Effect of Chemical Composition of Fine Aggregate on the Frictional Behavior of Concrete–Soil Interface under Sulfuric Acid Environment

Through direct shear tests, this paper aimed to research the effect of fine marble aggregate on the shear strength and fractal dimension of the interface between soil and concrete corroded by sulfuric acid. More realistic concrete rough surfaces than the artificially roughened surfaces were formed by immersing four concrete plates in plastic buckets filled with sulfuric acid for different periods of time. The sand was adopted to imitate the soil. 3D laser scanner was employed to obtain the digital shapes of concrete plates subjected to sulfuric acid, and the rough surfaces were evaluated by fractal dimension. Large direct shear experiments were performed to obtain the curves of the interface shear stress and shear displacement between sand and corroded concrete plate. The method of data fitting was adopted to calculate the parameters of shear strength (i.e., friction angle and the cohesive) and the parameters of the Clough–Duncan hyperbolic model. The results indicated that as the corrosion days increased, the surface of the concrete plate became rougher, the surface fractal dimensions of the concrete corroded by sulfuric acid became bigger, and the interface friction angle became greater. The friction angle of the interface and the fractal dimensions of the surface of the concrete plate containing crushed gravel and marble sand were smaller than that of the concrete plate containing crushed gravel and river sand.

STRUCTURAL FEATURES OF THE ASSEMBLIES OF THE JOINING OF TRAM RAILS TO ROAD COVERAGE

In the modern world, the priority is the development of clean urban electric transport. The constructive solutions used in the construction of the tram wheel in the past years are outdated and do not meet modern requirements. One of these problems is the destruction of asphalt coating in the places of road coverage to tram rails, which worsens the operational characteristics of tram crossings. The reasons for this problem can be attributed to the following: Not enough asphalt concrete near the rails; low adhesion of asphalt and metal from which rails are made; dynamic loads and vibrations arising from trams and motor transport; bad base of tram train and others. One of the options for increasing reliability and durability is to use as a road covering of tram plates. This solution is used in Ukraine and the European Union. German company RailBeton developed solutions for railway crossings - BetoCross. This system is a modular construction of reinforced concrete slabs, which are pulled together by steel strips. With the help of a system of fastenings and bearings, the flooring is fastened to rails, which provides vertical and horizontal stability of their position and stabilization under the influence of loading. To reduce the dynamic influence, the plates are based on reinforced concrete sleepers through the intermediate layers of the elastostomer. The load from the automobile transport is transferred to the broken beam. In addition to the positive features, the BetoCross system, due to the large number of connections, ties and bearings, requires frequent maintenance and maintenance. The Ukrainian state enterprise "Starokostiantyniv plant ZBSH" developed a similar technology, reinforced concrete plates with the help of a screw fastening through rubber gasket fixed to a special bridge type wallpaper. At a step of wallpaper 0,6 m the plate is attached to each wallpaper from two sides, with the length of the plate itself is 2,7 m. that is, on one plate there are five points of fastening on each side. Loads from the automobile transport, similar to the German technology, are transferred to the rubble balast and the basis. These technological solutions have found their application on railway crossings, and need some improvement for use in urban electric transport. The article reviews the constructive decision on the organization of the mentioned site, which is proposed by RS ENGINEERING in Kharkov. In the proposed solution instead of the crushed balast used monolithic reinforced concrete slab with supporting elements. The arising loads from the rolling stock and transport are transferred through the supporting elements to the concrete slab, which redistributes them on the rubble basis. As a road cover are used reinforced concrete plates covering RS-Slab. The plates are divided into 3 types: Road, interroad and external, which in turn have several sizes. The plates are bound to the supporting elements by means of screws in four points. To reduce dynamic influence between the film and the reference element, a rubber elastomer is laid. Depending on the size of the plates have different number of cutting sites. Also because of the design features possible option when the slab simultaneously relies not on all the supporting sites, these options should be taken into account when calculating the scale and choosing a class of concrete. This solution allows to solve the problems of road surface destruction on the side of the rails, keeps more load from transport, compared to asphalt. At the same time, there are factors that need to be studied in detail when designing and before implementing the solution in mass production. These include: Investigation of the influence of violation of standard assembly plates on the stress-deformed state of the element; determination of thickness and acceptable physical characteristics of the gasket on the plate supports; detailed development of a node for fixing plates. The use of reinforced concrete plates as a road coating has a number of advantages before asphalt concrete: Resistance to destruction on the rails; installation regardless of weather and temperature conditions; resistance to loads from trucks. At the same time, this decision has certain peculiarities that require detailed study, which is a branch of further research.

