Papers by Keyword: Concrete Durability

Abstract: Concrete deterioration is a major concern for structural engineers, as it can weaken and damage structures, posing safety risks. One of the most effective ways to protect concrete from deterioration is to modify it with pozzolanic materials. Pozzolanic can react with calcium hydroxide (Ca (OH)₂) in concrete to form strong, durable cementitious compounds. So this research aims at enhancing the durability of concrete structures against aggressive media attacks. Nanosilica (NS) was used in concrete mix design with different addition percentages of 0, 1, 1.5, 2, and 2.5 by cement weight. The durability of hardened concrete specimens was investigated as follows: measuring water absorption and contact angle; and determining chloride permeability by ion exchange chromatography. Also, the resistivity of concrete against both 3% sulfuric acid and 5% sodium chloride solutions was estimated. Finally, the electrochemical impedance spectroscopy (EIS) was used to determine corrosion resistance of the reinforced concrete. The experimental results detected that NS has a significant mechanism for improving concrete performance as follows: water absorption of concrete modified with 2% NS (M4) decreased by 41% as compared to the control sample, and contact angle increased by 66%. Meanwhile, the chloride permeability decreased by 24%. Moreover, NS is mainly responsible for enhancing concrete durability against aggressive media attacks up to 2% by cement weight. As compared to the control concrete specimen, the durability of the M4 specimen increased by 39% against sulphate attack and by 42% against chloride attack. The study provided a good solution for the problem of concrete building deterioration, especially when it is exposed to aggressive environments. Key words: Concrete durability, pozzolanic materials, nanosilica.

Abstract: This research investigates the effects of waste tire steel fibers (WSFs) on the durability characteristics of concrete, specifically examining water absorption, carbonation, and split-tensile strength. The integration of WSFs into construction materials offers a viable solution to address the growing environmental challenges associated with discarded tires. Although existing studies have touched upon the incorporation of WSFs in concrete, there remains a significant lack of comprehensive long-term data regarding the properties of WSF-reinforced concrete. To address this knowledge gap, this study analyzes the performance of locally sourced WSFs from Bratislava, Slovakia, focusing on the hardened properties of concrete beyond the conventional curing period of 28 days. The investigation applies C20/25 concrete, integrating various percentages (0%, 0.50%, and 0.60%) of raw WSFs in a hybrid composition, which consists of 30% industrial steel fibers and 70% WSFs. The experimental analysis encompasses assessments of split-tensile strength (STS), rapid carbonation depth (CD), and water absorption (WA) for specimens aged 600 days. Results indicate that hybrid WSF-reinforced concrete (HRC) exhibits reduced carbonation depth and water absorption in comparison to conventional concrete, alongside an improved split-tensile strength. The findings suggest that HRC has significant potential as a substitute for traditional concrete in various civil engineering applications. Nevertheless, further studies are necessary to evaluate the performance of HRC under extreme environmental conditions.

Abstract: This study investigated the potential of Kevlar aramid fiber reinforcement to enhance the mechanical properties and mitigate pathologies in concrete structures. The objectives were to analyze improvements in flexural and compressive strengths and to evaluate the effectiveness of Kevlar in reducing pathological manifestations under the specific conditions and methodologies of this experiment. Experimental testing was conducted on prismatic and cylindrical concrete specimens, prepared following standard mix ratios and testing protocols. Kevlar fiber was applied to the specimens using an epoxy resin, ensuring adhesion and uniform reinforcement. The results, obtained under these controlled conditions, showed a 6.90% increase in flexural tensile strength, from 0.29 MPa to 0.31 MPa, and a 14% enhancement in compressive strength, from 14 MPa to 16 MPa. Pathological manifestations, such as crack propagation, were significantly mitigated in the reinforced specimens, demonstrating improved structural preservation and reduced degradation under tensile and compressive stresses. These findings, specific to the experimental parameters and standards employed, confirm the dual benefits of Kevlar reinforcement. The study highlights its effectiveness in improving durability, reducing maintenance demands, and extending the service life of concrete structures, reinforcing its potential as a viable solution for advanced civil construction applications.

Abstract: Prolonged concrete mixing can occur due to transportation delays or logistical issues on construction sites, potentially affecting the material's properties. This study investigates the effects of extended mixing times on concrete's fresh and hardened properties utilizing four different types of Portland cement: PC-32, PC-40, PC-RS-32, and PC-LF. An experimental program involved materials characterization, concrete mix design, and systematic testing procedures. Fresh concrete properties, including slump, temperature, specific mass, and air content, were evaluated hourly for up to 8 hours of mixing. Hardened concrete tests encompassed electrical resistivity, dynamic modulus of elasticity, and compressive strength measurements. Prolonged mixing led to a significant loss of slump and plasticity, particularly for PC-LF cement. Specific mass and apparent density decreased with mixing time, while electrical resistivity declined hourly, indicating increased porosity and susceptibility to chemical attacks. The dynamic modulus of elasticity remained relatively constant, except for PC-LF cement. Compressive strength was maintained or slightly increased up to 7 hours but decreased for PC-32 and PC-LF cements at 8 hours. The study demonstrates the feasibility of prolonged mixing for up to 8 hours with proper precautions. The choice of cement type played a crucial role, with PC-40 cement exhibiting the best overall performance. Further research is recommended to investigate durability aspects, porosity characteristics, and methods to maintain workability during extended mixing times.

