Prevention of corrosion in post-tensioned structures: electrically isolated tendons

Post-tensioning structures with metallic ducts risk corrosion, rupture or collapses due to chloride ingress. The use of tight corrugated polymer ducts combined with electrically isolated anchorag-es (EIT) changed the situation. Laboratory and many field applications proved the tightness of the duct, showing resistance values higher or much higher than 50 kΩm, the acceptance criteria for a tight duct. The most important fact is that EIT tendons allow quality control and long-term mon-itoring of the duct tightness. EIT ducts (also with resistance values below the threshold criteria) can be monitored over the whole service life: only a progressive decrease of the measured re-sistance indicates a corrosion risk for this specific tendon. The most important structural elements can be easily monitored for the first time and damage initiation can be detected early. After a successful use in Europe EIT technology is now expanding progressively in the US

Durability challenges for new and existing reinforced concrete structures

Durability challenges for the building industry such as the change from the traditional portland cement to blended cements are discussed

Ag/AgCl ion-selective electrodes in neutral and alkaline environments containing interfering ions

Abstract Chloride ingress can lead to serious degradation of various materials and structures. Continuous measurements of local chloride concentrations is thus of uttermost importance for laboratory research, monitoring of structures, and predictions of the residual life span for the most common building materials. This work investigates the applicability of Ag/AgCl ion-selective electrodes for the non-destructive continuous measurement of local chloride concentrations in concrete and stone when exposed to chloride-bearing environments such as seawater. The work studies the stability of Ag/AgCl ion-selective electrodes in neutral and alkaline solutions and the sensitivity to the main interfering ions coming from the environment and from the material itself. The results indicate negligible interference from fluoride, sulfate, and hydroxyl but considerable from bromide and sulfide. In chloride-free alkaline solutions, Ag/AgCl ion-selective electrodes are not stable over time, but—upon chloride arrival—they permit again reliable measurements of the chloride concentration. The results concerning interference are discussed by taking into account typical exposure environments and it is concluded that the ion-selective electrodes can satisfactorily be used to monitor chloride concentrations in built structures made out of concrete or stone

Stainless steels: passive film composition, pitting potentials and critical chloride content in concrete

Stainless steel reinforcing bars show excellent corrosion resistance in concrete structures exposed to harsh environments. Only little information on the surface chemistry of these materials in alkaline media is available. This work reports XPS surface analytical results (thickness, composition of the passive film and of the interface beneath the film) obtained on black steel, FeCr alloys, DIN 1.4301, DIN 1.4462 and the nickel-free DIN 1.4456 after exposure to alkaline solutions simulating concrete. The pitting potentials of the steels could be related to the Cr(III)oxy-hydroxide and Mo(VI) content in the passive film. Ccrit, the critical chloride content for corrosion initiation in concrete, necessary for life-time predictions can be determined only with time consuming tests, especially for high-alloyed stainless steels. This work reports a correlation between Ccrit in concrete (made with CEM II A/LL and CEM I) and the pitting potential for carbon steel, Fe12%Cr alloy, DIN 1.4301 and DIN 1.4571 stainless steels. This could allow for the first time a quantitative estimation of Ccrit for stainless steels in concrete based on short-term solution tests

Kinetics of electrochemical dissolution of metals in porous media

Metals embedded in porous media interact electrochemically with the liquid phase contained in the pores. A widespread form of this, adversely affecting the integrity of engineered structures, is corrosion of steel in porous media or in natural environments. While it is well documented that the rate of this electrochemical dissolution process can vary over several orders of magni- tude, understanding the underlying mechanisms remains a critical challenge hampering the development of reliable predictive models. Here we study the electrochemical dissolution kinetics of steel in meso-to-macro-porous media, using cement-based materials, wood and artificial soil as model systems. Our results reveal the dual role of the pore structure (that is, the influence on the electrochemical behaviour through transport limitations and an area effect, which is ultimately due to microscopic inho- mogeneity of the metal/porous material interface). We rationalize the observations with the theory of capillary condensation and propose a material-independent model to predict the corrosion rate

Hydrothermally Stable WO3/ZrO2-Ce0.6Zr0.4O2 Catalyst for the Selective Catalytic Reduction of NO with NH3

A new catalyst WO3/ZrO2-Ce0.6Zr0.4O2 (15 wt% WO3/ZrO2:Ce0.6Zr0.4O2=50:50) has been developed for the selective catalytic reduction of NO with NH3. The redox component Ce0.6Zr0.4O2 was dispersed on the surface of acidic WO3/ZrO2 by the solution combustion method showing the best NO x reduction efficiency among the catalysts prepared by various modes of mixing of the components. The catalyst has been characterized by XRD, Raman spectroscopy and NH3-TPD. A NO x reduction efficiency of more than 90% was obtained between 300 and 500°C at α=NH3,in/NO x,in=1. The catalyst showed stable NO x reduction efficiency after hydrothermal ageing at 700°C. Sulfur poisoning promoted the NO x reduction efficiency at high temperatures at the expense of a reduced activity at lower temperatures, but the catalyst could be fully regenerated by heating in O2 at 650°

Liquid-Phase Catalytic Decomposition of Novel Ammonia Precursor Solutions for the Selective Catalytic Reduction of NOx

Aqueous solutions of NH3-precursor compounds (i.e. urea and methanamide) were catalytically hydrolyzed in the liquid phase by applying a pressure of 50bar during contact with the catalyst in a heated tube. Methanamide could be hydrolyzed on an Au/TiO2 catalyst to yield not only NH3, but also H2. Decomposition of urea under high pressure in the liquid phase could even be achieved without the addition of a catalyst. Due to the large excess of water present during decomposition, side products could be avoided. As the reactor tube is electrically heated, the presented method provides a possibility to reliably transform NH3-precursor compounds into gaseous NH3 independent of the engine exhaust gas temperature. The NH3-flow can be added to the main exhaust duct to enable the selective catalytic reduction of NOx at the light-off of the SCR catalys

Quantification of Gaseous Urea by FT-IR Spectroscopy and Its Application in Catalytic Urea Thermolysis

An analysis method was developed for the quantification of gaseous urea in model exhaust gases by FT-IR spectroscopy. The method was applied for the investigation of the catalytic thermolysis of urea, which is used as ammonia storage compound in the selective catalytic reduction of NOx in diesel engine

Enargite by XPS

X-ray photoelectron spectroscopy was used for characterizing the enargite surface. Freshly cleaved samples were analyzed at liquid nitrogen temperature. Enargite is a copper arsenic sulfide of formula Cu3AsS4; it is used as a minor ore of copper. Enargite is a potential source of arsenic and may create environmental problems through the release of toxic elements upon oxidatio

Limitations of the use of concrete resistivity as an indicator for the rate of chloride-induced macro-cell corrosion

An experimental setup was designed to study the impact of concrete resistivity on the rate of chloride-induced reinforcement corrosion. Small pieces of mild steel were used to simulate pits (anodes) that form when chlorides come into contact with the reinforcement. The galvanic current was measured between the simulated anodes and a cathode network. Comparisons were made between the galvanic current and the concrete bulk resistivity. The bulk resistivity was varied using two mortar mixes (made of plain Portland cement and a blended Fly ash cement) which were exposed in different temperature and moisture conditions. Despite a high scatter in the results, it was clear that the relationship between bulk resistivity and corrosion rate depended on the mortars tested. The findings presented in this paper and the accompanying work strongly indicate that concrete bulk resistivity alone does not provide sufficient information for assessment of the corrosion rate for chloride-induced macro-cell corrosio