Showing papers on "Asphalt concrete published in 1985"

Methodology for predicting asphalt concrete overlay life against reflection cracking

Abstract: This paper describes a new design methodology for the prediction of the reflection cracking life of asphalt concrete overlays. A mechanistic empirical approach is used in developing the present design procedure. The variables used and the form of the design equation were chosen based upon a mechanistic model which represents the actual process of pavement failure. An approach which makes use of principles of fracture mechanics and beam-on-elastic foundation theory is used in developing the mechanistic model. The mechanistically computed pavement responses are then regressed against observed distress on overlays to obtain the final design equations. The data collected on a large number of pavement sections located at various parts of the State of Texas and stored in the computerized data base at Texas Transportation Institute were available for the use of this research study. From these, 40 flexible pavement sections with bituminous concrete overlays were selected for the analysis. From the correlations obtained in the regression analysis, it is evident that this methodology may be employed successfully in the design of asphalt overlays. In the conclusion of the paper, the need to perform similar analysis on data collected from regions of varying climatic conditions is emphasized.

Heating device for use with asphalt pavement resurfacing equipment

Abstract: An asphalt pavement heating device, for use with an asphalt pavement recycling or repair apparatus which uses heaters to warm the asphalt to a pliable form thereby facilitating the recycling or repair process, wherein a pressurized combustible gaseous mixture of fuel and air is burned in a non-oxidizing blue hot flame which is impinging the pavement surface, said flame being formed in a firebox which is suspended on the front and/or underneath the carriage of the apparatus over the heated surface, said firebox having flexible or "sealing curtain type" side walls which drape to the surface thereby excluding the entrance of ambient air, said device being characterized by its capabilities to rapidly heat asphalt concrete pavement and its smokeless exhaust.

Mechanistic design concepts for conventional flexible pavements

Abstract: Mechanistic design concepts for conventional flexible pavement (asphalt concrete (AC) surface + granular base/subbase) for highways are proposed and validated. The procedure is based on ILLI-PAVE, a stress dependent finite element computer program, coupled with appropriate transfer functions. Two design criteria are considered: AC flexural fatique cracking and subgrade rutting. Fatique cracking is controlled by limiting the tensile strain at the bbottom of the AC layer. Subgrade rutting is controlled by limiting the stress-ratio at the granular layer-subgrade interface. Algorithms were developed relating pavement response parameters (stresses, strains, deflections) to AC thickness, AC moduli, granular layer thickness, and subgrade moduli. Extensive analyses of the AASHO Road Test flexible pavement data are presented supporting the validity of the proposed concepts. (Author)

Illi-pave mechanistic analysis of aasho road test flexible pavements

Abstract: The stress-dependent, finite element pavement model known as ILLI-PAVE was used to study the performance of AASHO Road Test flexible pavement sections. Analyses were conducted to identify significant relationships between the appearance of fatigue cracking in the asphalt concrete (AC) surface and the AC strain and subgrade deviator stress predicted by ILLI-PAVE. Deflection and temperature data from the road test were used with ILLI-PAVE to "back calculate" seasonal variations in subgrade support and load-induced pavement stresses and strains. The structural response-performance relationships identified explain the observed behavior of the AASHO Road Test pavement sections in a realistic fashion. Seasonal damage factors and weighting factors based on these relationships provide a mechanistic explanation of the seasonal effects that is consistent with experience. These results demonstrate that ILLI-PAVE is a powerful tool for pavement design and analysis. It provides an adequate and valid representation of the structural behavior of conventional flexible pavements and can be used to effectively evaluate nondestructive test (NDT) data and determine the structural characteristics of existing pavement systems. ILLI-PAVE, therefore, will serve as a sound basis for the development of mechanistic procedures for the design of new flexible pavements and for the selection of rehabilitation strategies for existing flexible pavements.

