High temperature resistant rubber asphalt

. Rubber Asphalt is the asphalt with rubber addition. The addition of rubber to asphalt was expected to have higher stiffness and longer durability that can be identified by its properties, that are softening point, penetration and ductility. The 60/70 penetration asphalt has been mixed with 7% rubber. Mixing of rubber with asphalt was quite a challenge. The liquid rubber or solid rubber should be processed through prevulcanization in the asphalt plant. The properties of the rubber asphalt have been investigated in the laboratory of BPJN West Sumatera. Hence, the properties of rubber asphalt have followed the Bina Marga standard for pavement mixture, i.e. the softening point value is >52⁰C, the ductility is more than 140 cm, and the burning point was above th e 310⁰C. By determined the index penetration of the rubber asphalt that is. Thus, it can be concluded that the 7% rubber asphalt has resulted in the higher resistance to higher temperature binder.


Introduction
The stability of the national roads in West Sumatra only 98.67% to 73.19% in a "good" conditions. The National Road in West Sumatra is 1,448.81 km length. The National Road which serves as the Primary Arterial Road is 657.81 km and the National Road which serves as the Primary Collector Road is 791.00 km [1].
Natural disaster factors are indeed difficult for us to avoid, such as road damage due to earthquakes or floods and others. However, we need to take lessons from what happened by trying to build higher quality roads in areas prone to natural disasters.
One of the important items related to the road pavement project besides maintaining the quality of asphalt hotmix is drainage or channels that can drain water out of the road immediately. Due to, stagnant water on the pavement will result in the aggregate stripping due to the reducing the adhesion of asphalt so that the road will be easily damaged. Moreover, the factors that often cause early damage to the highway are over tonnage/overloading of vehicles such as trucks, tronton, and others. As a consequent of there is a possibility of discrepancy in the planning of the pavement thickness which does not accommodate overtonnage vehicles to pass. To avoid premature damage to the road, the implementation during the construction of asphalt pavement must be considered, such as the number of passes, the temperature of the asphalt mixture when laying, the thickness of the hot mix asphalt that is spread, including the quality of the binder.
Since 1980s until now the rubber production in Indonesia has become the second largest natural rubber production in the world after Thailand. Indonesia's natural rubber production is around 3.6 million tons per year or about 31% of the world's natural rubber production. Moreover, only about 15% is used domestically while 85% is exported [2].
Research on the use of rubber as an additive to asphalt has been started since 1823. By 1930 Malaysia and Britain had made a mixture of latex and granulated type asphalt and rubber, called rubber asphalt. Mixing of rubber with asphalt was quite a challange. The liquid rubber or solid rubber should be processed through prevulcanization in the asphalt plant. Vulcanization has been a very essential part of all processes concerned with the manufacturing of rubber products based on dry rubber. A rubber becomes a thermoset after vulcanization. Unlike a thermoplastic, it is no longer sensitive to extreme temperatures. The solid rubber must first be masticated to soften to allow for the addition and homogeneous mixing of the curatives, namely Sulphur, zinc oxide, stearic acid and accelerators. As shown in Figure 1, it can be seen that the result of homogeneous mixing between rubber and asphalt ( Figure 1.b), resulted in the same appearance with the virgin asphalt as shown in Figure 1 The properties of the rubber asphalt have been investigated in the laboratory of BPJN West Sumatera. Rubber-asphalt has some advantages compared to asphalt alone in terms of resistance to deformation (rutting/cracking) in the longitudinal direction of the road surface around the wheel path of the vehicle, the aggregate of asphalt layer stripping, and the resistance to road cracks due to the changes of the ambient temperature [3].
Road damage can be caused by many things. For instance, weathering, high temperature, stagnant water on the asphalt surface and over loading over dimension vehicle. It can be resulted in shorten the design life, consequently resulted in higher maintenance cost [4]. Hence, by using rubber asphalt was expected to become one of the solution in reducing the acceleration of pavement damage.
Rubber asphalt might be applied to the pavement as a low-noise asphalt pavement with excellent noise reduction and road performance. Rubber asphalt is expected as one of the solutions to reduce early damage of the surface of the hotmix layer. Improving the resistance of asphalt surface layers is necessary to produce the life longer pavement. Frequently road repairs and maintenance due to early damage will increase the maintenance costs, that must be budgeted by the Government. On the other hand, the budget allocation for road repairs that can be provided by the government tends to decrease due to it is affected by the conditions of the global recession as a whole especially after the Covid-19 pandemic. Meanwhile, to prepare high viscosity modified asphalt rubber, a large amount of crumb rubber was added to asphalt binder, with Sasobit and waste cooking oil (WCO) [5]. Moreover, the addition 20%-25% of rubber indeks reduces the thermal sensitivity of modified asphalt, and significantly improve the high-temperature anti-rutting and mediumtemperature anti-fatigue properties [6]. With high amount of rubber added to asphalt in producing the modified asphalt, the asphalt becomes highly viscous, require a relatively high temperature on construction and mixing process [7,8]. For this reason, it is necessary to conduct research to determine the optimum rubber content that will produce maximum quality for asphalt pavement.
Therefore, the rubber asphalt was further investigated its stiffness properties to find out how strength is the binder to avoid the premature damage as well as its performance in binding the aggregates. Hence, one of parameter to determine the performance and quality of the binder is by calculating the penetration index, by means of conducting the Softening Point, Ductility, and penetration test in the laboratory.

