Research Into Structure Formation and Properties of the Fiber­reinforced Aerated Concrete Obtained by the Non­autoclaved Hardening

We have investigated the influence of the ratio cement:fly-ash and the temperature of mixing water on the properties of aerated concrete mixes and aerated concrete. It was established that the rational cement-fly ash ratio is 1:1; the mixing water temperature is 40 °C. Experimental research confirmed that the introduction of waste from salt processing and metakaolin to the formulation of binding compositions leads to the formation, rather than the metastable hexagonal calcium hydro-aluminates, of the stable compounds in the structure of partitions between pores of the hydrocalumite and hydrocarboaluminate type. That allowed the targeted structure formation of partitions between pores of the non-autoclaved aerated concrete, which improves the density of partitions and the strength of aerated concrete. It is shown that the introduction of polypropylene fibers to composition of aerated concrete does not affect the kinetics of swelling of the aerated concrete array. However, the introduction of polypropylene fibers improves the strength of aerated concrete based on the modified binding composition containing metakaolin by 47 %, the modified binding composition containing carbonate-containing waste ‒ by 32 %. For the aerated concrete of the В1.5–В2 class of strength, at a density within 615‒625 kg/m3, the estimated coefficient of thermal conductivity is 0.16 W/(m∙K), which makes it possible to reduce heat losses through external enclosures.Thus, there is reason to assert the possibility of the targeted control over the processes of forming a strong structure of partitions between pores using the modified binding compositions containing supplementary cementitious materials. The application of polypropylene fibers enables the reinforcement of aerated -concrete array, forming a strong structural frame of partitions between pores, and ensuring greater strength of the non-autoclaved aerated concrete

Studying the Railroad Track Geometry Deterioration as a Result of an Uneven Subsidence of the Ballast Layer

A method for calculating impairment of the track geometry under influence of dynamic loads in the course of passing the track unevenness by the rolling stock was developed. The method takes into consideration interrelated short-term processes of dynamic interaction and long-term processes of subsidence of the ballast layer in a mutual influence on each other. Mathematical model of dynamic interaction of the track in the form of a planar three-layer continual beam system with a two-mass discrete system corresponding to the rolling stock is the basis of the first part of the method. This model makes it possible to simulate dynamic loads from individual sleepers to the ballast when the rolling stock passes geometric unevennesses and the track elasticity unevennesses.The second part of the method is based on the phenomenological mathematical model of accumulation of residual deformations formed using the results of laboratory studies of subsidence of individual sleepers in the ballast layer. Peculiarity of this model consists in taking into consideration not only uniform accumulation of residual subsidence from the passed tonnage but also presence of a plastic component of subsidence which depends on the maximum stresses in the history of ballast loading by each sleeper.A new theoretical mechanism of development of the track unevenness was proposed. It takes into consideration not only residual subsidences of the ballast layer but also appearance of gaps under sleepers resulting in a local change of the track elasticity. This mechanism enables taking into consideration the ambiguous influence of subsidences with occurrence of gaps under the sleepers. Subsidence causes an increase in dynamic loads on the track and the ballast layer on the one hand and onset of the gap causes a decrease in the track rigidity and corresponding reduction of dynamic loads on the other hand.Practical application of the developed method was demonstrated on an example of quantitative estimation of long-term uneven subsidences of the ballast layer when changing the sleeper diagra

Study of the Stress-strain State in Defective Railway Reinforced-concrete Pipes Restored with Corrugated Metal Structures

Promising technologies for repair of defective reinforced-concrete pipes with the use of corrugated metal structures have been developed. As a result, it was established that the use of corrugated metal pipes in the major repair of reinforced-concrete pipes will eliminate need of stopping movement of railroad and motor transport. This will enable recovery works in a short time with practically no changes in conditions of operation of transport facilities.Vertical and horizontal pressure forces on the reinforced-concrete pipes strengthened with a corrugated metal pipe under the influence of static and dynamic loads from the railway rolling stock were calculated. It was established that the value of both vertical and horizontal pressures on a reinforced-concrete pipe arising from the action of rolling stock decreases with an increase in the filling height because of energy dissipation in the depth of soil. For the filling height above the pipe 1 m, the value of vertical pressure from the load C14 was 7.568 kPa and horizontal pressure was 2.523 kPa. The respective figures for vertical and horizontal pressures were 5.957 kPa and 1.986 kPa for the filling height 2 m and 4.912 kPa and 1.637 kPa for the filling height 3 m.According to the results obtained for static and dynamic pressure forces, the stress-strain state of the pipe in interaction with the soil filling was calculated by the finite element method. The results of calculation of the stress-strain state of the composite pipe showed that the maximum stresses occurring in the vault of the repaired pipe did not exceed maximum permissible values. The magnitude of the stresses in the pipe vault was 0.024 MPa and strains measured 9.3·10–4 m