Asphalt Overlay Design Procedures

Abstract: This synthesis will be of interest to pavement designers and others concerned with the design of asphalt concrete overlays. Information is presented on reasons for overlaying a pavement and on the vaious methods available for design of an asphalt overlay. A pavement overlay may be required because of inadequate ride quality, excessive pavement distress, reduced friction between tire and pavement, high user costs, or inadequate structural capacity for planned use. This report of the Transportation Research Boad discusses the current methods used for designing asphalt concrete overlays with emphasis on deflection-based and analytical procedures. (Author)

Development of Color Pavement in Korea

Abstract: A development of color pavement in Korea is presented. It includes an examination of pavement materials used, preparation of specimen, comparison tests between regular and colored mixture, mixing at asphalt plant, and placing colored mixtures in field. A synthetic resin binder with light yellow color was developed, and proved compatible for colored pavement through the several comparison tests: Marshall stability test, wheel tracking test, ravelling test, and accelerated weathering test. For the pigment, several different inorganic products were used: Fe\d2 O\d3 (IOR), Fe\d2 O\d3 (IOY), Cr\d2 O\d3, and ultra-marine blue. The mixing operation and paving method of color mixture were same as regular asphalt concrete mixture, but the quantity of pigment replaced that of mineral filler. After a successful trial placing, the mixture was placed in the plaza of Great Seoul Children Park and the sidewalk of new Banpo Bridge. The utilization of color pavement will provide better roadway environment and traffic safety, and will be accelerated by the beautification plan for 1986 Asian and 1988 World Olympic Games in Seoul.

Developing stochastic flexible pavement distress and serviceability equations

Abstract: The development of a method of predicting pavement performance in terms of present serviceability index and four primary distress types (area and severity) and the application of the method to the design of flexible pavements are summarized. The method is based on an S-shaped performance curve, the curve fit parameters for which can be determined using the methodology developed by Garcia-Diaz and Riggins. These parameters have been found for 164 pavement test sections located throughout Texas. The pavement test sections were categorized as three main types: asphalt concrete pavement on unbound base course, asphaltic concrete pavement on bituminous base course, and asphaltic concrete overlay. Data describing the pavement structure, including the thickness and elastic modulus of each layer, the environment, and the traffic for these pavements, were used to develop regression models for the curve fit parameters. A sensitivity analysis was made of these models to determine the effects of climate on pavement performance in four widely separated highway districts in Texas. The regression models along with the proposed performance equations and the stochastic form of these equations have been incorporated in the Texas Flexible Pavement System (FPS) design computer program. The modified version of FPS provides a listing of the optimal pavement designs selected on the basis of least total cost including material and user costs, overlay costs, and salvage values.

Pavement thickness designs using low-strength (pozzolanic) base and subbase materials

Abstract: Information is presented on combining laboratory test data for pozzolanic base and subbase materials with elastic layer theory and a limiting strain criterion to determine thickness designs equivalent to conventional asphaltic concrete and crushed stone pavement structures. A summary of laboratory testing in Kentucky is also presented. An example thickness design determination is given that includes an economic comparison of alternative designs with the conventional asphaltic concrete and crushed stone thickness design.

Maximizing the Beneficial Effects of Lime in Asphalt Paving Mixtures

Abstract: Laboratory and field tests were conducted to evaluate the use of hydrated lime as an antistrip additive in hot mix asphalt concrete. Batch and drum mix plants were used to prepare the paving mixtures. Lime was added dry and in slurry form. Individual aggregates and the total aggregate were separately treated with lime slurry and allowed to age for different time periods from a few minutes to 30 days before mixing with asphalt. Laboratory mixed and plant mixed asphalt concrete was tested using indirect tension and resilient modulus before and after moisture conditioning. Results indicate that lime is effective in reducing moisture susceptibility and that it is most effective when applied in the presence of moisture. In addition, a time delay after application of lime to aggregate is unnecessary. There are no significant differences in mixtures produced in batch and drum plants.

