Showing papers on "Asphalt concrete published in 1995"

Application of digital image processing to quantitative study of asphalt concrete microstructure

Abstract: Asphalt concrete (AC) is a strongly heterogeneous material that consists of asphalt cement, voids, fine particles, sand, and coarse aggregates A review of the literature reveals that the investigations of AC have mainly concentrated on the macroscopic behavior of the material based on the assumption that the mixture is homogeneous This assumption is mainly due to the extreme difficulty associated with the quantitative measurements of AC microstructure and the random nature of the aggregate distribution This paper applies an innovative digital image-processing technique to quantify the distribution, orientation, and shape of coarse aggregates (greater than or equal to 2 mm) in AC mixtures Results of the quantitative measurements of coarse aggregate distribution and shape in AC mixture are then presented and analyzed The quantitative results of AC microstructure clearly indicate the following findings: (a) the microstructure characteristics of coarse aggregates in AC mixtures can be accurately measured using the digital image-processing technique; (b) the area gradation of aggregate cross sections by the Feret diameter gives an excellent prediction of the sieve gradation of coarse aggregates (greater than or equal to 2 mm) used in the design of AC mixtures; (c) the major cross sections of coarse aggregate particles have the tendency to lie horizontally in the mixtures; and (d) comparison among two laboratory and two field compaction techniques provides valuable information related to compaction quality in terms of favorable aggregate distribution within the mixtures

Fatigue performance of asphalt concrete mixes and its relationship to asphalt concrete pavement performance in california

Abstract: In California, fatigue cracking is considered to be the most important type of distress affecting the performance of asphalt concrete pavements on major state highways. This report describes the results of a laboratory study of the fatigue response of a typical California asphalt concrete mix to define the effects of degree of compaction (as measured by air-void content), asphalt content, and aging on this performance parameter. The test results are then used in analytical simulations to estimate the effects of asphalt and air-void contents (with and without long-term-aging) on pavement performance. These simulations demonstrate that accurate construction control of air void content is more important than accurate control of asphalt content relative to the design target values. For example, a mixture targeted at 5-percent asphalt and 5-percent air voids will suffer a 30-percent reduction in fatigue life if the air-void content exceeds its target by 1-percent but only a 12- percent reduction if the asphalt content is shy of its target by 1 percent. Complicating this matter, however, is the likelihood that smaller-thanspecified asphalt contents will result in increased air-void contents. A mix design and analysis system for fatigue is presented; this system was initially developed as a part of the Strategic Highway Research Program (SHRP) Project A-003A. Its most attractive features include the ability to consider not only laboratory fatigue test results but also the anticipated environment and the ability to make risk assessments about design choices. Refinements to the original SHRP developed methodology are described, including improved procedures for computing pavement temperature profiles as well as calibrations which reflect uniquely California conditions. Analyses of "rich-bottom" pavements (pavements with larger asphalt content in the bottom lift) suggest added potential for improved pavement performance. Finally, a series of recommendations are presented for enhancing the fatigue performance of California pavements which include changes to current construction specifications and/or construction quality assurance procedures.

Correspondence Principle for Characterization of Asphalt Concrete

Abstract: In this paper, Schapery’s nonlinear elastic-viscoelastic correspondence principle based on pseudostrain concept is introduced as a means of separately evaluating important mechanisms of asphalt concrete under cyclic loading, including time dependence, damage growth, and fracture healing. Earlier work by Kim and Little and the findings from the present study have demonstrated that the correspondence principle can be applied to most of the testing conditions encountered in testing of asphalt concrete. The importance of using proper analytical representation of relaxation modulus in course of calculating pseudostrain is demonstrated using the cyclic data. At the loading frequencies typically used in asphalt-concrete testing (faster than 10Hz), the creep or relaxation data must be represented in a form that can accurately describe the short time behavior, such as the modified power law. It is concluded that the correspondence principle provides a means of more accurately modeling the damage growth and fracture healing of asphalt concrete under complex cyclic loading.

