Full-depth Reclamation Research Articles

Georgia's Use of Lime in Full-Depth Reclamation

The Georgia Department of Transportation completed its first roadway project using lime as a stabilizing agent in full-depth reclamation (FDR). The roadway is performing well after 1 year of service. The FDR was performed on a rural route (Huckabee Road) in Jones County, Georgia, where base and pavement failures had been observed along the roadway. This route served as an excellent candidate for the new process, because the base and pavement failures observed were mainly caused by the instability of the underlying subgrade material, which consisted of micaceous, clay–silt soils. Rather than total reconstruction, lime stabilization was recommended, and a provisional specification was written. Construction began in April 2006 and included reclamation to a depth of 14 in. (35 cm) and incorporation of 56.0 lb/yd2 (30 kg/m2) of lime. The provisional specification required the use of hydrated lime, commercial granular lime, or pelletized quicklime for stabilization; the pelletized quicklime was used. Soil and falling weight deflectometer testing before and after reclamation indicated that substantial improvement, both in the soil properties and structural strength, was achieved by the new process.

Long-Term Performance of Reflective Cracking Mitigation Techniques in Nevada

Hot-mix asphalt (HMA) overlay is one of the commonly used methods for rehabilitating deteriorated pavements. The Nevada Department of Transportation (DOT) uses HMA overlays as a rehabilitation technique for the majority of the state's flexible pavements. One major type of distress influencing the life of an overlay is reflective cracking. In the past, Nevada DOT has experimented with a number of techniques— such as cold in-place recycling, reinforced fabrics, stress relief courses, and mill and overlay—to reduce the impact of reflective cracking on HMA overlays. Several projects were constructed under each category. The long-term field performance of various Nevada DOT reflective cracking mitigation techniques was evaluated; the techniques were used on flexible pavements at 33 field projects. Performances of the various projects were analyzed by fatigue, transverse, and block cracking measurements from Nevada DOT's pavement management system data. In addition, the statistical approach called principal component analysis was used to asses the effectiveness of each of the reflective cracking techniques. The study indicated that cold in-place recycling and mill and overlay were the most effective treatments for reflective cracking of HMA overlays over HMA pavements under Nevada's conditions, except when the existing pavement experiences severe alligator cracking. In such situations, it is recommended that HMA pavement be subjected to reconstruction or full-depth reclamation.

Understanding Internal Structure Characteristics of Foamed Asphalt Mixes with Fracture Face Image Analyses

The rate of use of full-depth reclamation with foamed asphalt to rehabilitate cracked pavements is increasing worldwide. However, the state-of-the-art understanding of foamed asphalt mixes and the state-of-the-practice engineering application are largely empirical because of the lack of in-depth knowledge of this material's internal structure characteristics. A fracture face image analysis framework for quantification of the asphalt mastic phase distribution in foamed asphalt mixes, which is a key microscopic structure characteristic, is described. Fracture face asphalt coverage is a quantitative indicator of asphalt spot distribution on fractured faces and is primarily a function of the asphalt dispersion in the mix, the relative strengths of the asphalt mastic and mineral filler phases, and the boundary conditions of specimen compaction and testing. Fracture face image analyses combined with laboratory testing results are presented. It was found that (a) the strength of the asphalt mastic phase is much less susceptible to moisture conditioning than the strength of the mineral filler phase, (b) filler contents that are too low or too high both negatively influence the effectiveness of asphalt stabilization, and (c) the image analyses show that the impact of asphalt grade on the asphalt distribution in the mix dominates the effectiveness of asphalt stabilization but not the strength of the asphalt cement itself. Additionally, engineers can perform a qualitative fracture face asphalt distribution check at the project level of mix design to diagnose mix problems, for which an interim guideline is proposed.

