to determine average penetration depths; chloride concentration profiles were obtained from potentiometric titration of grinded powder samples. Apparent chloride diffusion coefficients were then obtained from the results of spraying AgNO3 and titration, the latter by non-linear regression curve-fitting to Fick’s second law of diffusion. A good agreement between results from both methods reveals that the use of AgNO3 in field is acceptable in predicting the rate of chloride ingress in concrete sustaining stress. The chloride diffusivity for each profile, relative to that of the unstressed section, was related to the compressive and tensile stresses in the concrete section. The experimental results indicate the dependence of chloride ingress and concentration on the type and level of sustained stress. An analysis of the results to study the effects of the w/c ratio using colourimetric (silver nitrate spray) and potentiometric titration methods was also completed.

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. / I Sverige, som i många andra länder, anses förebyggande underhåll avkonstruktioner och broar vara viktigt. Det har flera fördelar, som att förlängalivslängden eller bruksskedet, minska behovet av reparationer och förhoppningsvisminska kostnader och miljöpåverkan. En stor del av Sveriges brobestånd börjar bli relativt gammalt. Det gör attförebyggande underhåll får mer uppmärksamhet och ges större vikt. Idén att mindreåtgärder kan förbättra och/eller förlänga standarden på bron och förskjuta behovetav reparationer eller förebygga skador med en minskning i livscykelkostnader ärgenerellt i ägarens intresse. En typ av förebyggande underhåll är den årligatvättningen av broar. Tydliga positiva effekter kan ses på fogar, dränering samt bronsvisuella intryck men en viktig fråga är hur tvättningen påverkar kloridinträngning från huvudsakligen tösalter i armerad betong. Hypotesen är att högtryckstvätt tarbort föroreningar på ytan, vilket på lång sikt minskar kloridmängden i betongen. Den praktiska erfarenheten ska ha varit positiv i Sverige, men ingen forskning har utförtspå vilken effekt högtryckstvättning har på kloridinträngningen i en bro av betong. En studie om det förebyggande brounderhållet hos Trafikverket och kommuner harutförts med hjälp av Trafikverkets och föregångarna Vägverkets dokument, annanlitteratur, en enkät till kommuner samt medverkan och observationer av detpraktiska vid utförandeentreprenaders årliga utförande av underhållet. Fält- ochlaboratorieprover för undersökning av tvättningens effekt på kloridinträngningenhar utförts. En fältstation på en kantbalk på en bro har installerats och följts undertre års exponering, med vinterklimat, vinterunderhåll samt årlig tvättning i juni. Enaccelererad provningsmetod har utvecklats för att simulera den årliga exponeringenoch undersöka effekterna av högtryckstvättning i en långtidssimulering på baranågra veckor. Ur praktisk synvinkel verkar brounderhåll vara ganska likt i Sverige och andraländer. Dock verkar beskrivningar och tillgängliga ekonomiska medel för underhålloch reparation visa större skillnader, vilket kan ha en stor påverkan på broarnasskadestatus. För fältstationen, är resultatet efter ett års exponering inte speciellttydligt förutom den förväntade skillnaden mellan de två undersökta betongtyperna(en äldre och en modern, mer beständig kvalitet). För år två syns en mindre skillnadmellan tvättade och otvättade prover. Skillnaden kan inte observeras i resultaten förår tre dock. Orsaken till detta måste undersökas vidare. Detta görs genom dekontinuerliga provningarna som fortsätter. Den accelererade provningsmetoden har utvecklats och kontinuerligt förbättrats.Formen och nivån på kloridinträngningen kan anses rimliga och jämförbara (påformen) med fältprover. Dock finns det ett behov av att undersöka påverkan avnaturligt regn vilket kanske har samma eller större effekt på att späda utkloridmängden som att högtryckstvätta ytorna en gång per år. Andra aspekterbehöver också undersökas, till exempel när och hur ofta underhållet ska utföras. Ettförsta steg att möjliggöra det har avslutats med utvecklingen av den accelereradeprovningsmetoden. / <p>QC 20220509</p> / Förebyggande Brounderhåll

Concrete in its unaltered form allows the mass transfer of fluids into and out of its microstructure. These fluids can contain detrimental solutes which change the chemistry of the cement paste and/or the corrosion properties of the reinforcement bars, most noticeably hydrogen carbonates (HCO3-), oxygen (O2) and chloride ions (Cl-). Water and its solutions containing salts, mostly sodium chloride (NaCl), can also cause physical damage due to phase changes (freezing and thawing).  External application of hydrophobic agents onto the cement paste surface is a well-known method to alter the mass transfer at this interface. Bulk application of hydrophobic agents in ready mixed concrete is also a possible route but alters the entire cement paste. This thesis presents relevant aspects concerning the use of bulk hydrophobic agents in concrete within a spectrum water to cement ratio   (w/c) = 0.40-0.50. The main focus was on triacylglycerides (TAG) and alkyl alkoxysilanes (“silanes”) with application rates 1-3% based on cement weight.  