Soil and Material Inputs for Mechanistic-Empirical Pavement Design

This paper describes the contribution of geosynthetic reinforcement to improved stiffness of a granular layer originally constructed as a working platform but serves as a subbase layer after pavement structure is constructed. Large-scale model experiments were conducted that demonstrate the improved stiffness of granular layers reinforced with 4 types of geosyntetics. The load-elastic deflection data is analyzed by dividing the granular layer into sublayers including a reinforced sublayer with a thickness of 100 mm to isolate the effect of reinforcement on elastic modulus. The comparison of the elastic modulus parameter of this layer to that of the unreinforced sublayers indicate that there is an increase of 1.1 to 3.0 times in the elastic modulus depending on the type of geosynthetic. This improvement is also a function of the overall layer thickness because of the effect of shear strain amplitude that is not accounted for in the elastic modulus model.

Resilient modulus is a key input property of pavement foundation geomaterials, i.e., subgrade soil and base/subbase unbound aggregate, for the mechanistic-empirical design of flexible pavements. Recent research at the University of Illinois has focused on the development of a mechanistic model for the response analysis of geogrid reinforced flexible pavements. This model utilized the finite element approach and considered the nonlinear, stress dependent pavement foundation behavior in a similar way to the level I analysis approach in the 2002 Pavement Design Guide. To validate the response model as well as to develop pavement distress models, nine full-scale flexible pavement test sections, geogrid reinforced and unreinforced, were recently constructed. To quantify the effectiveness of geogrid reinforcement on low volume flexible pavements, the fine-grained subgrade soils were carefully constructed and maintained at California Bearing Ratio (CBR) values 4% or lower throughout the test sections. A complete suite of laboratory and field tests were performed to characterize the pavement geomaterials for mechanistic analysis of the test section response. This required both monitoring of the pavement layer properties during construction and also development of modulus characterization models from multiple regression analyses of the laboratory test data.

Most of the current design methods for geofoam used in pavement structures adopt the allowable working stress concept. These design methods do not fit rationally in conventional pavement design practice such as the AASHTO pavement design guide. To design flexible pavement structures according to AASHTO, the resilient modulus, M_r, for EPS geofoam would need to be estimated. The standard test method for estimating resilient modulus is not suitable for geofoam. Reinforced concrete slab is commonly poured over geofoam subgrades and below the pavement structure. The beneficial contribution of the concrete slab to improving the performance of the geofoam subgrade is not quantified in current design practice. Modified tests were performed to determine resilient modulus values for geofoam. Equivalent resilient modulus estimates were obtained considering the combined response of geofoam subgrade and concrete slab. The estimates were derived from finite element models, reported back calculations from FWD surveys and by correlations. The resilient modulus values obtained for the combination of geofoam and concrete slab are in a range that enables use of conventional pavement design by AASHTO methods.

This paper provides a resource for the design of Roller Compacted Concrete (RCC) for port pavements. Field and laboratory testing results on the properties of RCC, from mix design through field placement, have been collected and compared to existing published correlations. Issues related to the design and construction of RCC pavements, with an emphasis on port pavements, are discussed. Starting with a one-acre test area in 2002, the Virginia Port Authority (VPA) embarked on a large-scale pavement replacement project at Norfolk International Terminals (NIT) that, when complete, will include approximately 56 ha (140 acres) of RCC pavement. To date (Summer 2006), over 18 ha (45 acres) have been placed. The first 6 ha (15 acres) of RCC (including the test area) has been in use for over 3 years. The performance of the installed RCC has been excellent.

Rubblization is an in-place rehabilitation technique that involves breaking the concrete pavement into pieces. This process results in a structurally sound, rut resistant base layer which prevents reflective cracking (by obliterating the existing concrete pavement distresses and joints) that can then be overlaid with Hot-Mix Asphalt (HMA). The design of the structural overlay thickness for rubblized projects is difficult as the resulting structure is neither a true rigid pavement nor a true flexible pavement. The HMA overlay thickness design methodology currently used in the state of Iowa is purely empirical. In the Mechanistic-Empirical (M-E) design approach developed for the analysis and design of rubblized concrete pavements in Iowa, the tensile strain at the bottom of the HMA layer (ɛ_t) is used to predict fatigue life using an HMA fatigue design algorithm and the vertical compressive strain on top of the subgrade layer (ɛ_c) is used to consider subgrade rutting. In the current study, the use of Artificial Neural Networks (ANN)-based structural models for predicting the critical strains based on FWD deflection data, is successfully demonstrated. The ANN-based structural models were validated by comparing the ANN-based strain predictions with the field-measured strains from an instrumented trial project at highway IA-141 located in Polk County, Iowa.

