Non-Nuclear Method for Density Measurements

Quality control (QC) and quality assurance (QA) are necessary to ensure fulfillment and compliance to specifications, guidelines, manuals, and programs which outline methods and requirements during construction. Density, an important part of quality control, can be used to evaluate the quality of Hot Mix Asphalt (HMA) and soil compaction. This study investigated new technologies used for QC and QA by comparing the Pavement Quality Indicator (PQI) model 301 with a nuclear gauge and core sample measurements for HMA. For soil QC and QA, non-nuclear technologies—the Electrical Density Gauge (EDG), the Moisture Density Indicator (MDI), and the Light Weight Deflectometer (LWD)—were also investigated against a nuclear gauge and traditional non-nuclear methods of measurement. Overall, the nuclear gauge shows higher accuracy and higher correlation with cores than the non-nuclear gauges tested in this study. A thorough investigation of calibration methods was also performed, both in the lab and on the field, to improve the accuracy of the PQI‘s results. Data analyses showed that the accuracies of the non-nuclear soil gauges are somewhat lower than that of the nuclear gauge. With an improved methodology to create soil models for the EDG and standardized ways to develop the LWD‘s target values, the EDG and LWD could have a similar or better accuracy than the nuclear gauge. With the EDG and the Soil Density Gauge (SDG), both recently ASTM approved, nonnuclear soil technology is the future. Furthermore, the non-nuclear gauges could be a better alternative to a nuclear gauge when the following benefits are considered: (1) economic savings; (2) faster data measurement (PQI); (3) elimination of intense federal regulations and safety concerns; (4) elimination of licensing and intense training

Non-Nuclear Method for Density Measurements

Quality control (QC) and quality assurance (QA) are necessary to ensure fulfillment and compliance to specifications, guidelines, manuals, and programs which outline methods and requirements during construction. Density, an important part of quality control, can be used to evaluate the quality of Hot Mix Asphalt (HMA) and soil compaction. This study investigated new technologies used for QC and QA by comparing the Pavement Quality Indicator (PQI) model 301 with a nuclear gauge and core sample measurements for HMA. For soil QC and QA, non-nuclear technologies—the Electrical Density Gauge (EDG), the Moisture Density Indicator (MDI), and the Light Weight Deflectometer (LWD)—were also investigated against a nuclear gauge and traditional non-nuclear methods of measurement. Overall, the nuclear gauge shows higher accuracy and higher correlation with cores than the non-nuclear gauges tested in this study. A thorough investigation of calibration methods was also performed, both in the lab and on the field, to improve the accuracy of the PQI‘s results. Data analyses showed that the accuracies of the non-nuclear soil gauges are somewhat lower than that of the nuclear gauge. With an improved methodology to create soil models for the EDG and standardized ways to develop the LWD‘s target values, the EDG and LWD could have a similar or better accuracy than the nuclear gauge. With the EDG and the Soil Density Gauge (SDG), both recently ASTM approved, nonnuclear soil technology is the future. Furthermore, the non-nuclear gauges could be a better alternative to a nuclear gauge when the following benefits are considered: (1) economic savings; (2) faster data measurement (PQI); (3) elimination of intense federal regulations and safety concerns; (4) elimination of licensing and intense training

Evaluation of Tack Coating Practices for Asphalt Overlays in Nebraska

The strength of the bond between asphalt layers affects the lifespan of pavement structures. It is also a key factor in preventing major pavement distresses, such as slippage cracking and delamination. This research project evaluates and compares the effectiveness and performance of different tack coating approaches to ensure the proper bond strength is achieved in asphalt concrete (AC) interlayers through an experimental study. Various tack coat materials, including different types of emulsified asphalt and asphalt binders, at multiple application rates and dilution ratios were investigated. In the first part of this study, laboratory-prepared samples were used to evaluate the sensitivity and effectiveness of the direct shear testing (DST) method, which was selected for the characterization of the AC interlayers where different tack coats were treated. Then, emulsified asphalts and binders were applied to a field test section by varying application rates. The DST was performed under a monotonic loading condition at three different testing temperatures. Interlayer shear strengths were used to rank the performance of the tack coats. In addition, cyclic DST was conducted to investigate fatigue behavior of the interlayers treated with different tack coats. The parameters obtained from the monotonic DST were compared with the fatigue DST results. In general, the test results showed superior interlayer performance from CFS-1 and CRS-2P at double application rate (i.e., 0.16 gal/yd2 residual application rate) and CFS-1 at the standard application rate (i.e., 0.08 gal/yd2 residual application rate). Moreover, CRS-2P provided the shortest breaking time among all the emulsified tack coats. With regard to the correlation between the monotonic and cyclic DST results, the maximum shear force showed an acceptable correlation with the fatigue test results, and the interlayer bond energy, which can also be determined using a monotonic DST, is a good (or better) predictor of the fatigue-related shear resistance of the tack coats due to its higher correlation with the fatigue test results

