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Concrete cylinder piles produced by a centrifugally cast, vibrated, roller compacted process have shown promising corrosion durability in marine environments. Three bridges in the Florida Panhandle with approximately 40 years of service in aggressive marine service were examined. A newly constructed marine bridge utilizing concrete cylinder piles was also examined to verify corrosion performance of piles manufactured with modern building materials and construction compared to piles built several decades ago. Survey of the marine bridges showed minimal corrosion distress despite low design concrete cover to steel hoop reinforcements (20-40 mm). Typical concrete distress included minor rust staining but not necessarily indicating corrosion of reinforcement steel. Thin longitudinal cracks were frequently observed but were likely caused by mechanical damage from pile driving rather than stemming from corrosion distress. Chloride ion diffusivity was low, in the order of 1x10-13 m2/s. Other measured parameters such as concrete resistivity, porosity, and water absorption indicate low permeability. Chloride analysis of cracked and uncracked concrete cores from the older bridges in this study did not show pronounced preferential chloride penetration. Chloride analysis from the contemporary marine bridge did show some preferential transport of chloride ions at shallow depths through cracks with further evidence of lower electrical resistivity indicating enhanced electrolyte transport. The pore water pH of concrete samples from the contemporary bridge was high despite the presence of pozzolanic materials suggesting that normal chloride threshold values may be valid.

Epoxy-coated rebar (ECR) has been used in approximately 300 Florida bridges, in an attempt to control corrosion of the substructure in the splash-evaporation zone. Early severe ECR corrosion was observed in the substructure of several Florida ECR bridges (Group 1) where the substructure was built with permeable concrete of high apparent chloride diffusivity DApp. Other ECR bridges built during the same period and having similar DApp were projected to show corrosion damage starting on the following decade. Examination of several of those bridges (Group 2) confirmed that projection. Other recently examined Florida ECR bridges (Groups 3 and 4) were built with very low to moderate permeability concrete having correspondingly low to moderate DApp values at normally sound concrete locations. Those bridges were projected not to show early corrosion at normal locations and that projection has also been confirmed. However, some incidence of thin structural cracks exists affecting a small fraction of the substructure. Chloride transport there is much faster than through the matrix in otherwise low permeability concrete and work has confirmed that early corrosion can develop there. A predictive ECR corrosion model was applied that replicated most of the damage function features observed in the field. The model divides the substructure in separate elements with individual chloride exposure, concrete permeability, concrete rebar cover, and extent of ECR coating imperfections. Additionally, a model for projecting impact of preexisting cracking on corrosion damage was developed. The projections indicate that relatively isolated cracking should only create topical concrete damage with reduced maintenance requirements. However, model projections indicated that even though assuming that the incidence of damage is limited to a small region around the crack, if the crack orientation with respect to the rebar were adverse and chloride transport were greatly enhanced (as it could be expected in relatively wide cracks), corrosion damage from localized concrete deficiencies could significantly increase maintenance costs. Electrochemical Impedance Spectroscopy (EIS) measurements of ECR in extracted cores showed good potential for non destructive characterization of the extent of coating damage. A possible method accounting for frequency dispersion effects in the high frequency response (of importance to assess extent of defects) was introduced.

External sulphate attack on concrete can lead to cracking, expansion and sometimes loss of cohesiveness of hardened cement paste. Therefore, aside from using sulphate resistant cementitious binders, it is important to design concrete which can resist sulphate penetration. In this research, both ASTM C1202 and NT Build 492 electrical migration tests were modified such that sulphate rather than chloride penetration resistances were measured. Modifications included exposing concrete specimens to Na2SO4 rather than NaCl solutions and measuring the depth of sulphate penetration visually using BaCl2+KMnO4 rather than AgNO3 solution. Nine concrete mixtures of varying w/cm, slag replacement and cement types were tested in both original standard tests and modified tests to evaluate the influence of these material variables on test results and compare chloride to sulphate results. It was found that while migration coefficients and total charge passing were lower for sulphate, the influence of material variables were relatively similar.

