The critical step for any subsequent instrumental analysis of cementitious binders is to stop their hydration reactions, i.e., to remove free water. One of the most available techniques is a solvent exchange method. However, the solvents are known to be strongly bound in ordinary Portland cement (OPC) paste and alter the results of thermogravimetric analysis (TGA) and sensitive hydrates, while their effect on TGA response of alkali-activated slag (AAS) has not been comprehensively investigated. Therefore, the objective of this paper is to track the effects of fundamental aspects of the solvent exchange on the TGA response of AAS with different sodium activators (hydroxide, carbonate, waterglass) and to support these results by X-ray diffraction and effluent gas analysis. All solvents used (acetone, diethyl ether, isopropyl alcohol, ethanol, and methanol) affected the TGA response of all tested pastes, and their effect was enhanced by prolonged immersion time. All solvents induced an additional mass loss at around 800 °C and, especially for OPC paste, increased in situ carbonation, even in an inert atmosphere. Methanol and ethanol had a detrimental effect on ettringite and decreased the basal distance of the C–(A)–S–H gel, while they only marginally affected gaylussite. For AAS, hydration stoppage by washing out the alkali-rich pore solution with water was also investigated and can usually be recommended (except for its detrimental effect on gaylussite), as it is more efficient than organic solvents, which lack solubility for activators. Methanol and ethanol are the most suitable alternatives, particularly for NaOH.

This paper deals with the influence of periodic freezing on lightweight concrete characteristics. Sets of lightweight concrete prismatic specimens are cyclically frozen in range from +20C to -20C and non-destructively tested after every 25 cycles. Freeze-thaw resistance is determined from measurement of the frost-attacked and non-frost-attacked (referential) specimens. The referential specimens are air/water-cured. Non-destructive methods, especially ultrasonic impulse method and resonance method are used for determination of specimen's degradation. Experiments are finished with destructive test in order to determine the static modulus of elasticity.Příspěvek se zabývá vlivem cyklického zmrazování na vlastnosti lehkého betonu. Sady vzorků ve tvaru hranolu jsou cyklicku zmrazovány v rozmezí +20C do -20C a nedestruktivně zkoušeny po každém 25tém cyklu. Mrazuvzdornost je určena z meření provedených na zmrazovaných a nezmrazovaných (referenčních) vzorcích. Referenční vzorky byly ošetřovány střídavě na vzduchu a ve vodě. Pro určení degradace vzorků byy použity dvě nedestruktivní metody - ultrazvuková a rezonanční. Experimenty jsou ukončeny destruktivními zkouškami za účelem určení statického modulu pružnosti betonu

Cement-based composites belong among the basic building materials used in civil engineering. Their properties are given not only by their composition but also by their behaviour after mixing, as well as by the methods of curing. Monitoring the processes and phenomena during the early stages of setting is vital for determining the resulting properties and durability. The acoustic emission method is a unique non-destructive method that can detect structural changes as a cement-based composite is setting. It can also detect the onset and growth of cracks during the service life of a cement-based composite since the moment it has been mixed. The paper discusses the use of the acoustic emission method with a focus on the early stage of the lifespan of a cement-based composite including the measures necessary for its use and description of the parameters of acoustic emission signals.

The modulus of elasticity is a property of concrete, which is known for its high variability of values. A high enough value of the modulus of elasticity is a critical requirement in complicated concrete structures and in order to attain it, a number of factors must be taken into account, as it is subject to many. Curing is one of the most important influences. It can be described as an effort to maintain the temperature of concrete within the correct limits, prevent loss of water and the shrinkage connected with this. This paper describes an experiment focused on the observation of the development of the dynamic and static modulus of elasticity in dependence on the method of curing. The experiment worked with air-entrained as well as non-air-entrained concrete of the C 30/37 strength class. The results show that the curing method strongly affects not only the development, but also the final values of the concrete modulus of elasticity