Prithvi S. Kandhal

EFFECT OF ASPHALT FILM THICKNESS ON SHORT AND LONG TERM AGING OF ASPHALT PAVING MIXTURES

It is generally believed that an asphalt paving mixture should have an adequate asphalt film thickness around the aggregate particles to ensure reasonable durability (resistance to aging) of the mixture. The minimum asphalt film thickness generally recommended ranges from 6 to 8 μm. However, no significant background research data are available in the literature to support these recommended minimum asphalt film thicknesses. Some states specify minimum asphalt film thickness for mix designs. This study was undertaken to quantify the relationship between various asphalt film thicknesses and the aging characteristics of the asphalt paving mix so that an optimum film thickness desirable for satisfactory mix durability could be established. Mixes prepared with asphalt binder film thickness ranging from about 4 to 13 μm were subjected to accelerated aging using Strategic Highway Research Program (SHRP) procedures to simulate both short- and long-term aging. Both the aggregate (RD) and the asphalt cement (AAM-1)...

Using Warm-Mix Asphalt Technology to Incorporate High Percentage of Reclaimed Asphalt Pavement Material in Asphalt Mixtures

The use of reclaimed asphalt pavement (RAP) helps save natural resources and money. The percentage of RAP that can be utilized successfully in hot-mix recycling is primarily dictated by practical considerations. To avoid deterioration of the aged binder, RAP should not be exposed to relatively high temperatures. This study investigated the feasibility of using a warm-mix asphalt (WMA) additive, Sasobit H8, in successfully recycling hot-mix asphalt (HMA) with 75% RAP at a lower temperature. A control HMA was prepared with extracted aggregates and PG (performance grade) 64-28 binder at 150°C. Another HMA was produced with PG 52-28 binder at 135°C. Two WMA mixes were prepared with Sasobit H8 at 125°C, one with PG 52-28 and the other with PG 42-42 binder. Samples with design asphalt content were compacted by using 75 gyrations of the Superpave gyratory compactor. Their voids, tensile strength at −10°C, rutting potential at 60°C, and moduli at 0°C, 25°C, and 40°C (at different times) were determined and compared. The moduli samples were subjected to 60°C in between the tests. The results show that it is possible to produce mixes with 75% RAP with similar air voids as virgin mixes at lower than conventional temperatures using 1.5% Sasobit. The addition of a significantly lower grade of binder, PG 42-42, at a rate of 1.5% by weight of mix produced a mix that is most comparable with a virgin mix.

WASTE MATERIALS IN HOT MIX ASPHALT - AN OVERVIEW

Numerous waste materials result from manufacturing operations, service industries, sewage treatment plants, households and mining. Legislation has been enacted by several states in recent years to either mandate the use of some waste materials or to examine the feasibility of such usage. The hot mix asphalt (HMA) industry has been pressured in recent years to incorporate a wide variety of waste materials into HMA pavements. This has raised the following legitimate concerns: (a) engineering concerns such as effect on the engineering properties (for example, strength and durability), impact on production, and future recyclability; (b) environmental concerns such as emissions, fumes, odor, leaching, and handling and processing procedures; and (c) economic concerns such as life cycle costs, salvage value, and lack of monetary incentives. The waste materials can broadly be categorized as follows: (a)industrial wastes such as cellulose wastes, wood lignins, bottom ash and fly ash; (b) municipal/domestic wastes such as incinerator residue, scrap rubber, waste glass and roofing shingles; and (c) mining wastes such as coal mine refuse. A general overview of preceding waste materials including the research work done in the past and their potential for use in HMA pavements is given in this paper. ‘Assistant Director, National Center for Asphalt Technology, Auburn University, Alabama WASTE MATERIALS IN HOT MIX ASPHALT AN ovERvIEw Numerous waste materials result from every aspect of society including manufacturing, service industries, sewage treatment plants, households and mining. The disposal of waste products is primarily done as follows: (a) Landfills (b) Incineration, and (c) Recycling in other products However, problems are being experienced because of the insufficient capacity of landfills, air pollution associated with incinerators, and limited alternatives for recycling. Legislation has been enacted by several states in recent years to either mandate the use of some waste materials or to examine the feasibility of such usage. About 450 million megagrams (Mg) of hot mix asphalt (HMA) are produced in the United States at a cost of about

DESIGNING RECYCLED HOT MIX ASPHALT MIXTURES USING SUPERPAVE TECHNOLOGY

12 billion. The HMA industry has been pressured in recent years to incorporate a wide variety of waste materials into HMA pavements. This has raised the following legitimate concerns ~. ENGINEERING CONCERNS The following concerns must be addressed from the engineering viewpoint.

