Advances in Pavement Engineering

The Federal Aviation Administration's (FAA) National Airport Pavement Test Facility (NAPTF) was constructed to generate full-scale testing data to support the investigation of the performance of airport pavements subjected to complex gear loading configurations of new generation aircraft. During the first test program, two gear configurations, a six-wheel dual-tridem landing gear, Boeing 777 (B777), in one lane and a four-wheel dual-tandem landing gear, Boeing 747 (B747), in the other lane were tested simultaneously using the National Airport Test Machine (NAPTM). To monitor the effect of time and traffic on pavement structural responses, Heavy Weight Deflectometer (HWD) tests were conducted on the trafficked lanes and on the untrafficked centerline of flexible test sections as trafficking progressed. Rut depth measurements were made at regular intervals during trafficking. Using the HWD deflection measurements, Deflection Basin Parameters (DBPs) were derived. The potential for using the DBPs to characterize the structural degradation in airport flexible pavements as a result of traffic loading was explored. The DBPs were also used to compare the severity of B777 traffic with that of B747 traffic on the flexible test sections. The trends in DBPs with respect to traffic were compared with rutting trends. The Area Under Pavement Profile (AUPP), Surface Curvature Index (SCI), and the Impulse Stiffness Modulus (ISM) were found to be sensitive to pavement structural degradation under traffic loading. In most cases, the DBPs under B777 and B747 trafficking are comparable indicating similar structural degradation. The DBP trends agree well with the rutting trends.

The resilient modulus is used in the characterization of base and subgrade soils and in the design of pavement structures. The resilient modulus of subgrade soils can be estimated by using expensive and time-consuming laboratory test results or from overestimated backcalculated values from nondestructive test results. These limitations imply that the need of a simple and inexpensive insitu geotechnical test method to estimate the resilient modulus of subgrade soils. The dynamic cone penetration test is considered as a simple, rapid, and economical insitu test in geotechnical applications. However, the application of the dynamic cone penetration test in evaluating the resilient modulus of pavement subgrade soils is not well known. The objective of this paper is to develop correlations to predict the resilient modulus of subgrade cohesive soils from the dynamic cone penetration test parameters, soil type, moisture content, and dry unit weight. Twelve laboratory-compacted large soil samples of two cohesive soil types and six test locations in two existing pavements were used to perform the dynamic cone penetration tests. Laboratory resilient modulus and soil property tests were also performed. The preliminary estimation models were developed for the prediction of the resilient modulus of subgrade soils from the dynamic cone penetration test parameters, moisture content, dry unit weight, and other soil properties. The models predicted separate data sets that were not used in their development, indicating the success of the application of the dynamic cone penetration test in evaluating the resilient modulus of pavement subgrade soils.

This paper defines and presents imaging based aggregate morphological shape indices of 39 coarse aggregate materials recently collected in a pool fund research study. Using a three-dimensional imaging system, University of Illinois Aggregate Image Analyzer (UIAIA) and following test procedures previously established for the UIAIA, imaging based morphological indices were defined for the three-dimensional shape, size, angularity, and surface texture properties from the acquired images of the coarse aggregate particles. Using statistical techniques, four categories were established for commonly used coarse aggregate types based on image analysis shape property data. A definite relationship was shown to exist between coarse aggregate angularity and surface texture imaging indices, which were also linked to laboratory and field performances of asphalt mixtures.