Evaluation of Dowel Bar Inserter Practices in PCC Pavements with Magnetic Tomography Technology

Dowel Bar Inserters (DBI) are automated mechanical equipment that position dowel bars in Portland Cement Concrete (PCC) after concrete is placed. Compared to the alternative approach, which is using dowel baskets, DBIs offer advantages in cost and speed of construction. However, as dowel bars are not anchored to the subgrade similar to dowel baskets, there is a concern about the quality of dowel placement using this equipment. Improper placement of dowel bars can lead to reduced load transfer between slabs, which results in pavement distresses such as faulting and spalling at joints. To determine the accuracy of dowel placement by DBI, the Nebraska Department of Roads has used an MIT Scan-2 device to scan the joints in projects where a DBI was used. This device uses a nondestructive magnetic imaging technique to capture the position of dowel bars inside the pavement. The aim of the this project is to analyze the MIT Scan-2 data of the joints constructed using a DBI, and to compare them with the corresponding field performance data. This will allow us to judge if DBI is a reliable alternative for dowel placement, and to improve Nebraska’s current specifications for dowel placement tolerances. To meet the objectives, the MIT Scan-2 data of scanned joints were initially compared with dowel placement specifications suggested by national agencies. It was observed that the longitudinal translation and rotation of dowels in a portion of scanned joints fell outside recommended tolerances. The longitudinal and vertical translation of the dowels were respectively higher and lower than the average values reported by a similar study (Khazanovich et al. 2009). MIT Scan-2 data and field performance data were then compared to find any linkage between pavement distresses and dowel misalignment levels, enabling us to potentially improve Nebraska’s current specifications as well as conclude if any of the distresses were caused by low placement accuracy of the DBI. No linkage was found between pavement performance and dowel misalignment levels for over 220 joints that were investigated in this study. No transverse cracking was observed during field investigation, and the spalling at joints was likely to be the result of joint saw-cut operations. However, measured distress from joints with missing or completely shifted dowels show that high severity dowel misalignment has an adverse effect on joint performance

Evaluation of Dowel Bar Inserter Practices in PCC Pavements with Magnetic Tomography Technology

Dowel Bar Inserters (DBI) are automated mechanical equipment that position dowel bars in Portland Cement Concrete (PCC) after concrete is placed. Compared to the alternative approach, which is using dowel baskets, DBIs offer advantages in cost and speed of construction. However, as dowel bars are not anchored to the subgrade similar to dowel baskets, there is a concern about the quality of dowel placement using this equipment. Improper placement of dowel bars can lead to reduced load transfer between slabs, which results in pavement distresses such as faulting and spalling at joints. To determine the accuracy of dowel placement by DBI, the Nebraska Department of Roads has used an MIT Scan-2 device to scan the joints in projects where a DBI was used. This device uses a nondestructive magnetic imaging technique to capture the position of dowel bars inside the pavement. The aim of the this project is to analyze the MIT Scan-2 data of the joints constructed using a DBI, and to compare them with the corresponding field performance data. This will allow us to judge if DBI is a reliable alternative for dowel placement, and to improve Nebraska’s current specifications for dowel placement tolerances. To meet the objectives, the MIT Scan-2 data of scanned joints were initially compared with dowel placement specifications suggested by national agencies. It was observed that the longitudinal translation and rotation of dowels in a portion of scanned joints fell outside recommended tolerances. The longitudinal and vertical translation of the dowels were respectively higher and lower than the average values reported by a similar study (Khazanovich et al. 2009). MIT Scan-2 data and field performance data were then compared to find any linkage between pavement distresses and dowel misalignment levels, enabling us to potentially improve Nebraska’s current specifications as well as conclude if any of the distresses were caused by low placement accuracy of the DBI. No linkage was found between pavement performance and dowel misalignment levels for over 220 joints that were investigated in this study. No transverse cracking was observed during field investigation, and the spalling at joints was likely to be the result of joint saw-cut operations. However, measured distress from joints with missing or completely shifted dowels show that high severity dowel misalignment has an adverse effect on joint performance

