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Reduced performance in concrete infrastructures is mainly caused by the formation of cracks, which may arise due to deteriorating mechanisms during service life. In most cases, reduced performance calls for urgent repairs to the degraded section. Therefore, it is highly desirable to develop dimensionally stable, ductile repair materials that can attain adequately high strength in a limited amount of time, compensate for significant deformation due to mechanical and environmental loadings, and prevent early-age shrinkage cracks. In this paper, the performance of such a material (high-early-strength engineered cementitious composites, HES-ECC, with very low early-age shrinkage capacity) was investigated by studying mechanical properties and dimensional stability. Composites were produced with different water to cementitious materials and slag to Portland cement ratios. In order to enhance composite properties in terms of ductility and early-age shrinkage characteristics, saturated lightweight aggregates replaced sand in the mixtures. The experimental results show that the majority of HES-ECC mixtures developed in this study attained compressive strength values of more than 20.0 MPa and minimum flexural strength of 6.0 MPa within 6 h. Moreover, the HES-ECC mixtures exhibited strain-hardening behavior with strain capacities comparable to normal strength ECC, as well as substantially reduced autogenous shrinkage strain, both of which are unlikely to trigger the formation of cracks in tension at early ages. The integration of these conflicting parameters suggests that HES-ECC can easily meet the need for fast and durable repairs.

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Background: The Covid-19 epidemic has greatly changed the lifestyles and habits of millions of people around the world, and it has been observed that these changes have become permanent. Aim: The aim of our research is to examine the anxiety levels of female and male athletes for catching the new type of corona virus (Covid-19). Method: The survey method, one of the quantitative research models, was used in the study. The population of the research consisted of athletes (n=198) who were actively involved in sports in various sports clubs and in various branches in the districts of Istanbul, on the European side (Bakırköy, Güngören, Zeytinburnu). The data were collected online by applying the survey technique. The New Type Coronavirus (Covid-19) Anxiety Scale of the athletes (SYTKYKÖ) was used as a data collection tool. As a statistical procedure, it was determined that the data did not show normal distribution and Mann Whitney U, Kruskal Wallis-H analyzes from non-parametric tests were used. Findings: It is seen that there is a difference between the anxiety levels of catching Covid-19 according to the gender of the athletes, their education level, the status of people around them catching covid-19, the level of chronic disease, and their training status. There was no difference between the anxiety levels of catching Covid-19 according to the age, sports branch and years of doing sports of the participants. Result: As a result, it was concluded that the anxiety levels of the athletes of catching Covid-19 were high. Key words: Pandemic, anxiety level, sports

Although SiO2 is produced mostly from mineral sources like quartz, it has recently been obtained from lignocellulosic natural resources, such as rice husk (hull). Several methods for extracting silica (SiO2) from rice husks are available in the literature. These methods are based essentially on heat treatment and/or extraction. This study represents a thorough account of heat treatment and acid-base extraction, to obtain silica from rice husks with a high purity and to eliminate other inorganic impurities. Rice husks, considered to be a potential silica source, were pretreated with various acids, base and water and then thermally degraded in a fixed bed reactor under an inert gas atmosphere (N2). The materials produced in these conditions were characterized by BraunerEmmett-Teller analysis, for surface area and pore volume, by Fourier transform infrared spectroscopy, powder X-ray diffraction, X-ray fluorescence, and scanning electron microscopy.

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In medical applications, the compliance and integration of bone with implant are a critical issue. Biocompatible metal substrates coated by suitable materials such as calcium phosphates, especially hydroxyapatite, exhibit excellent biocompatibility, high mechanical strength, good corrosion resistance and toughness. The use of these type of material coatings on the implant surfaces has recently drawn attention of many researchers. Many methods such as sol-gel and dip coating, electrochemical and electrophoretic deposition, plasma spraying, hot isostatic pressing and pulsed laser deposition have been employed for the production of hydroxyapatite artificially. Among these methods microwave-assisted precipitation technique in a simulated body fluid solution is the simplest and most efficient way to produce hydroxyapatite. Hydroxyapatite with a suitable molar ratio of Ca/P is bioactive, biocompatible and osteoconductive, and enhances direct attachment of implant to the bone. In this study, hydroxyapatite powders were produced by microwave-assisted precipitation. The powder samples were analyzed in detail by SEM-EDX, XRD and FTIR. Analysis results showed that experimental parameters such as microwave irradiation power and exposure time had a considerable effect on Ca/P molar ratios, surface morphologies and crystallinity of the powders.

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