Extending Full Depth Reclamation Service Lives

About the report:

The Virginia Department of Transportation (VDOT) has successfully used in-place recycling strategies on approximately 40 pavement rehabilitation projects in the state during the past decade. One such technique, full-depth reclamation (FDR), is usually selected as an alternative to conventional reconstruction to rehabilitate failing pavements where distresses are within the pavement system foundation. To perform FDR, equipment pulverizes, stabilizes, and compacts the bound layers and a predetermined portion of the unbound layers of the existing pavement to form a new stabilized base. Despite its advantages, cement-stabilized FDR may be prone to shrinkage cracking, which remains a critical concern for long-term pavement longevity. Such cracking is primarily induced by hydration and curing processes that generate tensile stresses exceeding the tensile strength of the material. These cracks may then propagate through the asphalt surface, following the underlying pattern in the base layer, and are commonly referred to as “reflection” cracks.

To mitigate shrinkage-related issues, microcracking may be employed to reduce the severity of shrinkage-induced cracking in cement-treated layers by introducing a network of fine cracks to relieve initial stresses within the first 24 to 72 hours after construction. Several transportation agencies have implemented microcracking on FDR. However, the results show that the technique has not always been effective in preventing cracking. Consequently, further research has been recommended to improve the understanding of the microcracking mechanism, its long-term performance, and its interaction with these influencing factors (Louw et al., 2016).

In this study, cement-stabilized FDR test cells were constructed at Virginia’s Accelerated Pavement Testing Facility to assess the differences in performance between microcracked and nonmicrocracked FDR test cells having two different cement contents. A relatively thin hot mix asphalt surfacing was placed over the FDR layer. The selection of a thin layer allows the experiment to focus on responses in the FDR layer. The test cells were instrumented and subjected to loading using a Heavy Vehicle Simulator throughout various weather conditions. The test was conducted during an approximate 2-year period.

The study found that although microcracking resulted in higher deflections, higher vertical stresses, and similar tensile strains than nonmicrocracked test cells, microcracking led to reduced transverse crack development at the pavement surface and within the FDR layer. The reduction in stiffness at early ages from microcracking was also found to mostly or fully recover at later ages. The study recommends that VDOT develop guidance for the construction of FDR projects stating that blend ratios of 1:2 reclaimed asphalt pavement to aggregate base are preferred to blend ratios of 1:1 reclaimed asphalt pavement to aggregate base. The study recommended that VDOT’s Materials Division use the correlations between unconfined compressive strength and elastic modulus or modulus of rupture developed during this study. VDOT’s Materials Division and the Virginia Transportation Research Council should conduct field trials of approximately 5 to 7 FDR projects within the state to evaluate the effectiveness of microcracking for longer times and at different source material combinations.

_{Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.}

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