Applied Mechanics and Materials Vols. 725-726

Abstract: The article introduces the results of the experimental research of the duration of the first heating of concrete at temperatures of +90° and +150°C causing the maximum reduction of its strength during the subsequent axial compression.

Abstract: Compounds were developed and properties studied of the composites on gypsum binding agent and light filling materials, exfoliated vermiculate and perlite providing high fire resistance to mortars on their base. The conducted selection of compounds with the use of a number of non-flammable fiber additives (fiberglass, chrysotile asbestos fiber) showed that the compounds with fiberglass additives had the biggest design quality ratio. The degree of influence of high-speed mortar mixture mixing on its properties was determined. Mixing speed increase up to 600 rpm allowed increasing of the design quality ratio for composites in average by 7-10%. Positive influence of fine-dispersed mineral additives (Cambrian loam, liquid perlite) on increase of retained strength of fire-resistant composites and screens after high-temperature tests was detected. Behaviour of fragments of fire-resistant screens on the basis of developed composites depending on their thickness and composition was studied at test unit providing temperature increase up to 1100°С within 180 minutes.

Abstract: The aim of the present research was to determine special features of hydration process of two commercial microfine cements compared to CEM I 42.5N cement with similar mineralogical composition. The influence of cement fineness and composition on the hydration process was investigated by isothermal calorimetry of cement pastes and quantitative X-ray powder diffraction of hydration products at 1, 3, 7, 14 and 28 days.

Abstract: The most popular grout solutions are based on the application of cement-based materials. They are most frequently being used for grouting of prestressing tendons. Besides, there are some kinds of grease or wax having a good flexibility of the coat layer, while providing adjustability of prestressing force inside strands. Main objective of the paper is to explore the conditions and review other relevant aspects in applying injection gel for covering the prestressing tendons.

Abstract: The article tackles a mechanism of vibration effect on the construction mixes in two representations: corpuscular and phenomenological. It is known that the construction mixes belong to heterogeneous systems, where processes take place in case of vibration effect that are characterized by tixotropy property, i.е. inversability of interaction forces between the particles in case of imposition and removal of mechanical effects. It has been stated that it is more reasonable to find the qualitative and quantitative relations of various processes (phenomena) in the form of generalized relationships obtained by the methods of similarity theory and dimensions of quantity. Presented are the criterial dependencies of changing efficient viscosity of mixes under effect of vibration from the process working parameters. Proposed are the modified Reynolds and Froude criteria for the mixes vibrating processes. It is reasonable to use the method of object internal vibratory protection when designing the vibratory agitation equipment helping reduce the level of vibration influence on the environment on the one hand, and use the vibratory effects on the material being processed to a maximum extent, on the other hand. In order to implement this method it is proposed to use the equalized eccentric vibration exciters. A number of industrial samples of vibration mixers have been presented.

Abstract: Fly ash represents a residue that occurs as a product of burning finely milled particles of coal in thermal power plants. The fly ash in the construction of embankments in road construction can be used with or without the addition of binders. For the construction of embankment from the ashes, aside embankments (trapezoid shape) are placed. Justification of this study is the fact that so huge amounts of this material are left aside, while there are great possibilities for using of natural materials in the construction of roads.

Abstract: Finite-element modeling of reinforced concrete structure fracture process was carried out using models of nonlinear concrete with damage accumulation. Mechanism of cracks initiation in reinforced concrete structures was ascertained and kinetics of cracks growing in concrete due to corrosion of rebars was obtained. Fracture processes of road bridge fragment and railway bridge ballastless bed under corrosion of rebars was simulated.

Abstract: Geogrids are designed to be a support structure in geotechnical and civil engineering applications. Geogrids manufactured with the extrusion of a polymer must posses the necessary level of tensile strength and low creep. In this paper, a study on application of stepped isothermal method for prediction of creep behavior of extruded polypropylene geogrid used for soil reinforcement was carried out. On the basis of the obtained data, a possibility of creep prediction for structures with geosynthetics for periods of time much longer than experimental measurements was demonstrated.

Abstract: This study deals with design and evaluation of mechanical properties of the I-shape beam made from plain weave fiberglass fabric and epoxy resin. The possibility of production of I-beam with fiberglass laminate stitched layers has been demonstrated and the prototype of glass-fibre-reinforced epoxy I-beam was manufactured. Tensile properties of fiberglass of manufactured samples were investigated. The results showed that the investigated fiberglass composite has a sufficiently high tensile strength comparable to steel. However, the modulus of elasticity of the samples is quite low.

Abstract: Formulation of the model suitable for the description of the full material deformation diagram is considered, with axial compression applied, and a loosening component added to elastic and plastic deformation. The materials involved are initially heterogeneous environments like rocks and artificial construction materials, like concrete. Such materials, being in a stationary state, stable for small disturbances, can be interpreted as dissipative structures after the limit of elasticity is reached. The deformation and destruction processes are analysed as instability hierarchy, resulting from self-organization. Methods of mathematical catastrophe theory are applied for the model construction. The energy state function is presented as the sum of the potential function, responsible for reversible deformations and disturbances. The latter involves an imperfection parameter (a controlling one), connected with damageability and responsible for the structurization process. The state equation is obtained by energy function minimization on the order parameter and is supplemented with the kinetic equation for the imperfection parameter. The synergetic methods are shown to be advantageous for the problems of formulating physically well-grounded nonlinear defining equations.