Alternative Strategies for Rehabilitation of Low-Volume Roads in Nevada

An overview of the attempt by the Nevada Department of Transportation (NDOT) to find alternative rehabilitation strategies to rehabilitate its low-volume road network effectively is provided. Because of Nevada's continuing growth, NDOT is faced with the challenge of how to balance its available funding between pavement preservation and capacity improvement projects. NDOT is responsible for 13,000 lane miles of roadway, of which 3,385 lane miles (26%) qualify as low-volume roads. The low-volume roads have a two-directional average daily traffic of 400 or less. Five roadway projects with a combined total of 111 centerline miles were rehabilitated with 29 combinations of structural and surface strategies. The rehabilitation strategies investigated included full-depth reclamation with lime, cement, asphalts, and foamed asphalt. Various cold-mix, cold-in-place recycling with millings and different rejuvenating agents, and surface treatment test sections were constructed. The constructability issues that were reported during construction are discussed. In addition, pavement condition is examined and laboratory testing is reviewed. Results suggest that NDOT can use alternative rehabilitation strategies in place of its conventional method of 2-in. plant-mix bituminous surface overlay and chip seal to rejuvenate its low-volume roadway network. A cost saving of approximately $100,000 per centerline mile is anticipated.

Georgia's Use of Cement-Stabilized Reclaimed Base in Full-Depth Reclamation

The Georgia Department of Transportation (GDOT) has obtained favorable results from the initial use of cement-stabilized reclaimed base (CSRB) in a pilot full-depth reclamation (FDR) in rural southeast Georgia. CSRB is produced when portland cement is added to sand–clay base from an FDR, and it is used to underlie hot-mix asphalt. GDOT initiated its first FDR in 2004 on County Road (CR) 52 in Long County. A 4.8-km corridor of CR 52 was overlain with a 12.5-mm Superpave® mix, including a 1.8-km section reconstructed with FDR. Samples of the in situ sand–clay base and pavement were obtained for a mix design to determine if these materials would react satisfactorily with portland cement. With the same laboratory design strength requirement for a soil–cement base, the desired level of unconfined compressive strength was obtained at 6% cement. A provisional specification for CSRB was developed, and a 152-m trial section of 12.5-mm mix over CSRB was constructed in July 2004. Construction procedures were adjusted after the trial section was placed, and the remainder of the FDR and overlay was completed. Construction costs for the 1.8-km FDR section were reduced 42% using FDR. Falling weight deflectometer readings taken after construction indicated that deflections were significantly lower in the FDR section than in the overlay-only section. The road is performing well after nearly 1 year of use. GDOT is considering development of a permanent specification for CSRB on non–state routes.

Georgia's Use of Cement-Stabilized Reclaimed Base in Full-Depth Reclamation

The Georgia Department of Transportation (GDOT) has obtained favorable results from the initial use of cement-stabilized reclaimed base (CSRB) in a pilot full-depth reclamation (FDR) in rural southeast Georgia. CSRB is produced when portland cement is added to sand-clay base from an FDR, and it is used to underlie hot-mix asphalt. GDOT initiated its first FDR in 2004 on County Road (CR) 52 in Long County. A 4.8-km corridor of CR 52 was overlain with a 12.5-mm Superpave® mix, including a 1.8-km section reconstructed with FDR. Samples of the in situ sand-clay base and pavement were obtained for a mix design to determine if these materials would react satisfactorily with portland cement. With the same laboratory design strength requirement for a soil-cement base, the desired level of unconfined compressive strength was obtained at 6% cement. A provisional specification for CSRB was developed, and a 152-m trial section of 12.5-mm mix over CSRB was constructed in July 2004. Construction procedures were adjuste...

