Petr Novosad

Unfoldings of bounded hybrid petri nets

The unfolding is a useful partial-order based method for analysis and verification of the Petri net properties. This technique can cope well with the so-called state space explosion problem, especially for the Petri nets with a lot of concurrency. The paper formalizes the concept of the unfolding for bounded hybrid Petri nets and introduces the algorithm for its computing.

Mixing of Different Particle-Size Fractions of Fly Ash to Increase its Activity in Cement Composites

Fly ash residue from coal burning process in power plants have been used as an active additive in concrete since middle of nineteenth century. Nowadays, we are trying to maximize its reactivity in cement composites by several methods. One of the methods is mechanical activation by mixing several size fractions to reach ideal particle size distribution. Ideal particle size distribution of fine components in cement composites helps to reach maximal compactness and thus increases strength and durability. In this paper we present results of compressive and tensile strength of cement-fly ash mortars with mixing 3 size fractions origins in 3 electrostatic precipitators from power plant Tušimice. Fly ashes from 1st precipitator, 2nd precipitator and 3rd precipitator were mixed with ration 10:4:1, 5:4:1 a 0:4:1.

Comparison of Automated Concrete Shrinkage Measurement Methods

Volumetric changes are deformation properties of concrete that are caused by external or internal forces and can be reversible or irreversible. Relatively significant and irreversible volumetric changes occur during the hydration of clinker minerals during the first stages concrete setting and hardening. From the “real-world” point of view, the volumetric changes associated with drying are the most important – these take place when the leftover mixing water evaporates. The current legislation addresses the volumetric changes of concrete relatively briefly and the calculations of the assumed autogenous shrinkage according to Eurocode 2 are generally related only to the concrete’s strength class, not to the composition of the concrete mixture. The principle of determination of volumetric changes is classified by the standard ČSN 73 1320, which requires the measuring devices with an accuracy of at least 1∙10-5 of expected proportional deformation. In this experiment, the volumetric changes of the concrete will be monitored by two different measurement methods. Several different test mixtures will be prepared to monitor these changes continuously with an automatic measuring device. In one case, the measurement will take place from the point of fresh concrete and, in the case of the others, immediately after the acquisition of the handling strength, i.e. from the age of 1 day.

Modification of Technological Properties of Laboratory Premixes

Sulfur binders belong to the group of airbrushes. They can therefore only harden and harden in the air. The main raw material, gypsum, can be mined in several places in the world. Even in the Czech Republic there is a deposit of natural gypsum in Kobeřice u Opavy. [5] In spite of this fact, we use mostly industrially produced gypsies, because the natural gypsum deposit has only very limited capacity. The Energogypsum, produced in the Czech Republic by ČEZ Energetické Produkty s.r.o., is the waste product of flue gas desulphurization using the wet limestone scrubbing method. Like the chemosynthesis, it is characterized by its high purity (the content of pure CaSO4 2 H2O is at least 90%). The one in the Czech Republic is manufactured by Precheza, a.s. in Přerov. The use of sulphate binders is varied. A better form in the form of alpha plaster is used to produce self-leveling floors and dentistry. Less-quality beta gypsum has a larger application. From it we can produce both gypsum and monolithic partitions. We can also use it for the production of plasterboard and gypsum fiber boards and, last but not least, as internal plasters for its good fire performance. [1] Plasters are being prepared today in two different ways. Firstly, they are still prepared in the original outpatient way directly on the building from individual raw materials, but they are also industrially produced in the form of dry mortar mixtures, which are mixed on the building only with water. The second way is more progressive with the fact that nowadays it is even more widespread. For many builders, however, it remains financially scarce. That is why we have recently begun to find a compromise solution that will satisfy both the technical and the economic ones. This is the development of the so-called binder premixes, ie the industrially produced mixed binder, which is mixed only with sand and water on the site. The situation on our market shows that the recently developed special premix for lime-cement plaster and mortar mixtures is very positive for the building public and therefore the effort is to generalize this mixed mortar in the production raw material base and, in addition, to develop its analogue based on sulphate binder. [2]

Verification of Rheological Properties of Self-Compacting Concrete with Reinforcement

The paper presents results of mechanical and physical tests of self-compacting concrete with fibre reinforcement. Self-compacting concretes belong to special types of concretes with filling ability without invoking external dynamic forces. Especially high storage rate and concrete access even in densely stored reinforcement, high homogenisation, low water-cement ratio and exclusion of external vibrations are benefits of SCC concretes. The highest risks that must be considered when designing this type of the concretes are their resistance to segregation, sedimentation, blocking and bleeding. Several SCC formulas with two types of fibres (steel, polypropylene) were designed and compared and the effects of fibres reinforcement on concrete selected properties were monitored in fresh and hardened condition, too.

Failure of Concrete at High Temperatures - The Influence of the Type of Cement

Experimental work verifies behavior of concrete with various types of cement and aggregate when exposed to high temperatures. Concrete samples differed in the aggregate used (two modes - basalt aggregates, lightweight aggregates), combined with four types of cement (CEM I 42.5 R – Mokrá Czech Republic, CEM II/B-M (S-LL) 32.5 R – Mokrá Czech Republic, CEM II/B-S 32.5 R – Cemex Czech Republic, CEM III/B 32.5 N-SV – Cemex Czech Republic). Properties were determined before and after thermal loading. The aim of the presented experiments was to verify behavior of different types of cement in concrete at high temperatures and the effect of various types of cement for subsequent damage concrete samples after exposure to high temperatures.

Testing of Action of Direct Flame on Concrete

The paper states results of experimental exposition of concrete test specimens to direct flame. Concrete test specimens made from various mixtures differing in the type of aggregate, binder, dispersed reinforcement, and technological procedure were subjected to thermal load. Physicomechanical and other properties of all test specimens were tested before exposition to open flame: density, compressive strength, flexural strength, moisture content, and surface appearance. The specimens were visually observed during exposition to open flame and changes were recorded. Exposed surface was photographically documented before thermal load and at 10-minute intervals. Development of temperature of the specimens was documented with a thermocamera. After exposition to thermal load and cooling down, concrete specimens were visually observed, network of cracks was photographically documented, and maximal depth of spalled area was measured.

Algorithm for Computing Unfoldings of Unbounded Hybrid Petri Nets

The paper formalizes the concept of the unfolding for unbounded hybrid Petri nets and introduces the algorithm for its computing. The unfolding is a useful partial-order based method for analysis and verification of the Petri net properties. This technique can cope well with the so-called state space explosion problem, especially for the Petri nets with a lot of concurrency.

Alkali-Activated Matrix Based on Metakaoline with Lightweight Aggregate

The paper focuses on design and verification of mix-design of lightweight concrete with alkali-activated matrix with lightweight aggregate Liapor. Alkali-activated matrix was designed on the basis of ground metakaoline and micronized limestone. Mixes of concrete with alkali-activated matrix and lightweight porous aggregate Liapor of size fraction 8 mm were designed and their rheological and physico-mechanical properties were tested. To reduce shrinkage and to increase resistance to high temperatures, dispersed polypropylene fiber reinforcement was used and testing specimens made from this concrete with alkali-activated matrix were exposed to thermal load and tested.

Functional Vibro Pressed Pavement with Ecological Benefits

The paper describes results of functional tests of photo catalytic materials directly in matrix of prefabricated vibro pressed pavement blocks. Resulting surfaces of photo catalytic concrete products were tested with respect to conversion of NOx and surface was analyzed with Scanning Electron Microscope (SEM), so called element maps were elaborated by means of Energy Dispersive Spectroscopy (EDS).