The grain-size-distribution (GSD) of a soil is intimately related to its pore size distribution and hence, the GSD holds a close relation with the soil-water characteristic curve (SWCC). In addition, the plasticity index (PI) is a measure of the water holding capacity of the soil and therefore, it plays an important role in shaping the SWCC. This paper presents two sets of statistically derived equations that describe the SWCC of non-plastic and plastic soils. Data from 154 non-plastic soils and 63 plastic soils were analyzed. Soil samples were collected as part of the National Cooperative Highway Research Program (NCHRP) 9–23 project entitled Environmental Effects in Pavement Mix and Structural Design Systems. Samples were obtained from underneath paved roads of 30 sites located throughout the United States. The soil samples were subjected to laboratory testing that included index testing and SWCC testing. SWCCs were determined using a newly developed pressure plate device capable of overburden pressure application, continuous measurements of moisture content, and volume change monitoring. In addition to the collected field data, a database of published soil index properties and SWCCs was incorporated to the analysis. Each SWCC data set was fitted with Fredlund and Xing curve, which provided an S-shaped curve with four parameters, a_f, b_f, c_f, and h_rf. Using multiple regression analysis, equations were derived for these four parameters based on predictors derived from GSD and PI. The equations presented in this paper are useful in predicting the SWCC of any given soil without carrying out actual SWCC testing and they can easily be incorporated into computer codes to solve various unsaturated soil mechanics problems such as determining moisture beneath covered areas.

A laboratory study was undertaken to investigate the effect of wet-dry (W-D) cycles on aggregate bases, namely, Meridian (M), Richard Spur (RS), and Sawyer (S), stabilized with cement kiln dust (CKD), class C fly ash (CFA), and fluidized bed ash (FBA). Cylindrical specimens were molded, cured, and subjected to W-D cycles prior to testing for resilient modulus (M_r). It was found that the M_r values for most of specimens decreased as W-D cycles increased. Sawyer aggregates stabilized with CKD, however, exhibited an increase with W-D cycles up to 8, beyond which a decrease in M_r occurred. It is believed that such a decrease/increase in M_r values may be attributed to the deceleration/acceleration of pozzolanic reactions. Laboratory observations revealed visual degradation of only Sawyer specimens stabilized with fluidized bed ash after 16 W-D cycles; no M_r tests were performed on the degraded specimens.

Excessive settlements occur in granular soils where specified field compaction is based on Standard Proctor (ASTM D 698, AASHTO T 99) maximum dry unit weights. A laboratory test program evaluated alternative test methods for granular soil compaction control and showed that a Vibrating Hammer method (similar to British Standard BS 1377:1975, Test 14) has great promise for laboratory compaction of these soils. A One-Point Vibrating Hammer test on an oven-dried soil sample provides the maximum dry unit weight and water content range for effective field compaction of granular soils. The maximum dry unit weight obtained is comparable to that from other current methods such as the Vibrating Table test (ASTM D 4253) and the Modified Proctor test (D 1557), and is greater than that from the Standard Proctor test (ASTM D 698). This test method is applicable to a broader range of soils than current vibratory table compaction tests (up to 35 percent nonplastic fines and up to 15 percent plastic fines). The equipment is relatively inexpensive and is portable enough to be taken into the field. The test is easier and quicker to perform than the other methods mentioned above and provides reproducible and consistent results. The paper also introduces a simple calibration procedure to check that the vibrating hammer is supplying sufficient energy to the soil.

Pavements currently in existence in most airports have not been designed to sustain the loading imposed by heavier and bigger aircraft, like the Boeing 747-400, Airbus A-380 and Boeing 777. With the help of the National Pavement Test Facility of the Federal Aviation Administration based in Atlantic City, a finite element model will be created capable of predicting shear failures in the subgrade. The pavement test facility at Atlantic City will serve as a valuable source of data for the study and at the same time, the finite element modeling study will enhance the understanding of pavement behavior. Finite element analyses techniques will be used to determine the failure mechanism in a pavement system under moving aircraft loads. The three-dimensionality of the failure surface under actual wheel loads with wander requires that computationally intensive three-dimensional models be used. The finite element techniques employed are verified against available failure data from the National Pavement Test Facility.