Cold In-Place Recycling and Full-Depth Reclamation Projects by Nevada Department of Transportation

One of the biggest challenges that public agencies face is how to optimize available funding. With the price of bituminous materials 70% higher than 2 years ago and increased demand for capacity improvement projects, it is more important than ever to use in-place materials when rehabilitating pavement structural sections. Cold in-place recycling (CIR) and full-depth reclamation (FDR) are two pavement rehabilitation strategies that the Nevada Department of Transportation (NDOT) has used for more than 20 years. These strategies have allowed NDOT to save more than $600M over the past 20 years compared with complete reconstruction costs. In addition, traffic interruptions are minimized during construction, and natural resources are preserved. According to the Highway Performance Monitoring System data, NDOT has the highest percentage of its combined National Highway System Interstate and other roadways rated in the “good” category. The reason for this achievement is that NDOT uses a proactive Pavement Management System (PMS) to prioritize its pavement preservation projects. A considerable amount of CIR and FDR rehabilitation work is performed in conjunction with the proactive PMS. Because these strategies are more cost-effective than overlay, mill and overlay, or reconstruction, NDOT can rehabilitate more roads with less money. This report will describe how to select, design, and construct successful CIR and FDR projects. The performances of the strategies are evaluated, and life-cycle cost analysis is developed to demonstrate the cost–benefit of CIR and FDR versus conventional rehabilitation strategies.

Cold In-Place Recycling and Full-Depth Reclamation Projects by Nevada Department of Transportation: State of the Practice

One of the biggest challenges that public agencies face is how to optimize available funding. With the price of bituminous materials 70% higher than 2 years ago and increased demand for capacity improvement projects, it is more important than ever to use in-place materials when rehabilitating pavement structural sections. Cold in-place recycling (CIR) and full-depth reclamation (FDR) are two pavement rehabilitation strategies that the Nevada Department of Transportation (NDOT) has used for more than 20 years. These strategies have allowed NDOT to save more than $600M over the past 20 years compared with complete reconstruction costs. In addition, traffic interruptions are minimized during construction, and natural resources are preserved. According to the Highway Performance Monitoring System data, NDOT has the highest percentage of its combined National Highway System Interstate and other roadways rated in the good category. The reason for this achievement is that NDOT uses a proactive Pavement Managem...

Field Performance Evaluation of Class C Fly Ash in Full-Depth Reclamation: Case History Study

Class C fly ash is a coal combustion product from lignite or subbituminous coal obtained as a result of the power generation process. In recent years, efforts were taken to incorporate self-cementing fly ash into fulldepth reclaimed (FDR) material to improve the structural capacity of asphalt pavement base layers. In this study, existing asphalt pavement in County Trunk Highway (CTH) "JK" in Waukesha County, Wisconsin, was pulverized in place and mixed with fly ash and water to function as a base course. To evaluate the contribution of fly ash to the structural performance of the pavement, nondestructive deflection tests were performed with a KUAB 2m falling weight deflectometer on the outer wheelpath 4 days and 1 year after construction. The modulus of fly ash- stabilized FDR base course increased by 49% 1 year after construction. The structural capacity of the fly ash-stabilized FDR base course in CTH JK also has increased significantly as it ages, because of the pozzolanic reaction. The results of this study indicate that the FDR mixes with selfcementing fly ash may provide an economical method of recycling flexible pavements and reduce the need for expensive new granular base courses for road reconstruction.

Accelerated Pavement Testing Evaluation of the Structural Contribution of Full-Depth Reclamation Material Stabilized with Foamed Asphalt

Research was conducted to determine the effectiveness of the use of foamed asphalt-stabilized reclaimed asphalt pavement from full-depth reclamation (FAS-FDR) as base material for flexible pavements. The experiment, conducted at the Civil Engineering Infrastructure Systems Laboratory of Kansas State University, consisted of constructing four pavements—one with a 9-in. conventional Kansas AB-3 granular base and one each with 6, 9, and 12 in. of FAS-FDR—and subjecting them to a full-scale accelerated pavement test. All four pavement sections were loaded with 500,000 axle load repetitions, at room temperature and under moderate moisture levels in the subgrade soil. The measured stresses and strains as well as the permanent deformation (rutting) observed on the pavement sections indicated that FAS-FDR can be used successfully as a base material. The measured rut depths and compres-sive vertical stresses at the top of the subgrade suggest that a 1-in. FAS-FDR base shows performance equivalent to that of a 1-in. conventional Kansas AB-3 granular base. The effective structural number computed from the falling weight deflectometer tests on the as-constructed pavements showed that average structural layer coefficient for the FAS-FDR base material was 0.18.

