Leonard E Wood

Material characterization of hot mix recycled bituminous pavements

A detailed laboratory investigation was performed to characterize the performance of the hot mix recycled asphalt pavement in comparison with a virgin mix. A virgin mixture and three recycled mixtures were evaluated. Marshall size specimens were fabricated and evaluated using the pulse velocity, resilient modulus, indirect tensile strength, Hveem stability and Marshall stability tests. In addition the recycled binder itself was evaluated using a stage extraction technique and the thin film oven test results. Long term aging of recycled mixtures was also studied. Subjective conclusions were established for the performance of recycled mixtures under various conditions. Virgin mixture stiffness and strength parameters were higher than those of recycled mixtures. However, long term aging properties of two of the recycled mixtures were better than the virgin mix, especially when regarding the failure tensile strain. The thin film oven test and the indirect tensile test were identified as additional criteria for the choice of type and amount of recycling agent to be used. The results of this study will provide the highway engineer with a better understanding of the effect of different factors on the tensile and resilient characteristics of hot recycled bituminous paving mixtures.

A Laboratory Study of the Effectiveness of Various Admixtures on the Attenuation of Moisture Damage Upon Various Foamed Asphalt Mixtures

Durability characteristics of certain foamed asphalt mixtures were established during this laboratory investigation. Durability was characterized by a water sensitivity test and cyclic freezing and thawing. The various foamed asphalt mixtures were evaluated for durability after the mixtures had been compacted into 10.16-cm (4.00-in.) diameter by approximately 6.35-cm (2.50-in.) high specimens, and cured. Durability effects of different variables were determined in this laboratory study. These variables were foamed asphalt content (two levels for water sensitivity section, one level for freeze-thaw section), aggregate (three types, used in both sections), additives (three types, plus a set without additives), and additive content (two levels for each additive in the water sensitivity section, one level for each additive in the freeze-thaw section). One asphalt type, one mixing and testing temperature, one set of curing conditions, and one moisture content per aggregate were used. Resilient modulus and modified Marshall stability tests were used to monitor durability characteristics of the mix in the water sensitivity section. Durability in the freezing and thawing section was monitored by pulse-velocity, resilient modulus, and modified Marshall stability tests. When lime was used as an additive, durability, strength, and longevity of the foamed asphalt mixtures were substantially improved. The improvement achieved with the addition of lime was such that a material generally less suitable for bituminous mix, such as outwash sand or pit-run gravel, may rival a material more suitable for bituminous pavement mix such as crushed limestone. During this study there were similar rates of decline per freeze-thaw cycle for pulse-velocity and modified Marshall stability. Pulse-velocity, a nondestructive test, appears to be related to the destructive modified Marshall stability method. There seemed to be a good reproducibility of pulse-velocity values among similar specimens.

The Effects of Bag House Fines and Incomplete Combustion Products in a Drum Drier on the Characteristics of Asphalt Paving Mixtures, Phase II

The major purpose of this study was to use the high pressure-gel permeation techniques to evaluate the changes in asphalt subjected to different mix production parameters, including plan type, level of aging and fuel used in the burner of the drier. Additional objectives were to establish correlations between physical parameters of asphalts and their chromatographic parameters, and to determine whether the high pressure-gel permeation chromotography (HPGPC) technique could be used to detect burner fuel contamination in the mix produced by asphalt plants. This study determined that the HPGPC technique is an excellent comparative analysis tool, capable of detecting changes in the aging of asphalt, but not repeatably capable of establishing direct relationships between chromatograms and physical parameters. Results of the study also show that no significant differences could be found by HPGPC between mixes produced by drum plants and batch plants, or by plants using different burner fuels. HPGPC can also detect fuel contamination at the 1% contamination level, not detectable by physical measures. Finally, results of this study show that the 5 hour thin film oven test does not simulate aging produced by asphalt plants, and should be reevaluated.

MATERIAL CHARACTERIZATION OF HOT-MIX RECYCLED BITUMINOUS PAVEMENTS. EXECUTIVE SUMMARY

A detailed laboratory investigation was performed to characterize the performance of the hot mix recycled asphalt pavement in comparison with a virgin mix. A virgin mixture and three recycled mixtures were evaluated. Marshall size specimens were fabricated and evaluated using the pulse velocity, resilient modulus, indirect tensile strength, Hveem stability and Marshall stability tests. In addition the recycled binder itself was evaluated using a stage extraction technique and the thin film oven test results. Long term aging of recycled mixtures was also studied. Subjective conclusions were established for the performance of recycled mixtures under various conditions. Virgin mixture stiffness and strength parameters were higher than those of recycled mixtures. However, long term aging properties of two of the recycled mixtures were better than the virgin mix, especially when regarding the failure tensile strain. The thin film oven test and the indirect tensile test were identified as additional criteria for the choice of type and amount of recycling agent to be used. The results of this study will provide the highway engineer with a better understanding of the effect of different factors on the tensile and resilient characteristics of hot recycled bituminous paving mixtures.

