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The high stiffness of cement-bound aggregate (CBA) is recognized as its main drawback. The stiffness is described by the modulus of elasticity, which is difficult to determine precisely in CBA. Incorporating rubber in these mixtures reduces their stiffness, but mathematical models of the influence of rubber on the mechanical characteristics have not previously been defined. The scope of this research was to define a prediction model for the compressive strength (fc), dynamic modulus of elasticity (Edyn) and static modulus of elasticity (Est) based on the measured ultrasonic pulse velocity as a non-destructive test method. The difference between these two modules is based on the measurement method. Within this research, the cement and waste rubber content were varied, and the mechanical properties were determined for three curing periods. The Edyn was measured using the ultrasonic pulse velocity (UPV), while the Est was determined using three-dimensional digital image correlation (3D DIC). The influence of the amount of cement and rubber and the curing period on the UPV was determined. The development of prediction models for estimating the fc and Est of CBA modified with waste rubber based on the non-destructive test results is highlighted as the most significant contribution of this work. The curing period was statistically significant for the prediction of the Est, which points to the development of CBA elastic properties through different stages during the cement-hydration process. By contrast, the curing period was not statistically significant when estimating the fc, resulting in a simplified, practical and usable prediction model.

Purpose: The main purpose of this paper is to develop a further understanding of professional accountants’ attributes and professional skills required by employers. This paper analyses the requirements of the labour market of the Republic of Croatia using the framework derived from IFAC’s International Education Standard (IES) 3 from 2015 to identify the specific dimensions of professional skills in job advertisements. Methodology: This study uses a qualitative data collection method to analyse the required professional skills of professional accountants from the accounting employers’ perception. We have used Internet research to collect primary data and analyse job advertisements. Content analysis was used to analyse job advertisements. Results: The evidence suggests that employers mostly required professional accountants with attributes categorised as the organisational skills dimension. They were followed by attributes categorised as the intellectual skills dimension, the interpersonal and communication dimension, and the personal dimension. Taking into account the professional skills dimension, a professional accountant is required to possess the ability to use appropriate information technology (IT), teamwork skills, responsibility, the ability to work independently, be analytical and committed to learning, since those were most highly ranked attributes in the collected job advertisements. Conclusion: This study revealed a ‘profile’ of a professional accountant considering the requirements of employers regarding professional skills. Future research should take into consideration further analysis regarding the required skills using different data sources and explore the required skills within different accounting related professions and various sectors and sizes of accounting employers.

The aim of this study was the verification of unmanned aerial system (UAS) application in vehicle swept path analyses by analysing the advantages and disadvantages and comparing field test results with two software solutions. In this study, swept-path analyses were performed for two vehicle types and two turning angles. UAS images were used to extract the vehicle swept path and the results were compared with two commonly used swept-path analysis software. The results indicated larger deviations between the swept paths for an angle of 125° for a light truck. For both analysed vehicles and turning angles, larger deviations were observed for the outermost point trajectory. Passenger cars occupy less space performing 125° turns than software analysis predicts, indicating that they are on the safe side when designing vehicle manipulative surfaces. For the analysed light truck, a larger turning radius was observed than the predicted for a 125° turning angle, which may be caused by the approaching and turning speeds under which the test was performed. Finally, while the UAS recording process is relatively simple and fast, data processing is demanding and time-consuming. To fulfil its full potential within swept path analyses, UAS needs to be complemented by proper data analysis software solutions for faster and more accurate swept path extraction, which would improve and rationalise the traffic area designing process.

