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Present paper studies metakaolin as a supplementary cementing material (SCM ) for concrete in terms of compressive strength development and k-value concept of CEN /TR 16639:2014. Sixteen different concrete compositions are studied in the range of water-to-cement ratio of w/c = 0.50-0.65. Results indicate that the effectiveness of metakaolin depends on the applied w/c-ratio and the applied cement substitution ratio; the smaller the w/c-ratio, the more effective the metakaolin; the higher the cement substitution ratio, the less effective the metakaolin. The k-value decreases by the increase of w/c-ratio, independently of the age of concrete. The higher the cement substitution ratio, the smaller the k-value. The k-value tends to reach a final value in time. [ABSTRACT FROM AUTHOR]

In the hardened cement paste - through pozzolanic reactions - additional hydration products can be formed by the use of supplementary cementing materials (SCM s). The expected results of these processes are: increase in strength, decrease in permeability and the improvement of other important durability properties. In the present research, properties of mortar mixtures were investigated with different cement substitution rates of SCM s both in fresh and hardened conditions. The consistence of mixtures was determined by flow table test, and the change in workability was repeatedly measured until 120 minutes. The specimens were stored in water up to the age of 7 days then under laboratory conditions (in climate chamber of 20±3°C temperature and RH=65% relative humidity) up to the age of 28 days. Afterwards half of the specimens were immersed into and stored under water and the other half was kept continuously under laboratory conditions. The properties of the hardened specimens (flexural tensile strength, compressive strength, water absorption, apparent density and apparent porosity) were investigated at the age of 28, 56, 90 days. Seven mortar mixtures were made of CEM I 42.5 N Portland cement with different cement substitution ratios of metakaolin (MK ) and/or silica fume (SF). Quartz sand was used as aggregate with the range of 0/2 mm particle size. The results of consistence measurements showed that the flow values of the fresh mortar mixtures which contain SCM s are smaller comparing with the reference mixtures (without SCM s), since the physical properties of these materials (particle size, specific surface area, particle shape, etc.) influence the consistence. The specimens with smaller substitution ratio showed more effective utilization of SCM s in the view of strength. The water absorption and apparent porosity were higher, and at the same time the apparent density was smaller than those of the mixtures with higher substitution ratios. [ABSTRACT FROM AUTHOR]

Reinforced concrete is a widely used construction material. However, corrosion of steel reinforcement might be a danger to its durability. In this paper the corrosion mechanism of steel reinforcement in concrete is introduced. Literature and case studies are reviewed on concrete crack width and its effect on reinforcement corrosion. The results found in different sources proved to be inconsistent. Crack width variation within concrete cover is presented as a reason. The influencing factors of reinforcement corrosion in concrete are collected with special regard to crack geometry. [ABSTRACT FROM AUTHOR]

Preliminary results of a two years long research and development project is introduced in this paper. One novel type of 2D deformed steel fibre (with the product name of PetiX) and four different types of 3D deformed steel fibres (PetiX V45; PetiX V90; PetiX S45; PetiX S60) were designed, manufactured and tested under laboratory conditions. The laboratory tests showed promising results. Superior performance of certain types of 3D deformed steel fibres was observed. Considerable improvement of the bond performance of steel fibres was realized in concrete and increased flexural toughness of SFRC prismatic specimens tested in flexure was demonstrated. [ABSTRACT FROM AUTHOR]

Spatial variographic analysis has been performed on rebound index data collected in-situ at the bottom surface of a concrete floor over 130 m² of testing area. Possible use of geostatistical methods in terms of semivariogram, madogram and rodogram analysis was demonstrated. It has been revealed that the classical methods of geostatistics may be further refined for more satisfactory use in the spatial variability analysis of in-situ rebound hardness test results on concrete structures and a possible direction toward the use of empirical estimation of extremal coefficient functions is proposed. [ABSTRACT FROM AUTHOR]

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EU laws have been the most effective driving force of Latvian and Hungarian environmental legislation in order to improve recycling of packaging waste. In Latvia and Hungary the waste diversion strategies have focused on establishing treatment capacity and setting up schemes for separate collection, which largely cover packaging waste. Despite all improvements done in this area, still large amount of glass wastes is dumped into landfills and alternative solution for this waste glass utilization could be the application in concrete as a supplementary cementitious material (SCM). Laboratory tests were carried out on cement paste specimens, in which waste glass powder (WGP) addition was used as a SCM. Cement was substituted with WPG at levels of 20% or 30% per mass. It was demonstrated that the WGP addition is applicable in view of drying shrinkage with total deformation up to 2.5 ‰ in the period of 592 days. The WGP addition contributes to a slowdown in the rate of hydration of the cement paste, so the early age shrinkage cracking tendency becomes more favourable, which can be seen in the longer cracking time result during the ring tests. [ABSTRACT FROM AUTHOR]

