Evaluation of Hot Mix Asphalt Moisture Sensitivity Using the Nottingham Asphalt Test Equipment, July 2005

Moisture sensitivity of Hot Mix Asphalt (HMA) mixtures, generally called stripping, is a major form of distress in asphalt concrete pavement. It is characterized by the loss of adhesive bond between the asphalt binder and the aggregate (a failure of the bonding of the binder to the aggregate) or by a softening of the cohesive bonds within the asphalt binder (a failure within the binder itself), both of which are due to the action of loading under traffic in the presence of moisture. The evaluation of HMA moisture sensitivity has been divided into two categories: visual inspection test and mechanical test. However, most of them have been developed in pre-Superpave mix design. This research was undertaken to develop a protocol for evaluating the moisture sensitivity potential of HMA mixtures using the Nottingham Asphalt Tester (NAT). The mechanisms of HMA moisture sensitivity were reviewed and the test protocols using the NAT were developed. Different types of blends as moisture-sensitive groups and non-moisture-sensitive groups were used to evaluate the potential of the proposed test. The test results were analyzed with three parameters based on performance character: the retained flow number depending on critical permanent deformation failure (RFNP), the retained flow number depending on cohesion failure (RFNC), and energy ratio (ER). Analysis based on energy ratio of elastic strain (EREE ) at flow number of cohesion failure (FNC) has higher potential to evaluate the HMA moisture sensitivity than other parameters. If the measurement error in data-acquisition process is removed, analyses based on RFNP and RFNC would also have high potential to evaluate the HMA moisture sensitivity. The vacuum pressure saturation used in AASHTO T 283 and proposed test has a risk to damage specimen before the load applying.

Quality Control/Quality Assurance Testing for Joint Density and Segregation of Asphalt Mixtures, TR-623, 2013

Longitudinal joint quality control/assurance is essential to the successful performance of asphalt pavements and it has received considerable amount of attention in recent years. The purpose of the study is to evaluate the level of compaction at the longitudinal joint and determine the effect of segregation on the longitudinal joint performance. Five paving projects with the use of traditional butt joint, infrared joint heater, edge restraint by milling and modified butt joint with the hot pinch longitudinal joint construction techniques were selected in this study. For each project, field density and permeability tests were made and cores from the pavement were obtained for in-lab permeability, air void and indirect tensile strength. Asphalt content and gradations were also obtained to determine the joint segregation. In general, this study finds that the minimum required joint density should be around 90.0% of the theoretical maximum density based on the AASHTO T166 method. The restrained-edge by milling and butt joint with the infrared heat treatment construction methods both create the joint density higher than this 90.0% limit. Traditional butt joint exhibits lower density and higher permeability than the criterion. In addition, all of the projects appear to have segregation at the longitudinal joint except for the edge-restraint by milling method.

Investigation of Warm-Mix Asphalt for Iowa Roadways, TR-635, 2013

Phase II of this study further evaluated the performance of plant-produced warm-mix asphalt (WMA) mixes by conducting additional mixture performance tests at a broader range of temperatures, adding additional pavements to the study, comparing virgin and recovered binder properties, performing pavement condition surveys, and comparing survey data with the Mechanistic Empirical Pavement Design Guide (MEPDG) forecast for pavement damage over 20 years of service life. Further objectives detailing curing behavior, quality assurance testing, and hybrid technologies were as follows: * Compare the predicted and observed field performance of existing WMA trials produced in the previous Phase I study to that of hot-mix asphalt (HMA) control sections to determine if Phase I conclusions are translating to the field; * Identify any curing effect (and timing of the effect) of WMA mixtures and binders in the field; * Determine how the field-compacted mixture properties and recovered binder properties of WMA compare to those of HMA over time for technologies common to Iowa; * Identify the protocols for WMA sample preparation for volumetric and performance testing that best simulate field conditions. The findings of this study indicate that WMA additives do show statistical differences in mixture properties in some of the mixes tested. These differences will not always be statistically different from mixture to mixture. Multiple factors, such as WMA additive type, amount of recycled asphalt material, construction conditions, and mixture variability all play a role in determining the extent of which WMA and HMA mixes differ. Other significant findings of this study include effects of curing, aging in recovered binders from HMA and WMA cores, and the influence of recycled asphalt shingles (RAS) used with WMA. These findings will be of interest to owner agencies and contractors utilizing WMA technologies.

