## 6 Effect of Zeolite Addition on Asphalt Viscosity  
The criterion determining the possibility of coating the aggregate grains with a binder membrane correctly, with the required thickness, is not the temperature of the asphalt but its viscosity. With this assumption, the base for assessment of WMA addition efficiency may be the results of viscosity tests. Additionally, with regard to zeolites, attempts are made to determine this parameter, yet obtained results are not unambiguous. The results which are presented below are related to dynamic viscosity determined using rotational viscometer according to ASTM D4402-84 procedure. The first studies of rheological properties of asphalt with Aspha-Min zeolite addition were conducted by [PERSON] et al. The viscosity of PG 62-22 and PG 70-28 asphalts, determined with rotational rheometry decreased after adding zeolite, but this change was not significant [35]. The results of studies by [PERSON] and [PERSON] [36,37], indicate an increase in PG 64-22 bitumen's viscosity after using 0.6% of Aspha-Min zeolite (by weight of the binder). The reference material in their publication included PG 64-22 asphalts of several crude sources. The viscosity increased in case of pure virgin asphalt [38], binder crumb rubber modifier (CRM), and rubberized warm asphalt binders after artificial short-term aging with rolling thin film oven (RTFO) [39,40]. The addition of 4%, 6%, and 8% Advera asphalt also resulted in an increase of PG 64-22 asphalt viscosity at 135 \({}^{\circ}\)C, 150 \({}^{\circ}\)C, and 165 \({}^{\circ}\)C [41]. Extensive studies of asphalts with zeolite addition were also performed by [PERSON] et al. They used both synthetic and natural zeolite (clinoptilolite) as addition. The characteristics of synthetic zeolite properties suggest that this was a synthetic zeolite with Linde A structure type. Asphal penetration grade 50/70 was modified with zeolite material, at 3%, 4%, 5%, 6%, 7%, with regard to bitumen mass. The analysis of results indicates decrease in asphalt viscosity, both at 135 \({}^{\circ}\)C, as well as 160 \({}^{\circ}\)C, with 5% zeolite addition [42; 43]. [PERSON] and [PERSON] also researched changes in viscosity over time, in the case of binder samples, poured immediately prior the testing [39]. Determinations were performed for two temperatures, 120 \({}^{\circ}\)C and 135 \({}^{\circ}\)C, at three time intervals of 30, 60, and 90 min. Viscosity of pure bitumen with zeolite at 135 \({}^{\circ}\)C was constant over time, whereas at 120 \({}^{\circ}\)C it presented an increasing tendency. Viscosity of rubberized warm asphalt binders decreased in 60 min of measurement, after which it increased regardless of test temperature. In each case the viscosity of asphalt with zeolite was higher than the reference bitumen viscosity. Viscosity was also a subject of analyses conducted by [PERSON] et al. [16]. Viscosity determinations were also performed at two temperatures of 135 \({}^{\circ}\)C and 160 \({}^{\circ}\)C and 4 time intervals: 15, 30, 45, and 60 min after adding zeolites to asphalt. For each determination a new sample was prepared. Tests used asphalt penetration grade 35/50, NaP1 synthetic zeolite, natural clinoptilolite and their variations modified with water. The analysis of results indicated decrease in viscosity after 45 min after zeolite addition to the asphalt, regardless of the addition type and test temperature. Testing the viscosity of asphalt with zeolite addition is difficult in terms of performing and interpretation. Zeolite is a solid body, insoluble in asphalt and its presence itself interferes with the result. On the other hand, zeolite water leading to asphalt foaming is released gradually over time which results in the possibility of viscosity being variable over time. The results of tests presented above used different types of zeolite structures which, according to recent studies, impacts the asphalt foaming effect [16].