Variability of the in-situ rebound hammer tests is composed of the inherent variability of the measuring method and the spatial variability of the concrete performance properties. In-situ, Schmidt rebound hammer tests were performed at the bottom surface of a concrete slab, with dimensions of 25.0 m × 7.5 m. The studied region on was 22.0 m × 6.0 m. The analysis of the inherent variability of the rebound hammer tests was limited to the comparison of the statistical location parameters; mean, median and mode values. The spatial variability was analysed by contour plots and semivariograms of the statistical location parameters. It was demonstrated that the geostatistical methods may be applicable for the much smaller scale concrete structures than the scale of geological formations. Semivariograms and semivariogram models seem to be useful tools for the characterisation of spatial variability of concrete structures. [ABSTRACT FROM AUTHOR]

Ecological and environmental benefits support the use of waste glass powder (WGP) as supplementary cementing material by the decrease of the amount of landfills, by the reduction of non-renewable natural resource consumption, by the reduction of energy demand for cement production (less cement is needed), and the reduction of greenhouse gas emission. Laboratory tests were carried out on cement paste specimens, in which waste glass powder (WGP) addition was used as a supplementary cementitious material. Cement was substituted with WPG at levels of 20% or 30% per mass. It was demonstrated that the WGP addition improves the workability of fresh pastes, and can be effectively used as cement replacement for compressive strength. It was also demonstrated that the particle size of the WGPs (specific surface area) has a stronger influence on the effectiveness of the cement replacement than the chemical composition. The effectiveness of the cement replacement increases as the specific surface area increases [ABSTRACT FROM AUTHOR]

The rebound hammer test of concrete can provide an alternative to drilled core tests for estimating the in-situ compressive strength of concrete. The variability of concrete strength is recognised during the strength assessment and the design strength of concrete is specified as its characteristic compressive strength by taking the variability of the strength of concrete into account. In the present paper, particular topics of the inherent variability of the rebound hammer tests are discussed. Different types of Schmidt hammers are compared in this sense. The precision of the original N-type Schmidt hammer is demonstrated to be superior to original L-type or Silver Schmidt N-type hammers. Observations are confirmed by normality tests. Results imply the need for further research. Measurement errors made by the operators of the rebound hammers are analysed. Differences among the repeatability and reproducibility are demonstrated. As a closing remark the need of revealing the connection between the variability of compressive strength and rebound index, as well as the need of the spatial variability analysis of rebound index are highlighted [ABSTRACT FROM AUTHOR]

Development and application of Fibre Reinforced Polymer (FRP) reinforcements in concrete structures have been accelerated in the last three decades. Durability of FRP reinforcements is expected to exceed that of conventional steel reinforcements as FRP reinforcements do not tend to corrode. Present paper intends to review experiences on characteristics of fiber reinforced polymers (FRP) for civil engineering applications and to discuss design considerations by applying FRP bars or tendons embedded in concrete as prestressed or non-prestressed reinforcement. Test results on FRP indicate high tensile strength, high fatigue strength as well as low relaxation and creep. Design recommendations are based on work carried out more than fifteen years ago on first generation reinforcing products. Design guidelines are necessary to enable the use of new materials, they should be made flexible enough to accommodate future developments and facilitate the quick adoption of innovative products. Present paper, therefore, introduces the most recent European research action (COST TU1207) that aims to develop a new generation of design guidelines for FRP materials based on European Standards. [ABSTRACT FROM AUTHOR]

Hardness testing is considered to be the earliest method of material testing. For the measurement of hardness of stones and other porous solid materials mostly dynamic testing devices are applied in practice, however for scientific purposes indentation hardness tests are more suitable methods. In present research Brinell macro hardness tests and depth-sensing indentation (DSI) tests (aka. instrumented indentation tests, IIT) were performed on 15 different types of porous solid building materials, recording the complete loading-unloading responses. The studies have shown that earlier observations found in the literature for the Brinell hardness of concrete can be extended to all porous solid building materials. [ABSTRACT FROM AUTHOR]

Crack width in reinforced concrete structures is usually considered to be constant within the concrete cover by design codes. This simplification can lead to inaccurate or uneconomical design and it is completely misleading for a possible crack repair design. Aim of present experimental studies is to investigate the application possibilities of PU injection resins for active cracks in dynamically loaded structural concrete members. Present paper summarizes the results of the preliminary studies carried out with epoxy injection resin for a detailed survey of the variation of crack widths within the concrete cover of reinforced concrete tensile members. The paper highlights the significance of different concrete covers on the variation both of internal and surface crack widths, confirms several findings of previous studies including the influence of the so-called Goto cracks, and appreciates the recently developed proposal of the fib Model Code 2010 concerning the variation of the crack width along the concrete cover in the form of a power function. [ABSTRACT FROM AUTHOR]

The author presents insights on rheology as a scientific discipline. He notes that complicated deformations are formed under mechanical stresses due to internal structural of real materials. He states that rheology covers various topics in the development and processing of polymers, ceramics, adhesives, mortars and concretes, among others.

An introduction is presented which discusses various article within the issue on topics including the first paper in of Építőanyag-Journal of Silicate Based and Composite Materials that explicitly shows the interdisciplinary nature and an article on biotechnology by Aleksandr L. Urakov.

An introduction to the journal is presented in which the guest editors features the diverse applications of ceramic materials in Hungary and Russia.

An obituary is presented for professor Balázs György.