Dear research colleagues,
On the 4PB Platform site (http://www.civil.uminho.pt/4pb/acp-f-model.htm) I have placed two new documents on the application of the ACP-F model for 4PB tests.
The first document "Application of the ACP-F model on two similar Dutch mixes" is a comparison between two similar Dutch asphalt mixes. One mix is produced in the traditional hot way and the other one is warmly produced by foaming. It appears that the fatigue properties of the foam produced mix are lower and also it seems that the low endurance strain amplitude is a bit lower. Because sometimes the initial drop in stiffness modulus is high also only for mix 2 a definition Nmn* is used in which instead of N the square root of N is taken. These values are in general close to Nph. In my personal view, Nmn* should be taken in the case the slopes of the evolutions for Smix in phases II and III don’t differ much.
The second document "Application of the ACP-F model on a heavy polymer-modified Dutch asphalt mix" is an investigation of the fatigue properties of a heavily polymer-modified mix. The traditional fatigue life definition Nf,50 leads to nonrealistic fatigue life values (slope of the Wöhler curve was 11). This is because the drop in phase I is already high which resulted in a fatigue life Nf,50 in the middle of phase II “Crack initiation). Using the other possibilities for the fatigue life (N1, Nph and Nmn [ASTM def.] lead to slope values of 7. xxx which are more realistic.
Finally, I like to mention that even in phase III the PID of the 4PB devices in these tests were able to control the strain amplitude with a deviation of +/- 1 microstrain.
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