This research study focuses on the laboratory mechanistic evaluation of soil-cement mixtures reinforced with processed cellulose-fibers (PCF). The fibers are derived from the processing of wood and have enhanced micro-crack stabilization due to higher fiber density, high length-to-diameter ratio, bond strength and tensile strength. Four soil types from various project sites in the state of Louisiana were acquired and tested. Laboratory tests including the durability, unconfined compressive strength, indirect tensile strength, and indirect tensile cyclic load tests were conducted on both with and without PCF soil-cement mixtures. The results indicated that the mechanistic characteristics of the PCF soil-cement mixtures were functions of fiber dosage, soil-type and curing time. In general, the durability, unconfined compressive strength, indirect tensile strength and fracture toughness values either remained same or exhibited higher values for PCF soil-cement mixtures. It was found that optimum fiber dosage is required for soil modification. The indirect tensile cyclic load test data indicated that the resilient modulus of the PCF soil-cement mixtures either remained same or was greater than soil-cement mixtures alone. Moreover, the horizontal plastic deformation rate is significantly lower for soil-cement-fiber mixtures. The implication of the results is that the PCF reinforcement at optimum fiber percentage may mitigate the tensile or shrinkage crack formation in the soil-cement mixtures for road bases thereby improving the structural capacity and performance of pavements.

This paper presents properties of new synthetic lightweight aggregates (SLAs), made of plastic and fly ash, and their implications for use as aggregate in pavements systems. These aggregates are manufactured through a thermal process that combines and co-extrudes plastic and coal fly ash. The plastic acts as a matrix material that binds and encapsulates the fly ash particulates. In this study, index and compression properties are presented for SLAs made with different plastic types. All aggregates have an approximate fly ash to plastic ratio, by weight, of 80:20 and use fly ash with carbon contents of 15% to 30%. Index properties presented for the various SLAs include gradation, specific gravity, and water absorption capacity. A series of one-dimensional compression tests, at moderate and elevated stresses, were performed to compare the compression behavior of SLAs with that of traditional aggregate (sand). The results shows that SLAs have relatively substantial elastic deformation and rates of secondary compression but also exhibit substantial rebound upon unloading when compared to sand. However, at elevated stresses, the rate of secondary compression for both the SLAs and sand approach similar values, with some SLAs actually exhibiting a slower rate of secondary compression. Overall, the compression results show that SLAs will have advantages (e.g., lightweight, stress absorption) and disadvantages (e.g., excessive deformation) over the use of traditional granular materials in pavement systems.

Over 130 tests were performed on three soils of Chennai, while studying experimentally the relation between pulse velocity, dry density, water content and compacting effort. Laboratory test specimens were prepared by static and dynamic compaction methods in CBR mould (150 mm dia.), Proctor mould (100 mm dia.) and split mould (38 mm dia.). P-wave velocity was measured on each of the compacted specimen by adopting the direct transmission method. Unconfined compressive tests were also conducted on compacted samples of 38 mm diameter to establish the relation between compressive strength and pulse velocity. All soils tested exhibited an increasing pulse velocity with increase in dry density until the optimum water content. A rapid drop in pulse velocity was observed subsequently with decrease in density irrespective of the type of soil, compaction method, energy of compaction and size of the specimen. The peak velocities and maximum densities were within ± 1 % variation of water content in all the compaction methods, irrespective of the soil type and compaction energies studied. This observation is in conformity with the findings of earlier investigators. Further the pulse velocity measured on the compacted soils was correlated with compaction density, compaction moisture content, strength and modulus, and sets of empirical relations among these parameters are presented for the soils tested. These equations are validated through a set of data obtained on another soil of Chennai.

The fundamental mechanisms behind the initiation and propagation of reflective cracks in asphalt concrete overlays are not well understood. A novel approach is currently underway to investigate reflective cracking by integrating laboratory tests and numerical analysis to develop and validate an approach to predict reflective cracking in pavement structures. Asphalt overlays are subjected to thermal and mechanical loadings, which induce a combination of tension and shear in the overlay. The selection of a laboratory fracture test that has the ability to induce a range of mode-mixity at the crack tip is paramount for the integrated approach to be successful. A promising test geometry that has successfully been used for obtaining Mode I (tensile opening) fracture properties of asphalt concrete is the single-edge notched beam (SE(B)). With a slight modification to the notch location, mixed-mode (combination of opening and shearing) fracture can be investigated with the notched beam geometry using the same testing fixtures, instrumentation, etc. Test procedures have been developed for the SE(B) test that allow investigation of the crack front profile, discrete crack growth using crack detection gages, and variation of fracture energy with temperature. A single mixture was tested using the proposed mixed-mode test geometry with various notch offsets. Through the initial stages of the SE(B) test development, the test provided satisfactory results in terms of the expected trends in fracture energy.

