Browse

1 - 10 of 934 items :

  • Environmental Management x
Clear All

Abstract

Most of the railway lines in Slovakia were built in the second half of the 19th century, or until 1918 (the establishment of Czechoslovakia). Except for the post-World War II period, when approximately 71 % of the Slovak lines had to be renewed, limited funds have been spent on repair and reconstruction works on the lines located in the Slovak territory. As some trans-European corridors cross the Slovak territory and the Slovak Republic assumed obligations arising from the AGC and AGTC agreements, the line modernization is more than desirable. The primary objective of the modernisation of railway lines in the territory of Slovakia is to ensure a high-quality and safe railway, which by its qualitative parameters corresponds to the standards of developed European countries. In this context, the paper deals with a section of the modernised corridor no. Va, specifically the section Považská Teplá - Žilina. During the period 2014-2017, quality diagnostics of the performed work was carried out on the sub-ballast layers of the above-mentioned line. Consequently, we carried out an analysis of the obtained values of the deformation resistance of the subgrade surface, as the weakest element in the construction of the sub-ballast layers.

Abstract

Currently, significant development of methods supporting decision making under uncertainty conditions is observed. One of such methods includes Bayesian networks used in many fields of economy and science. The paper presents the use of the Bayesian network method in civil engineering problems with particular emphasis on construction engineering projects. In addition to the existing examples of the use of the method cited, the authors’ method for the risk estimation of additional works is presented.

Abstract

This paper depends on a test examination on basalt fibres which started from volcanic shakes and were dissolved at high temperatures. These stones were accessible from the world’s profound hull. M30 evaluation of concrete was structured according to is 10262:2009 with basalt fibres. The fibres alongside mineral admixtures were utilized in three distinct extents, that is 0 %, 1 %, 2 %, 3 % by heaviness of cement. The goal was to decide the characteristics of fibre reinforced concrete with various fibre extents. The strength properties, for example, compressive strength, split tensile strength, flexural strength, shear strength and the impact on strength of concrete when it was unprotected to sulphate attack after stipulated extended ages of curing were contemplated and thought about. From the examination, it was discovered that the basalt fibre expanded the strength of concrete notwithstanding when unprotected to sulphate attack bit by bit when compared with consistent concrete. The ideal strength of concrete was accomplished with an enlargement of 2 % basalt fibre.

Abstract

The distance a person is willing to commute has a direct influence on her/his employment opportunities and wage level. It raises a lot of interesting questions, especially whether intra-urban commuting (due to a well-developed transport infrastructure, geographical concentration of job opportunities, etc.) is connected with any wage returns, and how they differ in comparison with those of inter-urban commuting. This article uses three data-sets at national (N1 = 1,884; N2 = 933) and local (N3 = 3,193) levels from the Czech Republic, and different approximations of commuting in order to contribute to the discussion. It provides robust evidence on positive wage returns to both inter-urban and intra-urban commuting, comparable with Western countries. The differences between large national and limited urban labour markets are reflected in functional form: wage returns are linear for intra-urban and non-linear for inter-urban commuting. The article also explores the validity of different measures of commuting time and distance provided by the on-line application Mapy.cz, and suggests that it represents a suitable approximation in the case of missing or limited data.

Abstract

Considering that the unevenness of the road surface is the primary source of the kinematic excitation of the vehicle, it is necessary to map the unevenness, and then to describe it mathematically. The data sets thus obtained represent an important input for numerical simulations of the motion of vehicles on the road. This paper deals with the analysis and comparison of results from two methods of mapping the surface of the road - exact levelling and spatial scanning. The obtained results are evaluated qualitatively and quantitatively by methods of mathematical statistics and probability theory.

Abstract

This article is a dimensioning study of the landfill locker dike of the city of Casablanca, where the geotechnical parameters of waste have particular limitations, theses limitation are a common characteristic for most developing countries. Considering the very small available land area in general, the objective is to achieve an optimal dimensioning of the locker to maximize the volume to be buried, while respecting the requirements of stability of the structure; namely, the model whose safety factor will be greater than 1.5. The Factor of Safety (FoS) was calculated by the Finite Element Method (FEM) using “PLAXIS 2D” software. The results show that, for both cases (with and without final cover), FoS, as obtained from both the analysis, show a similar pattern, with the maximum FoS for low inclinations, especially those lower than 15.95°. The critical FoS (< 1), was obtained for slopes strictly greater than 21.80°. The study also demonstrated that the 3.5H 1V model could be considered as the optimal one that satisfies the structural stability requirements (FoS> 1.5) and maximizes the volume to be buried. Nevertheless, the validation of this model is conditioned by a geometric modification (weakening the lateral slope of the landfill, by moving the dikes by 3 m) and the improvement of the mechanical characteristics of the soil of the peripheral dike, through replacing the material with the compacted clay. This model was validated by PLAXIS, which showed that the FoS for the phase preceding the anchoring of the final cover is 1.577, which reaches 1.604 after anchoring.