Abstract: The influence of volumetric hydrophobization of cement stone samples on mass transfer processes during hardening has been studied. It was found that the introduction of a hydrophobizing additive at the stage of sample production reduces the amount of water evaporating during drying. With increasing concentration of the hydrophobizer mass transfer processes are slowed down during the hardening of cement concretes, which affects their structural and phase composition, strength characteristics and durability.

Abstract: Cements have been used to encapsulate low and intermediate level radioactive wastes. Here, phosphate-modified calcium aluminate (CAP) cement is explored as an encapsulant for strontium radioanuclide-containing wastes. Electron microscopy indicates strontium chloride, used in place of strontium radionuclides, increases porosity in CAP possibly due to increased viscosity of CAP cement during mixing. X-ray diffraction analysis detects formation of halite phase suggesting strontium chloride reacts with cement to form sodium chloride not usually detected in CAP systems as well as formation of an amorphous phase in CAP cement when thermally treated at 90°C.

Abstract: The focus of the project GAČR 13-18870S is the research in concrete durability determined primarily by its surface layer quality. The surface layer can be difficult to assess for which reason the project makes use of available standardised and non-standardised test methods by means of which the concrete surface layer or its internal structure can be examined. One of these methods which is commonly used is Determination of resistance of cement concrete surface to water and defrosting chemicals. The paper presents the results of experiments performed with concretes differing only in w/c ratio and plasticiser content. Two more methods were used during the research based on the action of a thawing solution upon the surface of the specimen during freezing and thawing. The only difference between these methods is the direction in which the thawing agent acts on the test surface. The presumed experiment outcome was the existence of a strong dependence of the outcomes of the methods on the w/c ratio. The performed analyses confirmed the experiment presumption.

Abstract: Appropriate curing of concrete is of vital importance in development of desired material properties in concrete namely compressive strength, durability, and dense uniform microstructure. Improper and intermittent curing is considered as one of the major reasons for concrete failures as evident in the form of cracks that consequently lead to durability issues of structures. An experimental program was designed to study the behavior of concrete under various conventional and modern curing techniques. Numerous cylindrical specimens were tested with different conventional and modern curing techniques to quantify their effects on curing of concrete. Microstructural and compressive strength development analyses at different ages were conducted to monitor the effect of curing methods. This work is helpful in establishing the best curing techniques for attainment of compressive strength and durability in concrete.

Abstract: This work aims at studying the passive behaviour of new alloy corrosion resistant steel Cr10Mo1 and plain carbon steel (as a reference), in simulating concrete pore solutions contaminated with different concentrations of chloride (0 M, 0.2 M, 0.6 M and 1.0 M, as NaCl). The electrochemical behaviour was evaluated by linear polarization resistance, d.c. potentiodynamic polarization and electrochemical impedance spectroscopy. The surface films composition was investigated by X-ray photoelectron spectroscopy (XPS). The results show that the passivity of the corrosion-resistant steel has no significant decline with chloride contents increasing, while carbon steel hardly passivates with chloride above 0.6 M. The primary constituents of the passive films formed on the corrosion-resistant steel and carbon steel are very different; the former contains both Cr and Fe oxides while the letter consists of only Fe species. Cr oxides, as the key components for the passive film on the corrosion-resistant steel, can still remain stable and protective under high concentration of chloride, which supports the excellent passive performances of the corrosion-resistant steel in severe conditions.

Abstract: Corrosion of reinforcement steel bars is a major threat to the durability of concrete structures exposed to chloride contaminated environment. Patch repairing is widely practiced in affected structures to avoid further damage due to corrosion. Macrocell formation within the patch repair is identified as one main reason for the failure of patch repairs. In the present study, a group of patch repairing materials is tested for their potential to form macrocell corrosion after repaired in a chloride contaminated environment. The influence of parameters such as level of chloride contamination, type of repair materials and the area of steel bar receiving repair are presented based on macrocell current measurements. The selected repair materials for study were cement based, GGBS based and polymer based in its composition. It is found that the severity of macrocell depends on the driving potential existing between the repair and substrate concrete. The quality of substrate concrete and repair material influences the macrocell formation. The surface area of the steel bar that receives the repair also affects the macrocell current. The study will be used for the evaluation of repair materials for macrocell corrosion formation potential before their field application in a chloride contaminated environment.