Akhtarhusein Tayebali

Effect of Mineral Filler Type and Amount on Design and Performance of Asphalt Concrete Mixtures

Three methods for classifying aggregate particle shape and texture—AASHTO TP33, ASTM D3389, and the flow rate method—were evaluated. These methods were used to rank four natural river sands and a crushed granite from good to poor performance based on the criteria established by each method. Test results indicate that all methods easily distinguished the crushed aggregate from the natural river sands. The AASHTO TP33 and the flow rate method were found to be somewhat less sensitive to slight differences in particle shape and texture than was ASTM D3398. All the test methods were found to be repeatable, each having low coefficients of variation for all the aggregates tested. To evaluate the effect of particle shape and texture and mineral filler content on mix performance in permanent deformation, one natural sand ranked as average performing was selected and blended with the crushed granite in the proportion of 20 percent natural sand and 80 percent crushed granite. Asphalt-aggregate mixtures containing 4, 6, 8, and 12 percent mineral filler were designed by using the Marshall procedure and were tested in repeated shear test at constant height. Within the range of mineral filler type and contents used, results indicate that mixtures containing 100 percent crushed granite show lower accumulation of permanent strain than does an 80/20 blend of crushed granite and natural sand, and an increase in the mineral filler content of a mixture was found to decrease its accumulated permanent strain while increasing the mixture shear resilient modulus.

Effect of Crumb Rubber Particle Size and Concentration on Performance Grading of Rubber Modified Asphalt Binders

This study evaluates two aspects of the performance related Superpave binder specification methodology: (1) the applicability of the dynamic shear rheometer (DSR) to crumb rubber modified binders, and (2) the effect of crumb rubber particle size and concentration on the higher temperature performance grading of rubber modified asphalt binders. Results indicate that Superpave DSR test protocol is applicable to the modified binders used in this study. The average coefficient of variation for the different specimens thickness and replicate testing based on the measured property obtained was 6.2% and 6.5%, respectively. In general, the crumb rubber particle size did not affect the performance grading of the modified binders. A 7% crumb rubber modification increased the high temperature performance grading by one grade; whereas, the 14% crumb rubber modification increased the performance grading by two grades. For high temperature range, the unmodified and modified binders with the same performance grade appear to show similar characteristics.

Development and Evaluation of Dynamic Flexural Beam Fatigue Test System

Although both mix variables and environmental variables are known to affect the fatigue response of asphalt-aggregate mixes, other factors—including specimen fabrication procedure and test equipment and procedures—are equally important. The development of a dynamic flexural beam fatigue test system is described, and the effects of specimen compaction method and equipment type on the precision of in situ fatigue lives of asphalt-aggregate mixes predicted by using laboratory strain-life relationships are discussed. Results indicate a coefficient of variation of 41 percent in fatigue life for the new fatigue equipment compared with one of 93 percent for an earlier electropneumatic version. The specimen compaction method was also found to influence significantly the precision of the predicted fatigue life. A 33 percent difference in coefficients of variation between the fatigue response of rolling wheel—compacted specimens and kneading-compacted specimens was observed. Consequently, twice as many specimens ar...

Laboratory Evaluation of Warm-Mix Asphalt Mixtures for Moisture and Rutting Susceptibility

AbstractSince its introduction, warm mix asphalt (WMA) has garnered a lot of attention and interest from the pavement industry as a promising technology to replace the conventional hot mix asphalt (HMA). Despite its many benefits, including reducing emissions and fuel usage, definitive answers on the feasibility of replacing HMA pavements with WMA are yet to be answered. A major concern for WMA is susceptibility to moisture-induced damage. In this research study, mixtures prepared using three WMA technologies- viz. Sasobit, Advera WMA and the Foamer were evaluated for their moisture susceptibility and permanent deformation in comparison with an HMA mixture. Tensile strength ratio (TSR) and asphalt pavement analyzer (APA) tests were conducted on these mixtures. Results show that moisture-based WMA technologies (Advera and Foamer) are more susceptible to moisture damage. However, rut depths evaluated using APA, even for moisture-conditioned specimens, indicated WMA performance on par with that of HMA. Even ...

