Complex Maturity Method for Estimating the Concrete Strength Based on Curing Temperature, Ambient Temperature and Relative Humidity

The maturity method is deservedly considered one of the reliable indirect methods for determining the strength at the early stages of concrete curing. The main parameter in the calculation is the internal temperature of concrete that accumulates during the chemical reaction of concrete curing, while external factors such as ambient temperature and relative humidity are fallaciously omitted. In this work, the complex maturity method was developed based on ASTM C1074, accounting for the influence of ambient temperature and relative humidity and coefficients indicating their influence weight. The laboratory testing to measure the concrete strength by compression method and non-destructive sclerometer method were performed on concrete samples according to ASTM C109, GOST 22690, and GOST 10180. According to the calibration dependence of the existing and proposed methods results in comparison with the strength of cubic samples, the highest coefficient of determination R2 = 0.976 was revealed for the complex method of maturity, which indicates its reliability in contrast with sclerometer and traditional maturity methods. The determination of complex maturity allows for an evaluation of the current state of concrete strength, but also reduces the waiting time for concrete curing and increases the economic effect during construction.

Applying Ultrasound Detection Devices to Examine Pгореrties of Concrete Structures

The article considers the problems of diagnostics of reinforced concrete structures and creation the generalized calibration dependence for the use of ultrasonic devices. The results of the study of the influence of some factors on the results of measuring the dissemination time of ultrasonic vibrations are presented. The study was conducted using devices "Pulsar 1.1" and "Novotest IPSM-U" in compliance with regulatory requirements. Statistical processing of the obtained results (with visualization) was performed using the software package EXEL. Processing of the obtained data confirmed the multifactorial dependence of ultrasonic measurements on the concrete surface. The lack of clearly defined conditions for measurements reduces the reliability of the results. The use of ultrasonic measurements to obtain absolute values of the properties of concrete is not adequate. It is proposed to make changes to the regulations regarding the limits of application of ultrasonic measurements.

Choosing a Universal Air Collector Design for a Cylindrical-Shaped Hot-Wire Anemometer

Air flow measurement at the outlets of air terminal devices installed in ventilation systems is very difficult. At the outlets of anemostats, swirl diffusers, grilles, the air flow can swirl, contract, or expand sharply, change its direction, etc., which causes great measurement errors. Therefore, it was necessary to develop a universal measuring device that would make it possible to measure air flow rate with high accuracy. It should consist of an air collector (for collecting and rectifying air flow) and a sensor for measuring air flow rate (integral hot-wire anemometer). Several air collector designs have been investigated. The parabolic air collector was chosen as the rational one. It has low aerodynamic resistance and good air flow distribution. To reduce the influence of turbulence and air swirling, a cylindrical stilling channel with a built-in rectifying grille is connected to the air collector. Experimental studies on various air distribution devices made it possible to obtain a refined calibration dependence for an integral hot-wire anemometer, the dependence being used to calculate air flow rate. The influence of the aerodynamic resistance of an airflow meter on air flow rate is taken into account with the help of a correction that must be introduced into the values measured.

"Dose – effect" calibration dependence by frequency of unstable chromosomic exchanges in human lymphocytes in acute gamma irradiation by 137Сs in low doses for biological dosimetry

The calibration dependence of dicentrics and rings chromosomes with an accompanying fragment induction in human lymphocytes by in vitro 137Сs acute gamma irradiation of blood in the dose range of 0.09 - 1.0 Gy is presented. The application of the obtained calibration curve for estimation of “biological” doses for overexposed 9 persons from the contract staff of the Chornobyl SSE is shown. Their doses calculated by the frequency of dicentrics and centric rings with consideration of operation duration and mode in the zone of influence of the radiation factor, significantly exceeded the doses determined by the methods of physical dosimetry.

Glazing effect for producing environmentally friendly ceramics for cladding applications

A simple, cost-effective and fast headspace gas chromatography method coupled with flame ionization detection (HS-GC/FID) for determination of ethanol was developed and validated for clinical and forensic toxicology purposes. HS-GC/FID is often used for alcohol determination in different biological and non-biological samples. The calibration dependence of the method was linear in the range from 0.15 to 4.00 g dm-3 (r2=0.999) with adequate accuracy (99-106 %) and precision. The limit of detection (LOD) was 0.006 g dm-3. The method was quantitative (LOQ) above 0.020 g dm-3. The new method was successfully used for determination of ethanol in biological samples of intoxicated patients, car accidents participants, participants in criminal acts, and postmortem samples, non-biological samples such as alcoholic beverages, alcohol-based herbal preparations, cosmetic preparations, etc. This method is easy to perform, making it suitable not only for the routine applications in clinical biochemistry and forensic laboratories, but also in different fields of industry (e.g. for pharmaceutical preparations, cosmetics, dietary supplements, etc.). Some of the applications for ethanol determination in different samples related to various clinical-forensic cases are presented.

