**4. Asphalt mixtures with reclaimed asphalt and pyrolytic rejuvenator**

Asphalt mixtures have to withstand dynamic loads as well as high and low temperatures without cracking or rutting. Several standardized laboratory tests enable the evaluation of these asphalt characteristics. Before implementation, characteristics of reclaimed asphalt (RA) had to be established. Several samples of reclaimed asphalt from the same stockpile were sieved into sub fractions and extracted bitumen was investigated. The results showed that the bitumen content in RA was 4.5%. Based on this, the required amount of fresh bitumen and rejuvenator for each asphalt mixture type AC 8 surf were calculated.

The bitumen content of all prepared asphalt mixtures was determined at 5% of the mass regarding the total asphalt mixture mass. Regarding to the established effects of pyrolytic rejuvenator on (non-aged and laboratory aged) bitumen, the addition of 20% of pyrolytic rejuvenator to the bitumen from reclaimed asphalt was established. Control asphalt mixture of fresh materials (0% RA) and asphalt mixtures with 20%, 40% and 60% of RA according to the weight of the stone aggregate were prepared in laboratory (set of asphalt mixture samples is described in **Table 9**). Each asphalt mixture with RA was produced without and with a pyrolytic rejuvenator. All together seven asphalt mixtures were prepared with the same B50/70 bitumen (from the same producer) as used in previous research.

All asphalt mixtures samples were mixed in a laboratory and compacted in accordance with EN 12697–30 [35]. Basic information about asphalt mixtures was gained by determining bulk density, EN 12697–6 [36], maximal density, EN 12697–5 [37], void content, EN 12697–8 [38], and indirect tensile strength (ITS), EN 12697–23 [39]. ITS is maximum tensile stress applied to a cylindrical specimen loaded diametrically until the break. Cylindrical specimens (nominal diameter 100 mm) were for ITS compacted by 50 impacts on each side at temperature 150°C. Water sensitivity tests were completed according to EN 12697–12 [40], in order to evaluate the effect of moister. Water sensitivity is expressed by ITSR – indirect tensile strength ratio. Two sets of four cylindrical specimens were prepared, compacted by 35 impacts on each side at temperature 150°C. One set of specimens was conditioned in water for three days; the other set was kept dry. The ratio between their ITS values expresses water sensitivity.

For determination of characteristics at low temperature thermal stress restrained specimen test (TSRST, EN 12697–46 [41]) was carried out. Asphalt


### **Table 9.**

*Standard properties of asphalt mixtures [22].*

### *Rejuvenator Obtained by Pyrolysis of Waste Tires for Use in Asphalt Mixtures with Added… DOI: http://dx.doi.org/10.5772/intechopen.99490*

mixtures were compacted in form of slabs, EN 12697–33 [42], from which prismatic specimens were cut. In TSRST, the specimen, whose length is held constant during the test, is subjected to a temperature decrease with a constant temperature rate. Due to the confined thermal shrinkage, cryogenic stress builds up in the specimen. The results of the tests are the progression of the cryogenic stress over the temperature range until break, σcry(T), and the failure stress, σcry,failure, at the failure temperature, Tfailure.

To check the behaviour of asphalt mixtures at elevated temperatures the formation of wheel tracking was checked according to EN 12697–22 [43].

Extracted bitumen from all asphalt mixtures was investigated according to before mentioned standard testing methods.

The siewing curve had to be adjusted for each asphalt mixture (**Figure 1**) because different shares of RA were added. In all figures addition of rejuvenator is designated with RA+rej. The curves overlap with each other well and bitumen from RA does not affect the siewing curve. The inhomogeneity of RA was successfully solved by presiewing RA into sub fractions (0/2 mm, 2/4 mm and 4/8 mm).

The densities were determined according to standard procedures and the results are given in **Table 9**. The difference between the densities and void content of individual asphalt mixtures was very small. Results confirm that mixtures were comparable.

The presence of water in the asphalt is expected. Moisture is one of the most important factors influencing the durability of asphalt. The combination of excess moisture and traffic load shortens the life of the asphalt. Moisture in asphalt causes two main destructive mechanisms: deterioration of adhesion and cohesion. Strong deterioration of adhesion can be observed as peeling of bitumen from the stone aggregate, and deterioration of cohesion is observed as softening of the binder, which leads to lower strength of asphalt. The water sensitivity of asphalt mixtures is expressed by the ITSR quotient, which represents the ratio of indirect tensile strength of wet and dry specimens, expressed as a percentage. **Figure 2** shows the results of the water sensitivity test. For all tested asphalt mixtures indirect tensile strength increased with the addition of RA and decreased only slightly when rejuvenator was added. Asphalt mixtures were less sensitive to water after the addition of RA, as the ITSR ratio increased. No significant effect on ITSR was observed with the addition of a rejuvenator.

**Figure 1.** *The sieving curves of laboratory produced asphalt mixtures AC 8 surf [22].*

**Figure 2.**

*The water sensitivity of the asphalt mixtures [1].*

Testing of wheel track formation was performed at an elevated temperature of T = 50°C. The differences between the sample results (**Figure 3**) were not significant, indicating that the selected test temperature was too low.