Evaluation of Performance of Full-Depth Reclamation Mixes

The full-depth reclamation (FDR) process consists of reclaiming all of an asphalt-bound section along with a predetermined amount of underlying base, with some additive. The objectives of this study were to determine the suitable compactive effort for designing FDR mixes, evaluate the benefits of using different types of additives in terms of improvement of pavement life, and determine suitable structural numbers for pavements recycled with different types of additives. The scope of work for this part of the study consisted of conducting falling-weight deflectometer (FWD) tests, testing an existing pavement before FDR, sampling of materials during FDR, determining the density of in-place material after compaction, compacting of loose mix in the laboratory, determining the density of the compacted samples, conducting FWD testing on the finished pavement, determining the resilient modulus of in-place cores, and analyzing the data to determine the suitable number of gyrations, improvement in pavement life, and structural numbers. It was concluded that samples should be compacted to 50 gyrations during mix design and that a minimum of 98% of density of in-place loose mix samples, compacted to 50 gyrations, should be achieved in the field at the end of compaction. Cost comparison showed that for the options considered in this study, recycling with emulsion (3.4%) and lime (2%) is the most cost-effective option. A visual evaluation of recycled sections after one year showed no significant distress in any section except the one with water as additive, in which a moderate amount of edge cracking was noted.

Laboratory Study of Full-Depth Reclamation Mixes

Full-depth reclamation (FDR) is the technique of in-place recycling of the asphalt-bound layer of a pavement along with part of the underlying unbound layer to produce an improved base material. The objective was to develop a mix design system for FDR and evaluate the performance of designed reclaimed materials from the western part of Maine. Mixes were prepared in the laboratory, and samples were compacted with the Superpave® gyratory compactor. The samples were then tested for bulk specific gravity and resilient modulus. Samples of mixes prepared with asphalt emulsion, water, emulsion plus lime, emulsion plus cement, and emulsion plus lime and cement were also tested for their resilient moduli at different cure times and for their shear strengths. Rut tests were also conducted with the samples under water to evaluate the stripping potentials of the different mixes. The test results showed that maximum density and resilient modulus criteria can be used to select the optimum additive content for water and asphalt emulsion mixes. Comparison of performance testing results showed that mixes with additives develop strength faster and show significantly higher shear strength and stripping resistance than mixes with water only. For the materials tested, addition of lime and cement with asphalt emulsion appears to increase the rate of gain in strength and, hence, to result in faster curing and to increase the shear strength as well as resistance against moisture damage. It is recommended that FDR sections with asphalt emulsion, lime, and cement be constructed and evaluated for in-place performance.

Full-Depth Reclamation Process

Many roads and streets fail structurally after having performed well for several years. The standby treatment of a hot-mix overlay does not address the real problem with most of these roads—inadequate roadbase strength. Public agencies throughout the United States are making fulldepth reclamation (FDR) one of the most popular pavement rehabilitation methods. The FDR process allows complete reconstruction using 100 percent of the existing pavement materials, while correcting grade, cross slope, and underlying pavement problems. In FDR a new base is produced by pulverizing the existing asphalt pavement and mixing it with some of the underlying granular materials. Additional structural strength can be achieved by incorporating new crushed aggregates, asphalt emulsion, foamed asphalt, and chemical stabilizers. Laboratory testing of the reclaimed asphalt pavement (RAP), the subgrade soils, and a mixture of the two will determine whether an additive is needed. The RAP testing should include an extraction for asphalt content and an aggregate sieve analysis. For soils, the minimum testing would include a sieve analysis, sand equivalent, liquid limit, plastic limit, and plasticity index. Guidelines for selecting stabilizers on the basis of these test results are included. Additional strength tests on the stabilized materials can be used in structural design of the pavement. A thorough project evaluation is essential to ensure success. This includes a pavement condition survey, a traffic study, and structural design, in addition to the testing. Proper construction procedures and quality control plus an experienced contractor are necessary.