EXPERIMENTAL RESEARCH OF PRECAST CONCRETE FLOOR BLOCKS WITH IMPROVED RESISTANCE TO HIGH TEMPERATURE

The paper presents possibility of usage of crushed clay bricks and roof tiles as an aggregate for concrete in precast concrete floor blocks. According to literature review, concrete with crushed brick and roof tiles as an aggregate has better thermal properties than regular concrete with natural aggregate. Applicability of concrete mixture for precast concrete blocks was tested regarding the requirements set in HRN EN 15037-2 Precast Concrete products – Beam and block floor systems – Part 2: Concrete blocks. Precast concrete blocks with crushed bricks and roof tiles were made and their mechanical properties after exposure to high temperature were tested. Based on experimental results, conclusions are made about usage of crushed bricks and roof tiles as partial replacement of natural aggregate in concrete for precast concrete blocks with improved resistance to high temperatures

Mechanical properties of self-compacting concrete with different mineral aditives after high temperature exposure

This paper presents an experimental research on the performance of high-strength self-compacting concrete (SCC) with different mineral additives after exposure to high temperature of up to 600°C. For this purpose, four SCC mixtures were studied: one reference and three mixtures where the Portland cement was replaced with mineral additive (fly ash, metakaolin and limestone) in certain proportions. After natural cooling in the furnace, compressive strength and static modulus of elasticity were determined and compared to results obtained from other studies and those provided in EN 1992-1-2 and EN 1994-1-2 for normal-vibrated concrete. Additionally, in order to characterize the damage of the specimens caused by high temperatures, AE parameters during compression test of heated and unheated specimens were also obtained

Micro-Mechanical Analysis of Corrosion Products Formed During Long-Term Carbonation Induced Corrosion of Steel

During corrosion distinct types of corrosion products form, composed of different ratios of ferrous ions and oxide, hydroxides. Corrosion products have different physical and mechanical properties, mainly density, resistivity, volume and modulus of elasticity compared to iron. Knowing properties of corrosion products is indispensable for service life modelling of structures and can give valuable insight into the long-term corrosion propagation process. In this study micro-indentation method was used to evaluate mechanical properties of different layers formed during long-term carbonation induced corrosion of steel in concrete. Investigation was performed on three sets of reinforced concrete samples, that underwent corrosion during 50, 60 and 70 years. Raman microspectroscopy was performed locally to determine and locate the constitutive phases of the corrosion system and to correlate them to the results of micro-indentation. Using grid technique, spatial distribution of phases with different mechanical properties was obtained for samples of different age. Comparison of values of mechanical properties for the same phases obtained on different samples, allowed hypothesis on their long-term behaviour

Positive interaction of industrial and recycled steel fibres in fibre reinforced concrete

In line with current ”green” transport initiatives, Croatia plans to build over the next investment period a high speed railway line which will connect central Croatia and its capital with coastal regions of the country. According to design documents, the track system will be built using ballastless concrete solutions. In the scope of the project “Concrete track system – ECOTRACK”, researchers from the University of Zagreb - Faculty of Civil Engineering analysed a new material, i.e. the rubberized hybrid fibre reinforced concrete (RHFRC), in order to find out whether its properties are adequate for the proposed concrete track system. The RHFRC contains by-products from mechanical recycling of waste tyres (rubber and steel fibres). The study of fibre and rubber interaction and their contribution to mechanical properties of the fibre reinforced concrete is presented, as extensive research on positive interaction between industrial and recycled steel fibres has not as yet been made. The results show that the RHFRC is an innovative, sustainable and cost-effective concrete, which is fully compliant with criteria prescribed in relevant standards

Distinct nonequilibrium plasma chemistry of C2 affecting the synthesis of nanodiamond thin films from C2H2 (1%)/H2/Ar-rich plasmas