Low temperature fracture of polyethylene-modified asphalt binders and asphalt concrete mixes (with discussion)

Abstract: This paper gives an in-depth discussion on the low temperature fracture properties of polyethylene-modified asphalt binders and concrete mixtures. Test results are presented for chlorinated polyethylene-modified binders as well as for stabilized and unstabilized polyethylene-modified binders. The objective of this research was to elucidate which fundamental toughening mechanisms, if any, are responsible for the change in low temperature properties of asphalt binders and aggregate mixes to which polyethylene has been added.

Low temperature fracture of polyethylene-modified asphalt binders and asphalt concrete mixes

Abstract: This paper gives an in-depth discussion on the low temperature fracture properties of polyethylene-modified asphalt binders and concrete mixtures. Test results are presented for chlorinated polyethylene-modified binders as well as for stabilized and unstabilized polyethylene-modified binders. The objective of this research was to elucidate which fundamental toughening mechanisms, if any, are responsible for the change in low temperature properties of asphalt binders and aggregate mixes to which polyethylene has been added.

Effects of tire – pavement contact pressure distributions on the response of asphalt concrete pavements

Abstract: The paper presents the development of a computer program VIEM for the elastic analysis of multilayered elastic pavements under the action of arbitrary tire–pavement contact pressure distributions. The techniques adapted in VIEM primarily involves the use of a two-dimensional numerical integration to integrate point load solutions over the distributed pressure after discretizing the contact area into a finite number of triangular or quadrilateral elements. Values of contact pressure are inputted at the node points of discretized area. Numerical verification of VIEM indicates that numerical solution of high accuracy can be efficiently calculated for the elastic response of multilayered asphalt pavements. As a result, the determination of displacements and stresses (strains) can be achieved using a personal computer. With the use of VIEM, a theoretical investigation is further performed to illustrate the effects of tire–pavement contact pressure distributions on the response of asphalt concrete pavements. An...

Inverted flexible pavement response and performance

Abstract: An inverted section consists of an unstabilized crushed-stone base sandwiched between a lower cement-stabilized layer and the upper asphalt concrete (AC) surfacing Two inverted full-scale instrumented pavement sections were tested to rutting or fatigue failure in a laboratory facility One inverted section had a 152-mm (6-in) cement-stabilized silty sand subbase The inverted sections were loaded up to 44 million load repetitions at failure A 289-kN (6,500-lb) uniform circular loading was applied to the surface and systematically moved to prevent a punching failure The inverted sections exhibited better performance compared to conventional and full-depth AC sections also tested The inverted sections had lower vertical stresses on the subgrade and lower resilient surface deflections than the other sections The rigid cement-stabilized subbase was effective in bridging a weak subgrade The inverted section made optimum use of the compressive characteristics of the unstabilized aggregate base where stresses were compressive A nonlinear finite-element program, GT-PAVE, was used to calculate the resilient pavement response GT-PAVE did a reasonable job of simultaneously predicting the measured deformation and stress and strain response at six points in the different layers of the inverted sections A sensitivity analysis indicates the use of a 152-mm (6-in) unstabilized aggregate base and a 152- to 203-mm-thick (6- to 8-in) cement-stabilized subbase to be an attractive inverted section design

Comparison of end result and method specifications for managing quality

Abstract: The results of a statistically designed experiment in which asphalt concrete cores and nuclear gauge readings were taken from five California projects are reported. Relative compaction for the projects was controlled with a method specification. Analysis of variance is used to separate test error and locational components of variance for specific gravity, asphalt content, air voids, lift thickness, and grading. Compaction results are compared with similar results from 16 end result specification (ERS) jobs studied previously. Relative compaction on the ERS jobs averages 3.1% higher in value. Findings on test precision, increased lot size, and materials variability are discussed.

Laboratory evaluation of crumb rubber modified mixtures designed using txdot mixture design method

Abstract: The Texas Department of Transportation has developed a mixture design procedure for crumb rubber modified (CRM) asphalt concrete mixtures. Eight CRM mixtures were designed using this procedure. Four wet process mixtures and four dry process mixtures, in addition to one control mix, were considered for material characterization and performance evaluation using the asphalt aggregate mixture analysis system (AAMAS). The control mixture was designed using the conventional design method. It was determined that CRM has the potential to significantly improve the fatigue cracking performance of asphalt concrete pavements, but only when the wet method is used and the binder is properly designed. The dry process should produce mixtures with a reduced propensity for rutting, but may have an adverse effect on cracking. Fine and coarse rubber can be added dry to the dense graded mix (0.5% by weight of aggregate) without having any adverse effects on the performance. Although state transportation departments must comply with the existing legislative requirements, tire rubber, like any additive, should be used only to address a given mixture deficiency or expected deficiency in a given situation.