External sulphate attack on concrete can lead to cracking, expansion and sometimes loss of cohesiveness of hardened cement paste. Therefore, aside from using sulphate resistant cementitious binders, it is important to design concrete which can resist sulphate penetration. In this research, both ASTM C1202 and NT Build 492 electrical migration tests were modified such that sulphate rather than chloride penetration resistances were measured. Modifications included exposing concrete specimens to Na2SO4 rather than NaCl solutions and measuring the depth of sulphate penetration visually using BaCl2+KMnO4 rather than AgNO3 solution. Nine concrete mixtures of varying w/cm, slag replacement and cement types were tested in both original standard tests and modified tests to evaluate the influence of these material variables on test results and compare chloride to sulphate results. It was found that while migration coefficients and total charge passing were lower for sulphate, the influence of material variables were relatively similar.

Yes / The focus of the construction industry has shifted towards the development of al-ternative, eco-friendly and green construction materials due to the energy-inefficient and carbon-intensive nature of Portland cement (PC) production and aggregate quarrying. Meanwhile, increased number of repetitive re-pair/renovation/maintenance activities and demolition operations for the end-of-life buildings generate significant amounts of construction and demolition waste (CDW). For the purposes of sustainability and upcycling wastes into high-value-added materials with improved greenness, components from CDW streams can be used in producing geopolymer concretes without using PC and natural aggre-gates, given the rich aluminosiliceous nature of CDW components. The focus of current work is therefore on the analysis of durability of aspects (i.e., drying shrinkage and resistance against sulfate attack, cyclic freezing-thawing, and chlo-ride penetration) of geopolymer concretes made entirely of CDW. Different types of bricks, tile, concrete, and glass were used in mixed form as precursors for ge-opolymerization while different-size grains of waste concrete were used as recy-cled aggregates. As alkali activators, sodium hydroxide, calcium hydroxide and sodium silicate were used. In a companion mixture, CDW-based precursors were replaced with slag and class-F fly ash. Results showed that sulfate and cyclic freeze-thaw exposure did not cause any noticeable weight and compressive strength loss in CDW-based geopolymer concretes, while chloride penetration was found comparable to PC-based concrete. While drying shrinkage was found high in entirely CDW-based geopolymer concrete and resulted in surface mi-crocracks, it was possible to lower the drying shrinkage substantially via substi-tution of CDW-based precursors with fly ash and slag. / The authors also wish to thank the support of Scientific and Technical Research Council (TUBITAK) of Turkey provided under projects: 218M102 and 117M447. / This paper is from the fib Symposium 2023, Building for the future: Durable, Sustainable, Resilient. 5-7 Jun, Istanbul, Turkey. / The full-text of this article will be released for public view at the end of the publisher embargo on 1 June 2024.