6 pages, 5 figures, 6 tables.We show that the concentrations of the species C2 (X 1Σg+), C2 (a 3Πu), and C2H exhibit a significant increase when the argon content grows up to 95% in medium pressure (0.75 Torr) radio frequency (rf) (13.56 MHz) produced C2H2 (1%)/H2/Ar plasmas of interest for the synthesis of nanodiamond thin films within plasma enhanced chemical vapor deposition devices. In contrast, the concentrations of CH3 and C2H2 remain practically constant. The latter results have been obtained with an improved quasianalytic space–time-averaged kinetic model that, in addition, has allowed us to identify and quantify the relative importance of the different underlying mechanisms driving the nonequilibrium plasma chemistry of C2. The results presented here are in agreement with recent experimental results from rf CH4/H2/Ar-rich plasmas and suggest that the growth of nanodiamond thin films from hydrocarbon/Ar-rich plasmas is very sensitive to the contribution of C2 and C2H species from the plasma.This work was partially funded by CICYT (Spain) under a Ramón y Cajal project and under Project No. TIC2002- 03235. One of the authors (F.J.G.V.) acknowledges a Ramón y Cajal contract from the Spanish Ministry of Science and Technology (MCYT). One of the authors (J.M.A.) acknowledges partial support from CICYT (Spain) under Project No. MAT 2002-04085-C02-02.Peer reviewe

Influence of fire barriers on fire performance of facades with combustible insulation

In today's modern society sustainability has become a key driver for innovation. Sustainability in buildings is, or at least it should be, strongly interconnected with energy efficiency and fire safety. Unfortunately, cases of fires in buildings all over the world are a wakeup call to start thinking of fire safety as an inevitable part of energy efficiency in buildings. Thermally enhanced building envelopes, due to materials used, can represent significantly increased fire load on façades. To determine their fire performance, it is necessary to move on from material level to the whole building level, i.e. full scale tests. This paper presents findings from comprehensive research on influence of fire barrier on fire performance of External Thermal Insulation Composite System – ETICS with combustible thermal insulation. To confirm findings, tests on identical ETICS systems were conducted in March 2014 and May 2014

Influence of fire barriers on fire performance of facades with combustible insulation

In today's modern society sustainability has become a key driver for innovation. Sustainability in buildings is, or at least it should be, strongly interconnected with energy efficiency and fire safety. Unfortunately, cases of fires in buildings all over the world are a wakeup call to start thinking of fire safety as an inevitable part of energy efficiency in buildings. Thermally enhanced building envelopes, due to materials used, can represent significantly increased fire load on façades. To determine their fire performance, it is necessary to move on from material level to the whole building level, i.e. full scale tests. This paper presents findings from comprehensive research on influence of fire barrier on fire performance of External Thermal Insulation Composite System – ETICS with combustible thermal insulation. To confirm findings, tests on identical ETICS systems were conducted in March 2014 and May 2014

Successful promotion of physical activity among students of medicine through motivational interview and Web-based intervention

Background Regular physical activity supports healthy behavior and contributes to the reduction of preventable diseases. Students in their social transition period are the ideal groups for interventions. The higher education period, associated with demanding changes and poor time management, results in a low level of physical activity. In this age, social media usually are a suitable channel of communication and multicomponent interventions are the most desirable. It has not been sufficiently investigated how effective a Web-based approach is among university students when it comes to physical activity in the long-term period. We combined a Web-based approach with motivational interviews and tested these two interventions together and separate to assess their impact on improving the physical activity of medical students 1 year after the intervention. Methods All 514 first-year students at the Faculty of Medicine in Belgrade were invited to fill in a baseline questionnaire. Also, they underwent measurement of weight, height and waist circumference. After that, students selected a 6 months intervention according to their preference: Intervention through social media (Facebook) (Group 1) or combined with a motivational interview (Group 2). Group 3 consisted of students without any intervention. One year after completion of the 6 months intervention period, all students were invited to a second comprehensive assessment. Analyses were performed employing a wide range of statistical testing, including direct logistic regression, to identify determinants of increased physical activity measured by an average change of Metabolic Equivalent of Task (MET). This outcome measure was defined as the difference between the values at baseline and one year after completion of the 6 months intervention period. Results Due to a large number of potential determinants of the change of MET, three logistic regression models considered three groups of independent variables: basic socio-demographic and anthropometric data, intervention and willingness for change, and health status with life choices. The only significant model comprised parameters related to the interventions (p < 0.001). It accurately classified 73.5% of cases. There is a highly significant overall effect for type of intervention (Wald = 19.5, df = 2, p < 0.001) with high odds for the increase of physical activity. Significant relationship between time and type of intervention also existed (F = 7.33, p < 0.001, partial η2 = 0.091). The influence of both factors (time and interventions) led to a change (increase) in the dependent variable MET. Conclusion Our study confirmed the presence of low-level physical activity among students of medicine and showed that multicomponent interventions have significant potential for positive change. The desirable effects of the Web-based intervention are higher if an additional booster is involved, such as a motivational interview