Effect of Density on Marshall Stability of Hot-Mix Asphaltic Concrete, MLR-82-01, 1982

The Iowa D.O.T. specifications do not require 100 percent of 50 blow Marshall density (generally 94%) for field compaction. However, stabilities are determined in the Laboratory on specimens compacted to 100 percent of Marshall density. The purpose of this study is to determine the stabilities of specimens compacted to various densities which are below 100 percent of the 50 blow Marshall density.

Calibration and Reliability of a Nuclear Asphalt Content Gauge, MLR-87-02, 1987

Based on results of an evaluation performed during the winter of 1985-86, six Troxler 3241-B Asphalt Content Gauges were purchased for District use in monitoring project asphalt contents. Use of these gauges will help reduce the need for chemical based extractions. Effective use of the gauges depends on the accurate preparation and transfer of project mix calibrations from the Central Lab to the Districts. The objective of this project was to evaluate the precision and accuracy of a gauge in determining asphalt contents and to develop a mix calibration transfer procedure for implementation during the 1987 construction. The first part of the study was accomplished by preparing mix calibrations in the Central Lab gauge and taking multiple measurements of a sample with known asphalt content. The second part was accomplished by preparing transfer pans, obtaining count data on the pans using each gauge, and transferring calibrations from one gauge to another through the use of calibration transfer equations. The transferred calibrations were tested by measuring samples with a known asphalt content. The study established that the Troxler 3241-B Asphalt Content Gauge yields results of acceptable accuracy and precision as evidenced by a standard deviation of 0.04% asphalt content on multiple measurements of the same sample. The calibration transfer procedure proved feasible and resulted in the calibration transfer portion of Materials I.M. 335 - Method of Test For Determining the Asphalt Content of Bituminous Mixtures by the Nuclear Method.

Early Strengths of Class F, C, and B Portland Cement Concrete, MLR-87-07, 1987

Fast track concrete has proven to be successful in obtaining high early strengths. This benefit does not come without cost. Type III cement and insulation blankets to accelerate the cure add to its expense when compared to conventional paving. This research was intended to determine the increase in time required to obtain opening strength when a fast track mix utilized conventional Type I cement and also used a conventional cure. Standard concrete mixes also were tested to determine the acceleration of strength gain when cured with insulation blankets. The goal was to determine mixes and procedures which would result in a range of opening times. This would allow the most economical design for a particular project and tailor it to that projects time restraint. Three mixes were tested: Class F, Class C, and Class B. Each mix was tested with one section being cured with insulation blankets and another section without. All used Type I cement. Iowa Department of Transportation specifications required 500 psi of flexural strength before a pavement can be opened to traffic. The Class F mix with Type I cement and using insulation blankets reached that strength in approximately 36 hours, the Class C mix using the blankets in approximately 48 hours, and the Class F mix without covers in about 60 hours. (Note: Class F concrete pavement is opened at 400 psi minimum and Class F bonded overlay pavement at 350 psi.) The results showed a significant improvement in early strength gain by the use of insulation blankets. The Type I cement could be used in mixes intended for early opening with sacrifices in time when compared to fast track but are still much sooner than conventional pavement. It appears a range of design alternatives is possible using Type I cement both with and without insulating blankets.

Evaluation of Long-Term Field Performance of Cold In-Place Recycled Roads: Field and Laboratory Testing, TR-502, 2007

Cold in-place recycling (CIR) has become an attractive method for rehabilitating asphalt roads that have good subgrade support and are suffering distress related to non-structural aging and cracking of the pavement layer. Although CIR is widely used, its use could be expanded if its performance were more predictable. Transportation officials have observed roads that were recycled under similar circumstances perform very differently for no clear reason. Moreover, a rational mix design has not yet been developed, design assumptions regarding the structural support of the CIR layer remain empirical and conservative, and there is no clear understanding of the cause-effect relationships between the choices made during the design/construction process and the resulting performance. The objective of this project is to investigate these relationships, especially concerning the age of the recycled pavement, cumulative traffic volume, support conditions, aged engineering properties of the CIR materials, and road performance. Twenty-four CIR asphalt roads constructed in Iowa from 1986 to 2004 were studied: 18 were selected from a sample of roads studied in a previous research project (HR-392), and 6 were selected from newer CIR projects constructed after 1999. This report describes the results of comprehensive field and laboratory testing for these CIR asphalt roads. The results indicate that the modulus of the CIR layer and the air voids of the CIR asphalt binder were the most important factors affecting CIR pavement performance for high-traffic roads. For low-traffic roads, the wet indirect tensile strength significantly affected pavement performance. The results of this research can help identify changes that should be made with regard to design, material selection, and construction in order to improve the performance and cost-effectiveness of future recycled roads.

