Innovative strengthening of RC columns using a layer of a fibre reinforced concrete

Reinforced concrete structures that are influenced by degradation, overloading, the thawing and freezing cycles, abrasive damage and corrosion of reinforcement, should be repaired or strengthened. Each of those mentioned situations lead to decreasing the load-carrying capacity of the construction. The damage of a structure or its member causes exceeding the serviceability limit states and ultimate limit states. For this reason, for further use of the structures, they have to be strengthened to increase the load-carrying capacity and to extend the remaining lifetime. A new method for strengthening the vertical members, e.g., columns, is using the fibre reinforced concrete layer and its increased tensile strength in comparison to common RC concrete. This article deals with the theoretical design of dimensioning the columns using a layer of fibre concrete around a column (wrapping). In this case, it is necessary to calculate the residual strength of fibre concrete, which is a crucial factor for the tensile strength of the element

Influence of the type of cement and the addition of an air-entraining agent on the effectiveness of concrete cover in the protection of reinforcement against corrosion

The concrete cover is the basic protection of the reinforcement against the influence of external factors that may lead to its corrosion. Its effectiveness depends mainly on the composition of the concrete mix, including the cement used. Depending on external environmental factors that may aggressively affect the structure, various types of cements and concrete admixtures are recommended. The paper presents the results of tests that allow us to assess the effect of the type of cement used and the air-entraining agent on the effectiveness of the concrete cover as a layer protecting the reinforcement against corrosion. In order to initiate the corrosion process, the reinforced concrete specimens were subjected to cycles of freezing and thawing in a sodium chloride solution. The degree of advancement of the corrosion process was investigated using the electrochemical galvanostatic pulse technique. Additionally, the microstructure of specimens taken from the cover was observed under a scanning electron microscope. The research has shown that in the situation of simultaneous action of chloride ions and freezing cycles, in order to effectively protect the reinforcement against corrosion, the application of both blast-furnace slag cement and an air-entraining agent performed the best.Web of Science1416art. no. 465

Condition assessment of selected reinforced concrete structural elements of the bus station in Kielce

The paper presents the results of the research aimed at assessing the condition of reinforcement and concrete cover in selected elements of the structure of the most recognizable structure in Kielce, i.e. PKS station, located at Czarnowska Street. Currently, demolition works are underway resulting from the planned modernization. The assessment of the corrosion risk of the reinforcement in the construction elements was carried out with the use of a semi-non-destructive electrochemical method. The use of this method made it possible to determine the probability of reinforcement corrosion in the selected areas and to estimate its rate. The protective properties of concrete cover were checked by the carbonation test (test using a 1% phenolphthalein solution) and phase composition analysis (X-ray diffraction analysis). In order to determine the position of the reinforcing bars and to estimate the concrete cover thickness distribution in the areas corresponding to the aforementioned measurements, ferromagnetic detection system was used

Implementation and usage aspects for floors in the residential houses

Concrete floors at the building’s rooms are made of concrete, as well as fibre-reinforced concrete, or with the reinforcement meshes of various kinds. On one hand, such aspects have an influence on technical capabilities, as well as cost and labour-consumption when making the floors; on the other hand, they influence operational properties. The floors, as a result of significant dimensions, are particularly vulnerable to cracks, following the overlapping effects of shrinkage and thermal strains, as well as mechanical loads. Detailed design guidelines concerning the implementation method and the recommended materials (application of the respective plasticising admixtures and reinforcement, various kinds of steel meshes or a distributed reinforcement as steel or polypropylene fibres) have been developed, in order to prevent the cases above. It is visible (according to a great deal of experimental research) that the abovementioned guidelines limit the undesired shrinkage effects. Nevertheless, average typical conditions for making the floors very often differ from those in the guidelines, which may lead to the appearance of future shrinkage cracks, irrespectively to the applied reinforcement. The paper presents conclusions from the analysis of research results for three types of concrete ground floors made in the detached residential house, in the same operational conditions, differing with the reinforcement applied. The research was conducted from the moment of implementation and then, during the initial operational period

Experimental verification of shrinkage due to drying in concrete under varying humidity conditions in accordance with the Eurocode2 standard

The concrete shrinkage depends on many factors. There are the concrete mixture, dimensions of the element and environment conditions, mainly humidity. All these factors can be imposed under laboratory conditions and controlled. In field conditions, however, a constant humidity is not possible to keep. The paper presents the impact of relative humidity changes on the values of shrinkage strains. The experimental results obtained on the specimens (with size 150x150x600 mm) were compared with the values calculated in accordance with the Eurocode 2 standard. The specimens were made with basalt aggregate without admixtures or additives. Two kinds of cement were used in preparing the specimens: Portland and blast-furnace slag cement. All specimens were treated in water for 10 days in the first days after demoulding and then subjected to testing. During the 56 days the temperature was 22 ± 2°C, while the humidity decreased proportionally from 91% to 47%. Strains were measured and the specimens were weighed to determine the mass loss. The experimental results were compared to the computational results. It should be concluded that they were not coherent in the case of ambient humidity exceeding 80% although it was accordance with the Eurocode 2 standard

