Workshop 4PBB First Steps for the perpetual pavement design: through the analysis of the fatigue life

Transcription

1 Workshop 4PBB First Steps for the perpetual pavement design: through the analysis of the fatigue life N. Hernández & D. Suarez

2 Introduction In Mexico, asphalt pavements often exhibit premature failures in a short period of time after their construction. One step is to implement new pavement structures such as the structure type known as "Perpetual Pavement".

3 Perpetual pavements Design principle consists in providing enough stiffness in the upper pavement layers to prevent rutting and enough total pavement thickness and flexibility in the lowest HMA layer to avoid bottom-up fatigue cracking. Fatigue Endurance Limit (FEL) Newcomb et al, 2000

4 January february march April May June July August September October November December Average temperature ( C) Pavement Design The study was conducted to design a pavement in the state of Nuevo Leon, Mexico. AADT 7022, 37.5 % heavy trucks and growth rate of 3.8% x10 6 ESAL s for 25 years Month

5 Pavement Design The main materials parameter used for the design is the modulus of each layer. Layer Mr E* Reference (MPa) (MPa) Standard High Modulus - 10,000 AASHTO TP Fatigue Resistant - 3,000 AASHTO TP Subgrade N CMT 1 03/02 Currently M-E methodologies are the most suitable for the design of perpetual pavements. Layer DAMA PerRoad 3.5 DISPAV-5 Thickness (mm) High Modulus Fatigue resistant Subgrade - - -

6 Asphalt Mix Design Mexico has implemented a new methodology for the design of asphalt mixtures called AMAAC Protocol. To ensure that the asphalt mixes has well performance by meeting the following specifications in the mix design: 1. FRL comply with a fatigue life 9.0E +07 at 20 C, 10 Hz, and strain level of 120 me 2. HM comply with dynamic modulus E* MPa at 20 C, 10 Hz, and strain level of 75 to 125 me

7 Asphalt Mix Design Aggregates 100% crushed limestone Mixtures Asphalt type Asphalt content (%) Void content (%) High Modulus PG Fatigue resistant PG

8 Asphalt Mix Design Universal Test System (UTM).

9 Dynamic modulus (MPa) Dynamic modulus. Test results According to AASHTO TP at 10 Hz of frequency and 20 C. Mixture Strain (me) E* HM_ E* average Phase angle Phase Angle (MPa) (MPa) (degrees) average HM_ HM_ FRL_ FRL_ FRL_ Specimen number E* (HM) E* (FRL)

10 Test results Fatigue. According to ASTM D (Determining Fatigue Failure of Compacted Asphalt Concrete Subjected to Repeated Flexural Bending).

11 Fatigue. Test results Three strain levels (700me, 500me, 300me) according to the NCHRP 646 Report (Validation of Endurance Limit of Fatigue for Hot Mix Asphalt). Mixture Va (%) Initial stiffness Strain (me) Cycles to failure (MPa) FRL_01B FRL_01A FRL_02A FRL_05A FRL_04B FRL_05B FRL_03A a FRL_03B HM_01A HM_02B HM_03A HM_05B HM_04B HM_05A HM_06A HM_06B

12 Test results The Fatigue Endurance Limit (FEL). FEL yˆ 0 t s 1 1 n 2 x x 0 S xx

13 Ln (Ln(Stiffness Ratio)) Test results Mixer Va (average ) (%) FEL (me) High Modulus Fatigue Resistant Results (ln (-ln stiffness ratio, SR)) versus the number of repetitions of the tensile strain. 2 0 SR = 0.5 (FEL) Stage I Stage II Stage III Ln (cycles)

14 Conclusions Mechanistic-Empirical methodologies were used to design a perpetual pavement (asphalt mix stiffness). The results of the tests indicate that dynamic modulus of the mixes even exceeded the proposed modulus. The fatigue resistant layer is 100% higher than high modulus layer in the fatigue test for all stain levels. The endurance limit of fatigue was found to be greater for the fatigue resistant mix (269me) than for the high modulus (120me). The presence of the endurance limit was also seen in the tendency of Weibull curve to show a flattening of the slope when tested at the endurance limit strain, indicating an infinite fatigue life.

15 Thank you