Dubravka Bjegović

POSITIVE INTERACTION OF INDUSTRIAL AND RECYCLED STEEL FIBRES IN FIBRE REINFORCED CONCRETE

AbstractIn 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 ...

Test protocols for migrating corrosion inhibitors (MCI®) in reinforced concrete

Corrosion induced deterioration of steel reinforcement (rebar) in concrete has increasingly become a greater world-wide concern. This insidious dilemma focuses on the potentially dubious structural integrity of many concrete structures. The steady rise of rebar corrosion and the eventual deterioration can be directly related to several influential factors, some of which include; poor quality construction materials, the increased use of de-icing salts, severe marine environments and increased atmospheric contaminants, such as carbon dioxide. Over the years various methods have been developed to protect either the rebar or the concrete. Today, the most recent emerging corrosion protection technology is that of Migrating Corrosion Inhibitors (MCIs). Recently, improved test methodologies have been developed which can better assess the effectiveness of corrosion inhibitors. Several of these recent electrochemical and non-electrochemical test methods were utilized to measure the effects of migrating corrosion inhibitors. This paper includes an explanation of these test methods and presents an overview of the test results. Testprotokolle fur migrierende Korrosionsinhibitoren (MCI®) in Stahlbeton Korrosionsinduzierte Zerstorung von Bewehrungsstahl in Stahlbetonbauwerken ist weltweit ein zunehmendes Problem geworden, wobei insbesondere die potentielle Gefahrdung der Standsicherheit vieler Bauwerke zu berucksichtigen ist. Die standige Zunahme der Bewehrungsstahlkorrosion und die mogliche Zerstorung kann direkt mit verschiedenen Einflussfaktoren korreliert werden; schlechte Bauausfuhrung, zunehmender Einsatz von Tausalzen, Meeresumgebung und zunehmende atmospharische Kontamination durch z.B. Kohlendioxid. Wahrend der letzten Jahre sind verschiedene Methoden entwickelt worden, um den Stahl bzw. den Beton zu schutzen. Der Einsatz von migrierenden Korrosionsinhibitoren (MCIs) stellt dabei die neueste Korrosionsschutz-Technologie dar. Seit Kurzem sind verbesserte Testmethoden zur Beurteilung der Wirksamkeit der Korrosionsinhibitoren entwickelt worden. Einige dieser neuen elektrochemischen und nicht-elektrochemischen Testmethoden wurden eingesetzt, um die Wirkung der migrierenden Korrosionsinhibitoren zu messen. In dieser Arbeit werden die entsprechenden Testmethoden erlautert und es wird ein Uberblick uber die Ergebnisse gegeben.

Application of ultrasonic methods for early age concrete characterisation

Concrete setting and hardening process are the most critical phases during construction work, influencing to properties of concrete structure, so the application of efficiency non-destructive test methods for early age concrete properties determination is crucial. Penetrometer, pull out and Vicat needle methods are standardised methods for young concrete characterisation. Paper shows that ultrasound methods have potential to be used for these purposes. Measurements of longitudinal compressive wave velocity through concrete and mortar during hardening process are performed. For mixtures preparation different additives were used. Obtained results indicate possibility for hardening process monitoring and time of cementitous materials setting determination.

C-D-c-t diagrams for practical design of concrete durability parameters

Abstract Structures (especially bridges), in Croatian coastal marine environment, are exposed to influence of different aggressive factors. Since many old structures have to be repaired and since many new have to be constructed in that area, there is a special interest of both, experts and the public to perform works with high quality standards. In this paper we propose a method for durability design of structures built in marine environment based on space and time distribution of chloride ions in reinforced concrete structures. This method, which is developed as the computer program CHLODIF, is applied during the construction of new Maslenica bridge.

Shrinkage Behaviour of Fibre Reinforced Concrete with Recycled Tyre Polymer Fibres

Different types of fibres are often used in concrete to prevent microcracking due to shrinkage, and polypropylene fibres are among the most often used ones. If not prevented, microcracks can lead to the development of larger cracks as drying shrinkage occurs, enabling penetration of aggressive substances from the environment and reducing durability of concrete structures. The hypothesis of the present research is that polypropylene fibres, used in concrete for controlling formation of microcracks due to shrinkage, can be replaced with recycled polymer fibres obtained from end-of-life tyres. To test the hypothesis, concrete mixtures containing polypropylene fibres and recycled tyre polymer fibres were prepared and tested. Experimental programme focused on autogenous, free, and restrained shrinkage. It was shown that PP fibres can be substituted with higher amount of recycled tyre polymer fibres obtaining concrete with similar shrinkage behaviour. The results indicate promising possibilities of using recycled tyre polymer fibres in concrete products. At the same time, such applications would contribute to solving the problem of waste tyre disposal.

