Jacek Domski

The article presents the results of laboratory tests published in dozens of publications. These tests focused on reinforced concrete beams with additional dispersed reinforcement that were loaded with torsional moments. The results of cracking and ultimate stress were presented depending on various factors influencing the beam’s load-bearing capacity, i.e., the degree of fiber reinforcement V_f, the angle of rotation θ, the compressive strength of the concrete f_c, the fiber slenderness l/d, the degree of conventional reinforcement ρ_tot, the proportions of the cross-section h/b, and the slenderness of the tested element. The frequency of occurrence of the aforementioned factors in the tests was also statistically analyzed. Additionally, the influence of fibers on the factors determining the torsional load-bearing capacity was examined. It has been shown that fibers can significantly contribute to increasing the torsional load-bearing capacity of beams and can even be characterized by a twofold increase. It has also been observed that despite the increased load-bearing capacity, beams with fibers are often characterized by lower torsional stiffness. Additionally, it has been found that fibers provide the greatest increase in load-bearing capacity for concretes with compressive strengths in the range of 25–45 MPa and for square cross-sections (b/h = 1.0). In addition, fibers can lead to the formation of torsional cracks at higher reinforcement factors (V_f). However, in terms of cooperation with conventional reinforcement, fibers are of little importance in transferring torsional stresses in the case of beams with a high conventional reinforcement factor ρ_tot > 3%.

This report presents the results of cracking tests on concrete beams. The test specimens were created in ten different series. Each series comprised two beams, six cylinders, and twelve cubic samples intended for the determination of strength properties. These samples varied in terms of the type of concrete mixture (fiber-reinforced fine aggregate concrete and plain concrete), the applied steel fibers (50/0.8 mm and 30/0.55 mm), the longitudinal reinforcement ratio in beams (0.6%, 0.9%, 1.3%, and 1.8%), and the inclusion (or exclusion) of compressed reinforcement and vertical stirrups. The fine aggregate concrete was made from waste sand, which is a byproduct of the hydroclassification process of gravel. The use of this sand in fiber concrete will help reduce the exploitation of natural resources and lower carbon dioxide emissions. Based on four-point beam bending tests, the study experimentally determined cracking moments, crack spacing, and crack width. Additionally, these results were compared with calculations proposed by L. Vandewalle and Domski, as well as with the methods outlined in Eurocode 2. The analyses conducted show that the best agreement between the research results and the calculations was obtained for Domski’s proposal. It follows that the average percentage error was 38.4%, indicating the safe use of this method.

W artykule przedstawiono analizę numeryczną odkształceńbelek żelbetowych w programie ATENA. Przyjęto cechymateriałowe, geometrię i schemat obciążenia belek na podstawiebadań laboratoryjnych, zrealizowanych w ramach rozprawydoktorskiej Mateusza Zakrzewskiego. Analizie poddano trzybelki, znajdujące się na jednym stanowisku badawczym, pracującew schemacie czteropunktowego zginania, w rozstawie siłco 90 cm. Wszystkie elementy próbne wykonano z betonu z dodatkiemodpadowych włókien stalowych z opon samochodowych.Zbrojenie belek stanowiły pręty stalowe, umieszczone w ichstrefie rozciąganej. Analiza obejmowała porównanie ugięć belekuzyskanych w programie ATENA z wynikami badań uzyskanymipod obciążeniem doraźnym w kilku fazach obciążenia.

Factory made steel fiber and steel fiber derived from worn tires was used to develop cement concrete, which was subjected to torsional forces. A dedicated stand for torsion tests, allowing for the measurement of force, deflection, and torsion angle, was used. The test results showed that both the factory-made fiber and the waste steel fiber significantly improved torsional properties of the concrete matrix. The test results of specimens made with waste fiber were characterized by slightly worse results compared to factory-made fibers, but there was a significant improvement in torsional properties compared to samples without fibers. Taking into account the financial and environmental benefits, the application of waste steel fiber recovered from car tires could be an interesting alternative to using commercially sold steel fiber applied for the production of construction elements subjected to torsional forces.

This report presents the results of long-term tests on concrete beams reinforced with steel cord. In this study, natural aggregate was wholly replaced with waste sand or with wastes from the production of ceramic products and ceramic hollow bricks. The amounts of individual fractions used were determined in accordance with guidelines for reference concrete. A total of eight mixtures were tested; these differed in terms of the type of waste aggregate used. Elements with various fiber-reinforcement ratios were made for each mixture. Steel fibers and waste fibers were used in amounts of 0.0%, 0.5%, and 1.0%. Compressive strength and modulus of elasticity were determined experimentally for each mixture. The main test was a four-point beam bending test. Beams with dimensions of 100 mm × 200 mm × 2900 mm were tested on a stand, which was specially prepared so that three beams could be tested simultaneously. Fiber-reinforcement ratios were 0.5% and 1.0%. Long-term studies were conducted for 1000 days. During the testing period, beam deflections and cracks were measured. The obtained results were compared with values calculated using several methods, considering the influence of dispersed reinforcement. The results enabled the best methods for calculating individual values for mixtures with different types of waste materials to be determined.

The research focuses on pozzolanic additives, which are compatible with traditional lime mortars, and enable the modification of the rheological, physical and mechanical properties of tested composites. It was noted that lime mortars with fluidised bed fly ash require sand without impurities to avoid possible ettringite crystallisation. The work presents siliceous fly ash and fluidised bed combustion fly ash to modify the frost resistance and mechanical properties of traditional lime mortars with and without the addition of cement. The results show better effects using fluidised bed ash. Traditional Portland cement CEM I 42.5R was used to activate ash and increase the results. The possibility of a significant improvement of properties is indicated with a hybrid addition to the lime binder of 15–30% ash (siliceous or fluidised bed ash) and 15–30% cement. Changing the class and type of cement provides an additional opportunity to alter the properties of the composites. For architectural reasons relating to colour, the suitability of lighter fluidised bed ash instead of darker siliceous ash and of white Portland cement instead of the traditional grey cement can be used. The proposed mortars can be the basis for future modifications with admixtures and additives, e.g., metakaolin, polymers, fibres, slag, glass powder and impregnating agents.

This study presents the results of laboratory experiments conducted to determine the mechanical parameters for cement mortar with various quantities of waste fibers, polypropylene microfibers, and steel microfibers. Waste fibers were used as samples and obtained using an end-of-life car tire recycling process. For comparison, samples with the addition of steel and polypropylene microfibers were tested. The same degrees of fiber reinforcement were used for all types of fibers. Ultimately, 22 mixtures of cement mortar were prepared. The aim of this study is therefore to present and compare basic mechanical parameter values. Compressive strength, flexural strength, fracture toughness, and flexural toughness were of particular interest. A three-point bending test was performed on three types of samples, without a notch and with a notch of 4 and 8 mm. The results show that the use of steel microfibers in the cement mortar produces a product with better properties compared to a mixture with steel cord or polypropylene fibers. However, the cement mortar with the steel cord provides better flexural strength and greater flexural toughness factors compared to the cement mortar with polypropylene fibers. This means that the steel cord is a full-value ecological replacement for different fibers.