Adam Hubáček

Behavior of High Strength Concrete at High Temperatures

Concrete is considered as a non-combustible building material. However, at High-Performance Concrete (HPC) is due to its dense structure more likely to occur in explosive spalling. This results in lost of load bearing capacity function of concrete. This paper deals with design, production and testing of the cement-based concrete with the use of different fibers (polypropylene fibers and cellulose fibers). It also assesses the influence of high temperature on strength, visual changes of specimens, changes of surface and degradation of testing specimens due to heat loads according to normative heat curve and also according to hydrocarbon curve.

Optimization of Concrete with High Volume of Fly Ash

The demand for concrete structures grows worldwide, which raises fears about sustainable development of Portland cement production. Its carbon footprint is relatively small compared to alternative building materials, but still it is not negligible. This argument together with lower cost and possibility of utilization of material, which would otherwise be disposed as waste, lead the research towards concrete with higher content of Portland cement replaced with fly ash. The experiment is divided into two parts: the first one determines influence of high volume fly ash replacement of Portland cement on behavior and properties of cement paste and mortar. The second part optimizes composition of concrete mix, in particular the granulometry of the cement-fly ash system in order to achieve maximal possible values of mechanical properties at high dosage of fly ash.

Systems and Regulations for Design and Application of Water-Tight Concrete Structures

The paper focuses on the problems of concrete for water-tight concrete structure and with systém and regulations for design and application of these structures. The theme is currently quite topical in the Czech Republic and abroad. The accent is put particularly on the requirements and properties of fresh concrete or self-compacting concrete for manufacture of specific concrete structures. Properties of hardened concrete will be also observed; in particular compressive strength, resistance to pressure water, durability and other parameters.

Possibilities of Increasing the Durability of Concrete Products by Technologies Based on Surface Hardening

Requirements of the quality of surface have increased recently for vibro-pressed concrete elements. As a consequence, there are new concrete products available with specially treated visual side - surface is coated with an impregnating paint and then hardened by infrared or ultraviolet light.The paper summarizes current knowledge of vibro-pressed concrete elements with surface treated in mentioned way. The focus is on description and effectiveness of individual methods, hardening principles and further possible treatments of surface of concrete aiming at higher durability of concrete. Observed parameters and properties of vibro-pressed concrete elements include resistance of surface to water and chemical de-icers, water absorbing capacity, resistance to wear, slip resistance and reduction of risk of efflorescence.

Water-Tight Concrete Constructions and Directives for their Design and Realization

The paper describes problems of water-tight concrete constructions, their design, manufacture and testing of quality in accordance with regulations and directives used in the Czech Republic and abroad. Current knowledge of water-tight constructions and water-tight concrete imply that main focus is on problems of use of water-tight concrete for construction of so-called white bath and preventing crack formation in concrete. Laboratory work is focused mainly on design of concrete based on individual regulations. Subsequently, influence of various types of cement and additions partly replacing cement on properties of water-tight concrete is examined. Research of heat development during hydration at early stages of maturing is and inseparable part of the experimental work, as well as development of compressive strength, water-tightness and frost resistance of concrete

Properties of Vibro Compacted and Pressed Concrete Products with Varnished Surface

Technology of so-called vibro compacted pressed concrete is currently used inter alia for manufacture of concrete products like concrete paving blocks, slabs, curbs or walling elements. Particularly wear layers of products for paving have recently been improved by special methods and technologies. The paper summarizes current knowledge of vibro compacted pressed concrete products with surface finish treated with hardened varnish. Main focus is on description of individual methods of finalizing wear layers of such products.

Research of Fire Resistance of Tunnel Lining Concrete

The article is involved with study of fire resistance of concrete for tunnel linings. It summarises the problems of present knowledge of concrete resistance in tunnels and deals with behaviour of concrete particular parts at exposure to high temperatures. Further possibilities of fire resistance improvement for production of concretes together with fire prevention are described in this paper.

Concrete with High Content of Fly Ash Intended for Constructions with Long Durability

The article deals with theme of high fly ash content concretes intended for long life constructions. Considering the still growing consumption of fly ash in construction concretes it is a live theme in the Czech Republic and abroad as well. The emphasis will be laid namely on characteristics and requirements for fresh concrete intended for construction of these specific concrete constructions. They are for instance waterproof constructions, tunnel linings, concretes for bridge and road constructions etc. Also the hardened concrete properties like compressive strength, resistance to pressure water, durability and further necessary parameters for obtainment of required properties of these concretes will be monitored.

Cement Based Heat-Insulating Materials for Use in Floor Constructions

Many architects, designers and builders struggle with the ongoing problem of how to fill the space between the load bearing foundations / ceiling land the flooring structure in the easiest and cheapest way while still retaining the optimum heating and sound insulating properties. In this age of hi-tech and plentiful amounts of construction materials, it is very difficult to focus on the market. On paper, very similar products from natural or artificially produced materials can be delivered to the construction site in a hardened state, most frequently in the form of boards or granulate or produced directly on-site or near a concrete plant and transported to for placement in a liquid state. This areas does concerns both new residential or industrial objects, as we as old objects which are waiting for reconstruction. During the project solution, various mixtures were designed that use the cement mortar and filler as a binder in the form of technical foam, expanded clay, vermiculite, perlite and hemp shives, so that when fresh the density does not exceed 1.400 kg / m3 and the materials can then be used as heat-insulating material in the flooring construction.

Plastic Shrinkage of Concrete – Measurement and Method for its Reducing

The paper touches on the issue of plastic shrinkage of concrete and cement mortars. In this connection, the volume changes were monitored batch of studied depending on the intensity of surface evaporation. Volume changes were measured on a prototype contactless gauge. The article outlines the possibility of suppressing plastic shrinkage by adding a polymer fibre reinforcement possibly coated fibres.