TOP-DOWN CRACKING IN

FLEXIBLE PAVEMENTS

INTRODUCTION

Top-Down cracks in pavements initiate at the

pavement surface and propagate downward.

The studies in TDCs are not given enough importance

till late 1990’s.

For many years, researchers have made an effort to

identify the underlying principles that govern this type of

failure.

Top-Down cracking must be dealt with during the

design, construction, maintenance and re-surfacing.

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Top-Down cracking on I-37 south of San Antonio,TX.

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TYPES OF TOP-DOWN CRACKING

Bottom up fatigue (or alligator ) cracking.

Surface down fatigue or longitudinal cracking.

Fatigue in chemically stabilized layers.

Pavement deformation or rutting.

Thermal cracking.

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Bottom up fatigue cracking on the pavement.

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Mechanism of bottom up fatigue cracking.

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Mechanism of surface down fatigue cracking.

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RUTTING IN A PAVEMENT

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CAUSES OF TOP-DOWN CRACKING

Pavement tyre loading such as load magnitude and tyre type effects.

Pavement temperature and temperature gradients.

Bitumen binder and mix aging.

Pavement structure.

Mix composition, raw materials and issues that related to the construction such as segregation of mix.

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CONSTRUCTION ISSUES

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Segregation of

coarse

aggregate

around

cracking.

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CONTROL OF TOP-DOWN CRACKING

Improved heavy vehicle loading control and appropriate

mechanical, axle and tyre technology implementation.

Improved renewable, specialized bitumen surface courses

with good permanent deformation resistance and enhanced

tensile and shear stress endurance.

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MAINTENANCE OF PAVEMENT SUBJECTED

TO TOP-DOWN CRACKING

A water proof layer to protect the underlying pavement.

Increased skid resistance.

A fill for existing cracks.

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FILLING THE CRACK WITH CRACK FILL.

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MAINTENANCE (continued…)

Crack seals

Fog seals

Slurry seals

Micro surfacing

Patches

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CONCLUSION

Top-down crack and segregation seem to have a direct

relation.

Climatic conditions, traffic, aging, structure and

construction qualities are the main causes pointed out for

the initiation and propagation of Top-down cracking

Top-down type cracking may be longitudinal,

transversal or even alligator cracking and may be

found either in or out of the wheel path.

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CONCLUSION (continued…)

More studies on accelerated loading tests may improve

understanding of the effect of construction quality

parameters on the development of TDC.

The studies related to the influence of bitumen aging and

fatigue on TDC is also limited in literature.

More studies on the modeling of the base and sub-

grade layers accounting for the Top-down is necessary.

No relation was found between crack location,

direction and depth.

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REFERENCES

Myers, L.A., “Mechanism of Wheel Path Cracking That Initiates

at the Surface of Asphalt Pavements”, Master’s Thesis, University

of Florida, Gainesville, 1997.

Myers, L.A., “Development and Propagation of Surface Initiated

Longitudinal Wheel Path Cracks in Flexible Highway Pavements”,

Ph.D. Dissertation, University of Florida, Gainesville, 2000.

Jacobs, M.M.J., “Crack Growth in Asphaltic Mixes”, Ph.D.

Dissertation, Delft, The Netherlands, Nelft University of

Technology, 1995.

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Matsuno. S, and Nishizawa, T. (1992). Mechanism of

Longitudinal Surface Cracking in Asphalt Pavement. Proceedings,

Volume 2, 7th International Conference on Asphalt Pavements, The

University of Nottingham, pp. 277-291.

Gerritsen, A.H.; Van Gurp, C.A.P.M.; Van den Heide, J.P.J.;

Molenar, A.A.A. and Pronk, A.C.(1987). Prediction and

Prevension of Surface Cracking in Asphalt Pavements.

Proceedings, 6th International Conference Structural Design of

Asphalt Pavement, The University of Michigan. Ann Arbor,

Michigan, July 1987, pp. 378-391.

REFERENCES ( continued…)

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THANK YOU