Design and Evaluation of Ultra-Thin Overlay with High Viscosity and High Elasticity †

Presented at the Second International Conference on Maintenance and Rehabilitation of Constructed Infrastructure Facilities


Introduction
Among the various pavement maintenance technologies, ultra-thin overlay has been increasingly used because of its engineering economy and construction convenience compared to traditional maintenance technologies such as micro-surfacing, slurry seal, and hot in-place recycling. Currently, the main ultra-thin overlay technologies include Nova Chip, UTAC, BBTM, etc. Ultra-thin asphalt concrete and super-thin asphalt concrete were firstly proposed in France. Subsequently, it has been widely used in many countries, including the United States, China, Australia, and South Africa [1]. Huang et al. carried out the performance evaluation of UTA-10 asphalt mixture and applied it to the maintenance engineering of cement bridge deck pavement [2]. Various types of ultra-thin overlay were constantly proposed, including warm mix ultra-thin overlay, cold mix ultra-thin overlay, and antiicing ultra-thin overlay. Mixture design methods and asphalt modification techniques were studied [3][4][5][6][7][8].
Recently, more research projects have focused on the development of functional ultra-thin overlay. Li et al. proposed a colored ultrathin overlay which had good skidresistance, water permeability, and, most importantly, a cooling effect [9]. Budiarto et al. proposed an ultra-thin surfacing hot mix asphalt (UTSHMA) with strong water permeability resistance [10]. Other functional ultra-thin overlay technologies such as porous ultra-thin overlay (PUAO) and self-healing ultra-thin overlay were also tested.
In summary, substantial studies have been conducted to develop ultra-thin overlay technologies and achieved many positive results. However, research on forming a comprehensive performance evaluation method and customized design method has rarely been reported. The purpose of this study is to verify the application of high-viscosity and high-elasticity asphalt in ultra-thin overlay and propose a design and evaluation method considering the durability of skid resistance and crack resistance.

Materials
The HVHE (high-viscosity and high-elasticity) asphalt was prepared by modifying base asphalt with HVHE modifier. The technical indexes and test result of the HVHE asphalt were listed in Table 1. The trackless tack coat emulsified asphalt was used as adhesive layer material to resist damage during construction and improve interlayer bonding. Basalt aggregates are used as coarse aggregates to ensure slip resistance. Limestone aggregates are used as fine aggregates to enhance the adhesion of asphalt mortar. The aggregates met the technical specifications of JTG E20-2011 [11].

Gradation Design of UT-10
The thickness of the ultra-thin overlay ranges from 1.5 to 2.5 cm. A gradation with a maximum nominal particle size of 10 mm was applied. Based on both OGFC-10 and SMA-10 mixtures, nine gradations, as shown in Figure 1, were developed to determine the range of the UT-10 mixture gradation. Five asphalt aggregate ratios were set from 5.2% to 7.2% with an interval of 0.5%. The immersion rutting test was conducted to determine the optimum air void ratio. The texture depth decay test and the TSRST test were carried out to obtain the optimum asphalt content.

Determination of Air Void Ratio
The results of the immersion rutting test are shown in Figure 2. They showed that the

Determination of Air Void Ratio
The results of the immersion rutting test are shown in Figure 2. They showed that the rutting deformation of Gradation 1, 2, 8, and 9 was around 2 mm, which is much larger than other gradations. The air void ratio of these four gradations ranged from 8% to 12%, indicating that it was difficult to drain water after it entered the semi-connected voids, and with the application of vehicle loads, water damage occurred, resulting in a larger rutting deformation. Therefore, the air void ratio of UT-10 mixture was determined to range from 12% to 15%.

Determination of Air Void Ratio
The results of the immersion rutting test are shown in Figure 2. They showed that the rutting deformation of Gradation 1, 2, 8, and 9 was around 2 mm, which is much larger than other gradations. The air void ratio of these four gradations ranged from 8% to 12%, indicating that it was difficult to drain water after it entered the semi-connected voids, and with the application of vehicle loads, water damage occurred, resulting in a larger rutting deformation. Therefore, the air void ratio of UT-10 mixture was determined to range from 12% to 15%.

Determination of Asphalt Aggregate Ratio
The results of the texture depth decay test are shown in Figure 3. They indicated that the texture depth attenuation increased with the rise in asphalt aggregate ratio, showing a slow growth trend at the three asphalt aggregate ratios of 5.2%, 5.7%, and 6.2%, and the anti-slip performance showed significant decay when the asphalt aggregate ratio exceeded 6.7%. The results of the TSRST test are shown in Figure 4. They indicated that the fracture temperature increased with the rise in asphalt aggregate ratio, and the anti-slip performance showed significant decay when the asphalt aggregate ratio exceeded 6.7%. For Gradation 3 and 5, when the asphalt aggregate ratio reaches 6.7%, the fracture temperature instead showed a slight increase.

Determination of Asphalt Aggregate Ratio
The results of the texture depth decay test are shown in Figure 3. They indicated that the texture depth attenuation increased with the rise in asphalt aggregate ratio, showing a slow growth trend at the three asphalt aggregate ratios of 5.2%, 5.7%, and 6.2%, and the antislip performance showed significant decay when the asphalt aggregate ratio exceeded 6.7%.

Determination of Air Void Ratio
The results of the immersion rutting test are shown in Figure 2. They showed that the rutting deformation of Gradation 1, 2, 8, and 9 was around 2 mm, which is much larger than other gradations. The air void ratio of these four gradations ranged from 8% to 12%, indicating that it was difficult to drain water after it entered the semi-connected voids, and with the application of vehicle loads, water damage occurred, resulting in a larger rutting deformation. Therefore, the air void ratio of UT-10 mixture was determined to range from 12% to 15%.

Determination of Asphalt Aggregate Ratio
The results of the texture depth decay test are shown in Figure 3. They indicated that the texture depth attenuation increased with the rise in asphalt aggregate ratio, showing a slow growth trend at the three asphalt aggregate ratios of 5.2%, 5.7%, and 6.2%, and the anti-slip performance showed significant decay when the asphalt aggregate ratio exceeded 6.7%. The results of the TSRST test are shown in Figure 4. They indicated that the fracture temperature increased with the rise in asphalt aggregate ratio, and the anti-slip performance showed significant decay when the asphalt aggregate ratio exceeded 6.7%. For Gradation 3 and 5, when the asphalt aggregate ratio reaches 6.7%, the fracture temperature instead showed a slight increase.  The results of the TSRST test are shown in Figure 4. They indicated that the fracture temperature increased with the rise in asphalt aggregate ratio, and the anti-slip performance showed significant decay when the asphalt aggregate ratio exceeded 6.7%. For Gradation 3 and 5, when the asphalt aggregate ratio reaches 6.7%, the fracture temperature instead showed a slight increase. Based on the results of the texture depth decay test and the TSRST test, the final determined asphalt aggregate ratio of UT-10 mixture ranged from 5.2% to 6.2%.

Evaluation of Mixture Performance
The results of the evaluation tests are shown in Table 2. It can be seen that the performance of the HVHE mixture with gradation 5, 5.7% asphalt aggregate ratios, and 13.9% air void ratio fully meets the technical requirements, and has excellent high-and lowtemperature performance.  Based on the results of the texture depth decay test and the TSRST test, the final determined asphalt aggregate ratio of UT-10 mixture ranged from 5.2% to 6.2%.