EVALUATION OF SUPERPAVE REPEATED SHEAR AT CONSTANT HEIGHT TEST TO PREDICT RUTTING POTENTIAL OF MIXES: PERFORMANCE OF THREE PAVEMENT SECTIONS IN NORTH CAROLINA

The repeated shear at constant height (RSCH) test to predict the rutting potential of asphalt aggregate mixes based on field performance of pavement sections in North Carolina has been evaluated. Three pavement sections in Buncombe, McDowell, and Montgomery counties were selected based on the degree of rutting severity experienced after several years in service. The pavement section in Buncombe County showed no rutting, whereas those in McDowell and Montgomery counties showed light and severe rutting distress, respectively. Results of this study indicated that the RSCH test can clearly identify the well-performing versus poorly performing mixes (i.e., Buncombe versus Montgomery counties). Although previous studies in which the French pavement rutting tester and the Georgia loaded-wheel tester were used indicated early rutting of the pavement in Buncombe County, the RSCH test indicated that the mix was not susceptible to excessive rutting—in line with field experience of no significant pavement distress observed in this pavement. For Montgomery County, the RSCH test clearly showed that the mix was susceptible to excessive rutting with the wheelpath cores distinctly showing potential for tertiary flow—in agreement with experience of significant rutting distress observed in this pavement.

Quantifying the Greenhouse Gas Emission Reductions Associated with Recycling Hot Mix Asphalt

ABSTRACT Market based policies to reduce greenhouse gas emissions have become increasingly popular in the last decade. These policies provide economic incentives for reducing greenhouse gas emissions. A life-cycle inventory model was developed to evaluate three alternatives for the management of waste hot mix asphalt (HMA) including, (1) recycling as new aggregate, (2) recycling as new HMA, and (3) disposal in a landfill. Global warming potential, environmental emissions, and total energy use were quantified for each management alternative. The recycling of used asphalt into new HMA results in a reduction of 16 kg CO2e compared to landfilling. Recycling used HMA as aggregate reduced GHG emissions by 9 kg CO2e A Monte Carlo analysis on the alternatives showed that the range of reduction for recycling as HMA was 12 to 26 kg CO2e and for recycling as aggregate 6 to 11 kg CO2e.

Importance of Normal Confinement to Shear Bond Failure of Interface in Multilayer Asphalt Pavements

Several direct shear test devices are used to evaluate the shear bond strength of tack coat materials in interlayer bonding in asphalt pavements. Some devices have the capability of evaluating strength in direct shear with normal confinement, whereas other devices do not have that capability or use passive confinement to evaluate the interlayer bond strength. The literature indicates that interlayer bond strength increases with the application of normal confinement. However, the question remains as to the level of normal confinement, if any, that should be used in direct shear testing to evaluate the interlayer bond strength for specification acceptance or design. This study presents a methodology to interpret laboratory bond strength test results in relation to the state of stress at the layer interface in a representative pavement section. The results confirm the importance of normal confinement for shear bond strength evaluation and provide guidance for the selection of the appropriate level of normal confinement.

Viscoelastic behavior of crumb rubber modified asphalt binders

ABSTRACT The Superpave binder specification characterizes asphalt binders using dynamic mechanical analysis based on the principles of linear viscoelasticity. Dynamic mechanical analysis of crumb rubber modified binders showed that the time-temperature superposition principle is applicable to the crumb rubber modified binders included in this study and the master curves for these binders can be analytically represented using various techniques applicable to unmodified binders. It was observed that the unmodified and crumb rubber modified binders with the same high temperature performance grading show different viscoelastic behavior over a range of frequencies.

Development of a procedure to determine the effectiveness of asphalt-removing solvents

Due to environmental protection requirements, most state and federal agencies are now required to use biodegradable solvents instead of diesel fuel or other hydrocarbon solvents. A variety of environmentally friendly and safe asphalt-removing solvents are available in the market. However, there is no quantitative standardized procedure to compare the efficacy of these solvents. This paper outlines the development of a procedure used to evaluate the cleaning efficacy of various solvents. The goal was to develop a standardized procedure that would yield quantitative and repeatable results. After evaluating various alternatives like metal and glass plates, ceramic tiles, and aluminum foils, the aluminum dish was found most suitable for the study. Test results obtained for solvent comparison were found to be consistent and repeatable, with the coefficient of variation for asphalt removed less than 10% for most solvents. Further, this study provides an outline for cost-effective analysis of solvents used in relation to diesel fuel and the procedure is able to rank solvents quantitatively.

A Procedure to Quantify Organic Antistrip Additives in Asphalt Binders and Mixes

Stripping is a phenomenon of loss of bond or adhesion between the asphalt binder and the aggregate in asphalt mixes. Stripping frequently results from the presence of water, and most agencies require the use of antistrip additive to control moisture damage. However, there is no simple and quick method for detecting the presence and the amount or percentage of organic antistrip additive in asphalt binders or mixes. This paper presents a procedure based on solid-state spectrophotometry to detect qualitatively and quantitatively the presence of amine-based antistrip additive in asphalt binders and mixes. The developed procedure gives results that are quantifiable and reproducible with low coefficients of variation.