The aim of the paper is to outline the possibilities and predictive values of the selected methods for determining air-pore characteristics in concrete and cement composites in general. Four samples (mixtures) of cement concrete without additives or admixtures were chosen for the measurement, differing in cement content while maintaining the consistency of fresh concrete S3 according to EN 206. Both standardized and non-standardized methods are used in Europe, therefore providing a possibility of comparing their outcomes. Keywords: concrete, durability, porosity, surface, covering layer, X-ray computed micro-tomography Namen~lanka je prikazati mo`nosti za splo{no napovedovanje izbranih metod za dolo~anje zna~ilnosti zra~nih por v betonu in v kompozitih iz cementa. Za meritve so bili izbrani {tirje vzorci (me{anice) betona brez dodatkov in primesi z razli~no vsebnostjo cementa ob zadr`anju konsistence sve`ega betona S3, skladno z EN 206. Standardizirane in nestandardizirane metode se uporabljajo v Evropi in zato omogo~ajo primerjavo rezultatov.
The focus of the project GAČR 13-18870S is the research in concrete durability determined primarily by its surface layer quality. The surface layer can be difficult to assess for which reason the project makes use of available standardised and non-standardised test methods by means of which the concrete surface layer or its internal structure can be examined. One of these methods which is commonly used is Determination of resistance of cement concrete surface to water and defrosting chemicals. The paper presents the results of experiments performed with concretes differing only in w/c ratio and plasticiser content. Two more methods were used during the research based on the action of a thawing solution upon the surface of the specimen during freezing and thawing. The only difference between these methods is the direction in which the thawing agent acts on the test surface. The presumed experiment outcome was the existence of a strong dependence of the outcomes of the methods on the w/c ratio. The performed analyses confirmed the experiment presumption.
This paper deals with determining the dependence of the value of the static modulus of elasticity of concrete in compression on the number of loading cycles. The deformation of specimens during multiple cyclic loading was measured in the elastic region of the stress-strain curve for concrete. The specimens were subjected to up to 1500 loading cycles. The main goal of the experiment was to ascertain whether the multiple cyclic loading causes significant changes in the static modulus of elasticity.
The pore structure of concrete is a very important material property influencing the durability of concrete. Concrete pore structure is influenced, among others, by the composition of concrete, water/cement ratio, aeration or cracking [1]. The experiment described in this paper understands concrete cover to be 40 – 60 mm from the surface of the specimen.The paper focuses on the determination of air void content in different concrete mixtures by means of microscopic analysis. Mixtures differ in the amount of cement and plastifying agent added while maintaining the consistency of the fresh concrete. In order to determine the air void characteristics, the experiment used manual and automated microscopic analysis.
Concrete's durability is currently a frequently discussed topic. The determination of concrete's durability is rather difficult since it depends on a number of factors, out of which the surface-layer quality is very important. One of the options for assessing its quality is the determination of concrete's resistance to water and de-icing chemicals. The testing is based on loading the concrete by cyclic freezing and thawing during the simultaneous action of a thawing solution. The damage to the surface layer manifests itself as scaling, i.e., the loss of small scales from the surface of the material. The resistance of concrete to water and de-icing chemicals can be determined by means of several methods; however, a universal method of evaluation has not yet been established in Europe. The goal of the experiment described here was to assess the influence of fresh concrete's composition on its resistance to water and de-icing chemicals using two different measurement methods (method A and C). A total of 9 fresh concrete mixtures were designed, from which specimens were made. The experiment was created and evaluated using the statistical method DOE (Design of Experiment). Based on the tests performed, it can be stated that a change in the content of cement and plasticiser in fresh concrete is visible in the results of both methods. However, more so in the results for method C, which is generally more sensitive to changes in fresh concrete's composition. Keywords: concrete, resistance, durability, de-icing chemicals Zdr`ljivost betona je pogosto obravnavana tema. Dolo~anje zdr`ljivosti betona je precej te`ko, ker je odvisno od {tevilnih faktorjev, med katerimi je pomembna tudi kvaliteta povr{inske plasti. Ena od opcij dolo~anja njene kvalitete, je dolo~anje odpornosti betona na vodo in na kemikalije proti zmrzovanju. Preizkus temelji na izpostavitvi betona cikli~nemu zamrzovanju in odtaljevanju s simultanim delovanjem raztopine za odtaljevanje. Po{kodbe povr{inskega sloja se ka`ejo kot lu{~enje povr{ine materiala. Odpornost betona na vodo in kemikalije za raztaljevanje se lahko dolo~i z ve~metodami; vendar pa univerzalna metoda za oceno tega v Evropi {e ni vzpostavljena. Cilj opisanih eksperimentov je bil oceniti vpliv sestavo sve`ega betona glede na njegovo odpornost na vodo in na kemikalije za raztaljevanje, z uporabo dveh metod (metoda A in C). Skupno je bilo pripravljenih 9 sve`ih betonskih me{anic iz katerih so bili izdelani vzorci. Eksperimenti so bili postavljeni in izvedeni z uporabo statisti~ne metode DOE (postavitev preizkusa). Na podlagi izvedenih preizkusov se lahko zaklju~i, da se spremembe v vsebnosti cementa in plastifikatorja v sve`em betonu poka`ejo pri obeh metodah. Vendar so bolj izrazite pri rezultatih metode C, ki je na splo{no bolj ob~utljiva na spremembe v sestavi sve`ega betona.
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