Date of Graduation

12-2024

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Braham, Andrew F.

Committee Member

Hall, Kevin D.

Second Committee Member

Barry, Michelle L.

Keywords

Full Depth Reclamation; Reclaimed Asphalt Pavement; Stabilization; Unconfined Compressive Strength

Abstract

Enormous amounts of money to replace all poorly maintained roads with brand new construction or with rehabilitation options like the mill and overlay which neglects the address of underlying pavement issues. To reduce the cost intensity of new construction of dilapidated pavements, state departments of transportation are seeking cost-effective techniques to rehabilitate roads. One of the techniques that have been explored and implemented by state DOTs is full-depth reclamation. Full depth reclamation (FDR) as a pavement rehabilitation technique is the reclaiming and recycling of an existing pavement with a predetermined amount of existing base layer. The combination of the reclaimed asphalt pavement (RAP) and the predetermined amount of existing base layer is often stabilized with virgin aggregates, chemicals or asphalt materials and then subjected to pulverization and densification, resulting in a new base layer with improved strength and structural stability. Despite the continued exploration of FDR, there is limited knowledge on the technique’s response to varying material qualities and quantities. This study aimed to characterize FDR mixes with a range of aggregates and soil types, investigate the effect of stabilization on FDR mixtures by evaluating the strength to determine the optimum design, and explore characteristics of stress-strain curves for a better understanding of the effect of material properties on FDR mixtures. These aims were achieved via the unconfined compressive strength (UCS) characterization of FDR mixtures.
The materials explored include bound material in the form of reclaimed asphalt pavement (RAP), unbound road base material of different qualities, subgrade materials, fat clay and low plasticity silt. Portland cement, foamed asphalt, and emulsified asphalt were used as stabilizing agents for the FDR mixtures. UCS tests under wet and dry durability conditions were performed on all test samples to provide an index of performance. The compressive strength and moisture susceptibility were evaluated to ascertain the efficacy of the stabilization methods based on the outcome of laboratory investigation. A dry strength threshold of 300-500 psi was defined.
Results showed bound asphalt influences cement hydration bond development with a 23% to 64% increase observed in dry strength of cement stabilized RAP/HQB/ML (1:8:3) compared to RAP/HQB/ML (5:4:3) mixtures and bituminous stabilizers were more suited for mixtures having more bound material content due to residual binder activation with the RAP/HQB/ML (5:4:3) 1% Portland cement plus 3% asphalt emulsion samples having a strength increase of 290%. It was also found that cement stabilization is more ideal for FDR mixtures with a clayey subgrade while bituminous stabilization worked better in mixtures with silty subgrades. Based on this study, 4% Portland cement by mass showed good results for the stabilization of FDR mixtures.
In conclusion, Portland cement stabilization worked with a wide range of materials and accommodated high plasticity mixtures. However, shrinkage cracking concerns may arise with higher cement contents. Portland cement-stabilized FDR mixtures typically have higher compressive strength values compared to mixtures stabilized with bituminous agents. The resistance of the cement stabilized mixtures to moisture damage was also greater than that of the mixtures stabilized with asphalt foam or asphalt emulsion at the same stabilization content as seen in all six FDR blends explored. Bituminous stabilization methods were not as versatile due to a limitation in the materials they can effectively treat chiefly caused by the percentage of fine particles (P200) ranging from 18.0% to 26.1% across the six material blends.

Download

Share

COinS