Impact of reinforcement on shrinkage in the concrete floors of a residential building

The type of floor in a building object results from the serviceability requirements, technical possibilities, and costs of its implementation. Concrete screeds constituting the structural layer of the floor can be made without reinforcement, with dispersed reinforcement, or reinforced with meshes of various materials. Due to the large surface dimensions, concrete screeds are susceptible to scratches as a result of occurring strains, service loads and unevenness of the floor. There are detailed recommendations on how to make floors, and on the materials used. However, the conditions in which floors are made often differ from those recommended. The article presents the results of measured strains on the surfaces of three screeds constituting the floor layer in a residential building. The screeds, which were made in identical environmental conditions, differed in the type of reinforcement used: steel mesh, dispersed polypropylene fibres, fibreglass mesh. In addition, strain measurements were carried out on concrete and fibre-reinforced concrete specimens made of the mix used to make the screeds. The results allowed the assessment of the effectiveness of the reinforcement used, the impact of environmental conditions on the values, and the analysis of differences in the course of strains in real elements and the specimens

Analiza struktury budownictwa mieszkaniowego w Polsce w latach 2009-2018

The article presents an analysis of the housing situation in Poland against the background of European Union countries that took place in the last decade, i.e. in the years 2009 - 2018. The average number of dwellings per 1,000 inhabitants was analysed, the relationship between the number of dwellings and their area was determined, and the increase in the number of dwellings completed over the period was determined divided into flats: individual, cooperative, company and communal, as well as flats intended for sale or for rent.Mieszkanie to z jednej strony zaprojektowany i konstrukcyjnie  wydzielony trwałymi ścianami lokal, a z drugiej strony przestrzeń, która jest niezbędna do zapewnienia bezpieczeństwa, prywatności oraz odpowiednich warunków do nauki i życia. W artykule dokonano analizy sytuacji mieszkaniowej w Polsce na tle krajów Unii Europejskiej. Przeanalizowano przeciętną liczbę mieszkań na 1000 ludności, zależność między liczbą mieszkań a ich powierzchnią oraz strukturę liczby  mieszkań oddanych do użytkowania na przestrzeni dziesięciu lat (2009-2018) z podziałem na mieszkania: indywidualne, sprzedaż lub wynajem, spółdzielcze, zakładowe i komunalne

Implementation and usage aspects for floors in the residential houses

Concrete floors at the building’s rooms are made of concrete, as well as fibre-reinforced concrete, or with the reinforcement meshes of various kinds. On one hand, such aspects have an influence on technical capabilities, as well as cost and labour-consumption when making the floors; on the other hand, they influence operational properties. The floors, as a result of significant dimensions, are particularly vulnerable to cracks, following the overlapping effects of shrinkage and thermal strains, as well as mechanical loads. Detailed design guidelines concerning the implementation method and the recommended materials (application of the respective plasticising admixtures and reinforcement, various kinds of steel meshes or a distributed reinforcement as steel or polypropylene fibres) have been developed, in order to prevent the cases above. It is visible (according to a great deal of experimental research) that the abovementioned guidelines limit the undesired shrinkage effects. Nevertheless, average typical conditions for making the floors very often differ from those in the guidelines, which may lead to the appearance of future shrinkage cracks, irrespectively to the applied reinforcement. The paper presents conclusions from the analysis of research results for three types of concrete ground floors made in the detached residential house, in the same operational conditions, differing with the reinforcement applied. The research was conducted from the moment of implementation and then, during the initial operational period

Impact of the air-entrained concrete with the blast-furnace slag cement on the intensity of reinforcement corrosion process

The concrete cover has significant impact on the intensity of reinforcement corrosion process in reinforced concrete elements. Depending on the type of corrosion risk different types of cement are recommended for concrete. In conditions of chloride corrosion, due to, for example, the use of de-icing agents in winter, it is recommended to use concrete with cement containing granulated blast-furnace slag. The risk of chloride corrosion due to the use of de-icing agents is often additionally associated with the frost and repeated freezing and thawing actions of structural elements. The liquid freezing in the pores of concrete increases its volume, which causes the increase of internal stresses and leads to cracks in the concrete cover increasing the diffusion of chlorides. In order to reduce this phenomenon the introduction of air-entraining admixture is beneficial. The paper presents the experimental results that allow to determinate the effect of the air-entraining admixture addition on the intensity of reinforcement corrosion in concrete with blast-furnace slag cement. The tests were carried out on two groups of reinforced concrete specimens subjected to freezing and thawing cycles in 3% NaCl solution. One group of specimens was prepared with the airentraining admixture addition and the other without it. The electrochemical tests of the reinforcement corrosion activity, based on the measurements of the corrosion current density were curried. The phase composition by X-ray diffraction and microstructure of concrete under the scanning electron microscope (SEM) coupled with the X-ray microanalyser (EDS) were examined. The results allowed to comprehensively assess the effect of airentrained concrete with blast-furnace slag cement on the degree of reinforcement corrosion risk in concrete caused by the simultaneous action of chlorides and frost