جستجوی مقالات مرتبط با کلیدواژه "پلی فسفریک اسید" در نشریات گروه "عمران"

Using Ethylene Bis(Stearamide) (EBS) decreases mixing and compaction temperature of bitumen and consequently decreases energy consumption of asphalt mixture production. In this study, polyphosphoric acid (PPA) is added to EBS-modified bitumen to mitigate low-temperature deteriora-tion of EBS. Also, the effect of adding PPA and EBS on high-temperature behavior of bitumen is investigated using supepave protocol and multiple stress creep and recovery (MSCR) test. For this purpose, PPA is added to EBS-modified bitumen (having 3% of EBS) in three different dosages of 0.5, 1, and 1.5% (based on the original bitumen weight). Then, using a dynamic shear rheometer, both superpave protocol test and the MSCR test are performed on all samples at high temperatures. Also, using a bending beam rheometer, the low-temperature behavior of all samples are evaluated. The results showed that while adding 0.5% of PPA did not change mixing and compaction tempera-ture of EBS-modified bitumen significantly, it can improve high-temperature behavior of bitumen. However, MSCR results showed that it is required to consider the high-temperature behavior of modified bitumen conservatively as the bitumen modified with 0.5% PPA and 3% EBS cannot meet standard requirement for three traffic categories.

The present research seeks to investigate the modification of bitumen emulsion with polyphosphoric acid and study the feasibility of using steel slag powder as an alternative to conventional rock material filler in the design of microsurfacing mixture in an attempt to improve the ultimate performance of the mixture. For this purpose, firstly, polyphosphoric acid was used to modify the bitumen emulsion at 0.4, 0.8, 1.2, and 1.6 wt% (by weight of residual bitumen). Next, the optimally modified bitumen emulsion was used in different microsurfacing mixtures. Five different mixtures of micro surfacing containing steel slag filler at 0, 2.5, 5.0, 7.5, and 10.0 wt% (by total weight of aggregates), as an alternative to material passing through 0.075 mm sieve, were prepared. The asphalt mixtures were assessed by means of wet cohesion test, wet track abrasion test, loaded wheel-displacement, and loaded wheel-sand adhesion tests. Results of the bitumen tests showed that the use of the polyphosphoric acid tends to improve the bitumen properties in terms of decreased penetration, increased softening point, and reduced thermal sensitivity. With increasing the dosage of the polyphosphoric acid to up to 0.8 wt% by weight of the residual bitumen, significant changes were seen in the penetration and the softening point, which led to improved performance of the bitumen emulsion. Results of the asphalt tests on the samples showed that the mixtures containing steel slag filler at 7.5 and 10.0 wt% outperformed the other mixtures. Indeed, the mixture containing steel slag at 7.5 wt% could improve the cohesion, abrasion resistance, bleeding resistance, and vertical displace resistance by 29.2, 64.5, 18.6, and 44.0%, respectively. The corresponding figures for the mixture containing the slag at 10.0 wt% were 25.0, 64.3, 23.3, and 42.9 wt%, respectively.

Changing the rheological and mechanical behavior of pure bitumen is one of the most important reasons of usage of bitumen modifiers. Polyphosphoric acid is newer additive compared to other additives used in the road construction industry. This additive is used to improve the performance behavior of bitumen and improve bitumen rheological properties such as rutting. In this article, the effect of polyphosphoric acid on performance behavior of bitumen and asphalt mixtures with similar mechanical and chemical properties, but with different chemical compositions, is discussed. Various experiments have been conducted in the field of bitumen and asphalt mixture modification with polyphosphoric acid polymer. The results showed that the addition of PPA can improve the high temperature performance and reduce the temperature sensitivity of the modified bitumen, but it has a slight effect on the low temperature performance. According to the results, bitumens modified with polyphosphoric acid have better fatigue resistance compared to bitumens modified with SBS. Modifying bitumen with PPA leads to an increase in softness, a decrease in permeability, and a decrease in temperature sensitivity. The combination of PPA/SBR has the best rutting resistance in the asphalt mixture due to the highest strength and the smallest rut depth.

One of the most common methods to enhance performance of asphalt binder and mixtures is using polymeric and mineral additives. The polyphosphoric acid (PPA) is one of additives used to modify asphalt binder's characteristics during last two decades. In this research, to investigate the effect of this additive on fracture and crack propagation characteristics of asphalt mixtures, asphalt mixture specimens were fabricated by implementing with asphalt binder modified with three different dosages of PPA: 0.5, 1 and 1.5% by weight of asphalt binder. The semi-circular bending (SCB) test was performed on these specimens at five different test temperatures including -10, 0, 10, 25 and 40 degree of centigrade. The major output of this test was force-displacement curve. The Maximum force, fragility, fracture energy and toughness were determined for all specimens based on force-displacement curve. Also, notch mouth opening displacement was measured by using pictures captured during the SCB test. To compare asphalt mixture behavior, an index was presented in this research as fracture energy divided by noth mouth opening displacement. At a constant temperature, the greater index shows better performance of asphalt mixture. The results have shown that adding PPA at low temperatures is not useful but at moderate temperatures it can increase fracture properties of asphalt mixture. The optimum content of PPA at the moderate temperatures is determined between 0.5 to 1%.