Effects of Geosynthetic Reinforcement on the Propagation of Reflection Cracking and Accumulation of Permanent Deformation in Asphalt Overlays Khaled Sobhan, PhD Florida Atlantic University, Boca Raton, FL, U.S.A., Michael Genduso, E.I. Florida Atlantic University, Boca Raton, FL, U.S.A., Vivek Tandon, PhD., P.E. The University of Texas at El Paso, El Paso, TX, U.S.A.,

Rehabilitating Deteriorated PCC Slabs Deteriorated PCC becomes a stable sub- base Eliminates removal/delivery of fill Cost effective and efficient

Problems Associated With AC Overlays - Reflection Cracking - Causes of Reflection Cracking Load-induced differential movements Horizontal movements Curling and warping of PCC slabs Effects Poor road surface Water infiltration Susceptibility to further deterioration

Additional Concerns - Rutting - Causes of Rutting Behavior Heavy vehicle loads Slow, stopping, and standing traffic Compounded by high temperatures Effects Uneven road surface Ponding of water Accelerated deterioration

Objectives Quantify the effects of geosynthetic inclusion on fatigue life as well as permanent deformation behavior Identify the physical mechanisms involved with geosynthetic reinforcement Make recommendations for future testing

Test Equipment Computer controlled MTS machine Time, load, number of cycles, and vertical deformation recorded by MTS system Digital video acquisition focused on area of deformation

Test Specimen Setup mm x mm (18” x 6”) 76.2 mm (3”) thick overlay 13.3 mm (1/2”) plywood w/ 10 mm (0.4”) gap mm (4”) neoprene rubber base

Specimen Preparation Samples created in two lifts Steel mold Hand roller compaction Bulk specific gravity of kN/m 3

Materials Used Coarse Aggregate – rhyolite with chert and limestone Fine Aggregate – arroyo sand Superpave PG Binder Tensar Biaxial Geogrid (BX 1500)

Types of Samples and Placement Configuration All specimens created in 2 lifts Unreinforced control samples Tacked to bottom Embedded in bottom Embedded in middle

Test Procedure Static Tests Monotonically increasing Avg Load Value of Cif was 1110 N Cyclic/Fatigue Tests 2 hz LR 0.2 – 1.2 Established static strength criteria Sinusoidal loading to simulate field conditions

Failure Criteria C if initial – Cycles to initial crack formation C mf mature – Cycles to mature crack formation C tf terminal – Cycles to terminal crack formation

Fatigue Behavior Reinforced samples lasted many more cycles to terminal cracking at all LR’s Embedded samples showed the most significant performance improvement in terms of fatigue life

Analysis of PD At LR up to 0.4 reinforced samples accumulated less PD over a longer life Above LR of 0.4, reinforced samples accumulated slightly more PD over a significantly increased life

LR < 0.4 Performance of Reinforced Samples Lasted at least one order of magnitude longer Sustained about 40% less permanent deformation

LR > 0.4 Sustained 2 – 3 times more permanent deformation Lasted up to 2 orders of magnitude longer Performance of Reinforced Samples

Effects of Placement Location Tacked samples performed poorly Deeper embedment provides a stronger physical connection Proper embedment enables the materials to behave as a composite

Physical Mechanisms Tacked specimen Frictional resistance only Debonding occurs early Embedded specimen Direct resistance to tension Frictional resistance Geogrid remains effective longer

Quantification of Effects Fabric Effectiveness Factor (FEF) Useful in quantification of both cracking and PD performance

Conclusions Specimens with embedded geosynthetic reinforcement outperformed non-reinforced samples in terms of both fatigue life and rutting behavior Proper embedment is required to realize the benefits of geogrid Embedded geogrid provides physical reinforcement as well as energy absorption Debonding, or the separation of geogrid from the AC layer, is the failure mechanism With embedded specimens, this separation occurs gradually as shown by consistent rates of crack propagation and rutting

Recommendations for Future Testing Investigate feasibility of various placement techniques used in practice Evaluate and simulate the most efficient techniques in the lab Perform a cost benefit analysis

Acknowledgements Dr. Khaled Sobhan Dr. Vivek Tandon Florida Atlantic University

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