The Use of a Gyratory Testing Machine in the Evaluation of Cold-Recycled Asphalt Paving Mixtures

This study evaluated the feasibility of using the gyratory testing machine in the fixed roller mode for evaluating the long-term behaviour of cold-recycled asphalt mixtures. Cold recycled asphalt mixtures were compacted with the gyratory machine, and gyratory strain indices were obtained from the gyrograph recorded during the compaction process. The resilient modulus, Hveem stabilometer r value, and Marshall stability were obtained on the compacted recycled mixes at various curing times and were correlated to the gyratory strain indices. The scope of the study presented in this paper covered two types of pavement material and five types of added softening agents, which included a high-float asphalt emulsion ae-150, a foamed asphalt and the rejuvenating agents, reclamite, mobilsol, and dutrex 739. The results of the study indicated that the gyratory stability index (gsi) and the gyratory elasto-plastic index (gepi) could be used to detect unstable mixtures when the binder content was too high. The gsi and gepi correlated fairly well with the Hveem stabilometer r value of the recycled mix. However, they correlated poorly with the resilient modulus and Marshall stability of the recycled mix. Similar to the r-value test, the gyratory testing machine can be used to determine the optimum binder content of a cold-recycled mix. The scope of this study was limited to the use of the gyratory testing machine in the fixed roller mode. Tests using the oil filled roller mode had not been conducted in this investigation. For the covering abstract of the symposium see IRRD 286635. (Author/TRRL)

THE USE OF WATER IMMERSION TESTS IN THE EVALUATION OF THE EFFECTS OF WATER ON COLD-RECYCLED ASPHALT MIXTURES

The effectiveness of various immersion-mechanical tests in measuring the water susceptibility of cold-recycled asphalt mixtures was investigated. The immersion-mechanical tests involved subjecting compacted recycled asphalt mixtures to a 24-h water immersion process followed by mechanical tests. The various mechanical tests used in this study included the resilient modulus, Marshall stability, Hveem stabilometer S value, Hveem stabilometer R value, and Hyeem cohesiometer tests. The test values obtained from the wet specimens were compared to the values obtained from the dry specimens, and the effectiveness of the test methods was evaluated. The results of the study indicated that the resilient modulus, Marshall stability, Hveem S value, and Hveem cohesiometer tests were effective in measuring the changes in stiffness, stability, and cohesion of cold-recycled mixtures caused by water damage. The Hveem R-value test was not very sensitive in measuring the effect of water when a recycled mixture was relatively stable. However, the R-value test became very sensitive when a mixture was unstable, and thus it was very effective in determining the recycled mixtures that were highly water-susceptible. The water resistance of cold-recycled mixtures generally increased with curing time and compactive effort. The effects of the type of added virgin binder and the type of added virgin aggregate to the water resistance of cold-recycled asphalt mixtures were significant. The proper consideration of curing time, compactive effort, added virgin binder, and added virgin aggregate will help to attenuate the effect of water on cold recycled asphalt mixtures.

A Recommended Procedure for the Determination of Dynamic Modulus of Asphalt Mixtures : Technical Paper

The fundamental properties of asphaltic concrete are important to researchers as input to new design procedures being developed. The dynamic modulus of bituminous mixtures becomes a rational part of this new design procedure as a predictor of a pavements performance in service. A review of current literature indicated that many researchers are active in determining fundamental properties of bituminous paving mixtures under a wide variety of conditions. The main objective of this study was to determine a method for evaluating the dynamic modulus of an Indiana State Highway surface mixture. The main variables used in this study were stress level, cyclic loading rate, temperature, and asphalt type. A final procedure was developed incorporating the above mentioned variables. Material and sample preparation included a study on compaction procedures of four by eight inch high cylindrical specimens. A compaction technique was developed that yields uniform bulk, density of the four by eight inch high specimen. A secondary objective of this study attempted to correlate a physical property of the asphalt cement to the dynamic modulus of the bituminous paving mixture.