Rehabilitation of Concrete Pavements Utilizing Rubblization and Crack and Seat Methods (Phase II): Performance Evaluation of Rubblized Pavements in Iowa, TR-550, 2008

This Phase II follow-up study of IHRB Project TR-473 focused on the performance evaluation of rubblized pavements in Iowa. The primary objective of this study was to evaluate the structural condition of existing rubblized concrete pavements across Iowa through Falling Weight Deflectometer (FWD) tests, Dynamic Cone Penetrometer (DCP) tests, visual pavement distress surveys, etc. Through backcalculation of FWD deflection data using the Iowa State University's advanced layer moduli backcalculation program, the rubblized layer moduli were determined for various projects and compared with each other for correlating with the long-term pavement performance. The AASHTO structural layer coefficient for rubblized layer was also calculated using the rubblized layer moduli. To validate the mechanistic-empirical (M-E) hot mix asphalt (HMA) overlay thickness design procedure developed during the Phase I study, the actual HMA overlay thicknesses from the rubblization projects were compared with the predicted thicknesses obtained from the design software. The results of this study show that rubblization is a valid option to use in Iowa in the rehabilitation of portland cement concrete pavements provided the foundation is strong enough to support construction operations during the rubblization process. The M-E structural design methodology developed during Phase I can estimate the HMA overlay thickness reasonably well to achieve long-lasting performance of HMA pavements. The rehabilitation strategy is recommended for continued use in Iowa under those conditions conducive for rubblization.

Evaluation of Hot Mix Asphalt Moisture Sensitivity Using the Nottingham Asphalt Test Equipment, TR-555, 2010

Pavements are subjected to different stresses during their design lives. A properly designed pavement will perform adequately during its design life, and the distresses will not exceed the allowable limits; however, there are several factors that can lead to premature pavement failure. One such factor is moisture sensitivity. AASHTO T 283 is the standard test used in the moisture susceptibility evaluation of asphalt mixtures, but the results of the test are not very representative of the expected behavior of asphalt mixtures. The dynamic modulus test measures a fundamental property of the mixture. The results of the dynamic modulus test can be used directly in the Mechanistic-Empirical Pavement Design Guide (MEPDG) and are considered a very good representation of the expected field performance of the mixture. Further research is still needed to study how the dynamic modulus results are affected by moisture. The flow number test was studied in previous research as a candidate test for moisture-susceptibility evaluation, but the results of that research were not favorable. This research has four main objectives. The first objective of this research is to evaluate the usefulness of the dynamic modulus and flow number tests in moisture-susceptibility evaluation. The second objective is to compare the results to those achieved using the AASHTO T 283 test. The third objective is to study the effect of different methods of sample conditioning and testing conditions. The fourth objective of the research is to study the variability in the test results.

Crack Development in Ternary Mix Concrete Utilizing Various Saw Depths, TR-587, 2009

Early entry sawing applies sawing earlier and more shallowly than conventional sawing and is believed to increase sawing productivity and reduce the cost of the joint sawing operations. However, some early entry sawing joints (transverse joints) in Iowa were found to experience delayed cracking, sometimes up to 30 days. A concern is whether early entry sawing can lead to late-age random cracking. The present study investigated the effects of different sawing methods on random cracking in portland cement concrete (PCC) pavements. The approach was to assess the cracking potential at sawing joints by measuring the strain development of the concrete at the joints using concrete embedment strain gages. Ten joints were made with the early entry sawing method to a depth of 1.5 in., and two strain gages were installed in each of the joints. Another ten joints were made with the conventional sawing method, five of which were sawed to a depth of one-third of the pavement thickness (3.3 in.), and the other five of which were sawed to a depth of one-quarter of the pavement thickness (2.5 in.). One strain gage was installed in each joint made using conventional sawing. In total, 30 strain gages were installed in 20 joints. The results from the present study indicate that all 30 joints cracked within 25 days after paving, though most joints made using early entry sawing cracked later than the joints made using conventional sawing. No random cracking was observed in the early entry sawing test sections two months after construction. Additionally, it was found that the strain gages used were capable of monitoring the deformations at the joints. The joint crack times (or crack initiation time) measured by the strain gages were generally consistent with the visual observations.

