Materials Science Forum Vol. 1070

Abstract: The influence of the test specimen moulding method on the physical and mechanical properties and durability of hardened concrete was analysed, when the tests specimens were cast in two different ways: a) on construction site using wet spray type sprayed concrete technology and moulds (SCT method); b) in the laboratory using a vibrating table and moulds (NSCT method). The following properties of hardened concrete were analysed in comparison: density, compressive strength, water permeability, the depth of water penetration under pressure, and frost resistance of concrete. The prediction dependencies were created that can be used to calculate the values of density and compressive strength of the test specimens prepared using the SCT method when the values of density and compressive strength for the same concrete composition are known from the tests carried out in the laboratory, i.e. test specimens prepared using the NSCT method. The findings of this study show that in the case of using the SCT method, the addition of the accelerator into the concrete mixture on the building site has no significant effect on the formation of the test specimen structure compared to the concrete of the same composition without the accelerator.

Abstract: In current concrete practice, several types of air entraining admixtures are used. These admixtures aim to improve the durability of concrete in aggressive exposure conditions caused by negative temperatures in combination with salts. The current article attempts to describe the types actually used, namely, synthetic tensides and natural resins and to also compare their effect on the durability of physical and mechanical parameters. With these admixtures, air entrained concrete with different amounts of air content in the concrete are designed. Furthermore, the article describes methods for determining the parameters of air entrained concrete, as well as their advantages, disadvantages and their evaluation.

Abstract: This paper deals with the effect of combining high temperature and fluidised fly ash, not only on the compressive strength of concrete but also on the determination of the dynamic modulus of concrete test bodies. The use of high-temperature fly ash in concrete mixes has become commonplace. However, the demand for this type of active admixture has increased to such an extent that it currently far exceeds supply, especially after selective non-catalytic nitrogen oxide reduction (SNCR) was introduced and the switch to low-temperature combustion units. This lack of supply makes it necessary to look for other alternative solutions to this situation. The partial replacement of high-temperature fly ash with fluidised bed fly ash appears to be a possible solution.

Abstract: The production of lightweight concrete is mainly carried out in the traditional way using lightweight ceramic aggregates. The aim of the pilot research was to verify the possibility of producing lightweight concrete based on artificial aggregate in the form of agglomerated aggregate from high temperature fly ash. A representative of such aggregate is the artificial aggregate referred to as aploporite. This aggregate is characterised by comparable grain strength to ceramic aggregates but, on the other hand, has a relatively high absorption rate of up to 30 %. Concrete formulations with up to 50% replacement of natural aggregate by aploporite have been proposed in order to achieve the volumetric weights characteristic of lightweight concrete. The results obtained confirmed that it is possible to produce lightweight concrete with this aggregate and to achieve strengths comparable to those of ordinary concrete.

Abstract: The present paper deals with the determination of the mechanical and physical properties of the heavyweight concrete formulation used in the shielding construction of the reactor casing power plant. The recipe includes the use of baryte and cast-iron crumbs as fillers for the preparation of heavyweight concrete. The binder paste was obtained using CEM I 42.5 R with w/c ratio = 0.44 and a lignosulfonate-based plasticizer prepared according to the used Ralentol plasticizer's standard requirements, which is currently no more produced. The result of the concrete slump according to the S -cone was S1 (1 cm slump). The bulk density of fresh and hardened concrete was over 4000 kg m^-3. The compressive strength at 28 days exceeds 80 N mm^-2 and the flexural strength is 4 N mm^-2. The modulus of elasticity is 40 GN m^-2. The shrinkage of concrete is 0.52 ‰. The weight loss due to shrinkage rises to almost 1.3 %. The thermal properties of the heavyweight concrete are as follows: the thermal conductivity λ is 2.2 W m^-1 K^-1; the thermal resistance R for thickness d = 1 m is 0.44 m² K W^-1; volume heat capacity c_ρ rises to almost 2 J m^-3 K^-1 and thermal diffusivity a 10^-6 drops to 1,15 m² s^-1.

Abstract: Reducing waste from industrial production is a major issue of our time. The concrete industry is looking for ways to deal with the fresh concrete slurry waste that is produced during production. Worldwide, this sludge is often filtered and used for further application. However, in many concrete plants, such a facility is not economically beneficial and therefore solutions are being looked for to recover the slurry water without major modifications. This article deals with the recovery of sludge water in its fresh state immediately after its generation from concrete production. The tested concrete contains potable water replacement at 50 and 100% by weight. The resulting slump test decreased with increasing sludge water, whereas the resulting compressive strength of these concretes was higher than the concrete with fresh water.