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 selfcompacting concrete (SCC) with different mineral additives after exposure to high temperatures 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, acoustic emission (AE) parameters during compression test of heated and unheated specimens were also obtained which showed good non-destructive tool for identifying exposure temperature of the concrete needed for the assessment of concrete structures after fire.

Hybrid Fiber–Reinforced Concrete with Unsorted Recycled-Tire Steel Fibers

AbstractIn modern waste-management systems, an advantage is given to waste recycling and reuse, rather than to disposal. In the perspective of various initiatives taken worldwide in an attempt to c...

Fire Resistance of Steel Slag Aggregates Concrete

In this paper steel slag is considered as an aggregate which could improve fire resistance of concrete due to the fact that it is a material that occurs at high temperatures. For this purpose, three concrete mixtures were prepared ; concrete mixture with dolomite (reference mixture) and one concrete mixture with each of slags available in Croatia. The specimens of measurements 100/100/400 mm were demoulded 24 h after the casting, placed in a water tank for 7 days and after that placed in the chamber (temperature of about 2932 K (202 C) and humidity level of 955%) and finally kept there until the age of 28 days. After 28 days, the prisms were left in the laboratory room until the age of 56 days. At the age of 56 days the specimens, with moisture content within the limits 3 – 4 %, had been exposed to high temperatures impact. The specimens were put into the test furnace, heated to target temperatures of 373, 473, 673, 873 and 1073 K (100, 200, 400, 600 and 800 C) with the heating rate of 1 K/min and then kept at constant temperature for 1h. Upon cooling of the specimens, their residual mechanical properties (flexural strength, compressive strength and static modulus of elasticity), residual mass and residual pulse velocity were tested and compared with the same properties of reference concrete. Achieved results and microstructural analysis promote the theory that here observed slags could be used as fire resistant aggregates.

Shrinkage and Creep of Concrete Prepared with Quaternary Blended Cement

Environmental protection and energy saving are crucial problems set up against todays cement industry. The use of industrial by-products such as silica fume, slag, lime and fly ash in the concrete as cement substitution reduce cement production, and consequently lower the CO2 emission and save energy. This research work is inspired with the idea of replacing part of the cement with by-products of thermal power plants and metallurgical industry. Research already done in this area show that concrete prepared with blended cements has better permeability properties than the ordinary Portland cement concrete. In the present research emphasis was given on deformation properties of concrete and the effect of quaternary blended cements on total shrinkage, creep and mechanical properties of concrete. After performing shrinkage and creep tests and obtaining experimental results, shrinkage strain and creep coefficient were calculated according to European standard EN 1992-1 and Gardner/Lockman model, in order to compare the results and evaluate whether the values proposed by standards and model can be used during structural design of concrete prepared with quaternary blended cement.

Comparative full-scale fire performance testing of ETICS systems

U ovom radu prikazano je ispitivanje fasadnih sustava u stvarnoj veličini. Ispitivanje je provedeno s ciljem usporedbe ponašanja ETICS sustava s različitim toplinsko izolacijskim slojem (goriva izolacija, goriva izolacija s protupožarnom barijerom od negorivog materijala, negoriva izolacija) u uvjetima požara. Uzorci su izrađeni i ispitani u skladu s normom BS 8414-1:2002, a provedena su i dodatna mjerenja kako bi se dobili bitni podaci koji omogućuju bolje razumijevanje ponašanja ETICS sustava u požaru.A full-scale test has been performed to determine fire performance of different ETICS systems (combustible insulation, combustible insulation with fire barrier, noncombustible insulation). Test specimens were constructed and tested according to BS 8414-1:2002, while additional measurements were also conducted to obtain valuable information for better understanding of fire performance of systems used. U ovom radu prikazano je ispitivanje fasadnih sustava u stvarnoj velicini. Ispitivanje je provedeno s ciljem usporedbe ponasanja ETICS sustava s razlicitim toplinsko izolacijskim slojem (goriva izolacija, goriva izolacija s protupožarnom barijerom od negorivog materijala, negoriva izolacija) u uvjetima požara. Uzorci su izrađeni i ispitani u skladu s normom BS 8414-1:2002, a provedena su i dodatna mjerenja kako bi se dobili bitni podaci koji omogucuju bolje razumijevanje ponasanja ETICS sustava u požaru.