International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

The continuous evolution and development of the society caused a significant increase in the number of construction works. Regarding road works, in the recent years, these have escalated as the need for bitumen increased. Given Romania’s conditions, for fulfilling the need of bitumen economy and thus reducing the costs correlated with road pavement, due to the fact that this material is currently brought only from abroad, it is desired to design an asphalt mixture with a smaller quantity of contained bitumen or even replacing it with bituminous sand, a solution which is advantageous in areas where one can find these natural resources. In Romania, bituminous sand or oil sand can be found in two geographic areas, namely: in Bihor County, Derna-Tatarus-Budoi in Prahova County, at Matita, and Pacureti. Further, these bituminous sands have a naturally occurring bitumen percentage of approximately 20% in their composition. In this context, this paper aims to emphasize, through static and dynamic methods, the physical and mechanical characteristics of two bituminous asphalt mixtures containing bituminous sand from Derna – Tatarus – Budoi. Both of asphalt mixtures have been designed based on departmental normative CD 42-85, containing various sorts of crushed gravel, natural sand and bituminous sand and are intended to be used for the base course of the road pavement. Furthermore, one of bituminous mixtures is performed with bituminous sand and hard paving grade bitumen compared with the second one, which only contains bituminous sand, in this case the bituminous binder consisting in the bitumen contained into the oil sand.

Contemporary production of castings is inevitably associated with improvement of foundry mixtures, and in particular with quartz sands as a basic moulding material. The interest is motivated by opportunity of reaching mixture’s appropriate parameters at different combinations between sands and binding compositions. One option of particular importance in obtaining mixtures’ physical and mechanical, and technological properties is to get a greater number of contact points among individual grains of quartz sands.

The report examines the impact of dispersive mineral particles for increasing contact points of interaction between individual sand particles in the process of solidification. A theoretical basis for the possibility of applying such reinforcement in the preparation of mixtures is presented. An attempt for optimization has been done by some criteria – porosity, morphology, gas permeability and other properties.

Results and conclusions from the conducted tests have been graphically presented.

As a whole, the contemporary self-hardening foundry moulds and cores represent a result of chemical reactions between quartz sands and binders at mould formation after good homogenization in mixers. Mixtures are hardened, obtaing the necessary physico-chemical characteristics; thus they realize the geometry of the future cast. One of the most important characteristics is the strength of mixtures, especially the adhesion strength that is formed on the border between sand and binding composition.

In this report, an improved method on adhesive strength determination of foundry mixtures is presented. Some theoretical protection aspects of the shown method are considered. A technological sequence of the method work and way of measurement are given. In figures, practical results from measurements of adhesion strength according to “No Bake”are shown.

At the contemporary conditions of cast production there has been a permanent interest in economically more profitable technologies for obtaining moulds and cores of controlled properties. A part of this interest is related to quartz sands as a basic and the most common component in the practice of foundry mixture productions. State of sand surface and its influence in formation of foundry mould and core physico-chemical properties are of particular importance.
In this report, various conditions of mechanical activation on the surface of quartz sand in “a fluidized bed” are discussed. The theory of such activation necessity has been partly explained. The “time” factor in preserving the activated layer potential is noticed. The efficiency of the activated layer in producing foundry mixtures strength by the method “No Bake is shown.

The physical and mechanical properties of soil change dynamically following each tillage and rainfall. Some of the more important ones are bulk density, (g cm⁻³), hydraulic conductivity in soils, saturated with water, (cm day⁻¹), the rainfall curve, the temperature (^оС) and the capacities of soil to retain water at saturation point (cm³ cm⁻³). Theoretically, only the upper 30 cm of soil layer experience change in the physical and mechanical properties, caused by tillage. The actual depth of the changes in the soil depends on the production technology selected. Various types of tillage are applied worldwide, corresponding to the level of development of socio-economic formations and of the production technologies. In Bulgaria, the traditional annual ploughing of soil is applied, including on slopes, giving a prerequisite for the subsequent negative consequences, such as activation of erosion processes and degradation.