Moisture Sensitivity of Hot Mix Asphalt (HMA) Mixtures in Nebraska - Phase II
As a consequential effort to the previous NDOR research project (P-564) on moisture damage, this report presents outcomes from this project incorporated with the previous project. Performance changes and fundamental material characteristics associated with moisture damage due to various anti-stripping additives in asphalt mixtures are studied through various experimental approaches and a numerical simulation. Three additives (i.e., one reference additive, hydrated lime, and two alternative additives: fly ash and cement) are investigated by adding them into two types of mixes (SP2 for low-traffic-volume roadways and SP5 for high-traffic- volume roadways) where two different asphalt binders (PG 64-22 for the SP2 mix and PG 70-28 for the SP5) are used. Two asphalt concrete mixture scale performance tests, the AASHTO T-283 and the APA under water, and two local-scale mixture constituent tests, the boiling water test (ASTM D 3625) and the pull-off test, are conducted to characterize the effects of binder-specific anti-stripping additives on the binder-aggregate bonding potential in mixtures. The pull-off tensile strength tests are then numerically modeled through the finite element technique incorporated with the cohesive zone modeling approach to seek more fundamental scientific insights into the effect of each anti-stripping additive on the overall moisture damage resistance. Results from laboratory tests and numerical simulations indicate that the SP5 mixtures, where high-quality aggregates and polymer-modified binder are used, are fairly self-resistant to moisture damage without treating any anti-stripping additive and do not show any visible sensitivity among additives, whereas the effects of additives and their sensitivity are significant in the SP2 mixes that use the unmodified binder PG 64-22 and low-quality aggregates. With the limited amount of test data, hydrated lime seems to perform slightly better than other additives, particularly with longer moisture-conditioning time. Fly ash contributes to reducing moisture damage by improving binder-aggregate interfacial properties, which are validated from the integrated experimental-computational evaluation.
The Effect of Using Glass Powder Filler on Hot Asphalt Concrete Mixtures Properties
The early use of asphalt for road and street constr uction began in the late 1800s, and grew rapidly with the emerging auto mobile industry. Since that time, asphalt technology has made strides such that today the equipment, techniques and materials used to build asphalt pave ment structures are highly sophisticated. Waste glass has been used in highway construction a s an aggregate substitute in hot mix asphalt paving. Many countrie s have recently incorporated glass into their roadway specification s, which had encouraged greater use of the material. While the use of waste glass as filler in hot mix asphalt is still not widely experimented. In this research glass powder is proposed as an alt ernative to traditional lime stone powder (Gubraa) and ordinary Portland cement fillers in hot asphalt mixtures. Where, the effect of using waste glass powder as mi neral filler on Marshall Properties of hot asphalt concrete mixtures is investigated. N ine mixtures with three types of fillers (lime stone powder, ordinary Portland cemen t and glass powder) and three filler contents (4%, 7% and 10% by weight of total aggregate) are investigated. The main outcome of this research is the possibilit y of using glass powder as filler in hot asphalt concrete mixtures. The optimu m glass powder content is 7%. Where it is found that using of glass powder as fil ler with such replacement leading to produce asphalt mixture with higher stability (% of increase up to 13%), lower flow (% of decrease up to 39%) and lower density (% of decrease up to 10%) comparing to corresponding ordinary Portland cement or lime stone powder mixtures.
EFFECT OF COARSE AGGREGATE CONTENT ON STONE MATRIX ASPHALT DURABILITY AND LOW-TEMPERATURE CRACKING
The effects of coarse aggregate content on the resistance of stone matrix asphalt (SMA) mixtures to moisture damage, aging, and low-temperature cracking were evaluated. Extractions were also performed to determine whether the Marshall hammer crushed aggregates during the mixture designs. The coarse aggregate content was varied by changing the percentages of aggregate passing the 4.75- and 2.36-mm sieves. These sieves control the degree of gap in an SMA mixture. The percentages of aggregate passing the other sieve sizes were not varied. Moisture susceptibility was affected more by the type of aggregate and the type of stabilizer than by gradation, or coarse aggregate content. Decreases in long-term aging with increasing coarse aggregate content were provided by three of four sets of coarse aggregate contents. (The use of two stabilizers and two aggregate types provided the four sets of coarse aggregate contents.) However, these decreases in aging only occurred at the highest test temperatures, which were 16°C and 32°C. Long-term aging had no significant effect on the data compared with no aging at lower temperatures ; therefore, coarse aggregate content could have no effect. Studies concerned with the effects of coarse aggregate content on low-temperature cracking were inconclusive. The amount of aggregate broken during compaction increased with an increase in coarse aggregate content. The cumulative percentage passing the 4.75-mm sieve increased by more than 5 percent for the gradations closest to those recommended by FHWA's SMA Model Material and Construction Guidelines. The increases were as great as 15.8 percent.