Moisture-induced damage of asphalt mixtures can contribute to serious distress, reduced performance and increased maintenance of asphalt pavements. A recent study by the Texas Transportation Institute shows that surface free energies (SFE) of a HMA mix and its constituents (aggregate and binder) can be a valuable indicator of moisture damage in HMA because they relate to some of the mechanisms of moisture damage that are not addressed in the retained strength tests currently used by many transportation departments. To this end, the SFE of selected performance graded asphalt binders was evaluated from the measurement of dynamic contact angle between an asphalt binder and a liquid solvent. Dynamic Wilhelmy Plate Method (DWPM) was used for the dynamic contact angle measurements with some modifications including using cylindrical or tube samples instead of plate samples. Two different asphalt binders, namely PG 64-22 and PG 70-28, were used. Results show that PG 70-28 has higher energy of cohesion, which provides a higher cohesive strength than PG 64-22. Thus, PG 70-28 is expected to provide a better resistance to moisture-induced damage. Research is currently being pursued to evaluate the effect of anti-strip additives on the asphalt binders. The findings of this study suggest that the SFE concept can be used to develop new test methods for identifying moisture damage susceptible mixes during the design stage.

A review of material rheology established equations that express the dynamic modulus, phase angle, and resilient modulus of asphalt concrete in terms of basic rheological element properties. Asphalt concrete core samples from a national highway project site in Ohio were subjected to a variety of mechanistic laboratory test procedures. Examinations of the creep test data pointed out that the six-element solid model was the most realistic among relatively simple models to describe engineering behavior of asphalt concrete material under monotonic loading. The creep test data were analyzed further by the successive residuals method to determine the parameter values involved in the six-element solid model. In order to assess the six-element solid model's ability to predict dynamic behavior of asphalt concrete, the parameter values were then applied to the dynamic modulus, phase angle, and resilient modulus equations established earlier. The results showed that the equations were unsuccessful in predicting dynamic properties of asphalt concrete due to a short coming involved in the test set-up.

This paper presents the comparison between the results of the Semi-Circular Bending (SCB) test and that of the Indirect Tensile (IDT) test in characterizing the tensile strength of hot-mix asphalt (HMA) mixtures. Analytical and numerical simulations were employed to interpret the experimental results. IDT test, a standard test method of AASHTO and ASTM, is adopted by most state highway agencies. Despite its broad usage and many advantages, the permanent deformation under the loading strips is undesirable and in some cases unbearable for the evaluation of the cracking potential of asphalt mixes. SCB test could significantly reduce the loading strip-induced permanent deformation and thus is more suitable IDT for evaluating tensile properties of HMA mixtures. The results from this study indicated that SCB and IDT test were fully comparable and convertible.

A cohesive zone model (CZM) is employed to investigate fracture behavior of asphalt concrete. The separation and traction response along the cohesive zone ahead of a crack tip is modeled by an exponential cohesive law specifically tailored to describe the cracking in asphalt pavement materials by means of a softening cohesive law. This exponential cohesive model is implemented into a user-defined element (UEL) of the ABAQUS software. Using the CZM, first, crack propagation in a mode I single-edge notched beam (SE(B)) test is simulated such that the cohesive parameters of finite material strength and fracture energy are calibrated based upon the experimental results. Then, the mixed-mode SE(B) test is simulated using the calibrated cohesive parameters. The crack trajectory of the numerical simulation is found to compare favorably with experimental results.

