Investigation of technological parameters of bitumen batching system in the asphalt mixing plant

Justas Bražiūnas

Doctoral dissertation

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Bitumen Batching System (BBS) of Asphalt Mixing Plant (AMP) is transport technological equipment for intaking, storing, heating, transporting and batching (weighing and measuring) of a set mass (capacity) bitumen binder batches when producing hot mix asphalt (HMA) mixture. BBS consisting of containers, heating equipment, pumps, pipeline and a batcher is considered a complicated pipeline transport, which should not only transport liquid bitumen binder from one place to another, but batch it accurately and protect from possible damage. The subject of the dissertation belongs to transport engineering field as asphalt mixtures are used exclusively in transport infrastructure construction and its improvement for constructing roads, urban streets, parking lots, airport pavement, railway track underballast layer.

The first significant BBS technological parameter is percent deviation of discharged bitumen batches from the value set in the project, i.e. job-mix formula (JMF). Due to too small bitumen content not all mineral aggregate particles are coated with the film of required thickness and the mixture segregates (flakes) more, is dry and poorly compacted. When bitumen content in asphalt mixture is too high, weaker HMA mixture is produced due to high volumetric bitumen film thickness. The rational use of bitumen is important because bitumen is the most expensive component in HMA mixture.

The second technological parameter is bitumen temperature, which influences the physical, chemical, rheological and mechanical properties of the produced asphalt mixture. Bitumen may be rigid and friable at low temperature, liquid and fluid at high temperature and semi-rigid or rigid at medium temperature. Bitumen dynamic modulus due to temperature fluctuations from –30 to 50 °C change even 37,000 times (Jenks et al. 2011)! When asphalt mixture is produced of too cool and, therefore, too viscous (consistent) bitumen, it hardly turns into a thin film, which should coat all mineral particles with solid layers of appropriate thickness and make a strong compacted structure of the mixture. When too hot or overheated mineral aggregates are used, bitumen may burn: it degrades chemically, volatilizes, its colloidal composition changes and rheological properties deteriorate.

Oxidation is the factor influencing most on bitumen short-term ageing, which is extremely harmful at low temperature; when bitumen contact area with oxygen is huge, this interaction lasts for a long time. During the whole process of HMA production, when bitumen and oxygen reactions may occur, irreversible bitumen characteristics change, which worsens its penetration, softening point and friability temperature.

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145×205 mm
158 p.
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