Ing. Veronika Steinerová

Ing. Veronika Steinerová

15122 Ústav nosných konstrukcí

Several prestressing reinforced structures have recently collapsed due to chloride-induced steel corrosion. This study investigates the effect of the corrosion of hot-dip galvanized conventional prestressing steel reinforcement under hydrogen evolution on bond strength in normal-strength concrete. The impact of hydrogen evolution on the porosity of cement paste at the interfacial transition zone (ITZ) is verified through image analysis. The whole surface of prestressing strands is hot-dip galvanized, and their corrosion behavior when embedded in the cement paste is investigated by measuring the time dependence of the open-circuit potential. Concerning the uniformity of the hot-dip galvanized coating and its composition, it is advisable to coat the individual wires of the prestressing reinforcement and subsequently form a strand. It is demonstrated that the corrosion of the coating under the evolution of hydrogen in the cement paste reduces the bond strength of hot-dip galvanized reinforcement in normal-strength concrete. Image analysis after 28 days of cement paste aging indicates insignificant filling of hydrogen-generated pores by zinc corrosion products. Applying an additional surface treatment (topcoat) stable in an alkaline environment is necessary to avoid corrosion of the coating under hydrogen evolution and limit the risk of bond strength reduction.

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Ing. Veronika Steinerová

15122 Ústav nosných konstrukcí

In this study, the nature of boriding surface treatment mechanism of the steel prestressing strand is evaluated and then the corrosion resistance of the borided steel in hydrochloric acid is assessed (detection of the content of released iron and manganese in the exposure solution). The effect on the bond strength of the treated steel prestressing strand with normal strength concrete is also evaluated (pull-out test). Boriding was carried out in a boron carbide backfill with fluoride activators. This manuscript describes the first informative results on this topic.

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Ing. Veronika Steinerová

15122 Ústav nosných konstrukcí

Corrosion damage to conventional prestressing reinforcement placed in a grout channel stimulated with chloride anions can lead to unpredictable collapse of reinforced concrete structures. An expert report previously carried out on the condition of the Troja footbridge after its collapse indicated that corrosion of the prestressing reinforcement stimulated by chloride anions was the cause. In this paper, the possibility of applying corrosion protection in the form of a protective SiC-based plasma coating is studied. The barrier protection properties of the silicon carbide coating partially incongruently decomposed into elemental silicon and amorphous SiO2 were comparatively verified in hydrochloric acid - AAS solution by analyzing the iron content of the test solution after the exposure time. Furthermore, the bond strength of the reinforcement coated in this way with concrete of normal strength was verified by means of a pull-out test. Testing was carried out on standard cubic specimens with standard uncoated and ceramic coated reinforcement applied. Interpretation of the bond strength test results included measurement of changes in surface roughness (Ra) and contact surface angle of the coated ceramic.

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Ing. Veronika Steinerová

15122 Ústav nosných konstrukcí

In this study, the corrosion properties of plasma-sprayed Al2O3 coating (APSS) with a topcoat of zirconium-based conversion coating (ZrCC) and organofunctional silane coating (3-glycidyloxypropyltrimethoxysilane; GPTMS) on carbon steel are investigated in detail. Additionally, the bond strength of plain steel bars coated with this system in normal strength concrete are newly tested. The APSS coating exhibits significant porosity, with unfavourable open pores limiting the barrier protection effect. In contrast, the surface roughness (Ra) significantly increases, improving the bond strength between steel bars and concrete. Such increase in carbon steel roughness improves bond strength in concrete. The synergic application of ZrCC and GPTMS topcoats significantly enhances the corrosion resistance of the base coat (inhibition effect). The character of the GPTMS coating increases the wettability of the APSS coating, which further positively contributes to bond strength between plain bars and concrete. It is demonstrated that when the ZrCC topcoat is applied without GPTMS, the corrosion resistance increases insignificantly and the surface wettability decreases, negatively affecting bond strength in comparison with carbon steel coated using an APSS base coat only.