Fatigue is a distress that leads to failure in asphalt and portland cement concrete pavements. Finding better ways of understanding and explaining fatigue behavior in these construction materials will lead to the establishment of better design approaches to prevent fatigue failure. This paper presents a dissipated energy approach to fatigue characterization in both asphalt concrete and portland cement concrete. As a contribution to previous research on dissipated energy approaches, this paper presents a comparison of a dissipated energy approach to fatigue characterization to traditional or current fatigue approaches for these materials. Changes in the resistance of materials to applied cyclic loads over several cycles can be characterized by examining the change in dissipated energy from one cycle to the next and plotting the results as a function of the number of load cycles. This produces the dissipated energy ratio (DER) curve. The DER curves for asphalt concrete and portland cement concrete follow the same trend; a rapid decrease, followed by a plateau region for the majority of the fatigue cycles. The region of the dissipated energy curve that coincides with material failure is distinct as it shows a rapid increase of dissipated energy ratio with additional load cycles. The objective of this paper is to show the applicability of the DER approach to the fatigue behavior of concrete materials. The DER approach is compared to a viscoelastic continuum damage approach and the traditional 50% reduction in initial stiffness approach for asphalt concrete and to the Aas-Jakobsen and Hsu models for portland cement concrete. For each material, the number of cycles to failure determined from the dissipated energy approach correlates well with the number of cycles to failure predicted from existing models.

Cracks in asphalt pavements create irreversible structural and functional deficiencies that increase maintenance costs and decrease lifespan. The understanding of fracture behavior in asphalt concrete laboratory specimens is currently an open research area that comprises a vital link in the ability to design asphalt concrete paving mixtures and flexible pavement structures that resist cracking. Towards this end, a micro-fabric distinct element modeling (MDEM) approach was implemented in the two-dimensional particle flow software package (PFC-2D) to study the complex crack behavior observed in asphalt concrete fracture tests. This behavior was simulated with an MDEM model having complex morphological features, but relatively simple constitutive models in both the bulk material regions and at the material interfaces. A double-cantilever beam (DCB) test was used to verify the implementation of bilinear cohesive zone model (CZM) in PFC-2D, which yielded a favorable comparison between MDEM results and the closed-form reference solution. The MDEM approach was then employed to investigate the fracture behavior of asphalt concrete in a new disk-shaped compact tension test (DC(T)). The cohesive model parameters of material strength, critical displacement jump and fracture energy were calibrated in conjunction with the homogeneous DC(T) fracture model for a relatively simple mode-I fracture simulation with homogeneous bulk materials properties and a pre-defined crack path. The calibrated model was then extended to simulate fracture in a DC(T) specimen with a heterogeneous fabric description in an attempt to capture some of the more complex fracture mechanisms in the process zone, such as aggregate bridging, crack turning, and crack branching. Both homogeneous and heterogeneous models were successfully calibrated to experimental data, but further experimental validation is still needed.

In this study, an attempt was made to estimate the degree of compaction using specific parameters derived from two-dimensional image analysis of cut-sections of HMA specimens. This was done by studying the inter-particle distances in HMA specimens compacted using a Linear Kneading Compactor (LKC) at different air voids. The imaging parameters were based on nearest neighbor distance methods such as Delaunay triangulation and Voronoi tessellation schemes. A program was developed using an image processing software to analyze the changes in the coarse aggregate distribution and orientation during compaction. In the second part of the study, a two-dimensional cross-section of HMA was simulated in computer using the mixture design information. At the end of each simulation, all the parameters were measured and the results were compared with the results from image analysis. The results of the study indicated that the changes in inter-particle distances during compaction could be measured using two-dimensional image analysis of a sawed section of a sample. The study of the inter-particle distances would enable determination of compaction in different directions and comparison between different compaction techniques. Developing such a technique would help determine if a specimen is compacted to different degrees at different locations of the pavement and help in decreasing the differences between laboratory and field compaction techniques.