Effects of higher tire pressures on strain in thin ac pavements

Abstract: Since the oil embargo of 1973 and the attendant increase in fuel prices, pressures to increase truck sizes and weights have intensified. A second factor, which has also been on the increase but which has been given little attention, is tire inflation pressures. Inflation pressures have increased from in the vicinity of 80 psi to a typical value of 120 psi found in Texas tire pressure surveys in 1984. The objective of this paper is to evaluate the effect of this increase in tire pressures on tensile strains in thin asphalt concrete pavements. To determine the stress distribution between the tire and the road surface, the researchers used a finite element computer program developed at Texas Transportation Institute to study the effect of tire parameters on road surface friction forces. This computer program was used to develop the vertical pressure distribution and the horizontal surface shear forces for a free-rolling truck tire inflated to both 75 and 125 psi. A series of computer runs was made using ILLI-PAVE to determine the horizontal tensile strains for asphalt concrete surfaces 1, 1.5, 2, and 4 in. thick over an 8-in. granular base with three different moduli and a subgrade soil that is stress sensitive with an initial modulus of 10 ksi. This series of runs showed that increased truck tire pressures increase tensile strain and attendant fatigue cracking dramatically, that some thin pavement structures cannot provide adequate service, and that design procedures must be upgraded to consider pavement materials that can resist these high tensile strains. In general, to provide adequate service, materials should be either thin and flexible or thick and stiff.

Reducing the adverse effects of transverse cracking

Abstract: This research was initiated to identify methods of reducing the occurrence of transverse cracking. Eight (four repetitive) research sections were established to study three variations in the asphalt concrete pavement. The first variation was the comparison of low- and high-temperature-susceptible asphalt cement (AC) from two different sources. The second variable was to saw and seal transverse joints at spacings varying from 40 to 100 ft. The third variable was to increase the AC content in the asphalt treated base by 1 percent. The research sections were constructed with relatively few problems. Crack and joint surveys have been conducted on all research sections at intervals of less than 1 year since construction. No cracking was identified after the first winter season. The sawed joints also remained sealed through the first winter. At an age of approximately 1 1/2 years there was substantial cracking of the high-temperature-susceptible AC sections and substantial failure of the sealant material in the sawed joints. After almost 4 years, the asphalt pavement constructed with the high-temperature-susceptible AC produced a crack interval of 35 ft, the low-temperature-susceptible AC yielded an interval of 170 ft, and the low-temperature-susceptible AC with an increased AC content yielded an interval of 528 ft. The Pen-Vis number is an effective measure of temperature susceptibility of asphalt cements. The frequency of transverse cracking is affected by the temperature susceptibility of the AC. An increased AC content also reduces the frequency of transverse cracking.

Measurement of mixing efficiency in pavement recylcing

Abstract: Complaints have been voiced in recent years that the quality of asphalt cement has deteriorated, that it "isn't sticky", etc.. This is thought to have caused problems in mixes, such as tenderness, stripping, raveling, and premature aging. The oil embargo is mentioned as having contributed to this situation. The study reported in this paper was to determine the validity of these complaints. There are othe aspects of asphalt pavements to be considered as having caused these problems, such as changes in the manner of specifying asphalt grades, introduction of drum-mix plants, use of bag-house fines, new types of rollers (vibratory), etc. Several sets of data on asphalt cements were collected. These included the FHWA fingerprint file with test results on more than 400 asphalts collected in the period 1950-1970, programs of Asphalt Institute, some in cooperation with FHWA, in the 1970s, and new data collected by the authors in recent years up to 1980-81. The data sets are essentially 311 asphalts from 1950, 58 from 1960, 68 from 1977, 125 from 1979, and 77 from 1981. The oil embargo was in 1973. In addition, loose box samples of mix and field cores were taken from 50 construction jobs. The tests made to characterize the asphalt cements included kinematic viscosity at 275 F, absolute viscosity at 140 F, penetraton at 77 F and 39.2 F, softening point, and Rostler-Sternberg analysis. Samples were also aged in the thin-film oven test and the consistency tests repeated. The test results and the analyses of the data are presented in various ways--tables, bar graphs, scatter plots, etc. Statistical analyses are used to determine whether or not there are significant differences in the data according to year of production. Without going into these details, thee conclusions state that except for temperature susceptibility there have been no long term, significant changes in asphalt properties that can be identified by the analytical techniques being used. This does not mean that a decrease in asphalt quality has not occurred; if it does exist, current tests cannot detect it. (Author)

Establishing material properties for thin asphalt concrete surfaces on granular bases