Alterations to the compressive strengths have been observed and documented over a three-year period. The relative drop in mechanical strength is inversely proportional to w/c. The higher the addition rate, the lower the compressive strength. Chemical differences within the hydrophobic groupings (TAG or “silanes”) resulted in different outcomes. This was most noticeable in the water absorption, compressive strengths and chloride diffusion.  Freeze thaw testing did show noticeable differences, the use of “silanes” was detrimental in these tests even in deionsed water. The exact mechanism is unknown, but thin section analysis shows a lack of air entrainer (even when added on the fresh concrete mix) and extensive cracking in the entire cement paste. The scaling in concrete with TAGs was smaller but needs further improving.  The main properties intended with these agents were the ability to alter the mass transfer of water or solutions into the cement paste. Capillary suction and diffusion were examined. Increasing the w/c reduces the effectiveness of the hydrophobic agents to resist water uptake. This was seen in capillary suction and uni-directional chloride diffusion testing. Processed TAGs were more effective in reducing chloride diffusion than the unprocessed chemical whereas, in some cases, the “silanes” actually increased the amount of chloride ions transferred into the cement paste. Only a slight positive effect can be seen at the lower inclusion rate (1%). Increasing the w/c reduces the resistance to chloride ion diffusion with the same dosage rate.  A field test station close to vehicular traffic was also established in 2018 and 2019, but the specimens have not been tested at this point in time. It is hoped that these and other future studies will lead to a complete PhD project. / Betong i sin oförändrade form tillåter masstransport av vätskor i och ur dess mikrostruktur. Dessa vätskor kan innehålla skadliga lösta ämnen som förändrar cementpastans kemi och/eller korrosionsegenskaperna hos armeringsjärnen, framför allt vätekarbonater (HCO3-), syre (O2) och kloridjoner (Cl-). Vatten och dess lösningar som innehåller salter, mestadels natriumklorider (NaCl), kan till och med orsaka fysisk skada på grund av fasförändringar (frysning och upptining). Extern applicering av hydrofoba medel på cementpastans yta är en välkänd metod för att ändra masstransport genom denna gränsyta. Bulkapplicering av hydrofoba medel i färdigblandad betong är också en möjlig väg, och resulterar i förändringar i hela cementpastan. Denna licentiatavhandling presenterar relevanta aspekter rörande användningen av bulk-hydrofoba medel i betong inom intervall av vattencementtal = 0,40-0,50 (vct). Huvudfokus låg på triacylglyceroler (TAG) och alkyl-alkoxisilaner (”silaner”) med inblandning 1-3 % baserat på cementvikt. Förändringar av tryckhållfasthet har observerats och dokumenterats under en treårsperiod. Den relativa reduktionen i mekanisk hållfasthet är omvänt proportionell mot vct. Ju högre tillsatsmängd i cementpastan desto lägre tryckhållfasthet. Kemiska skillnader inom de hydrofoba grupperna (TAG eller "silaner") resulterade i olika resultat. Detta var mest märkbart i vattenabsorption, tryckhållfasthet och kloriddiffusion. Frysprovning visade märkbara skillnader, användningen av "silaner" var skadlig i dessa tester även i avjoniserat vatten. Den exakta mekanismen är okänd, men tunnslipsanalys visar på brist på luftporbildare (även om den tillsätts i stora mängder i den färska betongblandningen) och omfattande sprickbildning i hela cementpastan. Avskalningen i betong med TAG var mindre men behöver ytterligare förbättras. De huvudsakliga egenskaperna avsedda med dessa medel var förmågan att förändra masstransport av vatten eller lösningar till cementpastan. Kapillärsugning och diffusion undersöktes. Att öka vct minskar effektiviteten hos de hydrofoba medlen för att motstå vattenupptagning. Detta sågs vid kapillärsugning och enkelriktad kloriddiffusionsprovning. Raffinerade TAG:er var effektivare att minska kloriddiffusion än den oraffinerade, medan "silanerna" i visa fall faktiskt ökade mängden kloridjoner som överfördes inne i cementpastan. Något positiva effekt kan ses vid den lägre inkluderingstillsatsen (1 %). Att öka vct minskar motståndet mot kloridjondiffusion. En fältteststation intill fordonstrafik etablerades också 2018 och 2019 men provkropparna har inte testats vid denna tidpunkt. Förhoppningen är att dessa och andra framtida studier ska leda till ett komplett doktorandprojekt. / <p>QC 230330</p>