Integral Thermo-Anemometers for Average Temperature and Airflow Measurement in Ducts, at Anemostat Outlets and in Ventilation Grilles

When creating ventilation systems, it is important to correctly calculate the volumes of air inflow and outflow. If an error is made in the calculation or a redistribution of air flows is required, measurements are indispensable. The existing methods for determining the air flow rate by using point measurements in the cross-section are laborious and time-consuming, and taking readings at different time points introduces a significant error into the result. A. M. Pidhornyi Institute of Mechanical Engineering Problems of the National Academy of Sciences of Ukraine has developed a new hot-wire anemometer whose use greatly simplifies the measuring process. This device allows one to measure the average values of temperature and air velocity (flow rate) in the cross-section of air ducts or at the inlets and outlets of grilles and anemostats, and can be used in real time to monitor and control air flow rate and temperature in ventilation systems. The probe of the hot-wire anemometer is a metal shell with guides on which a sensitive element is laid. Its principle of operation is to change the heat transfer coefficient at different air leakage velocities. The anemometer is preliminarily calibrated in laboratory conditions at various velocities. There has been obtained a calibration dependence that can be used to measure the air flow rate at the inlets and outlets of air distribution devices and directly in the air ducts. To improve the measurement accuracy, it is necessary to provide the 90° angle of airflow leakage on the hot-wire anemometer probe. For this, special air collectors and air flow rectifiers are used.

Improvement of analytical determination of residual quantities of active substances of the triasole class in juices

Today, the most common among fungicides approved for use in Ukraine, as well as in other countries, are compounds of the triazole class. Juices, as a product of processing agricultural raw materials, can be consumed by a wide range of the population. The purpose of work was to develop analytical methods for compound of triazole (difenoconazole and propiconazole) in juices to ensure quality control of agricultural products grown with the use of these fungicides. Conditions for chromatography of difenoconazole and propiconazole using gas-liquid chromatography with capillary column SH-Rxi-5ms (30 m 0,25 mm) and electron capture detector were determined. Optimal conditions of difenoconazole chromatography were established: thermostat column temperature - 280 C, evaporator temperature - 290 C, detector thermostat temperature - 300 C. Retention time: isomer 1 - (6,91 +- 0,1) minutes, isomer 2 - (7,04 +- 0,1) minutes. The linear range of detection is 0,01-0,04 ug/cm3. The optimal conditions for chromatography of propiconazole were also established: the temperature of the column thermostat in the programming mode: initial T - 100 C with an exposure of 1 minute; from 90 C to 260 C - rate of temperature rise 40 C/min; exposure - 7,45 minutes; evaporator temperature - 270 C, detector temperature - 280 C. The retention time under these conditions was 3,49 +- 0,1 minutes for isomer 1 and 3,57 +- 0,1 minutes for isomer 2. The linear range of detection is 0,01-0,05 ug/cm3. The calibration dependence of the area of peaks of the investigated substances on their concentration was established and described by the linear regression equation.

INCREASING CALIBRATION ACCURACY OF THE HUMIDITY CONTROL MEASURING DEVICE OF BULK MATERIALS

For increasing accuracy of a measuring device, before carrying out measurement, implementation of graduation, which consists of the establishment of correlation dependence between indications of the measuring device and humidity of specific material, is required. For the creation of calibration dependence of the developed measuring device as the measured 10 test samples of ammonium nitrate (nitrogen) with humidity from 0% to 2.5%, with different intervals are selected. For determination of the humidity content of ammonium nitrate, it is measured the dependence of the frequency on the humidity content of the sample. For each test, several values of frequencies of the measuring generator entered in the table with a calibration frequency are received. In this work, the short review of the known methods on the creation of calibration dependence is carried out, the impossibility of application of exact methods for an objective solution because of removal need of an excessively large number of experimental data at the calibration of the measuring transducer is set and for some other reasons. The analysis of the application of some classes of functions is made for the approximation of an output characteristic. However, the described methods above should be exposed to modification and simplification. In this regard, it is offered to use the least-squares method for improvement of calibration characteristic of a measuring device in the work, the function of calibration dependence in the form of a polynom of the seventh degree is made and matrixes of a system of equations of derivatives of first order are constructed. Further, the help of applying the software environment of Mathcad calculates the made systems of equations. For this, the coefficients of the system of equations are presented in the form of a matrix, and the free terms - in the form of a vector. Further, utilization of the Gaussian method, correction factors were found, on the basis of which a mathematical model of the calibration dependence was built that allows for the optimal accuracy of the calibration of the measuring device.

Use of Magnetic Anisotropy Method for Assessing Residual Stresses in Metal Structures

A series of experiments on measuring of difference between the main mechanical stresses (DPMS) was carried out using a mechanical stress scanner based on the magnetoanisotropic method. The magnitude of the DPMS is fixed when a magnetic field is induced on a carbon steel plate under uniaxial tension. A direct proportional relationship is shown between the magnitude of the DPMS signal recorded by the scanner and the magnitude of tensile stresses in the plate in the region of elastic deformation of steel. Measurement of the DPMS signal in the central part of similar plates previously subjected to elastic-plastic bending showed that positive values of the signal are fixed in the surface layers of the metal on the inside of the plate, which corresponds to tensile residual stresses, while the negative ones concentrate at the external surface, which corresponds to compressive stresses. A transverse incision on a curved plate from the inside leads to a decrease in the value of the signal of the DPMS, which indicates a decrease in the level of residual stresses in the metal. The values of the DPMS signal in the central part of the curved plate, recalculated using the established calibration dependence on the value of the residual stresses, were compared with the values of the stresses established by calculation, based on the Henki’s theorem on the unloading of an elastic-plastic body. A satisfactory convergence was obtained between the experimental and calculated data.