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Elastic modulus of asphalt with chemically stabilized rubber bitumenThe chemically stabilized rubber bitumen (CSRB) has been developed by researchers from the company MOL and the Pannonian University (Hungary). The CSRB is made of used automobile tyres, and it improves the quality of pavement, while also enabling an efficient use of used automobile tyres. Mechanical properties of the chemically stabilized crumb rubber bitumen are analysed in the paper. Although test results have shown that CSRB properties are similar to those of the polymer modified bitumen, the CSRB results have proven to be better at low temperatures. Modul elastičnosti asfalta s bitumenom modificiranim gumenim granulatom kao vezivomBitumen modificiran gumenim granulatom (CSRB) razvili su istraživači tvrtke MOL i Panonskog sveučilišta (Mađarska). CSRB se proizvodi od rabljenih automobilskih guma, a njegovom se primjenom povećava kvaliteta kolnika i učinkovito postupa s rabljenim automobilskim gumama. Ovaj rad analizira mehaničke karakteristike asfalta s bitumenom koji je modificiran gumenim granulatom. Iako su rezultati ispitivanja pokazali da su svojstva CSRB-a slična svojstvima polimerom modificiranog bitumena, primjenom CSRB-a postižu se bolji rezultati pri niskim temperaturama.

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The use of crumb rubber from vehicle tyres in hot mix asphalt production has been a very promising option in the field of waste recycling and sustainability. The disposal of used vehicle tyres has been a serious and difficult issue. Due to their indestructible nature the options are burning or disposal, none of these are desirable in our global environment. The trials for using crumb rubber in hot mix asphalt started in the 1920s; these early applications used the so called dry method, where the rubber is considered as part of the aggregate instead of the binder. This method did not deliver the expected higher performance, and researchers have been looking into the so called wet process since the 1960s, where the rubber is added to the binder, modifying its properties. The modified binder is then added to the aggregate during asphalt production. Although many countries utilise the crumb rubber using the wet process, there is an ongoing problem with this technology, similarly to the application of polymer modified bitumens (PmBs): the storage stability of the product. This short-term segregation problem has been preventing the wide application of crumb rubber bitumen in road construction. Additionally, the high viscosity of product may cause difficulties during manufacturing and paving which should be considered when selecting aggregate grading. MOL Plc. developed and patented a procedure for producing chemically stabilized rubber bitumen (CSRB); the pilot scale production started in 2012 and the facilities are capable to produce 5000 tonnes of CSRB-equivalent of 150,000 tyres-in their Zala Refinery, Hungary. This paper discusses an asphalt research program conducted at Budapest University of Technology on a 10mm nominal aggregate size wearing coarse hot mix asphalt. This study presents the comparative analysis of asphalts containing PmB and CSRB separately. Prepared samples were subjected to performance based and related mechanical testing. The findings summarised in this paper suggest that performance of asphalt mixes produced with CSRB binder are similar or equivalent to asphalt mixes produced with PmB with regard to moisture sensitivity, stiffness and wheel tracking, while the low temperature cracking test showed higher and superior performance.

ABSTRACT. The aim of this study is to investigate the effect of various wax type warm mix additives on the rheological properties of Chemically Stabilized Rubber Bitumen (CSRB). The rubber bitumen samples were prepared by the modified wet process (HU 226481) and the bitumen tests were carried out according to the relevant standards. Two types of warm mix additives (polypropylene wax -produced by thermal cracking of polypropylene and Fischer-Tropsch wax) with different concentrations (1.0%, 3.0%, 5.0%, 7.0% by weight) were used in our research. The influence of these warm mix additives on the rheological properties was evaluated by Dynamic Shear Rheometer (DSR) test. Multiple-stress creep and recovery (MSCR) test was also used for the determination of percent recovery and non-recoverable creep compliance of wax-modified and neat asphalt rubber samples. According to the results of DSR tests the addition of the Fischer-Tropsch wax resulted a higher complex modulus (thereby stiffness) and favourable higher recovery values based on MSCR tests unlike the addition of polypropylene wax.

The rubber modified bitumen 45/80-55 (RMB 45/80-55) product has been used in Hungary as bituminous binder for asphalt mix production since 2013. It is a new kind of rubber bitumen manufactured using patented technology. Over the past 8 years, it has been used to construct or renovate more than 100 asphalt road sections. Originally RMB 45/80-55 was used to replace paving grade bitumen 50/70 in some road construction projects. However, asphalt laboratory results and road construction experience showed that its quality can also achieve or in terms of some parameters exceed that of asphalt mixtures manufactured with polymer modified bitumen 25/55-65 (PMB 25/55-65). Primarily, its excellent resistance to low temperatures and fatigue are outstanding, in this respect; it surpasses the results of asphalts made with polymer modified bitumen. Its favourable fatigue resistance compensates for its lower stiffness; therefore, favourable results were obtained in the case of track structure design too in comparison with PMB. Considering the road construction benefits of this new type of rubber bitumen, as well as the support of the environmentally friendly recovery of waste tyres and fitting into a circular economy, a wider spread of the RMB product is realistically expected in the future.