## 7 Effect of Zeolite Addition on WMA Properties
### Water Sensitivity  
Road surface is subject to negative effect of atmospheric conditions which may lead to loss of mechanical performance. As a result of using lower temperature of WMA production, the aggregate may not be sufficiently dry. Water droplets on the aggregate results in worse adhesion to asphalt which can also increase the susceptibility to water in case of asphalt mixtures. Additionally, the fatigue life of asphalt concrete subjected to action of water and frost is significantly lower [46; 47]. WMA water sensitivity is usually defined through a decrease of indirect tensile strength in the case of saturated samples and stored in water at elevated conditioning temperatures, with regard to the control dry samples (according to procedures described in EN 12697-12 and AASHTO T 283. [PERSON] et al. conducted water sensitivity studies on asphalt concrete (AC 16) with asphalt penetration grade 60/70, produced at three temperatures of 160 \({}^{\circ}\)C, 140 \({}^{\circ}\)C, 120 \({}^{\circ}\)C [24]. When comparing mixes with equal production temperature, it occurs that zeolite addition did not affect water resistance. However, having considered the fact that HMA and WMA with zeolite (production temperature decreased by 20 \({}^{\circ}\)C) ITSR index lower by 5%-8% was obtained. Studies involving WMA with zeolites that are conducted in Belgium on asphalt concrete 0/10 samples for top layers, with an asphalt penetration grade 50/70, which also indicated a decrease in water resistance measured with the ITSR index [25]. In their work, [PERSON] and [PERSON] focused on the possibility to used synthetic NaP1 zeolite, natural zeolite--clinoptilolite, and their variations modified with water [20]. The reference mix included asphalt concrete (AC 16), condensed using asphalt penetration grade 35/50 at 145 \({}^{\circ}\)C. Generally speaking, zeolite addition has a negative effect on water resistance. Only WMA samples (temperatures decreased by 30 \({}^{\circ}\)C) with NaP1 zeolite had higher ITSR indicator than HMA. Resistance to water is improved in the case of WMA with zeolite by the addition of 1.5% calcium hydrate, whereas a liquid anti-stripping agent turned out to be ineffective [27]. The positive effect of this addition was confirmed by analyses conducted by [PERSON] et al. [48]. Results are known for studies in which the ITSR index for WMA with zeolite was higher than for HMA samples, with the production temperature decreased from 160 \({}^{\circ}\)C to 135 \({}^{\circ}\)C. In the case of asphalt concrete samples (AC 12) with asphalt penetration grade 35/50, an increase was noted from 86.1% to 91.5%, whereas, with regard to asphalt modified with polymers (MODBIT 45/80-55), an increase was noted from 89.95 to 95.0% [13]. Durability of WMA samples cut out of the surface, was not lower than in the case of HMA samples [27; 49]. On the other hand, the resistance of WMA samples after saturating them with water was lower than in the case of HMA collected from the same test section [49]. The same correlation was achieved in the case of WMA including zeolite modified with water [20]. [PERSON] and [PERSON] determined moisture retained in the aggregate, or due to residual moisture left behind by the microscopic foaming process of the zeolite, to be the reason behind the decrease in water resistance of the WMA with zeolites [27]. According to authors, during the WMA production process the asphalt molecules occlude zeolites and, thus, they cannot absorb water. The pores of zeolites are closed by the asphalt molecules. At the same time, asphalt molecules are very large and cannot be absorbed by zeolite. There is a high risk that microfractures in asphalt at temperatures below freezing point may uncover zeolite pores which would allow them to absorb water. However, so far this phenomenon was not a subject of any research. Having considered small amounts of added zeolite material and zeolite pore size of 0.X nm, the described phenomenon should not affect resistance to freezing in the case of WMA embedded in the road surface.