Evaluation of Polymer-Modified Asphalt Concrete Mixtures

Abstract: Since the mid-1980s, polymer-modified asphalt concrete mixtures have been widely used to minimize rutting failures of flexible pavements. This research investigates the permanent deformation behavior of unmodified asphalt concrete mixtures as compared to the behavior of asphalt concrete mixtures modified with polyethylene. The rutting resistances of the mixtures as 40°C and 60°C are evaluated in the laboratory using the repeated-load permanent-deformation test. The data from the repeated-load permanent-deformation tests are used in the VESYS model to predict the rutting development of typical pavement structures built with both modified and unmodified mixtures. The analysis of the VESYS results indicate that the polyethylene-modified mixtures exhibit higher resistance to rutting than the unmodified ones. In addition, the layer coefficients of the polyethylene-modified mixtures were 75–85% higher than the layer coefficients of the unmodified ones.

On the low temperature cracking of asphalt pavements

Abstract: Fundamental concepts as well as factors influencing low temperature cracking are described in this report in a state of the art description of current knowledge. A compilation of laboratory test methods for the characterisation of low temperature behaviour of bituminous binders and mixtures is given, together with models for relating the measured properties to field performance. A summary of field investigations related to low temperature cracking is also presented and the current state of knowledge is discussed. Among the main factors influencing low temperature cracking of asphalt concrete mixtures are bitumen characteristics. A laboratory investigation was conducted using a total of five different plain bitumens and five polymer modified bitumens in three different types of mixtures (dense graded, split mastic and porous asphalt). In addition, various gussasphalt mixtures were analysed. Statistically significant relationships between binder characteristics (rheological as well as chemical) and fracture temperature of asphalt concrete mixtures were established. Another important factor with regard to low temperature behaviour of asphalt pavements is the degree of ageing; the older the pavement, the greater the incidence of thermal cracking. A test program was developed to evaluate the effect of long-term ageing on the low temperature cracking properties of asphalt concrete mixtures using Thermal Stress Restrained Specimen Test (TSRST). Thermal contraction characteristics of asphalt concrete mixtures are of significant importance for the occurrence of low temperature cracks. A new method for determination of the thermal volumetric contraction coefficient has been developed. (A)

Prediction of effective asphalt layer temperature

Abstract: The most widely used method for evaluating deflection measurements for overlay design analysis is the 1993 AASHTO "Guide for Design of Pavement Structures". Researchers and numerous users of the AASHTO overlay design procedure have challenged the accuracy of the AASHTO temperature correction procedure for deflections. In another paper presented at the 1995 TRB Annual Meeting a new temperature correction procedure was presented, and that procedure resulted in significant improvements over the AASHTO procedure. That procedure requires the middepth temperature of asphalt layers as input for the effective temperature of the layers. A new prediction method for an asphalt concrete middepth temperature on the basis of a data base approach is described. The major improvements over the AASHTO method are (a) air temperatures for the previous 5 days are not needed, which allows simpler and quicker deflection analyses in the North Carolina Department of Transportation (NCDOT), and (b) different temperature-depth gradients between the heating (morning) and the cooling (afternoon) cycles are taken into account. The comparison of the measured and predicted temperature demonstrated an acceptable degree of accuracy of this model for routine deflection analyses by state highway agencies. In addition to presenting the NCDOT temperature prediction procedure, an alternative temperature prediction model, known as BELLS equation, is also studied. Comparison of the measured pavement temperatures and the predicted values obtained by the BELLS equation showed underprediction of the one-third-depth temperatures at temperatures higher than 32 deg C (90 deg F).