Abstract

The paper deals with the determination of mechanical properties of fiber reinforced concrete in dependence on various dosages and recipe of concrete. The mechanical properties were determined for the default recipe of concrete, where the individual variants differ in the amount of fibers. The fibers dosing was 0, 25, 50 and 75 kg/m3. At the highest dosage of 75 kg/m3, the recipe is optimized with regard to the microstructure of the concrete. In the experimental program were determined compressive strength, modulus of elasticity, split tensile strength, flexural tensile strength and load-displacement diagram. The flexural tensile strength was determined based on a three-point and four-point bending test. Based on the evaluated data, the uniaxial tensile strength and the functional dependence for the resultant recipe of concrete with a dosage of 75 kg/m3 is with respect of the increasing importance and application of numerical modelling of building structures, the analysis is performed using non-linear calculation. The aim was to simulate the performed laboratory test and appropriately approximate the specific input parameters of the fiber reinforced concrete for nonlinear analysis.

Abstract

The microstructural evaluation of complex cementitious materials has been made possible by the microscopic imaging tools such as Scanning Electron Microscope (SEM) and X-Ray Microanalysis. Particularly, the application of concrete SEM imaging and digital image analysis have become common in the analysis and mapping of concrete technology. In this study, six samples of two-dimensional (2D) SEM images were spatially resampled to produce Geo-referenced SEM sample images. Subsequently, they were analyzed and the intensity histogram plot was produced to facilitate visual interpretation. The consecutive digital image analysis performed was the enhancement and noise removal process using two filtering methods i.e. median and adaptive box filter. The filtered resampled images, then undergone the unsupervised K-Means classification process to collectively separate each individual pixel corresponds to the spectral data. By spatial segmentation of K-Means algorithms, the cluster groups generated were carefully reviewed before proceeding to the final analysis. From the resulting data, the mapping of the spatial distribution of k-cluster and the quantification of micro-cracks (voids) were performed. The results of the SEM images (1st - 4th sample) showed a higher percentage of k-cluster data indicating a good correlation with the major elemental composition of EDX analysis, namely Oxide (O), Silicon (Si) and Carbon (C). Meanwhile, the subjective visual assessment of the image (5th and 6th sample) has confirmed the micro-crack developments on the concrete SEM images upon which the crack density was 3.02 % and 1.30 %, respectively.

Abstract

This experimental study aimed to use the ultrasonic pulse velocity method (UPV) in order to investigate the effect of rubber tire waste content and transducers’ diameters and frequencies on the evolution of ultrasonic velocities in time and to elucidate the correlations between UPV and the properties of various concrete mixtures. The incorporation of this waste involved volume substitution (0, 5, 10, 15 and 20%) of fine aggregates (sand) by rubber waste (RW) granulates. The dry unit weight, porosity, compressive and flexural strengths, and velocity of ultrasonic waves with different transducers - which presents the non-destructive technique - were evaluated. Rubberized concrete mixtures showed increases in porosity with lower dry unit weight compared to the control concrete. Compressive strength, flexural strength and ultrasonic velocity obtained by all transducers decreases with increasing RW content. These decreases are not influenced by the curing age of concretes. Decreases in the diameter and frequency of transducers caused reductions in ultrasonic velocity. These reductions are not influenced by the volume replacement of sand by RW. Correlations showed that ultrasonic velocity represents a reliable non-destructive technique for measuring the properties of rubberized concretes.

Abstract

Mortars are subjected to severe external stresses such as freezing, thawing, and drying during their lifetime. These stresses can lead to a loss of adhesion between the support and the mortar. The strength of the substrates with respect to their ability to receive a coating (mortar) is characterized in particular by the value of minimum tear resistance of the surface to be coated. In this work, the use of a non-destructive method which is both fast and easy to implement is employed to evaluate this support-mortar adhesion. The first method is based on the measurement of the velocities of the surface ultrasonic waves and the second by tearing tests using a specific dynamometer. The determination of the adhesion strength concerned two different supports (concrete beam and masonry block) coated with two types of mortar (a prepared cement mortar and a ready-to-use mortar) with two different thicknesses for each mortar (1 and 2 cm, respectively). The results of the two methods are then correlated for an estimation of the adhesion of the mortars.