Beneficial Effects of Selected Additives on Asphalt Cement Mixes, HR-278, 1987

Effects of polyolefins, neoprene, styrene-butadiene-styrene (SBS) block copolymers, styrene-butadiene rubber (SBR) latex, and hydrated lime on two asphalt cements were evaluated. Physical and chemical tests were performed on a total of 16 binder blends. Asphalt concrete mixes were prepared and tested with these modified binders and two aggregates (crushed limestone and gravel), each at three asphalt content levels. Properties evaluated on the modified binders (original and thin-film oven aged) included: viscosity at 25 deg C, 60 deg C and 135 deg C with capillary tube and cone-plate viscometer, penetration at 5 deg C and 25 deg C, softening point, force ductility, and elastic recovery at 10 deg C, dropping ball test, tensile strength, and toughness and tenacity tests at 25 deg C. From these the penetration index, the viscosity-temperature susceptibility, the penetration-viscosity number, the critical low-temperature, long loading-time stiffness, and the cracking temperature were calculated. In addition, the binders were studied with x-ray diffraction, reflected fluorescence microscopy, and high-performance liquid chromatography techniques. Engineering properties evaluated on the 72 asphalt concrete mixes containing additives included: Marshall stability and flow, Marshall stiffness, voids properties, resilient modulus, indirect tensile strength, permanent deformation (creep), and effects of moisture by vacuum-saturation and Lottman treatments. Pavement sections of varied asphalt concrete thicknesses and containing different additives were compared to control mixes in terms of structural responses and pavement lives for different subgrades. Although all of the additives tested improved at least one aspect of the binder/mixture properties, no additive was found to improve all the relevant binder/mixture properties at the same time. On the basis of overall considerations, the optimum beneficial effects can be expected when the additives are used in conjunction with softer grade asphalts.

Field Evaluation of Cold In-Place Recycling of Asphalt Concrete, HR-303, 1993

The average thickness of the existing asphalt cement concrete (ACC) along route E66 in Tama County was 156 mm (6.13 in.). The rehabilitation strategy called for widening the base using the top 75 mm (3 in.) of the existing ACC by a recycling process involving cold milling and mixing with additional emulsion/rejuvenator. The material was then placed into a widening trench and compacted to match the level of the milled surface. The project had the following results: (1) Cold recycled ACC pavement provided adequate pavement structure for a low volume road; (2) Premature cracking of the ACC in the widened pavement area was caused by compaction of the mix over a saturated subgrade; and (3) Considerably less transverse and longitudinal cracking was observed with 75 mm (3 in.) of cold recycled ACC and a 50 mm (2 in.) hot mix ACC overlay than with a conventional hot mix overlay with no cold recycling. More research should be done on efficient construction procedures and incorporating longer test sections for proper evaluation.

Pavement Texturing by Milling, HR-283, 1987

Experience has shown that milling machines with carbide tipped teeth have the capability of profiling most asphalt concrete (ac) and portland cement concrete (pcc) pavements. Most standard milling operations today leave a very coarse, generally objectionable surface texture. This research utilized a Cedarapids Wirtgen 1900C mill modified by adding additional teeth. There were 411 teeth at a 5 millimeter transverse spacing (standard spacing is 15 mm) on a 6 ft. 4 in. long drum. The mill was used to profile and texture the surface of one ac and two pcc pavements. One year after the milling operation there is still some noticeable change in tire noise but the general appearance is good. The milling operation with the additional teeth provides an acceptable surface texture with improved Friction Numbers when compared to a nonmilled surface.