Development and analysis of laboratory techniques for simulating segregation

Abstract: Objectives of this research were to develop laboratory techniques for simulating asphalt mixture segregation and determine mixture compactibility and physical properties. Segregation in asphalt concrete pavements occurs as a result of nonuniform distribution of the mixture components such as aggregate and asphalt. Mixture segregation can lead to premature pavement distress. Factors and steps in the production, transportation, and placement of asphalt mixtures associated with segregation include material type, mixture design, stockpiling and handling, plant type and operation, surge silos, truck loading and unloading, and laydown. Materials used in the study included gravel, natural sand, and an AC-20 asphalt cement. Aggregates were selected to meet the Indiana Department of Transportation specification for a No. 8 binder with a maximum aggregate size of 25.0 mm (1 in.). In order to simulate various degrees of segregation of the coarse and fine fractions, four artificially segregated asphalt mixtures were prepared in addition to the control asphalt mixture. As part of the study, specimens were compacted for the fine mixtures using the U.S. Corps of Engineers gyratory testing machine to determine the stability and compactibility indexes. Specimens were also prepared and tested using the indirect tensile test method. Slabs of the five mixtures were compacted using a laboratory linear compactor. Subsequently, these slabs were tested using the Purwheel tracking device to determine their rutting potential and moisture susceptibility. Results indicate that segregation affects the residual asphalt content, gradation, stability index, compactibility index, air voids, unit weight, indirect tensile strength, rutting potential, and moisture susceptibility of asphalt concrete mixtures.

Evaluation of rubber modified asphalt demonstration projects

Abstract: Eleven Ontario rubber modified asphalt demonstration projects were evaluated in terms of pavement performance and environmental impacts, including recyclability. On the basis of generally poor short-term performance of eight dry process (rubber modified asphalt concrete) projects, it appears that this method of crumb rubber modifier use should not be pursued unless there is considerable care in materials selection, mix design, and mix production and placement. The wet process (asphalt rubber) shows promise because it appears that asphalt rubber can enhance the durability of these asphalt mixes. Use of crumb rubber modifier in cold in-place recycling was not a technical success. A project with recycling of rubber modified asphalt concrete indicates no technical problems with recyclability. The economics (life-cycle cost) of the dry process are not favorable. If the incorporation of asphalt rubber does decrease maintenance costs or extend service life, there is a potential for savings through the wet process. Available asphalt technology, whether conventional or rubber modified, is capable of meeting environmental regulatory criteria. It is recognized that some technical issues require resolution to optimize rubber modified asphalt technology, and further work must be undertaken in such areas as long-term performance.

Using fiber-optic sensing techniques to monitor behavior of transportation materials

Abstract: Although not new to the communications or manufacturing area, fiber-optic sensors are only recently being applied to civil engineering structural evaluation. These sensors offer enormous potential within the transportation field to examine and characterize strain behavior in commonly used materials. Fiber-optic sensing research efforts conducted during the past 2 years on three materials relevant to the transportation industry are documented: portland cement concrete, steel, and asphalt concrete. Portland cement mortar beams were tested to determine the rate and magnitude of shrinkage. Impending fractures in steel structures may be avoided by real-time sensing, thereby minimizing potential safety problems. Steel beams were loaded to measure bending strains, as a precursor to beam crack detection. Finally the lateral strain behavior of axially loaded asphalt emulsion aggregate mixture (EAM) cylinders was studied. The EAM Poisson ratio was determined. Findings comparable with those calculated from theory, found in the literature, and obtained with traditional sensing techniques are presented. Whereas this fiber-optic sensing methodology offers great potential, the reliability and viability of this new measurement technique must be further assessed. This research advanced the development and use of this innovative technology.

Use of seismic pavement analyzer in pavement evaluation

Abstract: The Seismic Pavement Analyzer (SPA, patent pending) is an instrument designed and constructed to monitor conditions associated with pavement deterioration. It measures such conditions as voids or loss of support under a rigid pavement, moisture infiltration in asphalt concrete pavement, and delamination of overlays. The SPA detects these types of pavement conditions by estimating Young's and shear moduli in the pavement, base, and subgrade from the following wave propagation measurements: (a) impact echo, (b) impulse response, (c) spectral-analysis-of-surface-waves, (d) ultrasonic-surface-wave-velocity, and (e) ultrasonic-body-wave-velocity. The SPA records the pavement response produced by high- and low-frequency pneumatic hammers on five accelerometers and three geophones. A computer controls data acquisition, instrument control. and interpretation: measurements and interpretations are reported in both screen and data base formats. This paper briefly describes the device and summarizes the usefulness of the equipment in pavement evaluation. The results from several field tests are also discussed. The tests conducted so far have produced very promising results. The device is simple to use, and results have been reliable and repeatable.