Dans le cadre du projet de recherche de l'IFSTTAR « Approche performantielle et probabiliste de la durée de vie des ouvrages en béton armé », la thèse porte sur la modélisation du transport couplé ions-humidité au travers de bétons éventuellement carbonatés. Une plate-forme de modélisation multi-espèces, qui est basée sur les indicateurs de durabilité et avec différents niveaux de sophistication, a été utilisée. En condition saturée, le transport des ions a été décrit par l'équation de Nernst-Plank et complété par des isothermes des interactions ions/matrice. En condition non saturée, l'advection des phases liquides et gazeuses a été décrite par la loi de Darcy généralisée. L'influence de l'activité chimique sur l'équilibre entre l'eau liquide et vapeur d'eau, ainsi que la cinétique de fixation des ions chlorure ont été prise en compte dans les modèles. La fixation des ions alcalins a été également prise en compte, son influence sur le transport des ions chlorure a été étudiée. Les indicateurs de durabilité (porosité, perméabilité intrinsèque à l'eau et aux gaz) servant comme données d'entrée des modèles ont été déterminés par des mesures directes sur des bétons à base de ciment ordinaire et avec des fortes teneurs en additions minérales (cendres volantes et laitiers). Une méthode d'analyse inverse a été mise en œuvre à partir d'une routine qui intègre un algorithme d'optimisation qui nous a permis de déterminer les propriétés des matériaux plus complexes (coefficient effectif de diffusion, paramètres d'isotherme de fixation et perméabilité intrinsèque à l'eau) à partir des résultats d'essais. Le modèle pour des conditions saturées a été validé par des comparaisons entre des profils de chlorure issus des essais de diffusion et des profils de simulation. Des essais de séchage-imbibition avec une solution saline ou de l'eau pure sur les bétons sains et éventuellement carbonatés ont été réalisés pour valider le modèle en condition non saturée, ainsi que pour mettre en évidence l'influence de la carbonatation sur le transport des ions et sur les transferts hydriques. Outre la compréhension des mécanismes physico-chimiques liés à la durabilité des bétons et détermination des indicateurs de durabilité par analyse inverse, la plate-forme nous permet de prédire le transport des ions et d'humidité suivant la complexité des phénomènes et le niveau de sophistication exigé. Les études menées ont mise en évidence la pertinence et la fiabilité de la plate-forme de modélisation physico-chimique / As a part of the IFSTTAR's research project « Performance-based and probabilistic approach to the life cycle of reinforced concrete structures », this thesis focuses on the modelling of coupled ion-moisture transport through concrete which is possibly carbonated. A multi-species modelling platform, based on durability indicators and with different levels of sophistication, was used. In saturated conditions, ion transport was described by the Nernst-Plank equation and complemented by ion-matrix interaction isotherms. In unsaturated conditions, the advection of liquid and gas was described by the extended Darcy law. The influence of the chemical activity on the equilibrium between liquid water and water vapor, as well as the kinetics of the chloride binding, were included. The binding of alkali was also taken into account and its influence on the chloride penetration was investigated. As input data of the models, conventional durability indicators (porosity, intrinsic permeability for liquid water and for gas) were determined by direct measurement on different concretes made of ordinary Portland cement and containing high contents of supplementary cementing materials (fly ash and slag). An inverse method was implemented thanks to a routine which incorporates an optimization algorithm, allowing us to determine some complex properties (such as effective diffusion coefficient, binding isotherm parameters and intrinsic permeability to liquid water) from experimental results. The model for saturated conditions was validated by comparing the simulation results to experimental profiles obtained from chloride diffusion tests. Wetting tests, with saline solution or pure water followed by drying experiments, on sound concrete and possibly carbonated ones were led to verify the model for unsaturated conditions, as well as to highlight the influence of carbonation on the ion and moisture transport.In addition to a further understanding on the physico-chemical mechanisms related to the durability of concrete and the identification of durability indicators by inverse analysis, the platform allowed us to predict the transport of ions and moisture according to the complexity of the involved phenomena and the required level of sophistication. The relevance and the reliability of the modeling platform for transport were proved by the studies carried out

Slurry infiltrated fiber concrete (SIFCON) was first produced in 1979 in the USA, by incorporating large amounts of steel fiber in molds to form very dense network of fibers. The network is then infiltrated by a fine liquid cement-based slurry or mortar. The steel fiber content can be as high as 30 % by volume. This percentage usually does not exceed 2 % in normal fiber reinforced concrete (FRC) for reasons related to mixing and workability. Due to its high fiber content, SIFCON demonstrates unique and superior mechanical properties in the areas of both strength and ductility. Most of previous research work on SIFCON has focused mainly on investigating the mechanical properties of this material. On the other hand, the studies carried out in the field of durability of SIFCON are quite limited. v Therefore, it seemed that it would be worth to study the various durability aspects of SIFCON. In view of the above, the objectives of this study are to investigate and provide information about durability of SIFCON, mainly permeability, resistance to chloride penetration, freezing and thawing and drying shrinkage. This information will help in providing the necessary database and knowledge about the ability of SIFCON to withstand the conditions for which it has been designed without deterioration, especially when it is intended to be used in aggressive environments The investigations included studying the effects of the following on durability of SIFCON: (i) matrix type (slurry or mortar), (ii) fiber contents (7%, 9.5%, and 12% by volume), and (iii) steel fiber geometry (hooked or crimped). The results obtained indicated that SIFCON, especially when prepared using mortar not slurry, has shown good durability characteristics in spite of its apparent high water absorption. The SIFCON made with the highest possible fiber volume fractions showed the best results. However, it was concluded that SIFCON needs to be protected with suitable low permeability overlays to ensure ideal improved performance by protecting the steel fibers exposed on the surfaces especially against chloride attack.