The application of recycled rubber in cement bound base courses (CBC) has recently become a subject of research. There are several advantages of the application of rubber in CBC. One is the environmental benefit considering the major problem of disposing of end-of-life tires (ELT), whose number is rapidly increasing in the modern world. On the other hand, CBC is known as the most rigid course of pavement, and is very prone to cracking. Rubber has the potential to reduce the cracking, which is another benefit of its use in those courses. This paper presents laboratory research on a reference mixture and five rubberized mixtures with different fractions of recycled rubber. The mixtures are modified with 20 % of rubber as a replacement for sand. Three fractions of granulated rubber and two fractions of rubber threads are used. The research encompasses the impact of rubber of different sizes and shapes on the Proctor elements of the CBC mixture. Furthermore, specific surface area (SSA) and SEM analysis is presented. The SSA value was found to be the most influential factor on the optimal moisture content (OMC) values, which is confirmed by SEM images. SEM analysis showed that larger particles have a flatter surface and demand higher water content. Furthermore, the rubber particle shape has a greater impact on the mixture MDD compared to the particle size, while the rubber particle size has a greater effect on the OMC compared to the rubber particle shape. Finally, the effect of the rubber particle size and shape on the OMC and MDD can be neglected and the production of cement bound aggregate incorporating waste rubber can be designed and built using reference values of the OMC and MDD.

Road construction relies on natural material exploitation and it is necessary to find new ways of reducing its negative environmental impact. Simultaneously, number of tyres placed on Croatian (and world) market is constantly growing and the need for waste tyres management will begin to increase due to the wear and tear of tyres in use at the moment. This paper presents a review of latest international and domestic researches on waste rubber application in road construction with special emphasize on Croatian researches within this topic. Preliminary results of ongoing research on waste rubber application in cement bound mixtures are also presented.

Digital image correlation (DIC) is a method of point displacement measurement by an optical system. If two cameras are used for capturing the same point displacement, three-dimensional data are obtained using the 3D-DIC method. The areas of application of this method in pavement construction are diverse, but it is mainly used for displacement monitoring during standard tests of the failure of specimens due to load application. Furthermore, DIC technology was used only for testing particular material characteristics and assuming their influence on the overall pavement system. Within this research, DIC was applied in two areas: defining material mechanical characteristics and analyses of pavement structure behaviour under cyclic loading. The scope of this research was to gain more insights into DIC’s potential application within pavement behaviour analyses, specifically on cement-bound granular material (CBGM) characterisation. Results from this study confirm the suitability of 3D-DIC technology for pavement material characterisation. Furthermore, it is shown that certain trends of material behaviour defined on the simple material level of each independent pavement layer will significantly differ when it is placed in the system, and this kind of complex analysis is possible by using 3D-DIC technology.

The Geographic Information System (GIS) is a useful technology for managing spatial databases, which are the basis of the Pavement Management System. When creating a pavement management system in GIS, the needs and available resources of individual road authorities should be considered. This paper describes establishment of a simple database management system for small city administrations. The database was created by manual collection of pavement condition data at several unclassified roads in the city of Osijek. Based on collected data, the system calculates the PSI index and compares pavement condition.

Existing race circuits were created using one of the two methods - intuition or engineering. Under the intuitive approach, the track was completely built by adapting to the terrain and environment in which it is located. The engineering approach to racing circuit development involves planning, designing, and building a car park at a specific location to accommodate all the users. Racing circuit design is based on recommendations depending on the type of race to be held. In Croatia, Croatian Car and Karting Federation issued the Circular Motor Racing Track Ordinance that defines the minimum requirements for organization and equipment of racing circuits. This paper presents a conceptual design of a racing circuit that is designed as per international requirements (FIA and FIM regulations) to host international sports events. This conceptual circuit is planned to be located in Osijek, which is the largest city in Eastern Croatia. It has a great location potential for becoming a motor sport center. The selected location has a possibility of venue extension for additional content, such as a test vehicle polygon, training center, and karting racing circuit. The conceptual design includes all the criteria, such as horizontal and vertical alignments, water drainage, pavement design, safety measures, and construction elements.

