No abstract

To reduce water absorption of cement concretes resort to hydrophobization by introducing special additives in the manufacturing process of the product. In the study of liquid corrosion of hydrophobized cement concretes of the W4, W6 and W8 waterproofness grades in media of various degrees of aggressiveness, the terms for achieving a state close to the equilibrium concentration of calcium cations in the solution were established. Based on the experimental data on the liquid corrosion of cement concretes of various grades in terms of water resistance, the optimum amount of hydrophobizing calcium stearate additive was determined, which is sufficient to prevent corrosion damage in concrete, depending on the degree of aggressiveness of the medium. Tests of strength characteristics of hydrophobized cement concretes of the W4, W6 and W8 waterproof grades were carried out. It is established that when alkali and alkaline-earth stearates are introduced into concrete as hydrophobic additives, its strength is significantly increased compared to non-hydrophobized concrete samples. Some special cases of changes in the mass conductivity coefficient during colmatation of hydrophobized cement concretes of the W4, W6 and W8 waterproof grades are considered and graphically illustrated. Profiles of changes in the rate of colmatation and the thickness of the colmatant layer for cement concretes with and without hydrophobizing additives are presented. The profiles show that over time there is a weakening of the mass flow, which is obviously associated with an increase in the colmatant layer. The rate of colmatation is also reduced due to the fact that the layer of colmatant partially or completely clogged the pores and prevents further penetration of the aggressive medium deep into the concrete.

The contribution is focused on investigating the heat transfer via natural convection which originated as an effect of changed air density by heating the horizontal sample in the area given. For this research we used samples of a new material made in the Russian Federation -the foam concrete which was reinforced by PET fibres. The samples were heated by an electric heating device from the bottom. The temperature fields originating above the horizontal sample surface were visualised by means of the holographic interferometric contactless method in real time. The holographic interferograms of the temperature field were analysed, and then the local heat transfer parameters were calculated: the heat transfer coefficient α, and the heat conductivity coefficient λ.

No abstract