The existing I-5/I-805 intersection area in the City of San Diego, California has been beset serious pavement distress since I-5 and I-805 were completed in the mid 1960s and early 1970s, respectively. Two investigations had been performed by the California Transportation Department (Caltrans) in the early 1970s and 1980s to evaluate the distress that had occurred in two segments in this area. The investigation concluded that settlement in one segment was virtually complete in 1982 and future pavement distress was expected to be minimal, and settlement in the other segment should be complete before 2000. However, serious pavement distresses appear to be continuously developing after 1982 for the first segment, and so does for the second segment after 2000. Further more, many new serious pavement distresses were observed in some other segments in this area. Caltrans would like to reevaluate the embankment conditions for the whole area. Diaz Yourman & Associates (DYA) performed a pavement distress study for the subject area in 2005. A total of 10 segments with severe distresses were chosen for investigation and 29 borings were drilled in these segments (however, only three typical segments are presented in this paper for simplicity). It was found that major reasons for such distresses were ascribed to heavy rain storms, shale material degradation, construction quality, landslide movement, etc. The remaining settlement magnitude and its corresponding time periods were estimated for each segment, and rehabilitation alternatives were provided for each segment as well.

Several counties in Minnesota have used an emulsified asphalt to stabilize unimproved gravel highways in rural areas. This has been done in hopes of reducing dust on such roads, reducing the frequency and extent of maintenance, and improving ride quality. As applications of such a stabilization technique increase, the need to investigate and quantify the benefits of this technique is becoming more important. Several county roads in rural Blue Earth County, in south central Minnesota, were stabilized and monitored during the fall of 2005. Dynamic Cone Penetrometer measurements were taken periodically for several months following the stabilization of two gravel roads using emulsified asphalt. Due to the nature of the emulsion compound, the stabilized material was expected to increase in stiffness with time as curing of the emulsion occurred. The Dynamic Cone Penetrometer results verified that the stiffness did increase with time as expected with this stabilization process.

The Rolling Dynamic Deflectometer (RDD) is a state-of-the-art nondestructive deflection testing device that was developed at the University of Texas at Austin. Over the years, it has been used in many different highway and airport project-level studies. Since the RDD is able to collect continuous deflection profiles, nearly complete coverage of a runway system can be accomplished rapidly and cost-effectively. With this information, pavement engineers are able to pin-point critical sections where rehabilitation work is needed. This type of coverage is especially important in airport rehabilitation projects where considerable savings can be made if defective areas can be precisely identified and repaired. In this paper, four longitudinal deflection profiles collected along Runway 17L-35R at the Grayson County Airport are presented. Two of the longitudinal deflection profiles were collected near the centerline of the runway where most of the aircraft loading occurs. The other two longitudinal deflection profiles were collected near the runway edges. Part of the runway was built over 38 years ago and has remained in service to this date. There are a total of 8 different rigid and flexible pavement cross sections along the 17L-35R runway. Jointed Concrete Pavement (JCP) sections were constructed at the runway ends, while the interior of the runway was constructed with Asphalt Concrete (AC). As described herein, the deflection, or stiffness, characteristics of each pavement section are readily identified and evaluated using the RDD continuous profiles.

This paper describes a case study where asphaltic recycled pavement material (RPM) blended with Class C fly ash was used as base course during reconstruction of a 0.5-km section of asphalt pavement in Waseca, Minnesota. The RPM was blended with cementitious fly ash to increase its bearing resistance and stiffness. California bearing ratio (CBR) and resilient modulus (M_r) tests were conducted on the RPM alone and RPM blended with fly ash (referred to as stabilized RPM, or SRPM). Falling weight deflectometer (FWD) tests were also conducted on the as-built pavement. Addition of fly ash improved the bearing resistance and stiffness of the RPM significantly. After 7 d of curing, CBR of the SRPM (13 to 94) was three to nine times the CBR of the RPM alone (3 to 17) and M_r of the SRPM ranged between 50 and 120 MPa, whereas the M_r of the RPM was 47 MPa. The FWD tests demonstrated that the SRPM maintained its stiffness even after exposure to freeze-thaw cycling during the first winter after construction.

This paper reports results from an on-going research study conducted to evaluate the stabilization potentials of Sulfate Resistant Type V Cement, Class F Fly ash & Type V Cement, Ground Granulated Blast Furnace Slag, Lime & Polypropylene fibers and Lime. Rigid pavement test sections were constructed on the five sections of stabilized subgrade soils and these sections were instrumented and monitored for seventeen months. Instrumentation data obtained from strain gauges and pressure cells as well as elevation surveys were analyzed to address any heave related movements and load carrying potentials of treated subgrades. Overall, based on the monitored data, Cement-Fly ash, GGBFS and Type V Cement treatments showing effective treatments for stabilizing sulfate bearing soils with no heave distress.