Because the aged bitumen from RA increases the stiffness of the binder in the asphalt mixture, resistance to fatigue cracking is weakened in asphalt mixtures with a high amount of RA. In our study, the resistance to low temperature cracking was checked only on mixtures with the highest proportion of RA, as 60% of RA represents the worst conditions for asphalt resistance at low temperatures. The average results (three specimens were tested for each mixture) for three mixes are shown in **Figure 4**. Compared to the mixture with 0%RA, the failure temperature increased due to the added RA, which means deterioration of the mechanical properties of the asphalt mixture. The results for 60% RA mixture with the addition of pyrolytic rejuvenator show that the failure temperature decreased, and the resistance of the asphalt mixture with RA and the rejuvenator was therefore slightly better than the resistance of the basic mixture. The breaking stresses were similar for the three

**Figure 3.** *Results of the wheel tracking test at T = 50°C.*

*Rejuvenator Obtained by Pyrolysis of Waste Tires for Use in Asphalt Mixtures with Added… DOI: http://dx.doi.org/10.5772/intechopen.99490*

### **Figure 4.**

*Temperature dependency of cryogenic stress [1].*


### **Table 10.**

*Results of standard mechanical tests of extracted bitumen [22].*

tested mixtures, but the course of cryogenic stresses shows that the stresses were higher in the mixture with 60% RA than in the other two mixtures.

The extracted bitumen of asphalt mixtures was also investigated; the results are presented in **Table 10**. The highest value of the softening and Fraass breaking point was determined in bitumen from reclaimed asphalt (100% RA), meaning the bitumen was the most brittle and hard, as expected. The results showed that the addition of RA to asphalt mixtures without pyrolytic rejuvenator increased the softening point and Fraass breaking point and decreased penetration. However, the rejuvenator had a beneficial effect, as mixtures with the rejuvenator exhibited a lower softening point, Fraass breaking point and higher penetration than mixtures without pyrolytic rejuvenator. As expected, the bitumen became harder as the RA content increased, but the bitumen softened with the addition of a rejuvenator.

### **5. Conclusions**

In the presented research, several pyrolytic products were tested. Based on the results, the pyrolytic product 14 was selected as the most suitable for the purpose of rejuvenating. It had a homogeneous structure, was solid at room temperature and it flowed at elevated temperatures. The indicator of suitability for use as a rejuvenator was the pyrolytic product's low softening and Fraass breaking point and high penetration value.

In mixtures with reference bitumen, the low Fraass breakpoint value was not maintained. The penetration of bitumen was increased by adding a pyrolytic rejuvenator and the softening point was decreased. The results of standard mechanical tests confirmed that the pyrolytic product softened the bitumen, which is the basic purpose of the rejuvenator.

The next part of the research was dedicated to the determination of the optimal proportion of rejuvenator that would regain the original properties of bitumen from reclaimed asphalt. This part of the research was performed on non-aged and laboratory aged bitumen. The addition of rejuvenator was limited at the upper limit, as the prepared pyrolytic product contained polycyclic aromatic hydrocarbons (PAHs). The results of decreased softening point and increased penetration show that the bitumen softened due to the rejuvenator. The Fraass breaking point increased in aged bitumen after the addition of a rejuvenator, indicating deterioration in the properties of the bitumen.

Despite the added rejuvenator the elongation in the ductility test was maintained for non-aged bitumen and increased for aged bitumen. However, in proportion to the increase in the rejuvenator, the maximum force in the sample decreased. The elastic recovery of non-aged bitumen did not change due to the rejuvenator, while in aged bitumen it decreased after the addition of the rejuvenator. The results of BBR confirmed our expectations, as resistance at low temperatures was increased by the addition of a rejuvenator. The addition of 20% of the pyrolytic product changed most properties of the aged bitumen in order to approach the characteristics of the non-aged bitumen. Although a complete recovery of the aged bitumen was not reached, the pyrolytic product can be successfully used as a rejuvenator. After the addition of pyrolytic product, the properties of aged bitumen were restored in the direction of the properties of the non-aged bitumen.

The asphalt mixtures were less water sensitive when RA and rejuvenator were added. Results proved RA improved the adhesion and cohesion of bitumen. Rejuvenator did not deteriorate the cohesion significantly, even though it made bitumen softer.

The results of the TSRST test revealed that RA deteriorates the properties of asphalt mixtures. However, low temperature cracking resistance improved with the addition of a rejuvenator. The improvement was made to such an extent that the asphalt mixture with the highest proportion of RA and rejuvenator had slightly better resistance than the control asphalt mixture.

On the basis of all the results, it can be concluded that pyrolytic rejuvenator enables the increase of RA share in asphalt mixture.

*Rejuvenator Obtained by Pyrolysis of Waste Tires for Use in Asphalt Mixtures with Added… DOI: http://dx.doi.org/10.5772/intechopen.99490*
