Józef Jasiczak

Aspects of bond layer role in concrete repairs

The paper presents the role of a bond layer in the repair process of concrete and reinforced concrete elements as well as the place of its laying. For the purpose of a detailed analysis of the above problems two series of tests were carried out. In the first series of the tests, the influence of the state of the surface under repair (wet, oiled) on the adhesion of the bond layer is taken into account. In the second series, the influence of surface modification, grade of concrete and the placement of layers on the adhesion of bond layer to the surface was tested. It was shown that the use of a proposed polymer surface layer was possible both on wet and oil-contaminated surfaces. It was also proved that the adhesion of levelling layer (polymer–cement filler) to concrete is lower after sandblasting. The usage of the levelling layer under the polymer bond layer weakens their adhesion.

Impact Of Moisture Conditions On Early Shrinkage Of Ordinary Concrete With Changing W/C Ratio

Abstract Article presents the results of the effect of humidity on early shrinkage of normal concrete with variable W/C ratio. As known for a long time, shrinkage is dependent of many factors. One of them is the W/C ratio and the quantity of water which is located in the concrete mix. In article there were discussed changes taking place in the concrete mix, the methods of research and the partial results obtained by the authors of the paper. Shrinkage is a phenomenon well known and studied by various research centers. The total amount of shrinkage may depend on various factors such as humidity, temperature, composition of the concrete mix, the W/C ratio, the size of the item. The study was conducted to determine the amount of shrinkage in its early stages. It is very important for concrete floors contractors, precast manufacturers to start at the right time finishing work and prevent the formation of shrinkage cracks.

Comparison of the Impact of Protein Preparation and Modern Factory-Produced Admixture on the Air Entrainment Structure of Cement Paste: Modern and Historical Aspects

ABSTRACT This article presents the results of the impact of blood additive (protein preparation) on the structure of air entrainment of cement paste. The results have been compared to those obtained when using a classic air entraining factory-produced admixtures of good quality. Compressive strength of concrete has been tested and air entrainment characteristics of cement pastes have been assessed (air void distribution including diameter, total air content A (%), content of micro pores with diameter A300 < 300 µm, and specific surface area of air voids α (mm−1)). The study has been carried out on hardened cement paste with different content of air entraining substances. The analysis of the test results has shown that in terms of efficiency, intensity of action, and air entrainment characteristics the protein preparation clearly outperformed factory-produced air entraining additive.

Laboratory Tests of Adhesion of Steel Bars to Ordinary and Frozen Concrete

The issue of adhesion of steel to concrete is one of decisive features characterising reinforced concrete. Adhesion constraints to concrete are simplistically presented with shear stress evenly distributed on the side surface of reinforcement. However, an exact value of this stress depends on many factors and its estimation is very complicated. There is a lot of laboratory methods aimed at testing adhesion of the reinforcement to concrete but they frequently give different results. Sometimes, they are even contrary. In this paper, the state of knowledge on the steel-concrete adhesion, mechanism of its loss, and factors influencing it were reviewed. Own tests were conducted with two methods, pull-out and push-on, aimed at reflecting the operation of reinforced concrete structure and specifying the chemical adhesion, as well as the friction force of the reinforcement to concrete. The impact of the freeze-thaw cycle on this process was also studied. The interfacial transition zone on the steel-concrete boundary was analysed as well. The structure of boundary layer around the reinforcement in concrete is very similar to the zone of aggregate separation from paste. In the Polish and foreign literature, the thickness of the transition zone is estimated as 50-100 μm but only 10-20 μm of this zone has variable mechanical properties. The microstructure of the boundary line depends on the kind of concrete and reinforcement, presence and kind of additions, conditions of curing, and many other factors. In order to describe this phenomenon more precisely, own tests of the steel-concrete interfacial transition zone involving analysis of SEM images and identification of chemical composition of this EDS area were conducted.

Division of Series of Concrete Compressive Strength Results into Concrete Families in Terms of Seasons within Annual Work Period

The basic concrete characteristic which needs to be controlled is the compressive strength of concrete, the values of which are subject to various random influences, for example climatic conditions, conditions of production and changes in the properties of components. The efficient control requires not only the registration of the decreased or increased concrete strength but also specifying the place and the date of application of concrete batch with characteristics deviating from the project assumptions. The article presents the control procedure, taking into account a division of the series of test results for the compressive strength of concrete from an annual production into concrete families of statistically stable strength parameters, in the identified time intervals. The article presents examples of verification of a hypothesis concerning the attachment of a set of compressive strength results to a concrete family, using selected statistical tests.