Abstract: This paper investigates the influence of different types of silica fume on the crystallization process of medium density calcium silicate based products. The products are formed by a new technology that consists of two steps. In the first step, a mixture containing calcium silicate hydrates (C-S-H) is formed by reaction of lime with special silicas at temperatures below 100°C. This mixture is then molded into boards by a filter-pressing technique. In the second step, the boards are treated in hydrothermal conditions enabling the conversion of the C-S-H into important contents of xonotlite (Ca6Si6O17(OH)2); this is the most stable calcium silicate hydrate phase at high temperatures. In order to make C-S-H in pressure less conditions, the use of reactive forms of silica is required. In this work we used silica fume as reactive silica. To understand the influence of the silica fume on the formation of xonotlite, several properties were studied, such as particle size, purity and specific surface area (BET). It was found that the particle size distribution and degree of agglomeration for the silica fume were the most important properties. A proper dispersion technique must be applied in order to break the silica fume agglomerates, forming particles small enough to react with dissolved lime and to form C-S-H phases that are able to be converted into xonotlite under hydrothermal conditions. Finally, it was also found that the formation of xonotlite is favored by the use of high purity silica fume.
Abstract: The research is devoted to foamed concrete, which is a very perspective material in the modern construction industry. Foamed concrete is lightweight concrete and is in accordance with compressive strength and the use of it: constructive, constructive-insulating and lightweight foamed concrete.
Abstract: The goal of this work concerns the synthesis of a binder for restoration purposes that is physically and chemically compatible with dolomitic Roman cement, a historical binder used for the construction of significant architectural heritage objects in the 19th and 20th centuries. Dolomitic marlstone, the traditional raw material of dolomitic Roman cement, is not being obtained anymore and it is also hard to achieve a constant chemical composition. To address these issues, the experimental synthesis of a low temperature hydraulic binder using locally sourced raw materials, namely dolomite flour and clay, was performed. The developed synthesis technology provides economic and ecological advantages compared to other similar materials, such as lime with pozzolan additive, lime and cement mixtures and magnesium oxychloride cements. The raw material, dolomite flour, is a by–product in the manufacturing process; furthermore, the low firing temperature (800 °C) reduces the power consumption required to obtain the binder.The aim of the work is determination of porosity-related physical characteristics of dolomitic binder that is synthesized by using manufacturing by-product – dolomite flour – as basic raw material to evaluate it’s suitability for restoration purposes.
Abstract: Steel moulds in the form of a rigid cubical shell were developed in order to investigate single steel fibre pull-out resistance in concrete with expansive additive under restrained hardening conditions. The cubical shell (100 x 100 x 100 mm) with wall thickness of 5 mm was designed with two openings – a small 4 mm hole for fibre embedment in concrete and a larger opening for filling the concrete. Standard beam (100 x 100 x 400 mm) and cube (150 x 150 x 150 mm) samples were also manufactured and hardened under and without restrained conditions, where the restraint was realised by rigid standard steel moulds. All the restrained conditions realized by either the developed cubical steel shell (for single fibre pull-out) or existing beam and cube moulds simulate internal (from steel fibres in concrete) and external (from friction against sub-base) restraints that hinder expansion of the concrete due to the use of special expansive additives in a flooring slab structure installed on ground. Samples with a single hooked-end steel fibre (50 mm long and 0.75 mm in diameter), with and without expansive additive were manufactured and tested in the developed mould geometry. The results show that restrained expansion in concrete with expansive additives positively affects concrete compressive strength, single fibre pull-out and flexural behaviour. Concrete compressive strength increases by 7.5 %, single fibre delamination resistance increases by 24 %, the peak pull-out load by 10.8 % while the flexural strength increases by 3.1 %.
Abstract: The normative documents of Ukraine (DBN V.1.1.7 ̶ 2016)  establish that the limit of fire resistance of reinforced-concrete building structures is determined by the calculation method or by fire tests, and shall be at least 45 minutes. Taking into account the modern construction technologies, namely, the reduction of the section of the main building reinforced-concrete structures, it is expedient to use fire-retardant coatings to provide the necessary fire resistance limit.
Abstract: A foamed alkali-activated material (FAAM), based on tungsten mining waste (TMW) and waste glass (WG) was fabricated by using chemical foaming and pre-formed foaming methods. The compressive strength and density of the FAAM were investigated in terms of different parameters of formulation including foaming method, foam catalyzing agent and stabilizing agent. A FAAM made with aluminium powder consisted of smaller open macropores and exhibited higher compressive strength in comparison with organic surfactant counterparts which formed larger closed macropores. The final aluminium powder based FAAM reached a 7-day compressive strength in excess of 3 MPa and a density below 0.7 g/cm3. The incorporation of an appropriate amount of foam stabilizer led to a further 15% increase in compressive strength, 6% reduction in density and a thermal conductivity below 0.1 W/mK.
Abstract: Natural radionuclides K-40, and Th-232, U-238 (Ra-226) decay chain products contained in building materials are the main source of radiation dose received by population and the only source of indoor radiation exposure. Present work contains results of the study of natural radionuclide activity level in clay, clay ceramics and silica bricks used in Latvia. Obtained data show that radionuclide content in different clay products can differ up to five times. However, determined activity index values for all tested materials, except fireproof bricks, were below radionuclide concentration level permitted by EU and Latvian national regulations. Comparison with analogous data from other North European and Baltic countries shows that average concentrations of natural radionuclides and activity index values for clay and clay bricks used in Latvia are on the same level as in other countries, except Sweden.
Abstract: A modern method of processing steel parts by ion-plasma sputtering in vacuum is proposed as a solution to the problem of friction and wear. An ion-plasma coating based on Ti-Cu has been developed. Such parameters as microhardness, roughness, friction coefficient of the intermetallic, conglomerate and nitride coatings have been studied
Abstract: Thin films of ZnO, ZnO coated with TiO2 and ZnO modified with titania were prepared by using simple spray pyrolysis of zinc and titanium containing solutions. The photicatalytic activity of the obtained films was determined by degradation of MB solution under UV and simulated solar illumination. The photocatalytic activity of ZnO/TiO2 films depended on the content of titania, substrate surface roughness, surface area and deposition cycles. The highest activity under simulated solar light was detected for ZnO films containing 3 wt.% of TiO2.