Review of Cold In-Place Recycled Asphalt Concrete Projects, HR-392, 1998

Highway Research Project HR-392 was undertaken to evaluate cold in-place asphalt recycled (CIR) projects in the State of Iowa. The research involved assessment of performance levels, investigation of factors that most influence pavement performance and economy, and development of guidelines for CIR project selection. The performance was evaluated in two ways: Pavement Condition Indices (PCI, U.S. Corps of Engineers) were calculated and overall ratings were given on ride and appearance. A regression analysis was extrapolated to predict the future service life of CIR roads. The results were that CIR roads within the State of Iowa, with less than 2000 annual average daily traffic (AADT), have an average predicted service life of fifteen to twenty-six years. Subgrade stability problems can prevent a CIR project from being successfully constructed. A series of Dynamic Cone Penetrometer (DCP) tests were conducted on a CIR project that experienced varying levels of subgrade failure during construction. Based on this case study, and supporting data, it was determined that the DCP test can be used to evaluate subgrades that have insufficient stability for recycling. Overall, CIR roads in Iowa are performing well. It appears that the development of transverse cracking has been retarded and little rutting has occurred. Contracting agencies must pay special attention to the subgrade conditions during project selection. Because of its performance, CIR is a recommended method to be considered for rehabilitating aged low volume (<2000 AADT) asphalt concrete roads in Iowa.

Ice-Retardant Pavement, HR-290, 1991

During 1986, the City of Des Moines placed an experimental asphaltic concrete overlay containing an ice-retardant additive (Verglimit) on Euclid Avenue (U.S. Highway 6). Verglimit is a chemical multi-component deicer which is added to the surface course of an asphalt overlay. The additive was uniformly distributed through the mix at the asphalt plant, which allows exposure of the particles as the finished surface wears under traffic. During a snowfall, the exposed particles attract and absorb moisture creating a deicing solution which dampens the pavement. The Verglimit additive used on this project cost $1,180 per metric ton. The Verglimit was added at a rate of 6.3% by weight, which was 126 pounds per ton, or $66.38 per ton of hot mix asphalt. The purchase of Verglimit additive was funded by the Iowa Department of Transportation through a research project recommended by the Highway Research Advisory Board. The pavement surface experienced severe wetting due to the additive's affinity for water immediately after the project was completed and during periods of high humidity. This wetting created slippery conditions both on the project itself and where vehicles tracked the additive. The only way to remove the slipperiness was by flushing the street with water. The ice-retardant overlay appears to perform as expected in reducing the adherence of ice and snow, especially at temperatures just below freezing. It performs better in light snowfalls than in heavy ones. The ice retardant overlay is effective in eliminating thin coatings of ice due to freezing drizzle or widespread frost. The accident data showed a reduction in the number of snow and ice related accidents but due to the low number of this type of accident the results are inconclusive.

Crack and Seat PCC Pavement Prior to Resurfacing US 59 - Shelby County, HR-527, 1993

Asphalt concrete resurfacing is the most commonly utilized rehabilitation practice used by the Iowa Department of Transportation. The major problem with asphalt concrete resurfacing is the reflective cracking from underlying cracks and joints in the portland cement concrete (PCC) pavement. Cracking and seating the PCC prior to an asphalt overlay was the construction method evaluated in this project. There was cracking and seating on portions of the project and portions were overlaid without this process. There were also different overlay thicknesses used. Comparisons of crack and seating to the normal overlay method and the different depths are compared in this report. Cracking and seating results in some structural loss, but does reduce the problem of reflection cracking.

The Effects of Crushed Particles in Asphalt Mixtures, HR-311 and MLR-88-16, 1990

One of the most serious impediments to the continued successful use of hot-mix asphalt (HMA) pavements is rutting. The Iowa Department of Transportation has required 85% crushed particles and 75-blow Marshall mix design in an effort to prevent rutting on Interstate roadways. Relationships between the percent of crushed particles and resistance to rutting in pavement through the use of various laboratory test procedures must be developed. HMA mixtures were made with 0, 30, 60, 85, and 100% crushed gravel, crushed limestone, and crushed quartzite combined with uncrushed sand and gravel. These aggregate combinations were used with 4, 5, and 6% asphalt cement (ac). Laboratory tests included Marshall stability, resilient modulus, indirect tensile, and creep. A creep resistance factor (CRF) was developed to provide a single numeric value for creep test results. The CRF values relate well to the amount of crushed particles and the perceived resistance to rutting. The indirect tensile test is highly dependent on the ac with a small effect from the percent of crushed particles. The Marshall stability from 75-blow compaction relates well to the percent of crushed particles. The resilient modulus in some cases is highly affected by grade of ac.

