Asfaltgranulat inom betongkonstruktioner

Sammanfattning: The aim of this bachelor thesis is to produce a new recycling area for asphalt granulate, more precisely, to reuse it in concrete. Asphalt granulate consists of waste asphalt that have been crushed to a specific fraction. This material will be reused in concrete by replacing certain parts of the conventional aggregate. The aggregate that is used today mainly consists of ungraded crushed rock. Asphalt granulate is very similar conventional aggregate with the difference that it is covered with the binder bitumen. Thus, this thesis will examine how the asphalt granulate and the binder bitumen will affect the concrete characteristics. In simplified terms concrete consists of water, cement and a composition of crushed rocks in different fractions (aggregate). In this thesis, the aggregate is replaced with asphalt granulate quantity of 25, 45, 77 and 93 percent. These four different concrete mixtures will then be tested according to set European standards, both in fresh- and hard tempered conditions. The characteristics that will be tested in hardened state is frost resistance, compression- and splitting strength, compression strength at a temperature of 60 degrees. In the fresh state, the following has been measured: slump test, expansion and air content. The slump test and expansion measurement do not give an impression about the concretes properties in a hardened condition, it shows how workable the concrete is in a fresh state. Based on the results of this study it can be concluded that a higher amount of asphalt granulates in the concrete affect the compression- and splitting strength adversely. The compression strength also gets lower when the concrete is heated to 60 degrees. This indicates that it’s the binder bitumen on the asphalt granulates which affect the concretes properties. When the concrete reach its ultimate limit state, the various mixtures behave differently. Mixture 1 crack suddenly without any premonition, mixture 2-4 on the other hand fracture slower over a longer time. Frost resistance is usually directly linked to the air content in the concrete and although all four blends show good to very good frost resistance, it’s difficult to link it to the amount of asphalt granules in the different mixtures. The amount of air in the mixtures follows no direct pattern. Hence, it’s not possible to derive the results of the frost peeling to the asphalt granulate content. In fresh condition, the concrete tended to become firmer and more viscous when more asphalt granules were present in the mixture. However, it is not possible to directly derive the poorer workability to the granulate itself. Such conditions are most likely dependent on the distribution of the different aggregate fractions, which could not be identical in all concrete mixtures that were tested.