Currently, only empirical design methods are used in the application of well-known standards for pavement structure design. Given this fact, it is assumed that material characteristics correspond to average quality materials. Thus, the aim of this study included examining the influence of material characteristics on pavement design analyzing changes in the cement bound base layer (CBL) characteristics with respect to the occurrence of cracks and changes in the asphalt layer given typical seasonal changes. The study involved varying CBL modulus as 15 GPa, 10 GPa, and 5 GPa. Additionally, the moduli of asphalt layers were varied from 6 MPa to 2 MPa to simulate real conditions in pavement structure life. The analyses indicated that there was a significant difference in pavement behavior with respect to changes in material characteristics. Given these significant differences, it is extremely important to properly define material characteristics while using empirical design methods. Proper material characterization combined with the utilization of empirical and analytical methods increases the possibility of reducing layers thickness to design cost-effective structures.

Use of solid waste in place of conventional materials in civil engineering structures preserves natural resources and energy and avoids expensive and/or potentially harmful waste disposal. Many studies are investigating the application of waste materials in civil engineering structures. However, in an effort to find out new areas of waste materials utilization, the environmental impact of the installation of such materials in building structures often remains neglected. This study focused on the environmental aspect of the application of currently investigated waste materials in Croatia with an emphasis on heavy metal content. Heavy metal concentration in steel slag, river sediment, and biomass ash was measured, and the possibility of their use in road construction in accordance with currently valid legislation was assessed.

During road construction, granular materials for the unbound base course (UBC) and cement-bound base course (CBC) are mostly compacted by vibratory rollers. A widespread laboratory test for determining the optimal moisture content (OMC) and maximum dry density (MDD) of the mixture for installation in UBC and CBC is the Proctor test. Considering that the Proctor test does not produce any vibrations during compaction, this paper compares the Proctor test and the vibrating hammer test. The examination was conducted on UBC and CBC with varying cement content and aggregate types. All mixtures were compacted by both methods with the aim of determining the compaction and strength characteristics. The results indicated the high comparability of the two test methods for mixtures with natural aggregate in terms of MDD, OMC, density and strength characteristics (California bearing ratio (CBR) for UBC and 28-day compressive strength for CBC). For mixtures with higher cement content, the OMC difference depending on the laboratory compaction method used can be significant, so the laboratory compaction method should be chosen carefully, particularly for moisture-susceptible materials. This paper also reveals that by increasing the proportion of rubber in the mixture, the compaction and strength characteristics differ significantly due to the compaction method. Therefore, when using alternative and insufficiently researched materials, the compaction method should also be chosen carefully.

Application of nondestructive methods in assessing the properties of materials and mixes is very popular because of their simplicity and noninvasive nature. The ultrasonic method is, as one of nondestructive methods, used for more than 60 years in determining the properties of concrete mixes. However, only recently it has been applied application in studies of the stabilization mixes intended for road construction. The ultrasonic method is based on measurement of the travel time of longitudinal ultrasonic waves through the sample. In this paper, the investigation of stabilized mixes containing sand from river Drava stabilized with cement and fly ash are presented. The aim of the research was to determine the impact of changes in the composition of mixes and in the regime of care on the density, compressive strength and ultrasonic velocity. An additional goal was to analyze the relationship between the investigated properties of mixes and the ultrasonic velocity. The compressive strength of the stabilized mixture is determined by the destructive method according to Croatian Standards HRN.U.B1.030 Unconfined Compressive Strength as the average stress in a sample during uniaxial compression testing at the ultimate force. Testing of density and compressive strength of mixes and determination of the ultrasonic speed has been performed after 7, 28 and 90 days of curing at four different temperatures: 5 °C, 15 °C, 25 °C and 35 °C. The obtained results indicated the direct influence of fly ash quantity on the observed properties. Increase in the amount of fly ash caused a decrease in the mixture compressive strength, its density and ultrasonic velocity. A significant influence of treatment temperature on the compressive strength, density and ultrasonic velocity was also observed. Finally, correlation between density and ultrasonic velocity, as well as compressive strength and ultrasonic velocity was established. Exponential relationship between the compressive strength of stabilized mixes and ultrasonic velocity proved to be very strong, and similar to those obtained in previous studies by other researchers. Test results showed that the ultrasonic method can be useful in assessing properties of stabilized mixes.