Corrosion of steel reinforcement is the main focus of many studies on condition assessment of road infrastructure. The major uncertainty involves the behavior of steel rebar during dynamic loading imposed by traffic. Especially in countries that use deicing salts during winter, a combined loading situation emerges in which stress, frequency, and chlorides are present at the same time. Laboratory tests are conducted to evaluate the performance of single steel rebars simultaneously exposed to different model media (alkaline and chloridecontaining solutions), different frequencies, and different initial stress levels. These so-called chloride-exposed fatigue tests show the impact of chloride-induced corrosion on the performance of dynamically loaded rebar. Despite the well-known low susceptibility of construction steel to enhanced stress-induced damage in a corrosive medium, the recorded behavior indicates altered electrochemical performance under dynamic load. The results allow for an alternative view of the assessment of service-life design of infrastructure.

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Here we report on a study of a rheological behavior of sodium alginate and montmorillonite suspension. We find that viscoelastic behavior of this suspension is dramatically affected with increasing volume fraction of montmorillonite platelets. Addition of montmorillonite generally leads to gel formation, which is attributed to interactions of montmorillonite and alginate via H-bonding and attraction between the positive edges of the platelets and the anionic backbone of the biopolymer. A critical concentration for the measured system was observed at 20 wt.% montmorillonite, where a crossover to a gel-like structure was detected. The observed gel has a rubber plateau, which develops further with higher montmorillonite concentration. In this physical gel the relaxation maximum was detected, which is associated with the breaking and reformation of the bonds between the platelets and the biopolymer. For this transient behavior, we find that a Maxwell type viscoelasticity quite well describes the relaxation time and the observed G'-G" crossover. We believe that this gel-like behavior plays an important role in formation of highly ordered nanostructures that develop during the drying of these bio-nanocomposite suspensions.@en

Proof loading of bridges is an option to study existing bridges when crucial information is lacking. When proof loading is chosen, the question arises which maximum load should be attained during the test to demonstrate sufficient capacity, and which criteria, the “stop criteria”, based on the measurements during the test, would indicate that the test needs to be aborted before reaching the maximum desired load. A review of the literature identifies the stop criteria in currently used codes and guidelines. Beams sawn from the Ruytenschildt bridge were tested in a controlled way in the laboratory and analyzed with regard to the stop criteria from the literature. Recommendations are given for the future development of stop criteria for flexure and shear. These recommendations will form the basis for a guideline on proof loading of existing concrete bridges that is under development in The Netherlands. @en

“Maturity” method is commonly used to predict concrete strength development based on the temperature history of concrete. Basically, concrete strength development is estimated using the relationship between maturity index and strength e.g. ASTM C 1074 elaborates the procedure of this standard practice, where the, maturity index can be expressed either as temperature-time factor using the Nurse-Saul equation or as the equivalent age at a specific temperature using the Arrhenius equation. According to Saul, concretes of the same mix at the same maturity have approximately the same strength whatever combination of temperature and time are relevant in order to make up that maturity. In cement-based materials, strength increases with the progress of cement hydration. The amount of hydrated cement depends on how long the concrete has been cured and at what temperature levels. When electrical current flows through the cement-based material, the temperature development will be increased compared to control conditions, initially leading to accelerated cement hydration and increased strength. Various experiments on electrical curing and maturity method of cement-based materials have been performed and reported. However, the effect of electrical current flow on the maturity of cement-based materials is still not well understood.This paper deals with the influence of stray current on the maturity levels of cement-based materials. Varying levels of electrical current density were applied to mortar specimens. The maturity levels were determined based on the relationship of electrical properties (i.e. electrical resistance), thermal properties (i.e. temperature development) and mechanical properties (i.e. strength) of cement-based materials.@en

Service life of reinforced concrete structures exposed to chloride enriched environment is well known to be mainly determined by steel passivity breakdown in the event of chloride-induced corrosion initiation and propagation. Since Cl- induced (localized) corrosion is caused by the free (water-soluble) chloride, present in the pore network of a reinforced concrete structure, quantifying the level of free chloride locally, e.g. via embedded Ag/AgCl electrodes (chloride sensors), is a generally accepted and applicable approach to monitor the time to corrosion initiation. The measurement is essentially a potential (voltage) reading over time and as such logically depends, among other factors, on the electrical and microstructural properties of the surrounding medium. Therefore, an accurate determination of the time to corrosion initiation significantly depends on the properties of relevant interfaces, such as the steel|cement paste interface and/or the Ag|AgCl|cement paste interface. In this paper, steel rods were coupled with Ag/AgCl sensors and embedded in cement paste cylinders. The specimens were immersed in simulated pore solution, containing 855 mM chloride concentration. Electrochemical impedance spectroscopy (EIS) was employed for quali-/quantification of the corrosion process on the steel surface (medium to low frequency response), while simultaneously providing information for the electrical properties of the bulk cement-based matrix through the high frequency response. The open circuit potential (OCP) values of both sensors and steel rods were recorded for more than 30 days. The results show a good agreement between sensor readings and steel electrochemical response i.e. time to corrosion initiation was recorded via steel OCP readings, whereas the relevant chloride content was estimated via the sensors’ OCP readings. @en

Most concrete structures are designed to last for at least 50 years or more. During their lifetime these structures are exposed to various environmental actions. On going cement hydration guarantees a stronger concrete in terms of bond between the aggregates, fewer voids, and depercolation of capillary pores, which is of particular importance for cover concrete. Thus, a properly cured cement-based material is the ultimate preparation for a long service life, since it prevents the surface from drying. A new environmentally friendly, water-based curing compound, made of sodium alginate bio-polymers, has recently been developed at TU Delft that could help to achieve these goals. Experimental Rapid Chloride Migration tests and Environmental Scanning Microscope observations are conducted on different samples to investigate the functional properties, e.g. ion transport, and microstructural investigation, to examine the performance of the new bio-based curing compound. Mortar samples were cured at 50% RH and 20 °C both with and without surface addition of the bio-based compound. Two different types of cement, CEM I and CEM III/B, were tested to study differences in curing performance. Significant beneficial effects were observed at the mortar surface when applying the bio-based curing compound showing reduced diffusivity. The results showed a very good quality surface with a high quality and durable microstructure. Also, a higher curing sensitivity was observed for the CEM III/B samples compared to samples prepared with CEM I.@en

The stability of chloride ion selective electrodes in highly alkaline solutions is an important aspect when reliability and feasibility within reinforced concrete applications are concerned. The sensitivity of these electrodes largely depends on the properties of the AgCl layer, including uniformity, porosity, orientation, thickness, etc. These can be varied for optimum performance through adjusting the current density and anodizing time. In this study the Ag|AgCl electrodes were prepared in four different current density regimes and the resulting microstructural properties of the AgCl layer were correlated to potentiometric response in chloride-containing solutions, including synthetic concrete pore solution and cement extract. It was found out that lower level of the current density within the anodization process results later on in increased sensitivity and stability of the electrodes..@en