CONSTRUCTION AND PERFORMANCE OF ULTRATHIN ASPHALT FRICTION COURSE

Mix design procedures for recycled asphalt pavements require the selection of virgin asphalt binder or recycling agent. This research project was undertaken to develop a procedure for selecting the performance grade (PG) of virgin asphalt binder based on the Superpave PG grading system. Blending charts, similar to the viscosity blending charts, were constructed and evaluated based on test parameters obtained from the dynamic shear rheometer (DSR). The criteria for selection was based on Superpave performance grading (PG) specification. The criteria based on the fatigue parameter was determined to be too liberal and, therefore, was not recommended. An alternative criteria based on the high temperature stiffness was recommended.

Study of Longitudinal-Joint Construction Techniques in Hot-Mix Asphalt Pavements

The Novachip process, also known as ultrathin friction course, was developed in France in 1986. The process utilizes a single piece of equipment to place a thin, gap-graded hot mix asphalt (HMA) onto a relatively thick layer of polymer modified asphalt emulsion tack coat. Two Novachip projects were constructed in Alabama in 1992 to achieve the following objectives: (a) Document the materials and the construction procedures utilized in the construction of the Novachip surface course, and (b) monitor and evaluate the performance of the Novachip test sections at regular intervals for a period of three years. This paper gives the construction details and performance of Novachip after 4 1/2 years in service. Since this was the first Novachip project in the U.S. with the machine imported from France, some equipment related problems were encountered. The surface texture of Novachip is very similar to that of a typical open-graded friction course. No significant raveling was observed on the two projects after about 4 1/2 years in service, which indicates very good bond between Novachip and underlying surface. Novachip surface has significantly higher pavement surface friction numbers compared to dense-graded HMA wearing course. It appears to be a potential alternate for chip seals, microsurfacing, and open-graded friction course.

Control of Volumetric Properties of Hot-Mix Asphalt by Field Management

There is a need to identify suitable longitudinal-joint construction techniques for multilane, hot-mix asphalt pavements that can minimize or eliminate cracking at the joint and raveling adjacent to the joint. It is believed that the longitudinal cracks result primarily from the density gradient that is usually encountered across the joint. This density gradient can be attributed to low density at the unconfined edge when the first lane is paved and relatively high density at the confined edge when the adjacent lane is paved. Seven different longitudinal-joint construction techniques were used on I-25 in Colorado in 1994, including various rolling procedures to compact the joint, provision of a vertical face with a cutting wheel, and use of rubberized asphalt tack coat on the face of the unconfined edge. Two longitudinal-joint construction techniques were used on I-79 in Pennsylvania in 1994: the conventional technique (control) and the New Jersey—type wedge joint. The latter technique uses a 3:1 taper at...

Field Management of Hot Mix Asphalt Volumetric Properties

Significant differences in the volumetric properties of laboratory-designed and plant-produced hot-mix asphalt (HMA) generally exist as demonstrated by FHWA Demonstration Project No. 74. The volumetric properties include voids in the mineral aggregate (VMA) and voids in the total mix (VTM). Guidelines for HMA contractors are needed to reconcile these differences and maintain control of volumetric properties during HMA production. The HMA mix design and field production test data (such as asphalt content, gradation, and volumetric properties) from 24 FHWA demonstration projects were entered into a data base and statistically analyzed. The objective was to identify and, if possible, quantify the independent variables (such as asphalt content and the percentages of material passing the No. 200 and other sieves) that significantly affect dependent variables VMA and VTM. The statistical analysis methods consisted of correlation analysis, stepwise multiple-variable analysis, and linear-regression analysis. On t...

A review on absorption of asphalt into porous aggregates II. Methods for determination and minimization of absorption

The Federal Highway Administration (FHWA) Demonstration Project No. 74 has clearly shown that significant differences exist between the volumetric properties of the laboratory designed and plant produced hot mix asphalt (HMA) mixes. The volumetric properties include voids in the mineral aggregate (VMA) and the voids in the total mix (VTM). This project was undertaken to develop practical guidelines for the HMA contractors to reconcile these differences thereby assisting them to consistently produce high quality HMA mixes. The HMA mix design and field test data from 24 FHWA demonstration projects were entered into a database. The data included mix composition (asphalt content and gradation) and volumetric properties. The data were analyzed to identify and, if possible, quantify the independent variables (such as asphalt content and the percentages of material passing No. 200 and other sieves) significantly affecting the dependent variables (such as VMA and VTM). Based on the preceding work, troubleshooting charts have been constructed to correct and reconcile differences between the volumetric properties of the job mix formula and the produced mix.

A REVIEW ON ABSORPTION OF ASPHALT INTO POROUS AGGREGATES I PHYSICOCHEMICAL MECHANISMS AND VARIABLES AFFECTING ABSORPTION

ABSTRACT In the second part of this review we examine current laboratory practice for the practical determination of asphalt absorption into porous aggregates. It is found that current practice relies heavily on empirical relations, to bridge the gap between laboratory test results and field behavior. Certain proposed methods for minimizing the consequences of asphalt absorption are also reviewed, although more work is required before they can be recommended for implementation.