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Ing. Veronika Steinerová

15122 Ústav nosných konstrukcí

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Ing. Veronika Steinerová

15122 Ústav nosných konstrukcí

This article presents the results of research on the growth kinetics, microstructure (SEM/EDS/XRD), and corrosion behavior of Zn-5Al coatings obtained using a high-temperature hot dip process on B500B reinforcing steel. The corrosion resistance of the coatings was determined using the neutral salt spray (NSS) test (EN ISO 9227). Based on chemical composition tests in micro-areas (EDS) and phase composition tests (XRD), corrosion products formed on the coating surface after exposure to a corrosive environment containing chlorides were identified. In the outer layer of the coating, areas rich in Zn and Al were found, which were solid solutions of Al in Zn (), while the diffusion layer was formed by a layer of Fe(Al,Zn)3 intermetallics. The growth kinetics of the coatings indicate the sequential growth of the diffusion layer, controlled by diffusion in the initial phase of growth, and the formation of a periodic layered structure with a longer immersion time. The NSS test showed an improved corrosion resistance of reinforcing bars with Zn-5Al coatings compared to a conventional hot-dip-galvanized zinc coating. The increase in corrosion resistance was caused by the formation of beneficial corrosion products: layered double hydroxides (LDH) based on Zn2+ and Al3+ cations and Cl- anions and simonkolleite—Zn5(OH)8Cl2H2O.

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prof. Dr. Ing. Martin Pospíšil, Ph.D., Ing. Veronika Steinerová

15122 Ústav nosných konstrukcí

The paper describes some mechanisms and aspects influencing the testing of the cohesion of coated steel reinforcement bars (rebars) with concrete. Cohesion was verified on plain steel rebars with zinc and nickel coatings. One hot-dip zinc coating (Zn HDG) and three galvanic coatings, in particular zinc (Zn G), zinc-nickel (ZnNi) and nickel coating (Ni), were included in the experiment. The main goal of the work was to verify and describe the effect of these surface treatments on the cohesion of rebar with concrete. The evaluation of the coherence of the whole system was carried out according to the international standard RILEM RC 6 (pullout test). To complement the correlation of roughness to the final cohesion, roughness measurements were also performed on all tested surfaces. Furthermore, the paper deals with the ČSN EN 10348-2 standard and points out pitfalls that can make it difficult to design structures with coated steel reinforcement bars. The dependence of cohesion on the roughness of the coating was confirmed in the experiment. It has also been proven that corrosion of zinc in an alkaline environment reduces the cohesion of the coated rebar with concrete and creates a porous contact surface at the interface between the cement paste and the rebar. Due to the high roughness (compared to other surfaces), corrosion of zinc during hydrogen evolution did not affect the results of the adhesion tests for the hot-dip zinc coating, where the adhesion to concrete was higher than that of steel.

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prof. Dr. Ing. Martin Pospíšil, Ph.D., Ing. Veronika Steinerová

15122 Ústav nosných konstrukcí

Příspěvek popisuje korozní chování konvenčních galvanických povlaků Zn-Ni a Ni, a žárového Zn (HDG) v modelových pórových roztocích betonu s cílem užší diskuze o korozním chování povlaků s obsahem niklu jako efektivní ochrany výztuže betonu. Elektrochemické korozní chování (Ecorr (t), Rp (t)) jednotlivých povlaků je zaměřeno na hodnocení odolnosti povlaku vůči alkalickému prostředí a omezení koroze povlaku za vývoje vodíku. Komparační porovnání korozního chování jednotlivých povlaků je doplněno o analýzu precipitovaných korozních produktů prostřednictvím XRD (rentgenová difrakční analýza) a XPS (rentgenová fotoelektronová spektroskopie). Skladba korozních produktů je hodnocena rovněž na její předpokládaný vliv na soudržnost s betonem.

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Ing. Veronika Steinerová

15122 Ústav nosných konstrukcí

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prof. Dr. Ing. Martin Pospíšil, Ph.D., Ing. Veronika Steinerová

15122 Ústav nosných konstrukcí

Příspěvek popisuje důležité mechanizmy a aspekty, ovlivňující zkoušení soudržnosti povlakované ocelové výztuže s betonem. Soudržnost byla ověřována na hladkých ocelových tyčích s tenkými galvanickými povlaky na bázi zinku a niklu (ZnNi) a niklu (Ni). Pro ověření dosavadních výsledků byl do experimentu přidán i povlak žárového zinku (Zn HDG). Hlavním cílem práce bylo ověření a popsání vlivu těchto povrchových úprav na samotnou soudržnost. Hodnocení soudržnosti celého systému bylo realizováno podle mezinárodní normy RILEM RC 6, typu Pull-Out test. Pro doplnění korelace drsnosti na výslednou soudržnost bylo provedeno i měření drsnosti u všech testovaných povrchů. Závislost soudržnosti na drsnosti povrchu byla potvrzena. Prokázala se také skutečnost, že koroze zinku v alkalickém prostředí snižuje soudržnost povlakované výztuže s betonem. Koroze zinku za vývoje vodíku se vzhledem k vysoké drsnosti (v porovnání s ostatními povrchy) neprojevila u povlaku žárového zinku, u něhož byla soudržnost s betonem vyšší než u oceli.

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