Search Results (5)

In order to investigate the potential application of low-grade hard asphalt in high-temperature and high-altitude areas, various tests were conducted to analyze the performance and high-temperature rheological properties of 30#, 50#, and 70# matrix asphalt under thermo-oxidative aging and ultraviolet aging. The tests utilized for analysis included the examination of basic asphalt properties, Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), gel permeation chromatography (GPC), dynamic shear rheology (DSR), and multi-stress creep recovery (MSCR). The results indicate a progressive decrease in asphalt performance with increasing aging time. Prolonged exposure to thermal oxygen aging and ultraviolet irradiation significantly diminishes the plasticity of asphalt. The carbonyl index and sulfoxide index of asphalt increase after thermal oxygen aging and ultraviolet aging. Notably, 30# asphalt demonstrates greater resistance to aging compared to 50# and 70# asphalt under long-term high ultraviolet radiation. The LMS% of 30#, 50#, and 70# asphalt increases by 14%, 15%, and 16%, respectively. Following photothermal oxidative aging, a larger proportion of lighter components in the asphalt transforms into resins and asphaltenes. The high-temperature rheological properties of the three types of asphalt rank as 30# > 50# > 70#, while within the same type of asphalt, the high-temperature rheological properties rank as PAV > UV3 > UV2 > UV1 > RTFOT > virgin. Elevating temperature, stress level, and stress duration negatively impact the high-temperature stability of asphalt. In general, low-grade asphalt demonstrates superior anti-aging ability and high-temperature rheological properties during the aging process. Full article

Traditional hard-grade asphalts for high-modulus asphalt concrete (HMAC) are produced by using natural hard-grade asphalt to modify matrix asphalts. However, natural hard-grade asphalts are scarce and expensive. To find a sustainable alternative, this study presented a method to synthesize hard-grade asphalts using phenol formaldehyde resin (PFR), hexamethylenetetramine (HMTA) and matrix asphalts. Infrared radiation (IR) spectra analysis and fraction analysis for the modifiers and synthesize asphalts show that asphalt molecules can be cross-linked into larger polymeric groups by the thermosetting phenol formaldehyde resin (TPFR) which is the reaction product of PFR and HMTA. This process increased the asphaltene and resin fraction in asphalt, thus transforming a matrix asphalt into hard grade. With the dosing combinations of 4% PFR/15~20% HMTA, 6% PFR/8~10% HMTA and 8% PFR/5~5.7% HMTA, dynamic modules of HMAC were 14,000~16,000 MPa, which satisfied the basic application requirements for HMAC. The rutting resistance of the new hard-grade asphalts with the above dosage combinations completely exceeds the traditional product using the Trinidad Lake asphalt as the raw material. Increasing the amount of PFR/HMTA can further improve the rutting resistance. However, to ensure the fatigue and cracking resistance of the HMAC can get a level like the traditional product, the dosages of HMTA should be controlled below 15%. Full article

In order to evaluate the feasibility of using hard-grade asphalt concrete in China’s highway construction, based on the accelerated loading test of the full-scale track of the Research Institute of Highway Ministry of Transport (RIOHTrack), the long-term service performance of hard-grade asphalt concrete base pavement was studied, and its actual service effect was evaluated. The study found that hard-grade asphalt concrete has higher strength, modulus and high-temperature stability. Although the low-temperature performance is generally not as good as that of asphalt, with a penetration grade (PG) of 60/80, it has equivalent or better cracking resistance in the area where the RIOHTrack is located. During the five-year observation period, the rutting deformation of the pavement structure showed an annual fluctuation increase. In comparison, the rutting resistance of a hard-grade asphalt concrete base structure can be increased by approximately 16%, and the deflection value is smaller, so the long-term performance of the anti-rutting effect and structural bearing capacity are better. The study shows that hard-grade asphalt concrete base pavement is suitable for highway construction in parts of China, where the climate is similar to that of the RIOHTrack location, or the temperature is higher or the latitude is lower. Full article

The high-modulus asphalt mixture produced by hard asphalt has played a good role in reducing asphalt pavement rutting and improving pavement durability. It was widely used in the construction of various levels of road engineering in Europe. However, low-grade hard asphalt was rarely used in road engineering in China, and the use of hard asphalt for the design and construction of high modulus asphalt mixtures lacks sufficient engineering experience. Considering the above issues, comparative research on the performance of Chinese and French low-grade hard asphalt and mixture was carried out. In this paper, the performance of French 15# hard asphalt commonly used for EME (Enrobés à Module Elevé Class) high modulus asphalt mixture and China 15# hard asphalt was analyzed comparatively, where six typical high modulus asphalt mixtures corresponding to two low-grade hard asphalts were designed referring to the design requirements of French high modulus asphalt mixtures. The road performance of a high-modulus asphalt mixture was evaluated to verify the feasibility of its application in engineering. The research results show that the performance indicators of both Chinese and French asphalts meet the requirements of binder materials used in high modulus asphalt mixtures, and the performance of their corresponding mixtures of the two asphalts also meet the specifications of high modulus asphalt mixtures. However, the two asphalts and the performance of their corresponding mixture are slightly different. The high modulus asphalt mixture of Chinese low-grade hard bitumen can be used well in road engineering applications in China. It can strongly promote the wide application of high modulus asphalt mixture in China. Full article

Compaction of Hot Mix Asphalt (HMA) is a process aimed at obtaining the desired performance properties. Attainment of the required compaction can be hampered by external factors, which includes the presence of water. Water is known to cause quick lowering of the HMA temperature. The bottom face of the asphalt layers of a pavement is a sensitive point from the fatigue life point of view. In the site conditions, it is often difficult to obtain the required air void content at the bottom of an asphalt layer and excessive moisture content in the base course lying beneath the asphalt layer can be one of the causes. This article presents the results of tests carried out on a test section on which HMA was placed on an unbound aggregate base layer of varying moisture content. The material used for the binder course was asphalt concrete mixture composed of aggregate of minus 16 mm grading and 35/50 bitumen. Being relatively hard it is the most often specified bitumen for binder courses and also base courses. One of its characteristics is a considerable increase of viscosity with decreasing temperature, which hampers the process of compaction. The bulk specific gravity was measured to determine the variations in the air void content through the specimens. The complex modulus of elasticity and fatigue life were the other parameters which were determined on the specimens with different air void contents. The test results show worsening of the properties which have a decisive bearing on the service life of pavement. Full article