Behavior of Reinforced Concrete Plates under Pure Torsion

The behavior of reinforced concrete members under torsional loading has interested many researchers during the last decades. These researches focused mainly on the response of reinforced concrete beams at different reinforcement conditions and the size effects. On the other hand, the behavior of concrete plates or slabs has not been investigated clearly under pure and/or combined torsional loading. In the present study, nine reinforced concrete plates were prepared and tested under pure torsion. Effect of steel reinforcement ratio and size change was studied and they have a great effect on the plated strength, capacity, stiffness and ductility. As stated by torsion theories of reinforced concrete beams, the torsional strength of slabs was upgraded also with increasing in cross section and transverse reinforcement ratio.

Performance of ultra-high performance fibre reinforced concrete plates under impact loads

The next generation of concrete, Ultra-High Performance Fibre Reinforced Concrete (UHP-FRC), exhibits exceptional mechanical characteristics. UHP-FRC has a compressive strength exceeding 150 MPa, tensile strength in the range of 8-12 MPa, and fracture energy of several orders of magnitudes of traditional concrete. The focus of this research is to investigate and analyze the advantage of using UHP - FRC in impact resistance structures. To achieve these goals, two experimental testing programs and major numerical investigations have been conducted. The material experimental investigation has been conducted to determine the effects of strain rate on UHP - FRC. Two parameters are investigated, namely: compressive strength (80, 110, 130, and 150 MPa); and steel fibre content (0, 1, 2, and 3%). Experimental results showed that the rate sensitivity decreases with the increase in the compressive strength ; and the dynamic enhancement of tensile strength is inversely proportional to the fibre content. The structural impact testing program focuses on the dynamic response of full - scale reinforced concrete plates as well as generating precise impact measurements. Twelve reinforced plates with identical dimensions are tested under high-mass low-velocity multi-impacts. The investigated parameters include: concrete type (NSC, HSC, and UHP - FRC), fibre volume content, and steel reinforcement ratio. The results showed that the use of UHP -FRC instead of NSC or HSC is able to change the failure mode from punching to pure flexural; and UHP -FRC containing 3% fibre has superior dynamic properties. For plates with identical steel reinforcement, the total impact energy of UHP-FRC plate containing 3% fibres is double the capacity of UHP - FRC plate containing 2% fibres , and 18 times the capacity of NSC plate. A three-dimensional finite element analysis has been performed using ABAQUS/Explicit to model multi-impacts on RC plates and the applicability is verified using existing experimental data. Concrete damage plasticity (CDP) model is adapted to define UHP - FRC. The CDP constitutive model parameters for the new material are calibrated through a series of parametric studies. Computed responses are sensitive to CDP parameters related to the tension, fracture energy, and expansion properties. The analytical results showed that the existing CDP model can predict the response and crack pattern of UHP - FRC reasonably well.

Performance of ultra-high performance fibre reinforced concrete plates under impact loads

The next generation of concrete, Ultra-High Performance Fibre Reinforced Concrete (UHP-FRC), exhibits exceptional mechanical characteristics. UHP-FRC has a compressive strength exceeding 150 MPa, tensile strength in the range of 8-12 MPa, and fracture energy of several orders of magnitudes of traditional concrete. The focus of this research is to investigate and analyze the advantage of using UHP - FRC in impact resistance structures. To achieve these goals, two experimental testing programs and major numerical investigations have been conducted. The material experimental investigation has been conducted to determine the effects of strain rate on UHP - FRC. Two parameters are investigated, namely: compressive strength (80, 110, 130, and 150 MPa); and steel fibre content (0, 1, 2, and 3%). Experimental results showed that the rate sensitivity decreases with the increase in the compressive strength ; and the dynamic enhancement of tensile strength is inversely proportional to the fibre content. The structural impact testing program focuses on the dynamic response of full - scale reinforced concrete plates as well as generating precise impact measurements. Twelve reinforced plates with identical dimensions are tested under high-mass low-velocity multi-impacts. The investigated parameters include: concrete type (NSC, HSC, and UHP - FRC), fibre volume content, and steel reinforcement ratio. The results showed that the use of UHP -FRC instead of NSC or HSC is able to change the failure mode from punching to pure flexural; and UHP -FRC containing 3% fibre has superior dynamic properties. For plates with identical steel reinforcement, the total impact energy of UHP-FRC plate containing 3% fibres is double the capacity of UHP - FRC plate containing 2% fibres , and 18 times the capacity of NSC plate. A three-dimensional finite element analysis has been performed using ABAQUS/Explicit to model multi-impacts on RC plates and the applicability is verified using existing experimental data. Concrete damage plasticity (CDP) model is adapted to define UHP - FRC. The CDP constitutive model parameters for the new material are calibrated through a series of parametric studies. Computed responses are sensitive to CDP parameters related to the tension, fracture energy, and expansion properties. The analytical results showed that the existing CDP model can predict the response and crack pattern of UHP - FRC reasonably well.