The study explores the effect of elevated temperatures on the bond strength between prestressing reinforcement and ultra-high performance concrete (UHPC). Laboratory investigations reveal that the changes in bond strength correspond well with the changes in compressive strength of UHPC and their correlation can be mathematically described. Exposition of specimens to temperatures up to 200 °C does not reduce bond strength as a negative effect of increasing temperature is outweighed by the positive effect of thermal increase on the reactivity of silica fume in UHPC mixture. Above 200 °C, bond strength significantly reduces; for instance, a decrease by about 70% is observed at 800 °C. The decreases in compressive and bond strengths for temperatures above 400 °C are related to the changes of phase composition of UHPC matrix (as revealed by X-ray powder diffraction) and the changes in microstructure including the increase of porosity (verified by mercury intrusion porosimetry and observation of confocal microscopy) and development cracks detected by scanning electron microscopy. Future research should investigate the effect of relaxation of prestressing reinforcement with increasing temperature on bond strength reduction by numerical modelling.

This paper studies the effect of water as an oxidation agent and also of oxygen on zinc corrosion kinetics in active state in concrete, using high-sensitivity electrical resistance sensors. It was proven that zinc corrosion in active state is strongly affected by the presence of water at its surface. Zinc corrosion in real concrete in the absence of water can be misinterpreted as salt passivity. The presence of oxygen results in an increase of zinc corrosion rate, however at pH 12.6, passivity can occur. It was verified that corrosion products consisting primarily of Ca[Zn(OH)₃]₂·2H₂O cannot effectively passivate zinc surface in concrete, even after 1800 h of exposure and zinc, or hot-dip galvanized steel can corrode at an unacceptable corrosion rate (more than 4 µm·a⁻¹).

This article provides a comprehensive overview of the potential use of organofunctional silane coatings in the corrosion protection of concrete reinforcement in close relation to other commercially used coating technologies—i.e., epoxy coatings and bath hot-dip galvanizing coatings. The application technology of the steel surface is described in detail, and the corrosion performance and bond strength in concrete are compared. The paper also points out the possibility of improving the durability of epoxy coatings by the addition of silanes and, in the case of application to the surface of hot-dip galvanized steel, they can prevent corrosion of the coating by hydrogen evolution. The application potential of organofunctional silanes is also presented in the form of hydrophobic coatings on concrete surfaces or as corrosion inhibitors in simulated concrete pore solutions. The use of a suitable type of modified silane coating on the surface of carbon steel reinforcement can increase the corrosion performance and can also increase the bond strength in concrete. However, these facts need to be experimentally verified.

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.

Článek shrnuje aspekty zkoušení a ovlivňování soudržnosti výztuží s betonem. Úzce se zaměřuje na hodnocení míry vlivu nevyhnutelné koroze povlaku žárového zinku v čerstvém betonu na samotnou soudržnost. Ovlivnění soudržnosti vlivem vývoje vodíku a expanzních korozních produktů zinku je ověřováno na hladkých ocelových prutech. Povlak žárového zinku byl vytvořen konvenční ponorovou technologií. Realizováno bylo normované zkoušení soudržnosti výztuže s betonem na krychlích („vytahovací zkouška“) dle ČSN 73 1328. V závěrech jsou diskutovány i jiné vlivy, které mohou mít dopad na vývoj soudržnosti, především pak vliv obsahu chromanů v použitém cementu a samotná skladba vyloučeného povlaku