Labuz, Joseph F.

The objective of this project was to render the Falling Weight Deflectometer (FWD) and Ground Penetrating Radar (GPR) road assessment methods accessible to field engineers through a software package with a graphical user interface. The software implements both methods more effectively by integrating the complementary nature of GPR and FWD information. For instance, the use of FWD requires prior knowledge of pavement thickness, which is obtained independently from GPR.

Currently, MnDOT pavement design recommends granular equivalency, GE = 1.0 for non-stabilized full-depth reclamation (FDR) material, which is equivalent to class 5 material. For stabilized full-depth reclamation (SFDR), there was no guideline for GE at the time this project was initiated (2009). Some local engineers believe that GE of FDR material should be greater than 1.0 (Class 5), especially for SFDR. In addition, very little information is available on seasonal effects on FDR base, especially on SFDR base. Because it is known from laboratory studies that SFDR contains less moisture and has higher stiffness (modulus) than aggregate base, it is assumed that SFDR should be less susceptible to springtime thawing. Falling Weight Deflectometer (FWD) tests were performed on seven selected test sections on county roads in Minnesota over a period of three years. During spring thaw of each year, FWD testing was conducted daily during the first week of thawing in an attempt to capture spring thaw weakening of the aggregate base. After the spring thaw period, FWD testing was conducted monthly to study base recovery and stiffness changes through the seasons. GE of SFDR was estimated using a method established by MnDOT using FWD deflections, and the GE of SFDR is about 1.5. The value varies from project to project as construction and material varies from project to project. All the materials tested showed seasonal effects on stiffness. In general, the stiffness is weaker in spring than that in summer and fall.

The objective of this project was to provide a qualitative assessment of the Minnesota Department of Transportation's Intelligent Compaction (IC) Specifications. IC is an attractive approach to evaluate the compaction quality because it involves continuous and instantaneous evaluation of the soil through machine-drive power or drum vibration monitoring. Four construction sites utilizing IC were visited: (1) TH 36 in North St. Paul, involving both granular and nongranular soils; (2) US 10 in Staples, with granular soil; (3) TH 60 in Bigelow, with nongranular soil; (4) US 10 in Detroit Lakes, involving both granular and nongranular soils. The report integrates comments from the four site visits and provides an interpretation on the use of IC at each site. As the technology now exists on the equipment used at these locations, IC provides only an index, which is specific to the conditions associated with a particular site. An interpretation of comments provided the basis for the following recommendations: Use light weight deflectometers (LWD) for quality assurance of stiffness; Establish a procedure to determine the target LWD value; Eliminate calibration areas (control strips); Simplify IC data evaluation and presentation; Calibrate the IC roller and related transducers; Support development of alternative IC methodologies; Simplify or eliminate moisture corrections.

The objective of this project was to develop an efficient and accurate algorithm for the back analysis of pavement conditions measured by ground penetrating radar (GPR). In particular, more reliable information about the thickness of the asphalt concrete (AC) layer and the dielectric constants of the AC and base layers were obtained from the electromagnetic field measurements performed on roads using GPR. A brief introduction to the existing methodology for interpreting GPR images is reviewed, and the theory associated with electromagnetic wave propagation in layered structures is described. Utilizing the full waveform solution, algorithms for back analysis of pavement conditions were developed based on the artificial neural network approach and the frequency response function concept. Software called ''GopherGPR'' uses the GPR signal from one antenna to interpret the characteristics of the AC layer with no assumptions on material properties. Thus, the new technique has the capability of providing information not previously available.

The objective of the project was to outline best practices for the selection of asphalt pavement recycling techniques from the many choices that are available. The report specifically examines cold-in-place recycling (CIR), plain full depth reclamation (FDR), and mill & overlay (M&O). Interviews, surveys, and site visits were conducted at both Mn/DOT districts and counties, where relevant rehabilitation information was supplied on over 120 projects. A database was constructed to organize the details of these projects, and the parameters in the database included (1) cracking, (2) ride, (3) rutting, (4) age, and (5) traffic volume. From studying the existing rehabilitation projects in the State, Ride Quality Index (RQI) and Surface Rating (SR) were selected as the descriptors of pavement surface condition. A decision procedure based on the analysis of all available projects was developed. The decision procedure included (1) consideration of road geometrics; (2) pavement condition survey; and (3) structural adequacy evaluation. Furthermore, a step-by-step checklist was developed to provide local engineers with a simple and useful tool to follow the decision procedures. The procedure includes selection of rehabilitation method, pavement thickness design, materials mixture design, and construction.