Durability of reinforced concrete (RC) structures placed in non-aggressive environments is often sat- isfactory. However, under certain environmental conditions there are internal or external actions that significantly reduce their lifetime. Nowadays, lifetime assessment of deteriorating structures is focused on the isolated effect of the main deterioration processes (corrosion, fatigue, creep, etc.). However, it is paramount to study the combined effect of various deterioration processes because such interaction could reduce structural integrity. This study proposes a new model for lifetime assessment of RC structures subjected to corrosion- fatigue deterioration processes. The proposed model distinguishes between the following phenomena: chloride penetration, corrosion of reinforcement, concrete cracking and corrosion-fatigue of reinforcing bars. Chloride penetration determines corrosion initiation. Corrosion reduces the cross-section of reinforcing steel. The accumulation of corrosion products in the steel/concrete interface produces concrete cracking. Fatigue causes the nucleation and the propagation of cracks in steel bars. The interaction between corrosion and fatigue can only be taken into account when modeling the combined problem. Thus, pitting corrosion generates stress concentrations that nucleate cracks in the reinforcing bars. Cyclic loading and environmental factors affect the kinematics of crack propagation. There exists significant uncertainty related to the combined corrosion-fatigue problem. This study also addresses this problem by considering the uncertainty inherent in (1) material properties, (2) model and its parameter and (3) environmental actions. Time-invariant random variables represent the uncertainty of material properties and model. Stochastic processes consider the uncertainty of environmental actions. The proposed stochastic models for weather (temperature and humidity) take into account seasonal variations and global warming. The stochastic models for environmental chloride concentration differentiate between exposure to de-icing salts or the sea. Finally, a fuzzy approach accounts for the uncertainty related to corrosion rate. The proposed model is applied to the reliability analysis of RC members located in various chloride- contaminated environments. Overall results reveal that the combined effect of corrosion-fatigue de- pends on environmental conditions and strongly influences the performance of RC structures leading to large reductions in expected lifetime.

Les ciments sulfoalumineux (CSA) peuvent être une solution à l’amélioration de l’impact environnemental des bétons, grâce aux faibles consommations énergétiques et émissions de CO2 lors de leur fabrication. Leurs propriétés expansives, de rapidité de prise et de montée en résistance participent également à l’intérêt grandissant dans les domaines de la construction et de la préfabrication en béton pour ce type de liant. Toutefois, la durabilité des bétons sulfoalumineux reste encore méconnue ou discutée, notamment en milieux acides et face à la corrosion des armatures, en ambiance marine et par carbonatation. Les travaux présentés dans cette thèse se proposent ainsi d’étudier et de comparer la durabilité face à ces attaques, de bétons sulfoalumineux à celle de bétons de référence à base de CEM I et de CEM III/B. Ils s’appuient sur des caractérisations performantielles (indicateurs de durabilité, essais performantiels en conditions accélérées ou naturelles) et microstructurales (phases solides, porosité). Au préalable, l’application des caractérisations sus-citées aux bétons sulfoalumineux est vérifiée et discutée. La bonne résistance des bétons sulfoalumineux aux milieux acides est observée lors d’essais de lixiviation dynamique, à température et pH régulés. L’étude de la pénétration des chlorures (migration en régime permanent et transitoire, isothermes de fixation, exposition en zone de marnage) et de la carbonatation (naturelle et accélérée) de bétons à base de 8 ciments sulfoalumineux de laboratoire différents a permis d’établir des moyens d’améliorer leur durabilité potentielle. Ces moyens ont été appliqués à la fabrication d’un ciment industriel performant, dont la bonne durabilité reste toutefois à confirmer définitivement en conditions réelles. / Calcium sulfoaluminate (CSA) cements can be a solution to improve the environmental impact of concrete, thanks to the lower energy consumption and CO2 emission during their production. Their expansive, fast setting and rapid hardening properties contribute to the growing interest of engineers for concrete construction and prefabrication. However, the durability of sulfoaluminate concretes is not clearly assessed yet, especially in acidic and marine environments, as well as carbonation and chloride induced rebars corrosion. Thus, the aim of this thesis is to study and compare the durability, related to these attacks, of concretes made with CSA cements to ordinary Portland and GGBS cements based reference concretes. This study is founded on microstructural (solid phases, porosity) and performancial (durability indicators, natural and accelerated tests) characterization. Beforehand, the application of these characterizations to CSA concretes is verified and discussed. These show a good resistance to acidic environments when submitted to dynamic leaching tests at pH 3 and 5. The study of chloride ingress (steady and non-steady state migration, binding isotherms and tidal zone exposition) and carbonation (natural and accelerated) in concretes of 8 different laboratory CSA cements enabled us to find achievable means to improve their potential durability. These means were applied to the production of a performant industrial CSA cement, whose good durability has still to be assessed on field conditions.