Laboratory Performance Evaluation of CIR-Emulsion and its Comparison Against CIR-Foam Test Results from Phase 2, TR-474, 2009

Currently, no standard mix design procedure is available for CIR-emulsion in Iowa. The CIR-foam mix design process developed during the previous phase is applied for CIR-emulsion mixtures with varying emulsified asphalt contents. Dynamic modulus test, dynamic creep test, static creep test and raveling test were conducted to evaluate the short- and long-term performance of CIR-emulsion mixtures at various testing temperatures and loading conditions. A potential benefit of this research is a better understanding of CIR-emulsion material properties in comparison with those of CIR-foam material that would allow for the selection of the most appropriate CIR technology and the type and amount of the optimum stabilization material. Dynamic modulus, flow number and flow time of CIR-emulsion mixtures using CSS- 1h were generally higher than those of HFMS-2p. Flow number and flow time of CIR-emulsion using RAP materials from Story County was higher than those from Clayton County. Flow number and flow time of CIR-emulsion with 0.5% emulsified asphalt was higher than CIR-emulsion with 1.0% or 1.5%. Raveling loss of CIR-emulsion with 1.5% emulsified was significantly less than those with 0.5% and 1.0%. Test results in terms of dynamic modulus, flow number, flow time and raveling loss of CIR-foam mixtures are generally better than those of CIR-emulsion mixtures. Given the limited RAP sources used for this study, it is recommended that the CIR-emulsion mix design procedure should be validated against several RAP sources and emulsion types.

Manual of Laboratory Mix Design Procedure for Cold In-Place Recycling using Foamed Asphalt (CIR-foam), TR-474, 2007

The objective is to determine the optimum percentage of water needed to produce the best foam properties for a given asphalt binder. The optimum water content is determined by achieving the maximum expansion ratio and half-life of the foamed asphalt. Expansion ratio is defined as the maximum volume over its original volume and half-life is defined as the time in seconds for foam to become a half of its maximum volume.

Superpave Mix Designs for Low-Volume Roads, TR-414, Final Report, 2004

Most research current to the time of these projects was focused on use of Superpave mix designs on higher volume roads. Low volume roads have different requirements in terms of mix design, aggregate types, aggregate sources and project budgets. The purpose of this research was to determine if the Superpave mix design strategy for low volume roads was practical and economical. Eight projects were selected in five counties. The projects were completed in the summer of 1998. Performance evaluation of the resulting pavements was carried out annually. There was no significant increase in costs related to the use of Superpave. Nor were there any significant construction issues. There were some differences noted in placement and compaction in the field, but these were not serious.

Mix Design Development for Pervious Concrete in Cold Weather Climates

Portland cement pervious concrete (PCPC) is being used more frequently due to its benefits in reducing the quantity of runoff water,improving water quality, enhancing pavement skid resistance during storm events by rapid drainage of water, and reducing pavement noise. In the United States, PCPC typically has high porosity and low strength, which has resulted in the limited use of pervious concrete, especially in hard wet freeze environments (e.g., the Midwestern and Northeastern United States and other parts of the world).Improving the strength and freeze-thaw durability of pervious concrete will allow an increase in its use in these regions. The objective of this research is to develop a PCPC mix that not only has sufficient porosity for stormwater infiltration, but also desirable strength and freeze-thaw durability. In this research, concrete mixes were designed with various sizes and types of aggregates, binder contents, and admixture amounts. The engineering properties of the aggregates were evaluated. Additionally, the porosity, permeability, strength, and freeze-thaw durability of each of these mixes was measured. Results indicate that PCPC made with single-sized aggregate has high permeability but not adequate strength. Adding a small percent of sand to the mix improves its strength and freeze-thaw resistance, but lowers its permeability. Although adding sand and latex improved the strength of the mix when compared with single-sized mixes, the strength of mixes where only sand was added were higher. The freeze-thaw resistance of PCPC mixes with a small percentage of sand also showed 2% mass loss after 300 cycles of freeze-thaw. The preliminary results of the effects of compaction energy on PCPC properties show that compaction energy significantly affects the freeze-thaw durability of PCPC and, to a lesser extent, reduces compressive strength and split strength and increases permeability.

Computer Aided Detection and measurement of peripheral artery disease.

Computer-Aided Tomography Angiography (CTA) images are the standard for assessing Peripheral artery disease (PAD). This paper presents a Computer Aided Detection (CAD) and Computer Aided Measurement (CAM) system for PAD. The CAD stage detects the arterial network using a 3D region growing method and a fast 3D morphology operation. The CAM stage aims to accurately measure the artery diameters from the detected vessel centerline, compensating for the partial volume effect using Expectation Maximization (EM) and a Markov Random field (MRF). The system has been evaluated on phantom data and also applied to fifteen (15) CTA datasets, where the detection accuracy of stenosis was 88% and the measurement accuracy was with an 8% error.