Abstract: This report includes the results of an analytical study of thin asphalt pavements over flexible bases to define the engineering properties required for adequate performance. Since truck tire pressures have dramatically increased in recent years, included are the effects of the increased tire pressures on surface tensile strains, base shear stresses, and subgrade compressive strains. A finite element computer program developed for the FHWA was used to calculate vertical and horizontal surface shear pressure distribution for a bias ply truck tire inflated to both 75 and 125 psi. A series of ILLIPAVE computer runs was made to determine the horizontal tensile strains, lateral shear stresses, and vertical compressive strains for asphalt concrete surfaces 1, 1.5, 2, and 4 inches thick over 8- and 14-inche granular bases having three different moduli and a subgrade soil that is stress-sensitive with an initial modulus of 10 ksi. These results showed that some thin pavement structures cannot provide adequate service, and that design procedures must be upgraded to include materials service, these surfaces should be either flexible and thin on a stiff, thick base, or be stiff and thick. (Author)

The use of geogrids in the design of paved roads

Abstract: The article outlines the design method used, showing how geogrids differ from geotextiles giving examples of their application in several installations. Geogrids have a larger open area than geotextiles and can be made with exceptionally high moduli in one or two primary directions. Geogrids, when included into either an aggregate base layer or an asphaltic concrete layer, form a geocomposite which has greater stiffness and stability than aggregate alone. This can reduce both the magnitude of the vertical compressive strain on the top of the subgrade and the magnitude of the radial tensile strain at the base of the asphalt concrete layer. The paper concentrates on the effectiveness of geogrid reinforced aggregate base layers summarising research results from 1979 to the present time. These show that an increased life or reduced thickness of layer for the same life can be achieved. A guide based on the AASHTO interim guide has been developed. The pavement design procedure is illustrated with an example of the use of geogrids over a pumping subgrade, other examples show how geogrids and geotextiles can be used together. (TRRL)

Asphalt concrete overlay design procedure for portland cement concrete pavements

Abstract: The development and practical application of a reflection cracking analysis and overlay design procedure, which was developed for the Arkansas State Highway and Transportation Department, are described. The procedure is mechanistically based, but it is calibrated to the performance of experimental overlay sites in Arkansas and Texas. The procedure is incorporated into a computer program (ARKRC-2) for both existing pavement evaluation and overlay design. It considers asphalt concrete overlays and several techniques of reflection cracking control that may accompany overlay placement. These measures include bond breakers, stress-relieving interlayers, undersealing, and increased overlay thickness. The design procedure calls for a program of field measurements of vertical and horizontal slab movements to establish the potential for slab movement after overlay. Differential vertical slab movements are measured at joints (or cracks) by using a light-load deflection device (such as the Dynaflect). Measurements of horizontal slab movement are made over 2 or 3 daily temperature cycles at several existing joints (or cracks) by using a mechanical strain gauge. In the analysis procedure differential vertical slab movements are used to characterize load transfer and predict shear strains that will occur in the overlay under a simulated 18-kip axle load. Horizontal slab movements, on the other hand, are used to predict the maximum daily tensile strains that will be generated in the overlay during different seasons of the year. For both strain criteria, a fatigue-type approach is used to predict how long the overlay will last. A probabilistic distribution is then applied to the horizontal tensile (environmental) strain criteria, such that the overlay design can be based on a minimum tolerable level of reflection cracking over the design life. For joints (or cracked areas) that have problems with poor load transfer and would thus generate excessive overlay shear strains, it is recommended that some type of slab repair or undersealing operation be performed. (The findings of the original study for Arkansas indicated that other control measures such as increased overlay thickness and stress-relieving interlayers are not cost-effective compared with remedying the cause of the poor load trans- fer problem.) Besides providing a general description of the analytical models and the ARKRC-2 program (which can be adapted to almost any environment in the United States), examples of the overlay design nomographs developed for the specific construction materials and environmental regions found in Arkansas are also presented.