The use of residues, as the rice husk ash (RHA) in the concrete s production reduces the environmental impact caused in its productive chain. It means fewer energy s consumption, fewer natural resources waste, less environmental pollution and lower aggregated cost. In the present study, the viability of using residual RHA, in natura (non-ground) or ground, on structural concrete, in partial substitution to the Portland cement was investigated, starting from the durability chloride ions analysis. In such a way, five cementitious blends, two composed by natural RHA, two with crushed RHA and one as a reference sample were tested. The substitution s rates were 15% and 25%. The water/binder relations used were 0.45, 0.55 and 0.65. The samples were tested for chloride penetration according to ASTM C 1202 (Rapid Chloride Permeability Test) and for long-term test (colorimetric method). Additionally, the tests of axial compressive strength and water absorption by immersion, according to the ABNT prescriptions were conducted. The obtained results showed that is viable to use residual non-ground RHA as partial substitution to Portland cement in structural concretes. For the axial compressive strength at 91 days and to the same relation w/b, in general, the residual non-ground RHA blends showed higher performance than those presented by the reference mixture. In the RCPT the use of RHA resulted in decreases in the passing charges that, in general, promoted improvement in the mixtures ratings on the chloride penetrability, compared with the reference mixtures. In long-term test, the use of RHA burnt without temperature control, also promoted improvements in the mixture performances, compared to the reference mixtures, with reductions in the chloride penetration coefficients. But the mixtures were dissimilar when compared to those presented by the RCPT. In the case of water absorption by immersion, it was found that the use of RHA, in general, increased the concrete water absorption, however, the results presented by mixtures composed with RHA were close to those of reference ones. / A utilização de resíduos como a cinza da casca do arroz produzida sem controle da temperatura na fabricação de concretos reduz o impacto ambiental gerado na cadeia produtiva deste material, significando menor consumo de energia, menor desperdício de recursos naturais, menor poluição do meio ambiente e menor custo agregado. No presente trabalho investiga-se a viabilidade de se utilizar a CCA residual, ao natural ou moída, em concretos estruturais, em substituição parcial ao cimento Portland, a partir da análise da durabilidade aos ions cloretos. Para isso, foram testadas cinco misturas aglomerantes: duas compostas com CCA ao natural, duas com CCA moída e uma mistura de referência com 100% cimento Portland, a qual se confrontaram os resultados. Adotaram-se os teores de substituição de 15% e 25%, e as relações a/ag de 0,45; 0,55 e 0,65. Procederam-se os ensaios de resistência à penetração de cloretos segundo o método de penetração acelerada ASTM C 1202 (EAPC) e também, segundo o método de imersão em solução salina (EPCI). Adicionalmente, foram realizados os ensaios de resistência à compressão axial e de absorção de água por imersão, segundo prescrições da ABNT. Os resultados obtidos na investigação confirmam que é viável utilizar a CCA residual, ao natural ou moída, como substituição parcial ao cimento Portland, em concretos para uso estrutural. Quanto à resistência a compressão axial, aos 91 dias, as misturas compostas CCA, em geral, apresentaram desempenhos superiores aos das misturas de referência. No EAPC a utilização de CCA resultou em decréscimos nos valores das cargas passantes que, em geral, promoveram melhoria nas classificações das misturas quanto à penetrabilidade aos cloretos, em comparação as misturas de referência. No EPCI a utilização da CCA, queimada sem controle de temperatura, também promoveu melhorias no desempenho da maioria das misturas, em comparação às misturas de referência, com reduções nos coeficientes de penetração de cloretos. Porém as misturas apresentaram comportamentos diferenciados quando comparados ao apresentado no EAPC. No caso da absorção de água por imersão, constatou-se que a utilização de CCA, em geral, aumentou a absorção de água dos concretos, entretanto, os valores apresentados pelas misturas compostas com CCA foram próximos aos de referência.