When designing any civil structure, it is necessary to determine the properties of the various material components under conditions pertinent to their eventual use. Geosynthetic reinforced earthen structures are no different. Standard tension tests currently exist to determine basic material properties of geosynthetics used to construct reinforced walls, slopes, embankments and other static structures. However, because these material tests apply slow monotonic loads at room temperature, they may not properly represent conditions pertinent to geosynthetic reinforced pavements. A number of research projects have been conductedn the past to investigate possible differences in material properties using various temperatures, confinements, load types, and strain rates. This research effort conducted an extensive literature review to study the effects of these four parameters on geosynthetic material properties. Additionally, material tests were conducted to determine how cyclic loading affects geosynthetic material properties. Modifications were made to the existing wide-width test protocols (ASTM D4595 for geotextiles, and ASTM D6637 for geogrids) to incorporate cyclic loads. These dynamic wide-width strain-controlled tension tests demonstrated great promise for providing values of elastic material properties. The results from these tests showed that the modulus of the geotextile materials changed at various levels of initial permanent strain, while the modulus of the geogrids remained relatively constant. Future testing will be conducted to further examine similar effects due to temperature, strain rate, load type and confinement.

Geogrid products placed in pavement base layers apparently improve performance. Currently the only way to prove this is by evaluating full-scale roadways or laboratory-scale models of a pavement system, which is time-consuming and expensive, making them impractical on a project- or product-specific basis. Isolation of the improvement mechanism is difficult due to the multiple variables present in each component of the pavement system. The bending stiffness index test has been developed to isolate and measure geogrid performance in the base layer of a pavement system. The objective of this paper is to evaluate and refine the bending-stiffness index test described by Sprague et al. The effects of the apparatus and testing variations on the test results are addressed through a series of tests. The results show that the measured bending stiffness for a compacted base course alone is consistent with published values. In addition, the bending stiffness can be measured with enough resolution to distinguish an increased stiffness when the base course is reinforced with a geogrid. Also, the measured bending stiffness can be used to compare the effects of different geogrid products. The ability to distinguish the effect of a geogrid and to compare different geogrids decreases as the confinement stress on the base course increases.

Recent research at the University of Illinois has focused on the development of a finite element based mechanistic model to provide design tools and solutions for constructing geogrid reinforced flexible pavements. One essential feature of the mechanistic model is the representation of the soil/aggregate-geogrid interface by the use of a simple, realistic interface element having normal and shear spring stiffnesses between the geogrid and soil/aggregate continuum elements. Varying the shear stiffnesses in the interface elements specified the various levels of interface bonding, i.e., perfect bonding and partial bonding. The mechanistic model pavement response predictions including interface shear stresses compared favorably with the ABAQUS contact model results for a set of model parameters. Further, relative displacements computed at the soil/aggregate-geogrid interfaces were small and unlikely to cause any large movement or slip of the geogrid at the interface indicating the use interface elements with spring stiffnesses was adequate.

Finite element response models for geosynthetic base-reinforced pavements have most commonly been developed by direct inclusion of structural elements for the reinforcement sheet and contact surfaces between the reinforcement and surrounding materials. Models established in this fashion have historically shown a gross underprediction of pavement performance and corresponding benefit from the reinforcement. This indicates that fundamental mechanisms and processes involved in reinforced pavements are missing from a simple static, single load cycle response model analysis of the type described above. In particular, processes involving interaction of the reinforcement with surrounding pavement materials during construction and compaction of the base aggregate layer, and during repeated loading by vehicular traffic is absent from a simple analysis of the reinforced pavement. These processes lead towards the development of lateral confinement of the base aggregate layer that is otherwise absent or greatly diminished in pavements without reinforcement. This paper describes distinct response model modules created to account for effects of reinforcement on lateral confinement of base aggregate materials during roadway compaction operations and in-service vehicular loading. The combination of these response model modules results in a rational method for evaluating the performance of base-reinforced pavements. Results from the method are compared to several cases of observed reinforced pavement performance in previously constructed test sections.

