Black Space mixture parameter

The rheological data obtained from the frequency and temperature sweep testing on the RAP-FBMs was used to calculate the value of the Glover-Rowe parameter at 15^oC and 0.005 rad/ sec by means of equation 21, and evaluate the relative changes in the properties of the mixtures after the environmental conditioning process. Figure 6.17, shows the G-R parameter in the black space for the FBM-RAP mixtures, including also the Virgin HMA and the HMA-RAP mixture, as reference mixtures.

In this figure, the Virgin-HMA at the initial condition (i.e. before the environmental conditioning protocol) is at the bottom right, with low G-R and high δ values. As soon as it starts experiencing the environmental conditioning effects the G-R parameter analysis shows that it migrates towards areas where potentially more age hardening occurs (i.e. higher G-R parameter and lower δ values). When RAP material is incorporated, all the FAM mixtures also exhibit higher G-R and lower δ values with respect to the Virgin-HMA at the initial condition, indicating that age hardening is occurring with the RAP material. Furthermore, from this figure, it can also be seen that the Mechanical foamed-RAP mixtures are within the same area of the plot. However after 30 days conditioning, the Mechanical foamed-RAP mixture manufactured at 120^oC shows more ageing hardening compared to the same mixture manufactured at 90^oC, and for the same conditioning period. In general, the Mechanical

-0.80

-0.70

-0.60

-0.50

-0.40

0 5 10 15 20 25 30 35

𝛾

Conditioning time [days]

Virgin HMA - Environmental conditioning Virgin HMA - Ageing conditioning HMA-RAP - Environmental conditioning HMA-RAP - Ageing conditioning

Mechanical foamed RAP 90C - Environmental conditioning" Mechanical foamed RAP 90C - Ageing conditioning Mechanical foamed RAP 120C - Environmental conditioning Mechanical foamed RAP 120C - Ageing conditioning Zeolite RAP - Environmental conditioning" Zeolite RAP - Ageing conditioning

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foamed-RAP mixtures manufactured at 90^oC and 120^oC exhibit larger differences in the measured G-R and δ values at the different conditioning times compared to the Zeolite-G-RAP mixtures, as was seen in the corresponding master curves of these materials. The HMA-RAP mixture also shows a characteristic response when subjected to the environmental conditioning. From Figure 6.17, it can be seen that after 6 days conditioning, the rheological changes experienced in this mixture do not differ significantly from its initial condition. However, for further conditioning times, the G-R analysis shows that this mixture migrates towards areas where more age hardening is occurring, exhibiting higher G-R values and significantly lower δ values (decrease from 49^o before conditioning to 41^o after 30 days conditioning) with respect to its initial condition.

Figure 6.17 Glover-Rowe parameter for virgin and FAM mixtures containing RAP and different foaming technologies at 15^oC and 0.005 rad/sec after environmental conditioning

A similar plot was constructed with the data of the master curves for all the mixtures after ageing conditioning, as shown in Figure 6.18. However, the expected general trends of the mixtures after age conditioning is generally not seen from the G-R analysis. For instance, after age-conditioning, the mixtures show generally higher G-R parameter values with conditioning time, as expected due to the age-hardening related effects, but the δ moves toward higher or lower values with conditioning time.

This unusual behaviour of a more viscous response (i.e. higher δ values) after ageing, was also observed in the δ master curves for these mixtures at the low frequencies end, and verified in the δ

0.E+00

137

isochronal plots at high testing temperatures. Therefore, since the G-R parameter is calculated at a frequency value of 0.0005rad/s (which falls within the low frequencies area of the master δ curves, or high temperatures), the G-R analysis reflects the same response.

Figure 6.18 Glover-Rowe parameter for virgin and FAM mixtures containing RAP and different foaming technologies at 15^oC and 0.005 rad/sec after pure ageing conditioning

6.8 Conclusions

 Under dry conditions (prior to environmental conditioning), in general, the incorporation of RAP material to all the mixtures resulted in a generalized increase in stiffness compared to that of the Virgin-HMA. Indeed, while complete blending was initially assumed, to target a final penetration of the mixtures containing RAP with the two foaming technologies, equal to that of the Virgin HMA, the degree of blending was found to be a function of the production process and foaming technology used to manufacture the FAM mixtures, as was also seen in Chapter 5.

 In general, the presence of environmental conditions such as moisture and elevated temperatures were observed to modify the rheological properties of the RAP-FBMs. The Virgin-HMA exhibited a pronounced increase in |G*| probably due to oxidative ageing occurring during the

0.E+00 2.E+07 4.E+07 6.E+07 8.E+07 1.E+08

40 42 44 46 48 50 52 54

G-R parameter

Phase angle, [^o]

Virgin HMA-0 days (Ageing) Virgin HMA-6days (Ageing) Virgin HMA-15 days (Ageing) Virgin HMA-30 days (Ageing)

HMA-RAP-0 days (Ageing) HMA-RAP-6 days (Ageing)

HMA-RAP-15 days (Ageing) HMA-RAP-30 days (Ageing)

Mechanical foamed-RAP-90C-0 days (Ageing) Mechanical foamed-RAP-90C-6 days (Ageing) Mechanical foamed-RAP-90C-15 days(Ageing) Mechanical foamed-RAP-90C-30 days (Ageing) Mechanical foamed-RAP-120C-0 days (Ageing) Mechanical foamed-RAP-120C-6 days (Ageing) Mechanical foamed-RAP-120C-15 days (Ageing) Mechanical foamed-RAP-120C-30days (Ageing) Zeolite-RAP-120C- 0 days (Ageing) Zeolite-RAP-120C-6 days (Ageing)

Zeolite-RAP-120C-15 days (Ageing) Zeolite-RAP-120C-30 days (Ageing)

Age

hardening

138

conditioning process in the water bath at 60^oC, generating hardening of the FAM mixtures. The Zeolite-RAP mixture exhibited the highest relative decrease in |G*| among all the mixtures, suggesting that under the presence of moisture, the properties of this mixture could decrease more than in the other materials.

 The changes that occur in the phase angle due to age hardening (more elastic behaviour) for the Virgin HMA and the RAP-FBMs were seen in the low temperature and reduced frequency regions, where the bitumen behaviour is rheologically dominant.

 A comparison of the behaviour of the Virgin HMA and the RAP-FBMs after the environmental conditioning process in the water bath at 60^oC to that of the same mixtures conditioned in an oven at the same temperature but without the presence of water was conducted to factor out the ageing effects observed in the environmental conditioning process. This comparison showed that the ageing occurring in each mixture was different in each type of mixture, and at different combinations of testing temperatures and loading frequencies.

 In general the │G*│ values of all the mixtures increased in both processes. Although the relative ageing occurring in each process was different, the results confirm that there is an effect of ageing occurring in the bitumen present in the FAM materials while present in the water bath at 60^oC. The general increase in the │G*│ of the FAM mixtures after the environmental conditioning could be considered positive in areas where rutting in asphalt mixtures is the main concern in terms of performance. However, in areas where fatigue and low temperature cracking are the main phenomena of interest, additional increase in stiffness of the mixtures could be a major concern.

 Even with the limited conditioning periods, the main result from the │G*│master curves is that the impact of the environmental conditions on the properties of FBM mixtures with RAP materials is highly dependent on the foamed technology used and on the mixing production conditions (i.e. temperature of the aggregates in the Mechanical foamed RAP mixtures).

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Chapter 7 : Combined laboratory ageing