The objective of this work was to show that cone penetration testing (CPT) can be used for pavement applications, specifically estimating resilient modulus and organic content. A series of undisturbed samples were obtained from borings directly adjacent to CPT soundings. These samples underwent both laboratory resilient modulus and bender element testing. A statistical analysis was then performed on these results in conjunction with the data obtained from the CPT soundings to determine the feasibility of developing correlations between field and laboratory measurements of moduli. A relationship was developed between Young's modulus determined by bender element testing and that determined by resilient modulus testing. However, the correlation did not apply to the field-based seismic measurements of stiffness from the CPT soundings. The analysis presented with respect to the identification of highly organic soils via CPT testing shows that at this point the model identified using the discriminate analysis method is not currently sufficient to use in practice. The 10% increase in correctly classified soils, however, holds promise for the future, and the introduction of additional independent parameters within a significantly larger data set can be easily analyzed using the methods and tools presented here.

The objective of this project was to demonstrate the capabilities and limitations of ground penetrating radar (GPR) for use in local road applications. The effectiveness of a GPR survey is a function of site conditions, the equipment used, and experience of personnel interpreting the results. In addition, not all site conditions are appropriate for GPR applications. GPR is a nondestructive field test that can provide a continuous profile of existing road conditions. GPR utilizes high-speed data collection at speeds up to 50 mph, thus requiring less traffic control and resulting in greater safety. GPR has the potential to be used for a variety of pavement applications, including measuring the thickness of asphalt pavement, base and sub-grade; assisting in the analysis of rutting mechanisms; calculating and verifying material properties; locating subsurface objects; detecting stripping and/or layer separation; detecting subsurface moisture; and determining depth to near-surface bedrock and peat deposits. These applications are discussed in reference to 22 projects completed throughout the State of Minnesota.

The primary objective of this study was to quantify stiffness (resilient modulus) of aggregate base containing recycled asphalt and concrete pavements. After a survey of other state's specifications and implementation guidelines, Minnesota recycling projects were selected based on the availability of laboratory resilient modulus (MR) tests and field measurements from FWD. The projects were County State Aid Highway 3, Trunk Highway 23 and Trunk Highway 200. Based on the results of a parametric study, it was found that traditional peak-based analysis of FWD data can lead to significant errors in elastostatic backcalculation. A procedure for extracting the static response of the pavement was formulated and implemented in a software package called GopherCalc. Laboratory resilient modulus measurements were compared with moduli backcalculated from the FWD data. The FWD data was analyzed using conventional (peak-based) and modified (FRF-based) elastostatic backcalculation (Evercalc) as well as a simplified mechanistic empirical model called Yonapave. Laboratory values from sequences in the MR protocol that produced a similar state-of-stress were used. Additionally, a seasonal analysis of FWD test data revealed a significant increase in stiffness when the pavement is in the frozen state.

The objective of the research was to determine the strength and deformation characteristics of base material produced from recycled asphalt pavement (RAP) and aggregate. Various samples with different ratios of RAP and aggregate base were mixed (% RAP/aggregate): 0/100, 25/75, 50/50, 75/25. Laboratory compaction testing and field monitoring indicated that gyratory compacted specimens were closer to the densities measured in the field. Resilient modulus (MR) tests were generally conducted following the National Cooperative Highway Research Program 1-28A test protocol. MR increased with increase of confining pressure, but MR showed little change with deviator stress. The specimens with 65% optimum moisture contents were stiffer than the specimens with 100% optimum moisture contents at all confining pressures. Cyclic triaxial tests were conducted at two deviator stresses, 35% and 50% of the estimated peak stress, to evaluate recoverable and permanent deformation behavior from initial loading to 5000 cycles. The specimens with RAP exhibited at least two times greater permanent deformation than the 100% aggregate material. As %RAP increased, more permanent deformation occurred. In summary, the base material produced with various %RAP content performed at a similar level to 100% aggregate in terms of MR and strength when properly compacted.

This study deals with the experimental investigation of the effects of moisture and density on the elastic moduli and strength of four subgrade soils generally representing the range of road conditions in Minnesota. The testing approach involved i) reduced-scale simulation of field compaction, ii) field-type testing on prismatic soil volumes, and iii) element testing on cylindrical soil specimens. The field-type testing included: i) the GeoGauge, ii) the PRIMA 100 device, iii) the modified light weight deflectometer (LWD) device, iv) the portable vibratory deflectometer (PVD) and v) the Dynamic Cone Penetrometer (DCP). To compare the Young's modulus values stemming from the field-type and laboratory experiments, cylindrical specimens were extracted from the prismatic soil volumes and tested for the resilient modulus (Mr), small-strain Young's modulus using bender elements. The results reveal that both moisture and density have a measurable effect on the elastic modulus and strength of all four soils. On the element testing side, the small strain estimates from the bender element tests were in good agreement with the resilient modulus values. In the context of field testing, there was significant scatter of the estimated Young's moduli depending upon the particular testing device.