Construction of tensar reinforced asphalt pavements. polymer grid reinforcement: proceedings of a conference sponsored by the science and engineering research council and netlon ltd and held in london 22-23 march 1984

Abstract: The viability of reinforcing asphalt pavements structures with Tensar geogrid has been established by studies carried out in the UK and Canada. Substantial material cost savings and/or performance advantages can be realized for the reinforcement of asphalt concrete in new construction, overlay applications, granular bases and subgrades. In case of pavement spot repair and unbound granular base stabilization the geogrid can be hand laid. For the reinforcement of asphalt concrete in new construction and overlay applications the installation method must be automated and compatible with conventional paving procedures. Correct positioning and proper installation of the Tensar grid is crucial to performance. Tensar laydown equipment for tensioning the geogrid before placement of the paving mix has been developed and field tested. An alternate installation method is under development which uses a set of discs to roll the geogrid into the hot mix immediately after the paver. This paper also discusses the recycling of Tensar reinforced pavements and future developments. For the covering abstract of the symposium see IRRD 284425. (Author/TRRL)

Manganese-modified asphalt pavements: a status report

Abstract: This paper is a chronological account of the experimental asphaltic concrete highway sections that have been constructed using manganese-modified asphalt cements. Described are the potential performance improvements attainable with the chemical modifier and the changes that have been required in the way it is used to obtain benefits without undesirable side effects. The details of the laboratory testing before highway construction and the evaluations carried out with cores from highways after construction are related to the performance observed in experimental highway sections.

Changes in asphalt concrete durability resulting from exposure to multiple cycles of freezing and thawing

Abstract: Concern over water-induced damage in asphalt concrete pavements has resulted in the development of several new moisture susceptibility detection tests. This report compares two modifications of the water conditioning procedure for asphalt concrete specimens as described in the National Cooperative Highway Research Program (NCHRP) Reports 192 and 246. These modifications incorporate longer water exposure conditions for investigating the long-term durability of antistripping additives and paving mixtures. Significant and progressive changes in tensile strength were found to occur when asphalt concrete specimens were repeatedly exposed to freeze-thaw cycles. Factors, such as aggregate source, additive type, and additive quantity, influence the rate of strength loss during cyclical conditioning, and these rates are valuable in material selection. In particular, the sensitivity of cyclical conditioning to additive effectiveness was utilized to develop and select improved additives.

Heavy duty membranes for the reduction of reflective cracking in bituminous concrete overlays. final report

Abstract: The prevalence of reflective cracking in asphaltic concrete overlays is a major factor contributing to the premature failure of the pavement system. This reflective cracking is caused by cyclic stresses induced in the overlay by movements in the underlying pavement. Recent work done with heavy-duty membranes has shown that they may be useful in retarding this reflective crack formation. Seven different types of heavy-duty membranes were placed over Portland Cement Concrete pavement joints at one site in Pennsylvania before the roadway was overlayed with asphaltic concrete. Control sections, without any membranes, wre also built into the project for comparison purposes. This work evaluated the ability of these membranes to reduce the occurence of reflective cracking over transverse and longitudinal joints and to function as a waterstop once cracking has occurred. (Author)

Investigation of materials and structural properties of asphalt-rubber paving mixtures. volume i: technical report. final report

Abstract: Ground tire rubber is investigated as an additive in asphalt pavement construction. A blend of ground tire rubber and asphalt cement at elevated temperatures is called "asphalt-rubber". The blend consists of 18 to 26 percent ground tire rubber by total weight of the blend. Other systems in which rubber is considered an elastic aggregate were also studied. These mixtures are not considered asphalt-rubber because rubber is not blended with the asphalt cement prior to mixing with mineral aggregates. These materials are called "asphalt concrete rubber-filled" for dense graded mixes, and "friction course rubber-filled" for open graded mixes. Negative performance of some interlayer installations does not seem to be related to fundamental material properties but to inappropriate use of materials. Improved performance of such systems should be possible if use is limited to specific modes of pavement distress. Adverse performance of many asphalt-rubber seal coats studied can be related directly to a high incidence of flushing distress due to excessive binder. A design procedure is presented for asphalt-rubber seal coats which should reduce flushing incidence. Guidelines are included for preparation of specifications for construction of seal coats and interlayers. These guidelines, used in conjunction with the design procedure, should be helpful to agencies interested in asphalt-rubber paving systems. Volume II - Appendices contains the Project Identification, Distribution of Projects by Application Type, and Project Description.