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Supplementary cementing materials (SCMs) contribute to the hydration of Portland cement by physical phenomena (e.g. nucleation effect) or by chemical reactions (e.g. pozzolanic activity). The partial substitution of Portland cement with SCMs can significantly reduce the CO 2 emission during the production of concrete and, therefore, can make concrete a more sustainable and environmental-friendly material. Durability of concrete is considerably improved by the incorporation of SCMs. Due to the pozzolanic activity and the filling effect, use of SCMs can result high performance concrete having both enhanced mechanical characteristics and reduced permeability that leads to improved durability. Combined use of SCMs of ternary composition of SiO 2 -Al 2 O 3 -CaO (e.g. blastfurnace slag and fly ash) can lead to extraordinarily favourable durability performance of concretes at even large cement substitution ratios, however, very few experimental data exist on the combined use of silica dominated and alumino-silicate dominated SCMs (e.g. silica fume combined with metakaolin) at increased cement substitution ratios. Most important aim of the present research was to reveal if there is any advantage of the combined use of silica fume and metakaolin.

Bond of FRP reinforcement is expected to be more sensitive to temperature and rate of loading than conventional steel reinforcement. Present paper introduces experimental results on Carbon Fiber Reinforced Polymer (CFRP) wires of sand coated surface tested by pull-out tests in a multi-parameter laboratory test programme. In the experimental programme low, normal and high strength concretes, −25 °C, +20 °C and +65 °C testing temperatures, and static to impact loads were applied for the pull-out tests (with an order of 1000 in the increase of the rate of loading). Results indicate that the bond strength of the tested CFRP wires follows the change of temperature in a more pronounced manner than the concrete compressive strength does. A viscous-elastic, load rate dependent behavior can be realized in the bond response of the CFRP wires studied. Failure of bond is different for different concrete strengths, testing temperatures and loading rates. Results also indicate that the mathematical functions that are used for the modeling of bond of conventional steel reinforcements are not optimal for the CFRP wires studied.

Surface hardness testing of materials can be considered as the oldest method to get information about strength related material properties. In recent decades the rebound hammer has been the most popular surface hardness testing device for concrete uniting the advantages of its predecessors. In the technical literature numerous proposals are available for simple, two-parameter regression analyses of rebound surface hardness vs. compressive strength relationship of concrete. The remarkable diversity of the proposed curves implies the need of the more than two-parameter regression techniques to reveal the most pronounced parameters governing hardness behaviour. The objectives of present experimental studies were to carry out dynamic and static hardness tests, Young’s modulus and compressive strength tests on concrete specimens. From the development of the tested properties with time it can be concluded that the rebound hammers provide a hardness value for high strength concretes connected to the Young’s modulus rather than the compressive strength. Present paper includes a parametric simulation and a parameter fitting of the verified phenomenological constitutive model of the authors which recognizes the w/c ratio as the main driver of the interrelated material properties and gives a realistic formulation for the time dependent behaviour of the rebound surface hardness of concrete.

Durability of steel fibre reinforced concrete (SFRC) specimens is tested and evaluated. Concrete is mixed with moderately sulphate resistant CEM I 42.5 cement and does not contain airentraining agent. The aim of the research is to study how the dosage of high bond crimped steel fibre influences the durability damage kinetics of SFRC; freeze-thaw resistance, de-icing salt scaling resistance and resistance to water penetration are studied, completed with basic mechanical performance tests (compressive strength, modulus of elasticity, flexural tensile strength, splitting tensile strength, flexural toughness, fracture toughness, apparent porosity and vacuum water absorption). Results reveal the importance of the increased volume of the interface transition zone (ITZ) around the steel fibres in the first freeze-thaw cycles and the importance of the internal restrain activated by the steel fibres during later freeze-thaw cycles.

The combined influence of service temperature and loading rate on the compressive strength of concrete has been studied over a wide range of compressive strength. New simplified prediction formulae are proposed to take the influence of temperature and loading rate into account. It is demonstrated that the new formulae are suitable to effectively predict the compressive strength of concrete under the combined influence of temperature and loading rate. It is also demonstrated that the Dynamic Increase Factor, DIF is not a practical tool in the representation of the combined influence of service temperature and loading rate on the compressive strength of concrete.

Vasbeton szerkezetek teherviselese akkor lehetseges, ha van tapadas a beton es a bebetonozott acelbetetek kozott. A tapadast kozel szaz eve vizsgaljak acelbeteteken, es a jelenseg kellő reszletesseggel ismert. A befolyasolo tenyezők hatasat egyenkent, illetve egyes tenyezők kombinalt hatasat egyuttesen a szakirodalom tobbnyire targyalja. Szamos mechanikai modell is letezik a beton es betonacel tapadasanak leirasara. Hianykent jelolhetők meg a hőmersekleti hatasokkal kombinalt, kulonfele terhelesi modok mellett elvegzett es kulonfele terhelesi sebessegeket alkalmazo vizsgalatok. Mivel az acelbetetek korrozioja betonban is bekovetkezhet, ezert evtizedek ota folynak kutatasok olyan iranyokban is, hogy mely anyagokkal lehetne a hagyomanyos acelbeteteket es feszitőbeteteket kivaltani, ha tartossagi szempontok ezt indokoljak. Az epitőmernoki gyakorlatban az 1990-es evek ota vannak jelen a szalerősitesű polimer (FRP) betetek erre a celra. A szalerősitesű polimer (FRP) betetek az elektrolitikus korrozionak teljes...

Considerable corrosion of reinforced concrete members accelerated the research on non-metallic materials such as fiber reinforced polymers (FRP) for structural applications in non-corrosive reinforcement. This paper describes a comparative experimental study that was performed on prestressed concrete beams pretensioned with carbon-FRP or steel wires. Load-deflection responses are analyzed and pivot point of loading-unloading moduli under repeated loading is defined. Practical details are given on the prestressing technique and heat curing.