Asphalt concrete sample rutting machine

Abstract: The disclosed machine is comprised of a chassis, process control box and load wheel assembly. The chassis is designed to attach to commercially available controlled temperature heating baths. The primary functions of the process control box are to distribute electrical power, monitor sensor responses to electrical inputs, and to control the overall operation of the load wheel assembly. The load wheel assembly applies multiple load applications while not rolling off the surface of a standard asphalt concrete specimen.

Paving asphalt concrete composition

Abstract: A paving asphalt concrete composition consists essentially of an oil-impregnated vulcanized rubber crumb and an asphalt-aggregate mixture, in which the oil-impregnated vulcanized rubber crumb consist of 99-60% by weight of vulcanized rubber crumb and 1-40% by weight of an extending oil. This paving asphalt concrete composition is suitable for pavement of motorways, sidewalks, runways, taxiways, parking lots and the like.

Mechanistic evaluation of asphalt concrete mixtures containing reclaimed roofing materials

Abstract: Recycling of waste construction materials has gained popularity owing to increasing demands on landfill sites. This is evident by the use of ground rubber tire, glass, fly ash, and slag in asphalt pavements by various highway agencies in North America and around the world. Waste roofing materials also pose a heavy burden on landfill sites. Using reclaimed roofing materials (RRM) in hot mix asphalt (HMA) concrete pavements can lessen the demand on landfills. A study was carried out to determine the feasibility of using RRM in HMA pavement. This paper presents the results of a mechanistic evaluation of three asphalt concrete mixes containing 0, 15, and 25 percent of RRM. By using laboratory prepared specimens of RRM mixes, mechanical properties such as resilient modulus, creep and permanent deformation, fatigue, and moisture sensitivity of these RRM mixes were determined. Performance of representative RRM pavements were modeled using the VESYS performance prediction model. Performance parameters, such as rut depths, cracking index, and the present serviceability index, were used to assess potential improvements of asphalt concrete mixes using RRM. The results indicated that the mix containing 25 percent of RRM exhibited significant improvements in greater pavement rutting resistance, longer fatigue life, and better overall pavement performance compared with a conventional asphalt mix.

A review of crumb-rubber modified asphalt concrete technology

Abstract: This study presents an analysis of the characteristics of crumb-rubber modified (CRM) asphalt pavements. It is comprised of a state-of-the-art literature review and laboratory testing conducted with a Brookfield viscometer. The reaction that occurs between the rubber and asphalt is not a chemical reaction, but rather a diffusion process that includes the physical absorption of aromatic oils from the asphalt into the polymer chain of the rubber. The presence of CRM in asphalt produces a thicker binder, which increases aging and oxidation resistance. The presence of carbon black in CRM improves binder durability. The temperature susceptibility of the mix is reduced, causing more uniform fatigue characteristics. CRM applications have been met with various degrees of success because existing quality control and quality assurance methods have not been developed enough to ensure desired binder properties in the field.

Evaluation of the Hall Effect Sensor for Pavement Instrumentation

Abstract: This research evaluates a new concept to measure the tensile strains at the bottom of the asphalt concrete layer in flexible pavements. The concept consists of using the Hall Effect sensor in an H-gage configuration to measure the dynamic strains in flexible pavements. The evaluation program included both laboratory and field experiments to evaluate the fundamental and operational properties of the recommended gage design. The laboratory experiment showed that the Hall Effect gage can withstand the temperature and moisture conditions that are encountered during the construction and operation stages of hot mixed asphalt concrete pavements. It also indicated that the dynamic characteristics of the gage are suitable for measuring pavement strains under moving vehicle loads. The field experiment evaluated the in-service characteristics of the Hall Effect gage under a large number of combinations of vehicle speed, axle load, and tire pressure. The field data showed that the Hall Effect gage has good survivability and repeatability and it compares favorably with other strain gages that have been used in flexible pavements.

