# Low Temperature Resistance Increase for Bitumen by Compounding with Tar
## 1 Introduction  
Bitumen is one of the materials widely used in road construction all over the world. It is known that the operational characteristics of road asphalt concretes are mostly determined by the properties of bitumen [1, 2, 3, 4, 5].More strict requirements are specified relative to the properties of the bitumen used in sharp continental climatic conditions [6, 7]. In such climatic conditions, the asphalt concrete with bitumen should have sufficient resistance to the rutting under numerous repeated impact of heavy trucks in a hot summer season and to low temperature cracking at sharp, continuous and cyclic cooling in a cold winter season. In order to improve the operational properties (resistance to rutting and low temperature cracking) of asphalt concretes, bitumens are modified with different polymers [8, 9, 10, 11, 12, 13, 14, 15]. However, polymers, as a rule, essentially increase only high temperature resistance (resistance to the formation of plastic deformations) of asphalt concretes. Currently, the plants of Kazakhstan produce bitumens only with penetration grades 70-100 and 100-130. Low temperature cracks occur on pavements constructed with the use of bitumens of these grades (especially in the northern and eastern regions) during the first winter, and the number of them has increased from year to year. Meanwhile, it is known that bitumens of less viscous consistence have comparatively better low temperature characteristics. The objective of the paper is low temperature resistance increase for bitumen by compounding with tar. A review of the literature shows that the number of works devoted directly to the compounding of road bitumen with tar is extremely limited. Apparently, it can be explained by the fact that researchers of bitumen binders, as a rule, work with bitumen produced bythe plants. One of the causes for the limited amount of the investigations for this subject is perhaps connected with the increase in environmental requirements relative to the asphalt concrete pavements due to the content in them of the cancerogenic polynuclear aromatic hydrocarbons, which can be the source for contamination of soils and underground water [16; 17; 18]. However, the materials discussed below show the potential for road bitumen production using the tar. For example, in 2007, a patent [19] was issued in Russia for a method of producing the compounded bitumen, which provides mixing at a temperature of 110-130 \({}^{\circ}\)C for 10-15 min of tar and more viscous oil refining residue at the ratio of 20:80 by weight. Moreover, a method is patented for obtaining road bitumen of the grade 60-90 on penetration, which is realized by the compounding of oxidized bitumen with penetration P\({}_{25}\) = 55 0.1 mm and softening point T\({}_{\text{RB}}\) = 66 \({}^{\circ}\)C with tar (conditional viscosity 42 s) at the temperature of 160-180 \({}^{\circ}\)C at the ratio of 80:20 by weight [20]. Another method [21] is known, according to which a two-stage process is used to obtain road bitumen with the softening point T\({}_{\text{RB}}\) = 75 \({}^{\circ}\)C: at the first stage, a mixture of tar and asphaltite at the ratio of 50:50 by weight is compounded for 40 min at the temperature of 140 \({}^{\circ}\)C; at the second stage the obtained compounded mixture of the tar and the asphaltite is subjected to oxidation in a column at the temperature of 250-270 \({}^{\circ}\)C for 7 h.  
The possibility for the obtaining of polymer modified (SBS) road bitumen with improved characteristics, also using oxidized bitumen with penetration grade 70-100 and high-viscosity tars (P\({}_{25}\) = 95 and 110 0.1 mm), is given in a recently published paper [22]. Considering the above, in this work a viscous road bitumen with penetration grade 100/130, conventionally used in a road construction, is compounded with tar to obtain bitumen with improved low temperature operational characteristics.