Jaroslava Koťátková

Concrete and cement composites used for radioactive waste deposition

This review article presents the current state-of-knowledge of the use of cementitious materials for radioactive waste disposal. An overview of radwaste management processes with respect to the classification of the waste type is given. The application of cementitious materials for waste disposal is divided into two main lines: i) as a matrix for direct immobilization of treated waste form; and ii) as an engineered barrier of secondary protection in the form of concrete or grout. In the first part the immobilization mechanisms of the waste by cement hydration products is briefly described and an up-to date knowledge about the performance of different cementitious materials is given, including both traditional cements and alternative binder systems. The advantages, disadvantages as well as gaps in the base of information in relation to individual materials are stated. The following part of the article is aimed at description of multi-barrier systems for intermediate level waste repositories. It provides examples of proposed concepts by countries with advanced waste management programmes. In the paper summary, the good knowledge of the material durability due to its vast experience from civil engineering is highlighted however with the urge for specific approach during design and construction of a repository in terms of stringent safety requirements.

The Effect of Elevated Temperatures and Nuclear Radiation on the Properties of Biological Shielding Concrete

The paper reviews the so far known information about the properties of biological shielding concrete used in the containment vessel of nuclear power plants (NPP) and its behaviour when exposed to radiation. The damage of concrete caused by neutron and gamma radiation as well as by the accompanying generation of heat is described. However, there is not enough data for the proper evaluation of the negative impacts and further research is needed.

Hygric Properties of HPC with Natural Pozzolana

The water vapour transport and the liquid water transport of high performance concrete (HPC) with the content of natural pozzolana are the described in this paper. Studied properties are presented by means of water vapour diffusion coefficient, water vapour diffusion resistance factor and absorption coefficient respectively. The natural pozzolana (NP), namely natural zeolite, is used as supplementary cementitious material which affects the durability properties of the end product. The obtained results revealed the effectiveness of NP in the terms of both studied properties when used in small amounts, i.e. at about 20% of cement weight. On the other hand substitutions higher than 40% result in worsening of the resistance of the concrete to water and water vapour ingress and its movement trough the material.

Evaluation of Crack Formation in Concrete and Basalt Specimens under Cyclic Uniaxial Load Using Acoustic Emission and Computed X-Ray Tomography

The paper discusses the use of acoustic emission, stress-memory effect, and X-ray computed microtomography (μST) to detect the onset of destruction of specimens of concrete and basalt which are widely used in construction. It is shown that the most informative parameter is acoustic emission activity based on which the onset of the formation of a main crack can be identified. The geometry of the crack is determined using computed X-ray tomography.

Comparison of the Effects of Different Pozzolana on the Properties of Self-Compacting Concrete

The article compares the basic physical, mechanical and both liquid water and water vapour transport properties of self-compacting concrete containing different pozzolanic admixtures. Limestone, fly ash and metakaolin were used. A concrete mixture without any pozzolana was also manufactured as a reference. The best values of studied properties were recorded for the metakaolin concrete.

Differences in the Mechanical Properties of Lightweight Refractory Cementitious Composites Reinforced by Various Types of Fibers

Development of new composite materials is the worldwide extremely progressive branch of engineering activity. Composite materials are applied in many industries. The principle of composite materials is a combination of different materials providing an entirely new material with specific properties. Fiber-reinforced composites rank to the most frequently used composites because of their suitable mechanical properties. There were studied mechanical properties of fibre reinforced cementitious composites (FRCC) exposed to high temperatures of 600 °C and 1000 °C in the paper. For the production of refractory FRCC were used aluminous cement Secar®71 with 70 % of Al2O3. Various composites differed in the used type of fibers - basalt, carbon and ceramic fibres were applied in doses of 2 % by volume. For the experimental program were prepared prismatic specimens with the total dimensions of 40 × 40 × 160 mm3 and cured for 28 days in humid environment. Residual bulk density, flexural and compressive strength were investigated in the performed experimental program. The results showed the positive effect of the fibers used in refractory composition and the dependence on the length of the used fibers.

RESIDUAL PROPERTIES OF FIBER-REINFORCED REFRACTORY COMPOSITES WITH A FIRECLAY FILLER

The aim of our study was to develop a composite material for industrial use that is resistant to the effect of high temperatures. The binder system based on aluminous cement was modified by adding finely-ground ceramic powder and metakaolin to reduce costs and also to reduce adverse effects on the environment due to high energy consumption for cement production. Additives were applied as a partial aluminous cement replacement in doses of 10, 20 and 30% by weight. The composites were evaluated on the basis of their mechanical properties and their bulk density after gradual temperature loading. The influence of basalt fibers and modifications to the binder system were studied at the same time. Basalt fibers were applied in doses of 0.5% and 2.0% by volume. The results confirmed the potential of the mineral additives studied here for practical applications, taking into account the residual mechanical parameters after thermal loading. The addition of ceramic powder reduced the bulk density by 5% for each 10% of cement substitution, but the residual values were very similar. The bulk density and the compressive strength were reduced when basalt fibers were applied, and the flexural strength was significantly increased in proportion to the fiber dosages. Metakaolin seems to be a more suitable additive than the ceramic powder that was applied here, because there was a significant increase in the mechanical parameters and also in the residual values of all properties that were studied.

Effects of High Temperature Treatment on the Mechanical Properties of Basalt Fiber Reinforced Aluminous Composites

Article presents the results of an experimental program aimed at investigating of the mechanical properties of composites based on aluminous cement with the addition of basalt fibres, which could be used in the manufacture of components resistant to high temperatures, including the retention of mechanical properties. Silica composites based on Portland cement and silica aggregates are not able to resist the effects of high temperatures [1], therefore a heat resistant mixtures in this experiment includes only components that are able to resist the effects of high temperatures.

Fracture and Mechanical Properties of Fire Resistant Fibre Composites Containing Fine Ground Ceramic Powder

Significant advances in the field of building materials leads to increasingly frequent enforcement of these high performance materials in real constructions. Efforts to maximize the efficient use of non-renewable resources and especially energy-intensive materials lead to efforts to achieve maximum efficiency and usability [. Paper presents results of an experimental program focused on development of fire-resistance composites based on aluminous cement with fine ground ceramic powder (FGCP). Studied fibre composites were loaded by temperature 600 °C and 1000 °C. The influence of applied thermal load on composites was evaluated by means of fracture energy, compressive strength, bending strength and modulus of elasticity in bending.

The effect of hydrothermal curing on residual mechanical properties of refractory concrete

This paper describes the influence of hydrothermal curing conditions on final mechanical properties of refractory fibre-reinforced cement composite. The effect of age of specimens, when the hydrothermal curing process started, was investigated in the point of view of best achieved mechanical properties. The age of 24, 30, 36, 42 and 48 hours after fist contact water with cement was tested. The curing conditions in autoclave device were set on 150 °C and 0.45 MPa in 100% humidity environment. Hydrothermally cured specimens together with reference specimens cured in laboratory conditions were exposed to the action of elevated temperature on level 600°C and 1000°C for three hours. The dynamic modulus of elasticity, flexural strength, compressive strength and bulk density were measured to quantify the benefit of hydrothermal curing. Used refractory composite consisted of natural basalt aggregate, aluminous cement, fine ground ceramic powder, water with plasticizer and basalt fibres. All parameters were invest...