Ámos Dufka

Use of emanation thermal analysis to characterize microstructure development during Portland cement hydration

Portland cement hydration has been investigated by emanation thermal analysis (ETA), based on the application of radon atoms as radioactive indicators. This method enabled us to characterize continuously changes in the microstructure of the cement paste at selected temperatures. The numerical simulation of time dependences of the emanating rate during cement hydration was carried out. An agreement between the mathematical model and experimental results of the ETA was obtained.

To the Problems of Determination of Dynamic Elasticity Modules of Calcium Silicate Bricks by Means of Resonance Method

Modulus of elasticity of building materials can be determined in a static way (loading in a press) or by means of non-destructive test methods (ultrasonic pulse method and resonance method); the parameter is most frequently determined for concrete and both methods of determining elasticity modulus are codified in Standards. Elasticity characteristics of calcium silicate bricks were determined by means of resonance test method. Because the shape of calcium silicate bricks (a block with oblong foot) is different from the shape of test specimens for concrete (usually blocks with square foot), expected frequencies for verification of accuracy of measurement by resonance method were determined. Moisture content of calcium silicate bricks (water absorbing capacity is up to 12-14%) has influence on the value of resonance frequency. Difference between dynamic Youngs modulus of elasticity from fundamental longitudinal and transverse resonant frequency is on average 2.8%.

Evaluation of the Effect of Crystallization Additives on the Durability of Cement Composites

The paper deals with a comprehensive analysis of the influence of applied crystallization additives on the service life of self-compacting concrete (SCC), specifically when exposed to the effects of chemically aggressive environments. Attention is focused not only on the influence of a crystallization additive on the characteristics of the capillary porous structure of SCC, but mainly on its effects in terms of the long-term service life of self-compacting concrete. The effects of individual types of aggressive environments are evaluated on the basis of a set of physico-mechanical and physico-chemical analyses.

Determination of Properties of Concrete Floor after a Fire and Renovation

Concrete exposed to high temperature considerably changes its properties down to total destruction. The paper describes renovation of concrete floor damaged by a fire of a factory building. Individual steps of determination of damage of concrete floor structures caused by high temperatures are described. Structure of damaged floor was technically analyzed, redevelopment was designed and renovation works were carried out.

The Use of Geopolymers in Rehabilitation of Reinforced Concrete Structures

The subject of this paper is option analysis of the use of geopolymers as matrixes to repair mortars designated for rehabilitation of reinforced concrete structures. Due to their specific properties, geopolymers show a high potential mainly for special applications. Rehabilitation of reinforced concrete structures exposed to extreme conditions is a field in which it is possible to effectively take advantage of geopolymers ́ exceptional properties. In this particular case, we focus on comparing the behaviour of polymer-cement materials commonly used in the rehabilitation of reinforced concrete structures and the one of geopolymer-based mortars.

The Evaluation of the Effect of Crystallization Additives on Long Term Durability of Cement Composites

The article deals with the influence of crystallization additives on the life of self-compacting concrete (so-called SCC concrete), which are exposed to chemically aggressive environments. The focus is not only on the effect of the crystallization additive on the characteristics of the capillary-pore structure of SCC concrete, but especially long life durability of self-compacting concrete (two years expozition). The effect of individual types of aggressive environment is assessed on the basis of a set of physico-mechanical and physico-chemical analyzes.

Lightweight Mortar Containing High Amounts of Alternative Raw Materials with Increased Thermal Resistance

The paper researches lightweight mortars based on a high content of alternative materials. 25 – 30% heating plant slag was used in order to modify the matrix. Fly ash agloporite (a lightweight aggregate produced by self-combustion from fly ash) was used as an aggregate. Mortars were exposed to the temperatures up to 1,250° C. Two types of cooling were carried out at 1,000° C; controlled slow (in the furnace) and by shock (in water baths of approximate 18° C). Developed materials were further analyzed by various methods: monitoring changes in an observation furnace, physical–mechanical (to determine strength properties), physical-chemical (phase composition - XRD) and microstructural (SEM).

Polymercement Composites in Environment with Increased Concentration of Sulfate Ions and Extreme Temperatures

Polymer cement matrix based materials were designed within the frame of the research presented in this paper. Resistance of these materials to combination of several adverse factors was observed. Considerable proportion of input materials used were components from alternative material resources. Primary binder was replaced with fly ash and blast furnace slag. Dominant proportion of filling mass was taken up by agloporite – porous aggregate produced by self-baking from fly ash. The focus of the research was assessment of degradation of materials after long-term exposition (up to 90 days) to increased concentration of sulphate ions and high temperatures. Degree of degradation was evaluated on the basis of physico-mechanical and physico-chemical tests combined with microstructural analyses.

Molar Ratio and Polymer Modification Influence to Water Glass Coatings Matrix Basic Properties

This paper contains the continuation of basic research from 2012 - the molar ratio influence to water glass coatings basic properties (adhesion, diffusion properties, surface quality) was expanded with basic resistance (combination of sun, UV light and rain). Most silicate coatings for concrete protection are currently based on potassium water glass. Water glass matrix itself is, however, insufficient for coatings matrix and often is modified by polymer substances for the coating purpose. Combinations of water glass basic matrix (Sodium, Potassium, Lithium, Sodium - Lithium and Potassium - Lithium) with the appropriate polymer modifiers is also content of the presented paper. Polymer dispersions modification effect to basic properties and resistance to developed silicate coating binder is also part of paper.

The Development of Coating Systems Based on Alkali Activated Slag for Protecting Reinforced Concrete Structures

Theme of the article is the development of coating systems based on alkali activated stag intended for protection of reinforced concrete constructions exposed to chemically aggressive environments. At present mainly polymer based secondary protections are used for this purpose. The coating systems based on alkali activated slag have potential to surpass these generally applied types of secondary protections in many aspects. For instance for constructions exposed to synergic actuation of chemically aggressive environment and increased temperatures. Findings obtained from alkali activated slag coating exposed to selected aggressive environment types for six months are presented in this article.