Although repeated traffic loading causes damage to accumulate in asphalt pavements, the damage heals during rest periods (time between traffic loadings). Consequently, this healing enhances the fatigue life of the pavement. A method was developed to determine the healing rate of asphalt mixtures in terms of recovered dissipated creep strain energy (DCSE) per unit time. The healing properties of four different asphalt mixtures were evaluated with this approach. The test procedure consists of a repeated loading test and periodic resilient modulus tests. A normalized healing rate in terms of DCSE/DCSEapplied was defined to evaluate the healing properties independent of the amount of damage incurred in the mixture. From the test results, it was determined that the healing rates of the asphalt mixtures tested increased dramatically above 10掳C and were more affected by the aggregate structural characteristics (i.e., aggregate interlock, film thickness, voids in mineral aggregate) of the mixtures than by polymer modification. Although styrene-butadiene-styrene polymer modification reduced the rate of damage accumulation, it had no effect on the healing rate of the mixtures tested.
A laboratory investigation was conducted to evaluate the effects of styrene butadiene styrene (SBS) modification on the cracking resistance and healing characteristics of coarse-graded Superpave庐 mixtures. Four types of asphalt mixtures with 6.1% and 7.2% design asphalt contents using unmodified and SBS-modified asphalt cement were produced in the laboratory. Tests performed with the Superpave indirect tensile (IDT) test included repeated-load fracture and healing test, strength tests at two loading rates, and longer-term creep tests to failure. The test results showed that the benefit of SBS modifiers to mixture cracking resistance appeared to be primarily derived from a reduced rate of micro-damage accumulation. The reduced rate of damage accumulation was reflected in a lower m value without a reduction in fracture limit or healing rates. It was shown that the benefits of the SBS modifier were clearly identified by using the hot-mix asphalt fracture model, which accounts for the combined effects of m value and fracture energy limit on cracking resistance. It was also determined that the residual dissipated energy as determined from Superpave IDT strength tests appears to be uniquely associated with the presence and benefit of SBS modification and may provide a quick way to make relative comparisons of cracking performance. Longer-term creep test showed that time to crack initiation appeared to provide another parameter uniquely related to the effects of SBS modification. The key to characterizing the effects of SBS modifier on the cracking resistance of asphalt mixture is in the evaluation of the combined effects of creep and failure limits.
Pavement markings are the most widely used road traffic control device. However, such markings have a finite lifespan due to normal wear and tear of the road. They must be eventually removed and subsequently replaced. During highway construction, the use and subsequent removal of temporary pavement markings are common necessities. Current methods to remove markings have often been unsatisfactory, leaving pavement scars that can be mistaken for lines. Instead of removing existing markings, this paper presents seal coating treatments as a means of obscuring temporary pavement paint markings. These treatments would not adversely affect the pavement and would not leave any trace of the marking. Two experimental seal coating methods, modified slurry-seal coat and modified sand-seal coat, were developed and evaluated. The modified slurry-seal coat treatment adequately covered the pavement markings and attained satisfactory friction test results. However, the modified sand-seal coat treatment provided exceptional performance with regard to friction, coverage, and durability, proving to be a practical and successful method for covering temporary pavement paint markings. Cost analysis results indicated that the modified sand-seal coating could be installed at less cost than that incurred in current removable tape covering and mechanical painted traffic line removing methods. Finally, a draft specification for covering existing pavement markings with a sand-seal coat was developed, and the research team recommends the adoption of the modified sand-seal coat treatment as an optional method for the removal of temporary pavement paint markings.
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