Carboxymethylcellulose (CMC) and ultrasound gel (USG) seem to be suitable clear model fluids to substitute real ultra-high-performance concretes (UHPCs), enabling experimental monitoring of events occurring within these mixtures at similar flow behaviour. USG is eligible for UHPC mixtures with significant yield stress. CMC having a suitable concentration is better for UHPCs exhibiting indistinct yield stress. The rheological behaviour of real UHPC mixtures as well as substituting model fluids was measured using a non-standard system consisting of a vessel stirred by an anchor or a screw agitator. In addition, a standard rotational rheometer system with concentric cylinder geometry was used for optimization of the above-mentioned method of measurement and also for measuring the rheological parameters of the substituting model fluids. This article deals with the methodology for measuring the rheological properties of these substances and presents the results of the measurements using flow curves and rheological models.

The determination of the load bearing capacity of masonry in existing structures is not an easy task, even for experienced surveyors. For its assessment, it is necessary to know the compressive strength of the masonry units and mortar. Relatively good destructive and non-destructive methods were developed for the determination of the compressive strength of masonry units. However, mortar compressive strength determination is currently closer to a rough estimation rather than a deterministic approach. All of the currently used methods are either complicated, have a limited application, or are based on the surveyor’s experience only. Influence of the human factor on the results of testing is significant. The paper introduces the development of a new non-destructive method, which eliminates the influence of the human factor. The method is supposed to work as quickly and as easily as the Schmidt hammer used for concrete structure surveys. The new instrument was created where the compressive strength of mortar is assessed by hammering a steel bar into a joint with constant energy, while the depth of penetration is measured. The impact energy is provided by a steel spring with a prescribed stiffness, and the loading is provided by an automatic system similar to those used in air-soft guns.

The paper verifies anti-corrosion barrier protective properties of PE/PAK (polyethylene/polyacrylate), PE/PPE (polyethylene/polyproplylene) and PAD (polyamide) coatings of specific thickness on the surface of conventional ribbed bar B500B. Using pull-out test, the bond strength of such system was compared with bond strength of normal strength concrete (C30/37). Results of these tests show that key properties of coated systems are comparable to the previously tested epoxy coatings in case of their use in technical practice (protection of conventional rebar). In conclusion, their effective protective effect corresponds to minimal thickness higher than 300 μm but simultaneously lower the bond strength between the ribbed rebar and concrete. Keywords: corrosion of steel in concrete, organic coatings, bond strength, pull-out test, porosity

This article is focused on changes in the properties of colored concrete due to frost. In contrast to conventional concrete structures, fair-faced concrete is exposed to external conditions and is therefore also prone to degradation of its surface. The durability of the surface layers is mainly reflected in the color saturation and resistance to mechanical damage. Therefore, the paper focuses on measuring the change in color and strength characteristics after 75 cycles of frost resistance. The measurement was performed on concrete samples colored with yellow, red and green powdered metal oxide-based pigments. Based on the results, we can concluded the frost resistance of colored concrete depends primarily on the type of pigment used.

In this paper, the effect of gradually increasing amounts of KMnO4 (10−4, 10−3, 10−2 mol·L−1) in cement paste on the bond strength of a plain hot-dip galvanized steel bar was evaluated. The open-circuit potential of HDG samples in cement paste with various additions of MnO4− was monitored in order to follow a transfer of zinc from activity to passivity. Furthermore, the influence of the addition of these anions on the physicochemical properties of normal-strength concrete or cement paste was evaluated by means of hydration heat measurements, X-ray diffraction analysis, and compressive strength. The effective concentration of MnO4− anions prevents the corrosion of the coating with hydrogen evolution and ensures that the bond strength is not reduced by their action, which was determined to be 10−3 mol·L−1. Lower additions of MnO4− anions (10−4 mol·L−1) are ineffective in this respect. On the other hand, higher additions of MnO4− anions (10−2 mol·L−1), although they ensure the corrosion of the coating in fresh concrete without hydrogen evolution, but affect the hydration process of the cement paste that was demonstrated by slight water separation.