Quantitative determination of polymers in asphalt cements and hot-mix asphalt mixes

Abstract: The addition of polymers in asphalt cement has been widespread. Quantitative analysis of these polymers is essential to verify if specifications are being met. The analysis of two styrene butadiene rubber (SBR) latexes and ethylene vinyl acetate (EVA) and styrene butadiene styrene (SBS) polymers in three different asphalts was accomplished by Fourier transform infrared (FTIR) spectroscopy. Although the behavior of each SBR latex in each asphalt yielded somewhat different calibration curves, each latex-modified asphalt cement was successfully quantified. The values for latex determined by FTIR spectroscopy yielded a more linear relationship between the dynamic shear measurements and the latex concentration than the nominal values that accompanied the mixtures. Both EVA and SBS polymers were also quantified by using the analysis that was developed for the SBR latex-modified asphalt. The infrared analysis of SBR latex in asphalt was directly applied to the analysis of SBR latex in asphalt-aggregate mixes. Analysis of 3 weight percent SBR latex in asphalt concrete samples was achieved by removing the SBR latex-modified asphalt from aggregates and analyzing the latex content by FTIR spectroscopy. Three different aggregate types, gravel, granite, and limestone, were used.

Characterization of emulsion aggregate mixtures

Abstract: Emulsion aggregate mixtures (EAMs) are one type of low-quality cold-mixed asphalt concrete mixture. In Illinois, road-mixed and plant-mixed EAMs are used frequently as base or surface courses on low-volume rural roads (less than 1,000 average daily traffic). This research characterizes the EAM engineering properties that contribute to the observed performance of EAM pavements using laboratory testing. Dense-graded and open-graded aggregates treated with HFE-300 and CSS-1 emulsions are considered. Shear strength, repeated loading response (resilient modulus, permanent deformation), dynamic cone penetrometer, and curing effects are evaluated. The study concludes that EAMs are characterized as an improved granular material.

Behaviour of pavements with granular bases - prediction and performance

Abstract: To better model flexible pavements, a new nonlinear finite element program, GT-PAVE, has been developed. The program runs on a PC and considers the cross-anistropic behavior exhibited by unbound aggregate bases, handles residual compaction stresses, and eliminates horizontal tensile stresses in the base. Predicted response is compared with measured values at six different locations in 5 test sections. GT-PAVE is then used to compare the potential performance of selected inverted flexible sections with conventional ones and practical conclusions are made. An inverted section consists of an unbound aggregate base sandwiched between an asphalt concrete surfacing and a cement stabilized subbase. (A) For the covering abstract see IRRD 890992.

Properties of Microwave Recycled Asphalt Cement Binders

Abstract: Recycling asphalt concrete pavements are currently limited to about 40% to 60% of recyclable asphalt pavement (RAP) in the mixture, with the remaining material composed of new asphalt and aggregates. The use of microwaves for heating allows the possibility of recycling with 100% RAP material. The effect of microwaves on asphalt cement binders was evaluated using conventional viscosity and penetration tests. The binders were also evaluated using Gel Permeation Chromatography (GPC), Fourier-Transform Infrared Spectroscopy (FTIR), and Dynamic Shear Rheometer (DSR). Viscosity and penetration testing provided opposing results with each showing slight increases in value after microwaving of the binder. A noticeable change in the molecular size distribution was observed with the GPC with the addition of a recycling agent. An increase in complex shear modulus occurred at high temperatures or low frequencies after microwaving. This increase was more pronounced on severely oxidized or hardened asphalts. The increase in complex shear modulus did not correlate well with measured viscosity and penetration values. The steady-state viscosity values obtained followed the same general trend as the results from conventional viscosity testing.

Mix design methodology for a warrantied pavement: case study

Abstract: The application of a mix design procedure developed as part of Strategic Highway Research Program (SHRP) Project A-003A for a warrantied pavement project in California is described. Two mixes were designed for overlay of a "cracked and seated" portland cement concrete pavement, one a dense-graded asphalt concrete with a PBA-6 specification modified binder and the other an asphalt-rubber hot mix with a gap gradation. Both mixes were designed to meet rutting specifications for the pavement warranty. The mix design method considers mix performance measured using repeated load simple shear testing at constant height, traffic, site-specific temperatures, and reliabilty of test results and traffic predictions. The mixes were also evaluated for moisture sensitivity, using moisture-conditioning procedures developed as part of Project SHRP A-003A to determine the need for, and suitability of, using an antistripping additive. The mix design method developed in SHRP A-003A provided the contractor with a tool to predict the performance of the mix in terms of anticipated traffic during the warranty period and for site-specific temperature conditions. Both mixes were constructed as part of the overlay project in July 1993 and performed successfully during 1994.

