► Stainless steel reinforced mortar exposed to aggressive solution for 2years. ► Impedance spectra of passive and corroding stainless steel in mortar discussed. ► Real-time behaviour in mortar ...compared to literature pore solution results. ► Steels ranked based on their composition, performance and corrosion attack morphology.
Long-term corrosion behaviour of six stainless reinforcing steels embedded in mortar and exposed to chloride media was monitored by electrochemical impedance spectroscopy at the open circuit potential during the period of 2years. Corrosion behaviour of studied steels was divided into two phases characterized by different interfacial behaviour: (i) passive phase and (ii) pitting propagation phase. After 2years, duplex steel 1.4362 showed very good corrosion performance similar to austenitic steel 1.4401. Steel types with low Ni content but with high N and Mn content, 1.4597 and 1.4162, showed lower corrosion resistance compared to austenitic steel 1.4301.
The ability of carbonated mortar to provide corrosion protection of embedded steel was studied on mortars prepared with low-alkalinity binders. Three mortars were investigated, mortar based on ...ordinary Portland cement, mortar based on high volume of fly ash and silica fume and mortar based on slag and nano-silica. Analysis of impedance spectra after carbonation revealed an increase in electrical resistivity of mortar based on OPC and significant decrease in electrical resistivity of low-alkalinity mortar. After exposure to cycles of wetting and drying steel embedded in carbonated low-alkalinity mortars has lower open circuit potential, lower charge transfer resistance and significantly higher corrosion current density compared to steel embedded in OPC mortar. To explain differences in corrosion protection properties, an extensive microstructural testing of carbonated mortar was performed. Difference in corrosion properties were explained by the changes in mortar microstructure, mainly changes in pore size distribution.
This paper aims to investigate the possibility of utilizing steel slags produced in Croatian plants as a concrete aggregate. Aggregate properties were determined on coarse slag fractions (4–8, ...8–16 mm) according to the relevant European Standards. Considering the obtained results, slags were specified in accordance with the classes as given in the main European standard for aggregates, whereupon these classes were compared to the Croatian regulation requirements. The obtained results proved that coarse slag fractions can be suitable for concrete application. Therefore, concrete mixtures were prepared with coarse slag fractions whose hardened state properties (compressive and flexural strength, static modulus of elasticity, volume changes and corrosion susceptibility) were then compared with the properties of reference concrete made of commonly used natural aggregate materials, namely dolomite. According to the obtained test results it can be concluded that the observed slags can be a good substitute for natural aggregate materials.
•Precast concrete floor blocks made with crushed bricks and tiles (CBT) aggregate.•Increasing percentage of replacement of natural aggregate with CBT aggregate.•Concrete floor blocks with high ...replacement percentage meet the requirements.
The main objective of this paper is to demonstrate that it is possible to make precast concrete floor blocks with more than 50% replacement of natural aggregate with recycled aggregate made with crushed clay bricks and roof tiles. In first phase of the research, the physico-mechanical properties of concrete with recycled and with natural aggregate were tested. The second phase explored the properties of precast concrete floor blocks. Their geometrical, mechanical, thermal and acoustic properties were determined. Based on experimental research it can be stated that it is possible to make precast concrete floor blocks with recycled aggregate with the fulfilled thermal, cost and environmental requirements.
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•The morphology of the corrosion of steel in cement paste was studied in situ.•During galvanostatic corrosion, carbon steel reinforcement corroded homogeneously.•On ferritic stainless ...steel, deep corrosion pits formed and caused wider cracks.•The measured rate of steel loss correlated well with Faraday’s law of electrolysis.
In a X-ray microcomputed tomography study, active corrosion was induced by galvanostatically corroding steel embedded in cement paste. The results give insight into corrosion product build up, crack formation, leaching of products into the cracks and voids, and differences in morphology of corrosion attack in the case of carbon steel or stainless steel reinforcement. Carbon steel was homogeneously etched away with a homogeneous layer of corrosion products forming at the steel/cement paste interface. For ferritic stainless steel, pits were forming, concentrating the corrosion products locally, which led to more extensive damage on the cement paste cover.
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.
The use of slag as a fire-resistant aggregate was investigated in concrete and in structural members. Three mixtures of three-fractional concrete with type CEM I 52.5N cement were prepared: the ...reference mixture (dolomite fractions of 0–4mm, 4–8mm and 8–16mm) and two mixtures with coarse slag fractions (4–8mm and 8–16mm) and a fine dolomite fraction (0–4mm). At 56 days the specimens were exposed to high temperatures. Their residual mechanical properties (flexural strength, compressive strength and static modulus of elasticity) and residual mass were tested after cooling, and results were compared among specimens. To determine the fire resistance of a structural member with slag in the concrete mixture, fire resistance of reinforced-concrete beams with slag was compared with that of reinforced-concrete beams with dolomite. In these experiments, concrete beams were exposed to high temperature according to the ISO 834 temperature curve for 60min. The temperature increase within the beams during their exposure to high temperature in the furnace was also observed. Bearing capacity was tested after fire exposure and compared with bearing capacity of the beams at room temperature. The results showed that slag in combination with Portland cement did not increase fire resistance of concrete and its structural members. In order to create a structural member with improved fire resistance, slag should be combined with a binder that can better adapt to slag expansion under high temperature or be used as a partial replacement for coarse aggregate in concrete.
•Slag as a fire resistant aggregate in concrete mixtures and in structural members.•3 mixtures of 3-fractional concrete with the CEM I 52.5N cement type were prepared and exposed to high temperatures impact.•Concrete beams have been exposed to high temperature impact according to ISO 834 temperature curve.•Good fire resistance of the slag but it cannot provide satisfactory concrete fire resistance if combined with Portland cement.•Conclusions for the specimens have been verified on the beam testing results.
This paper presents the results of experimental research into the effect of brick and roof tile aggregates on the values of the modulus of elasticity of concrete made with crushed brick and roof tile ...aggregates. The main purpose of this paper is to compare the formulae given in the code provisions for estimating the concrete elastic moduli for lightweight and normal‐weight concretes with values obtained experimentally. Sixty two different concrete mixes including crushed brick and roof tiles were made and tested experimentally. The differences between the empirical and experimental static moduli of elasticity are shown. In addition, formulae for calculating the static modulus of elasticity over compressive strength are shown and compared with an experimentally estimated formula. As a result of this investigation, a universal equation for estimating the static modulus of elasticity over compressive strength for concretes with crushed brick and roof tile aggregates is proposed.
In this paper an investigation is made of the applicability of the ASTM C 1609 procedure for testing toughness of ultra high performance fibre reinforced concretes containing a large amount of fibre ...(≥2% by volume) and exhibiting deflection hardening behaviour. All mixtures exhibited deflection hardening behaviour, and the parameters varied included (1) the amount of steel fibres, (2) the type of steel fibres, (3) the size of the longest fibre, (4) the addition of polypropylene fibres, and (5) the size of the maximum aggregate grain in the concrete matrix. Based on comparison of the curves obtained from flexural toughness tests with the evaluation of the test results obtained according to ASTM C 1609 and with the statistical analysis, the authors recommended additional toughness parameters (P
100,3.00
, P
100,4.00
, P
100,6.00
, T
100,3.00
, T
100,4.00
, and T
100,6.00
) for the evaluation of toughness results. Such additional toughness parameters are calculated using a similar procedure as that specified in ASTM C 1609.
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.
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