Improved Asphalt Surfaces and Asphalt Resurfacing Performance through Crack Maintenance, HR-213, 1987

In 1980, a Vanguard High Pressure Water Blaster capable of providing 10 gallons of water per minute at 2000 psi was purchased to evaluate water blasting as a crack cleaning method prior to crack filling on asphalt concrete pavements. Afer some iniital trials demonstrated its effectiveness of removing dirt, debris and vegetation, it was included in joint and crack maintenance research on Iowa 7 in Webster County. The objective of the research was to evaluate six crack preparation methods and seven "sealant" materials. The cleaning and sealing was performed in the spring of 1983. Visual evaluations of the performance were made in the fall of 1983 and spring of 1985. Compressed air and/or high pressure water did not adequately prepare cracks less than 3/8 inch wide. Routing or sawing was necessary to provide a sealant reservoir. The water blaster was more effective than compressed air in removing dirt, debris and vegetation but this did not yield significant improvement in sealant adhesion or longevity. Periodic crack filling is necessary on ACC surfaces throughout the remaining life of the pavement.

Field Evaluation of Engineering Fabrics for Asphalt Concrete Resurfacing - Audubon County, HR-360, Construction Report, 1994

An asphalt concrete (ACC) overlay is most often the rehabilitative effort used to maintain the serviceability of either an ACC or PCC pavement. The major problem in durability of this ACC overlay comes from reflective cracking. These cracks usually open, allowing water to enter the unsealed crack and strip the ACC in the overlay. The stripping of the ACC allows accelerated deterioration at the crack. Two engineering fabrics were evaluated in this project in order to determine their effectiveness in reducing reflective cracking. These two materials are: PavePrep, Contech Construction Products, Inc., and Pro-Guard, Phillips Fiber Corporation. A 4.2 km (2.6 mi) roadway in Audubon County was selected for the research project. The roadway was divided into eight test sections. Four of the test sections are conventional resurfacing. The other four sections are split between the two engineering fabrics (two Pro-Guard and two PavePrep). A 75 mm (3 in.) thick overlay was placed over the entire project.

Portland Cement Concrete Utilizing Recycled Pavement, MLR-77-3, 1977

Two objectives were involved in this recycling project: To determine if the asphalt concrete surfacing from an existing roadway could be removed, the existing portland cement concrete pavement broken, removed, crushed to 1-1/2 inch minus, proportioned through a conventional central mix proportioning plant with the addition of concrete sand, and placed with a conventional slipform paver; and to determine if a two course, composite pavement, each course of different mix proportions, could be placed monolithically with conventional slipform equipment after being proportioned and mixed in a conventional central mix plant. The project was completed with no major problem. The objectives were satisfactorily met. The project was a success to the degree that the Iowa D.O.T. is proceeding with at least two projects for the 1977 construction season that will utilize the old pavement as appregate for the new pavement.

Asphalt Cement Containing AC-13, HR-522, Construction Report, 1985

Stopping and turning maneuvers on high traffic volume asphalt cement concrete surfaced roads and streets often causes distortion of the pavement. Distortion may show up as excessive rutting in the wheel path, shoving of the pavement and/or rippling of the surface. Often times repeated corrective work such as cold milling or heater planing is required in these areas to maintain the pavement surface in a reasonable condition. In recent years polymer additives have been developed for asphalt cement concrete paving mixes that show promise in improving the inplace stability of the pavements. AC-13 (Styrelf 13) available from Bitucote Products Company, St. Louis, Missouri is an asphalt cement that has been modified by an additive to exhibit characteristics of very high stability in asphalt mixes.

Frictional Properties of Asphalt Concrete Pavements in Iowa, MLR-87-5, 1987

Friction testing of pavements has been a continuing effort by the Iowa Department of Transportation since 1969. This report details results of tests of asphaltic concrete pavements on the primary and interstate road systems. Both sprinkle treated and non-sprinkle treated pavements placed between 1975 - 1985 are included. A total of 1785 miles representing 216 separate paving projects were examined. The effect of fog sealing sprinkle treated pavements was studied by testing friction levels before and after the application of the fog seals. Conclusions of the report are: 1. Current aggregate selection criteria for a.c. pavement surface courses provides adequate friction levels through 10 years and should remain effective through a 15 year design life. 2. Sprinkle treatment of pavements has, for the most part, provided macrotexture in the pavement surface as evidenced by smooth tire testing. 3. Fog sealing sprinkle treated pavements does not significantly alter the friction properties.