To mobilize sufficient reinforcement contribution in the geotextiles, large deformation must occur at the subgrade level but this may compromise the serviceability state of the unpaved road. Pretensioning of geotextiles was found to be very effective in enhancing the reinforcement potential of the geotextiles without this excessive deformation. This paper will report the findings from laboratory tracking tests and the application of pretensioning method in the field. Six types of geotextiles (nonwoven, woven and composite) were evaluated. The benefits of pretensioning were evaluated by comparing the rutting behaviour of the pre-tensioned systems over the control test systems that has no geotextiles. Pretensioningstrain for some geotextiles was also varied to investigate the benefits of pretensioning under different pretensioning strains. It was concluded that the amount of rutting improvement due to pretensioning is a function of geotextiles type and tensile modulus, survivability of geotextiles and the pretensioning strain ratio (ε_PT/ε_ULT). The pretensioning method was successfully implemented in an actual field project in Singapore, demonstrating the feasibility of this method.

This paper will discuss the County of San Diego's practice of placing surface treatments over pavement reinforcing fabric in the desert area of Borrego Springs. This road maintenance method consists of placing pavement reinforcing fabric, followed by a single layer of chip seal and fog seal on roads in an effort to reduce or eliminate the need for crack sealing. Because of extreme desert temperatures and exposure to flash floods, cracks on the road surface are a constant maintenance problem. Crack sealing is normally done to prevent moisture from penetrating into the pavement and cause rapid deterioration of the pavement and underlying base. However, due to the extensive number of surface cracks, the cost to crack seal depletes the funds needed to apply a surface treatment to the road surface. The use of fabric, in conjunction with chip sealing and fog sealing, has eliminated the Count's need for crack sealing and provides cost savings in their efforts to maintain public roads. This paper will address the placement of fabric in conjunction with chip sealing and fog sealing via contracts awarded to private construction firms. Life cycle cost analysis will also be included.

In 2002, the Greenville County, South Carolina, Department of Public Works (GCDPW) was asked by a paving contractor to allow the substitution of a thicker overlay in place of the specified paving fabric-thinner overlay remediation. The request prompted the PWD to facilitate a review of pavement performance to establish relative cost/effectiveness information for the various remediation methods used on County roads. The review has provided the potential to independently quantify the relative benefits of using paving fabric as compared to increased overlay thickness or other maintenance techniques. This paper presents the tabulation of data for an initial selection of roads, including the pavement condition at time of maintenance, the selected pavement maintenance technique and associated costs, and the subsequent pavement performance. Additionally, an evaluation of the data along with conclusions related to evidence of the effectiveness of paving fabric is presented.

In an effort to quantify the contribution of geotextile separators to the long-term performance of pavement sections, falling weight deflectometer (FWD) testing was carried out over a 12-year period at a test section in southwest Washington State. Five different geotextile separators as well as a soil-only control section were installed in the test section with a different base course thickness in the two lanes of a low volume but heavily loaded rural state highway. The performance of the separators was evaluated during construction and 5 and 12 years after construction. Field and laboratory tests were conducted on the subgrade, granular base materials, and the geotextiles as part of the effort to correlate the performance of the pavement section to the presence of the geotextile separators. As part of the most recent evaluation, the FWD results were analyzed using two recently developed interpretation methods, the FWD Area Program (version 2.0) and Evercalc Pavement Backcalculation Program (version 5.20). The results from the FWD Area Program generally showed a decrease in the adjusted deflections, and increases in the area parameter and subgrade modulus along the test section over the 12-year period. The greatest increase in subgrade modulus occurred in the six months following construction. The control sections exhibited behavior similar to the sections with geotextiles, suggesting that for relatively thick pavements, geotextiles separators may not provide a significant contribution to the long-term performance of the pavement. The Evercalc backcalculations indicated an increase in the adjusted pavement and subgrade moduli over the 12-year period. The sections that contained geotextiles generally showed an increase in the base course modulus, however, some of the analyses showed little to no increase in the base modulus in the control (soil only) sections. The results suggest that geotextiles might contribute to an increase in the base course modulus over time. These findings were also correlated with the results of the field and laboratory investigations.