Investigation of DSR Test Methods to Determine Binder Low Temperature Properties

The low temperature rheology of bituminous binders is of great interest because low temperature cracking is one of the primary asphalt pavement failure modes observed in cold-climate places such as Nebraska. Low temperature binder characterization/grading has been primarily conducted using the bending beam rheometer (BBR), while the dynamic shear rheometer (DSR) can alternatively be used to characterize the low temperature properties of binders with the recent advancement of DSR equipment that can cover a wide range of testing temperatures. This study investigates alternative testing-analysis methods using the DSR to determine low temperature asphalt binder properties that have been measured by the BBR. Toward that end, twelve different binders from four sources satisfying three different PG grading criterion common in Nebraska were selected. The binder samples were tested in the frequency domain at temperatures ranging from 60°C to -30°C under PAV-aged conditions using DSR. The 8-mm parallel plate geometry was primarily employed for the testing, while four binders were randomly selected and tested using the 4-mm parallel plate to investigate the influence of geometry on the results. BBR experiments were also performed as a parallel for each binder. Three methods were used to analyze and compare the data from the two different experiments (i.e., DSR and BBR) where each method utilizes a different scheme for converting the frequency domain results to time domain data to compare with the BBR results. The three methods are: (1) Western Research Institute’s (WRI) methodology; (2) NCHRP methodology; and (3) UNL’s mechanistic approach. It was observed that the DSR testing is quite promising, and sample preparation is crucial to obtain reliable-repeatable results. Moreover, in the proposed UNL’s mechanistic approach, it was observed that a single shift factor for creep compliance may account for different testing conditions, differences in physical hardening and temperature-dependent effects. The approach was then extended to seven additional binders to further examine its feasibility, and it was observed that the predictions from the proposed approach match well with the experimental values

MIDAS-VT-Pre: Software to generate 2D finite element model of particle/fiber embedded composites with cohesive zones

Studying the behavior of particle/fiber embedded composites has been a common and challenging problem in mechanics of materials area. Analysis of these materials can be effectively conducted by computational simulations such as finite element (FE) analyses. Creating a model that represents the actual microstructure of the composite is crucial to obtain a trustable result, but is often labor- intensive. Microstructure Inelastic Damage Analysis Software (MIDAS) Virtual Tester Preprocessor (MIDAS-VT-Pre) was developed to facilitate construction of two-dimensional microstructure FE models of particle/fiber embedded composites. MIDAS-VT-Pre is able to insert automatically cohesive zone interface elements in the mesh structure in order to simulate crack initiation and propagation. This program is tailored to generate the FE model of standard mechanical test configurations that are frequently used in laboratory settings. The output of this program includes mesh structure and boundary conditions. This information can be used to run FE simulation (i.e. virtual testing) using common FE software such as ABAQUS

MIDAS-VT-Pre: Software to generate 2D finite element model of particle/fiber embedded composites with cohesive zones

Studying the behavior of particle/fiber embedded composites has been a common and challenging problem in mechanics of materials area. Analysis of these materials can be effectively conducted by computational simulations such as finite element (FE) analyses. Creating a model that represents the actual microstructure of the composite is crucial to obtain a trustable result, but is often laborintensive. Microstructure Inelastic Damage Analysis Software (MIDAS) Virtual Tester Preprocessor (MIDAS-VT-Pre) was developed to facilitate construction of two-dimensional microstructure FE models of particle/fiber embedded composites. MIDAS-VT-Pre is able to insert automatically cohesive zone interface elements in the mesh structure in order to simulate crack initiation and propagation. This program is tailored to generate the FE model of standard mechanical test configurations that are frequently used in laboratory settings. The output of this program includes mesh structure and boundary conditions. This information can be used to run FE simulation (i.e. virtual testing) using common FE software such as ABAQUS

Nebraska Data Collection

Automated pavement performance data collection is a method that uses advanced technology to collect detailed road surface distress information at traffic speed. Agencies are driven to use automated survey techniques to enhance or replace their current manual distress survey because of the advantages of objective measurements, safety benefits, and reduced measurement time. As agencies move toward the transition to fully automated data collection methods, there are common concerns regarding how the output of the new method will match the current manual survey ratings and how they will be adopted into the existing Pavement Management System (PMS). This study evaluates the newly implemented automated distress survey technique and its implementation into the Nebraska Pavement Management System (NPMS). To meet the objectives, a user-friendly program was developed to convert the automated distress ratings into the current manual distress ratings format. Then, a data set that includes more than 7,000 miles of distress data collected by the automated method was converted to the manual data format and compared to the most recent manual rating data of those sections to assess the agreement between the two data formats after the conversion process. The results show that the automated pavement survey slightly overrates bituminous pavement distresses with only a few distress types that could not be properly detected. Finally, a regression analysis of a core pavement performance indicator, NSI, was conducted to examine how the new automated performance measurement system will ultimately affect NPMS decisions if implemented into Nebraska’s pavement management system