This article was focused on the evaluation of neutral salt spray test effect (according to ISO 9124), procedure E4, on mechanical properties of load-bearing adhesive joints. The study also comprises the influence of substrate material (mild steel, aluminum alloys) and substrate surface roughness (verified by optical confocal microscopy). The experimental program contained acrylate-based adhesive and hybrid silicone polyurethane based adhesive which were applied in double lap joints loaded by shear.
P. Pokorný, D. Dobiáš, M. Vokáč, M. Kouřil and J. Kubásek
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.
P. Pokorný, R. Pernicová, M. Vokáč, I. Sedlářová and M. Kouřil
The paper summarizes the impact of produced hydrogen and calcium hydroxyzincate (Ca[Zn(OH)3]2·2H2O) on the formation of the porous structure of cement paste in the vicinity of hot-dip galvanized steel. These substances result from cathodic (hydrogen) and anodic (zincates-formed by reaction with hydroxides) corrosion reactions of hot-dip galvanized steel (or pure zinc) in the cement paste.
The cement binder pore structure was studied by means of mercury porosimetry and analysis of scanning electron microscopy and confocal microscopy images. The porosity of the cement paste at the galvanized steel / cement interphase increased as a result of galvanized steel corrosion while hydrogen was formed. Such a porous structure was maintained throughout the maturation of cement paste. Kinetics of galvanized steel corrosion related primarily to water transport through the binder. The formation of calcium zincate did not result in transition of galvanized steel from active to passive state corrosion.
To begin with, the intorduction of this paper summarises literature sources that wrongly interpret results of the bond strength between hot-dip galvanised reinforcements and concrete. The influence of the total reinforcement anchorage length on the bond strength results assessment was studied in detail. The numeric analysis of beam models with various testing anchorage lengths (the analysis input data comprised the results of previous bond strength tests carried out in a laboratory) unambiguously confirmed that when the bond strength between concrete and hot-dip galvanised reinforcement with a sufficient test anchorage length is tested in a beam test, the negative impact of the coating corrosion on bond strength with concrete may be biased. It is more objective to test bond strength with concrete in a pull-out test where a very short test reinforcement anchorage length is set out as a standard.
P. Pokorný, P. Bouška, T. Bittner, J. Kolísko, M. Vokáč, T. Mandlík and J. Müllerová
The paper evaluates extent of corrosion damage to composite glass-fibre fabric reinforcement in environment simulating concrete pore solutions (pH 12.6, 13.0, 13.5) and carbonated concrete contaminated with chlorides (pH 8.1 + Cl-) using the FT-IR and SEM/EDS techniques. Also, the effect of corrosion damage on tensile strength of segmented glass fibre as well as the presence of specific protective organic coating on glass fibre were studied. The results demonstrate local corrosion damage of samples at pH 13.5 and on the other hand high stability in environment simulating carbonated concrete and carbonated concrete contaminated with chlorides. The study also suggests unevenness of organic coating with occurrence of localized porosity which is related to aforementioned corrosion damage. Corrosion damage in FT-IR spectra manifests by changes in peaks signalling hydrolysis of protective organic coating and occurrence of peaks suggesting presence of Ca2+ rich corrosion products.