Production variability analysis of hot-mixed asphalt concrete containing reclaimed asphalt pavement

Abstract: A research project was undertaken to evaluate the production and construction viability of HMAC containing high quantities of RAP material. Four construction projects were selected for this purpose. Two of the projects used 35 percent RAP material (both type-C mixes), while the other two used 40 percent (a type-B mix) and 50 percent (a type-D mix) of the RAP material respectively. The projects differed in sizes, with total construction tonnage ranging from 10.9 million kg to 27.2 million kg. (12,000 to 30,000 tons). In all cases, dedicated stockpiles of RAP material were used. A series of tests according to TxDOT Special Specification Item 3007 (Quality control/Quality Assurance of Hot Mix Asphalt) were performed both in the hot-mix plant laboratory and the University of Texas at Austin Laboratory The tests included extraction, gradation determination, determination of asphalt content, Hveem stability testing, asphalt recovery, penetration, and viscosity tests. In general these high-percent RAP projects indicated a variability higher than that of a typical HMAC without RAP. The pay adjustment factors for gradation and asphalt content deviation were lower than typical values. The construction gradations were finer and than the job-mix formula target gradations, possibly a result of aggregate crushing during the milling operation.

Smoothness control in asphalt pavement construction: development of specifications, implementation, and results

Abstract: Surface smoothness on newly constructed pavement is a major concern of the highway industry. This smoothness, or riding comfort, is an indication of the quality of the newly constructed pavements since it affects road users directly. Smoothness specifications for asphalt concrete (AC) pavements now in effect in Kansas have evolved over the past few years through a number of revisions. Pavement profiles with short wavelengths and smaller amplitudes than the industry-accepted 5.1 mm (0.2 in.) can harm the ride quality of pavements. This experience has led the Kansas Department of Transportation to eliminate the 5.1 mm blanking band width in the profilograph trace reduction process. The implementation of this zero, or null, blanking band was successful and has resulted in smoother asphalt pavements in Kansas. The currently used specifications for AC pavements have been based on the consideration of a number of factors related to the construction of and the measurement of smoothness on AC pavement. The incentive payment amounts have been calculated to make these compatible with the incentive payments for concrete pavement. The results show that these smoothness specifications can be achieved by contractors, and the number of sections in the bonus range indicates that the incentive payments encouraged better-quality paving. These results should have a positive impact on AC paving in Kansas. Overall, an increasing number of miles of pavements with lower profile index values are being constructed since the implementation of smoothness specifications for AC pavements.

Use of skid performance history as basis for aggregate qualification for seal coats and hot-mix asphalt concrete surface courses

Abstract: The polish value (PV) test is a commonly used laboratory test procedure for evaluating the frictional properties of aggregates used in asphalt concrete surface courses. However, the success that has been achieved with this method is limited owing to the poor correlation between laboratory PV values and skid numbers measured in the field. In recognition that some low PV aggregates have provided good skid performance in the field, the Texas Department of Transportation permits aggregates to be qualified on the basis of their historical skid performance on in-service pavements. The current procedure used in developing the skid performance history is based on the guidelines established in the FHWA skid accident reduction program IM 21-2-73. The Texas Department of Transportation's experience with both of these approaches to skid control--aggregate source rating based on polish value and aggregate qualification based on past skid performance data--is documented. The skid performance approach is dealt with in greater detail. A number of shortcomings in the current procedure are identified. The variability in skid measurements and its influence on the reliability of the aggregate qualification procedure are discussed. An extension to the current procedure is proposed so that the reliability of prediction can be appropriately incorporated in the procedure. A research methodology to address the deficiencies in the current aggregate qualification procedure, and hence improve its reliability, is outlined.