The main components of asphalt mixtures are fractions of stone aggregates, filler and bitumen. The main component in produced asphalt mixture by mass represents stone fractions with about 85% by weight. When stone materials for the production of asphalt mixtures are replaced with secondary raw materials, then problems associated with acquiring suitable stone fractions can be avoided or at least significantly reduced. The study presents the possibility of use of foundry sand as a secondary raw material that is a substitute fraction of stone material in the production of asphalt mixtures.
The aim of the master thesis is to examine whether the waste moulding sand can be used as substitute for mineral fractions in asphalt mixtures. Additionally it was assumed that there can be even some improvement in terms of reducing the consumed energy for the production and building in of hot mix asphalt mixture. At the same time there must be ne decrease in the essential characteristics of the bituminous mixture, such as, for example, resistance to the resistance to rutting, water resistance and resistance to low temperatures. Because bentonites contained in the selected foundry sands is was expected easier compaction of the asphalt layers, or the possibility of compaction of asphalt layers at lower temperatures than normal. Similar effects to ease of compaction due to crystal bound water are known for zeolites.
The main part of the master work is designed to evaluate the contribution of foundry sand to compaction of asphalt mixtures. The goal of addition of foundry sand in asphalt mixtures, is not just adding large quantities of secondary raw materials, but also to prove additional positive effect on compaction at lower temperatures due to the presence of bentonite in which is still some active bound water. All significant tests of the intrinsic properties of asphalt mixtures were carried out to verify if addition of the foundry sand effect on these properties of asphalt mixtures.
It was found out that the addition of foundry sand substantially affect only on the ease of workability of asphalt layers. Only addition of 4% foundry sand has similar effect as the most commonly used low-temperature additives (paraffin waxes and zeolite). From the results it is evident decrease in some mechanical properties (stability and Marshall stiffness) for asphalt mixtures prepared at 120 °C in comparison with the mechanical properties of the asphalt mixtures prepared at 150 °C. But, according to the criteria of the standard JUS U.E4.014 all asphalt mixtures still meet the requirements. It should be noted that the standard JUS since 2003 is no longer in force and so criteria for the stability and deformation are no longer officially required for roads. In the standard EN 13108-1 are only categories or asphalt mixtures used in airports, required categories for concrete asphalt are determined by contracting authority. Although the mechanical properties of stability and deformation or their limit values are no longer required and determined by the standard for laboratory testing of asphalt mixtures for road construction, they were used to identify and define the change in two basic mechanical properties - stability and deformation. In this way it was possible to easily define if mechanical properties of asphalt mixture changed significantly with the addition of foundry sand at different temperatures. Decrease in production temperature and thus more impact on the stability of asphalt test, on the other hand the amount of added foundry sand effect on the indirect tensile strength ITSR.
So in the asphalt mixture can be added to the 9 % foundry sand, with no substantial effect on the quality of the asphalt layer.