Material and Construction Optimization for Prevention of Premature Pavement Distress in PCC Pavements, Phase III Final Report, 2008

Mixture materials, mix design, and pavement construction are not isolated steps in the concrete paving process. Each affects the other in ways that determine overall pavement quality and long-term performance. However, equipment and procedures commonly used to test concrete materials and concrete pavements have not changed in decades, leaving gaps in our ability to understand and control the factors that determine concrete durability. The concrete paving community needs tests that will adequately characterize the materials, predict interactions, and monitor the properties of the concrete. The overall objectives of this study are (1) to evaluate conventional and new methods for testing concrete and concrete materials to prevent material and construction problems that could lead to premature concrete pavement distress and (2) to examine and refine a suite of tests that can accurately evaluate concrete pavement properties. The project included three phases. In Phase I, the research team contacted each of 16 participating states to gather information about concrete and concrete material tests. A preliminary suite of tests to ensure long-term pavement performance was developed. The tests were selected to provide useful and easy-to-interpret results that can be performed reasonably and routinely in terms of time, expertise, training, and cost. The tests examine concrete pavement properties in five focal areas critical to the long life and durability of concrete pavements: (1) workability, (2) strength development, (3) air system, (4) permeability, and (5) shrinkage. The tests were relevant at three stages in the concrete paving process: mix design, preconstruction verification, and construction quality control. In Phase II, the research team conducted field testing in each participating state to evaluate the preliminary suite of tests and demonstrate the testing technologies and procedures using local materials. A Mobile Concrete Research Lab was designed and equipped to facilitate the demonstrations. This report documents the results of the 16 state projects. Phase III refined and finalized lab and field tests based on state project test data. The results of the overall project are detailed herein. The final suite of tests is detailed in the accompanying testing guide.

Investigation into Freezing-Thawing Durability of Low-Permeability Concrete with and without Air Entraining Agent, 2009

The aim of the present study is to investigate the effect of low-permeability concrete, made with reduced water‐to‐binder ratios (w/b) and/or supplementary cementitious materials (SCMs), on the need for air entrainment to achieve freezing‐thawing (F‐T) durability. In the present study, concrete mixes were made with different types of cement (Types I and IP), with or without fly ash replacement (15%), with different water‐to‐binder ratios (w/b =0.25, 0.35, 0.45 and 0.55), and with or without air entraining agent (AEA). All concrete mixtures were controlled to have a similar slump by using different dosages of superplasticizer. The rapid chloride permeability and F-T durability of the concrete samples were determined according to ASTM C1202 and ASTM C666A, respectively. The air void structure of the concrete was studied using the Air Void Analyzer, RapidAir, and porosity tests (ASTM C642). In addition, the general concrete properties, such as slump, air content, unit weight, and 28‐day compressive strength, were evaluated. The results indicate that all concrete mixes with proper air entrainment (ASTM C231 air content ≥ 6%) showed good F‐T resistance (durability factor ≥85%). All concrete mixes without AEA showed poor F‐T resistance (durability factor < 40%), except for one mix that had very low permeability and high strength. This was the concrete made with Type IP cement and with a w/b of 0.25, which had a permeability of 520 coulombs and a compressive strength of 12,760 psi (88 MPa). There were clear relationships between the F‐T durability and hardened concrete properties of non–air entrained concrete. However, such relationships did not exist in concrete with AEA. For concrete with AEA, good F‐T durability was associated with an air void spacing factor ≤ 0.28 mm (by AVA) or ≤ 0.22 mm (by RapidAir).

Managing Decisions Regarding Rural Expressway Routes and Associated Highway Bypasses, 2009

For several years, the Iowa Department of Transportation has constructed bypasses along rural highways. Most bypasses were constructed on the state’s Commercial Industrial Network (CIN). Now that work on the CIN has been completed and the system is open to traffic, it is possible to study the impacts of bypasses. In the past, construction of highway bypasses has led community residents and business people to raise concerns about the loss of business activity. For policy development purposes, it is essential to understand the impacts that a bypass might have on safety, the community, and economics. By researching these impacts, policies can be produced to help to alleviate any negative impacts and create a better system that is ultimately more cost-effective. This study found that the use of trade area analysis does not provide proof that a bypass can positively or negatively impact the economy of a rural community. The analysis did show that, even though the population of a community may be stable for several years and per capita income is increasing, sales leakage still occurs. The literature, site visits, and data make it is apparent that a bypass can positively affect a community. Some conditions that would need to exist in order to maximize a positive impact include the installation of signage along the bypass directing travelers to businesses and services in the community, community or regional plans that include the bypass in future land development scenarios, and businesses adjusting their business plans to attract bypass users. In addition, how proactive a community is in adapting to the bypass will determine the kinds of effects felt in the community. Results of statistical safety analysis indicate that, at least when crashes are separated by severity, bypasses with at-grade accesses appear to perform more poorly than either the bypasses with fully separated accesses or with a mix of at-grade and fully separated accesses. However, the benefit in terms of improved safety of bypasses with fully separated accesses relative to bypasses with a mixed type of accesses is not statistically conclusive.