Jiří Bydžovský

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.

Study of the Parameters of Lightweight Polymer-Cement Repair Mortars Exposed to High Temperatures

The article examines the research aimed at studying the basic physico-mechanical parameters of polymer-cement repair mortars with a modified composition. The objective of a composition modification was to achieve the parameters characteristic of fire-resistant repair mortars. For research purposes, a lightweight sintered aggregate-based ash body was used along with polymer fibres based on polyolefin. It was suggested to use a few recipes that have been subjected to high temperature stress up to 1200 °C. Subsequently the suitability of the formula composition was verified by determining the essential characteristics visual assessment of the structure, density, compressive strength and flexural strength. The results point to the suitability of the proposed formulas, although this will be verified by setting other essential material characteristics.

Study of Alternative Raw Materials Parameters for Modification of Cement-Bonded Particleboards Composition

The cement-bonded particle boards can be used among other also with reconstructions of various types of buildings as a part of final surface treatment. The paper deals with partial results of the research focused on optimisation of cement-bonded particle board composition with alternative raw materials. Specifically it is analyzing of basic parameters of the waste originating during processing (modification of surface format and quality) of the boards. Upon results and findings a design of new formulas of cement-bonded particle boards is mentioned further, i.e. the composition modified with above stated waste. The outputs presented in the article form an important initial information source in the solved questions. In view of subsequent phases of the research it is a relatively essential and also it can be said a key phase.

Possibility of Using the Technical Hemp as a Filling Component in External Thermal-Insulation Composite Systems

Combining air or hydraulic binders with hemp shives, we can gain a set of new building materials. These products achieve excellent performance characteristics for durable, environmentally sustainable buildings. Being together, these products create natural composite building material that can be used to create insulating elements for walls, floors and roofs and also to create excellent thermal and acoustic properties of the buildings. Hemp insulation material is created by connection of technical hemp shives with a binder consisting of cement and calcium hydroxide. The production process may vary depending on whether the hemp is mineralized or not. It can be generally said that dry components should be mixed at first (binder and shives) and then water should be added. During the production, all components of insulating material must be perfectly mixed. The paper deals with the proposal and testing of new hemp insulation composites. Tests of the hemp insulation described in this paper are not typical representatives of the tests of insulation materials. Due to the doubts about the insulating properties of the proposed material, there was testing carried out in such the ways as if it was the filling material based on lightweight concretes.

Epoxy Resin Coatings Crystallization and Influence of Crystallinity on Shore Hardness and Tensile Properties

The epoxy resins are very popular and plentifully used synthetic resins. The bisphenol A-based (DGEBA) and bisphenol F-based epoxy resins (DGEBF) crystallization is phenomenon which is for that kind of resins natural. They are undercooled liquids and they tend to form the crystal structure at the ambient temperature. The subject of the research is to determine the effect of some crystallinity of DGEBF on chosen mechanical parameters. The degree of crystallinity was counted through the specific weights of crystallized bisphenol F-based epoxy resins. The prepared crystallized samples of DGEBA/DGEBF mixtures were mixed in appropriate weight ratio with isophorondiamine (IPD) based curing agent. Measured was hardness Shore D according to EN ISO 868 standard and tensile parameters according to EN ISO 527-1 standard. Furthermore, the effect of crystallinity on chosen mechanical parameters was observed. It was found out that with the higher crystallinity maximum tensile stress and hardness increased close to the standard parameters amorphous DGEBA and DGEBF.

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).

Issue of Epoxy-Based Coatings System Crystallization and Effect of Partial Crystallinity on Mechanical Parameters

Crystallization of bisphenol A-based and bisphenol F-based epoxy resins is the common property of the oligomers. However, producers of paints, coatings and other systems based on these epoxy resins are making efforts to slow down the crystallization process as much as possible. Thereby the shelf life is prolonged, while improving the competitiveness of their products. The main topic is the generalization of factors influencing the crystallization process of bisphenol A-based and bisphenol F-based epoxy resins, the validation of new approaches to possibility of influencing their crystallization process, and the determination of possibility of using a certain degree of crystallinity of bisphenol A-based and bisphenol F-based epoxy resins when preparing and producing paint and coating systems. Two types of the epoxy resins in formulations of paint and coating and other systems, namely: diglycidyl ether of bisphenol A (DGEBA) and diglycidyl ether of bisphenol F (DGEBF) were used. The tendency to crystallize not only for the pure epoxy resins, but also various mixtures with reactive diluents, fillers, etc. was determined according to the standard ISO 4895 Plastics – Liquid epoxy resins – Determination of tendency to crystallize. Furthermore, the crystallinity of individual samples was determined. The effectiveness of potentially active nucleating agents such as precipitated calcium carbonate, DGEBA, and DGEBF crystals, etc. was selected and tested according to the ISO 4895 standard. The effectiveness of potentially active admixtures with crystallization retardation effect was selected and tested according to the ISO 4895 standard. Selected samples of the epoxy resins with a specified degree of crystallinity were cured with 3-aminomethyl-3,5,5-trimethylcyclohexylamine (IPD) based crosslinking agent. Mechanical parameters such as compressive strength and flexural strength were determined. The influence of crystallinity on selected mechanical parameters was also observed.

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.

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.

Volume Stability of Polymer-Silicate Based Materials Exposed to High Temperatures

This paper presents research into analysing the volume stability of composite materials based on a polymer-cement matrix. The attention was paid to the influence of extreme temperatures shocks. Materials of modified composition were gradually exposed to extreme temperatures and then cooled in furnaces. Cooling was carried out by two different ways, i.e. slow and rapid. Emphasis was placed on the aggregate type used – fine lightweight and dense. Also available materials from alternative resources which have positive effect on thermal stability of composites based on silicate matrix were considered.