Materials and methods
The Softening Point, Penetration, Ductility were tested for rubber asphalt, which then be used to calculate the Penetration Indeks of the rubber asphalt binder. By the Penetration Indeks value, the suitability of binder as the high quality binder that is resistance to high temperature can be assessed.
The information obtained from the softening point test provides a better insight into the relative effects of binder modification. Moreover, penetration value is a measure of hardness or consistency of bituminous material and the ductility value important to measure the adhesive properties of asphalt and its ability to stretch. In flexible pavement design, the binder must form a thin, ductile film around the aggregate to enhance the physical interlocking of the aggregate.
In this study, an experiment was carried out on asphalt that had been mixed with by 7% rubber to find out their properties, namely Penetration, Softening Point, Ductility, Flash Point, Specific Gravity, Loss on Heating, and Solubility. The data from the laboratory will be ensure with the minimum requirements in the Indonesia Standard Specification (SNI). The minimum value requirements on the properties of rubber asphalt should in line with the requirements of the Interim Special Specification of Highway Department SKh-1M.04-2021 are shown in Table 1  This investigation was conducted to assess the rubber which was added in 60/70 penetration of asphalt that expected to produce high quality of asphalt pavement resulted in higher stability value. Thermoplastic properties are possessed by asphalt materials, asphalt can change shape based on temperature, that soften if heated and turn hard if cooled [9].
Penetration Index values range from about -3 for high temperature sensitive asphalt to about +7 for highly blown low temperature sensitive asphalt (high Penetration Index). PI is an express function of A and therefore can be used for the same purpose.
The sensitivity of asphalt or the temperature susceptibility of asphalt can be seen in the A-value and PI (Penetration Index). These were calculated from the measured softening point temperatures and penetrations. The Penetration Index value is a function of the value of A. The more gentle the slope of A value, the lower the level of sensitivity of the asphalt to temperature changes, the better the resistance of the asphalt to temperature changes. On the contrary, the steeper the PI chart, the more sensitive the asphalt is to temperature changes. where SP = softening point temperature of asphalt. Softening Point is the most important index for measuring asphalt's high temperature performance [12,13].

Result and discussion
The result of the rubber asphalt properties as well as the virgin asphalt in accordance with the requirements of the Interim Special Specification of Bina Marga SKh-1M.04-2021, are presented on As seen on Table 2, the penetration value and the softening point of the rubber asphalt are lower than the virgin asphalt, hence its resistance to deformation at normal temperature was thereby enhanced. Thus, the burning point of the rubber asphalt is higher than the virgin asphalt. The higher the burning point value the more resistant of the binder to high temperature. Thus, the asphaltense, maltenes and resins as asphalt forming components are not easily lost due to heating. As the asphalt, will commonly be experienced during mixing and compacting.
Moreover, the ductility value does not decrease, as commonly happen if the asphalt is added with the additive [14,15]. Hence, the ductility is still more than 140 cm. Thus, it can be assumed the rubber asphalt is a suitable additive material for asphalt modification, due to it has the values of the penetration, softening point, and ductility in the range of standard requirement of the binder. Table 3 presents the calculated Penetration Index from the value of penetration and softening point test, for nine samples at the same condition.  Table 3 and in Figure 2.
The penetration index value that is close to positive indicates the low level of sensitivity of the rubber asphalt to high temperatures. This value is based on the softening point value which is in the range of 52 to 54. With the addition of 7% rubber to the asphalt, the penetration value decreases and the softening point value increases.
The results of the Penetration Index (IP) analysis show that the use of natural rubber improves the quality of asphalt due to it is less sensitive to temperature. This is based on the small A value compared to virgin asphalt and the Penetration Index value which is close to 1. The properties of asphalt which is not sensitive to temperature usually has a high stability value and more resistant to permanent deformation, but the susceptibility of the asphalt to cracking must also be considered.  Figure 2 shows the values of all the tests carried out on rubber asphalt. Based on the results of Softening Point and Penetration Index, rubber asphalt meets the requirements of conventional asphalt pavement as a binder. Rubber asphalt can be categorized as temperature-resistant asphalt, so it can be successfully applied to road construction in tropical countries. Rubber usually reduces the viscosity of high temperature asphalt; increase its workability when hot and its deformation resistance to cold, thus making it compact.

Conclusions
1. The use of rubber as an asphalt modifier increases the penetration index value on the asphalt 2. From the results of laboratory tests carried out, it was found that rubber asphalt has better properties than the requirements of the Highways Specification, namely penetration > 50, softening point > 52, ductility > 232, specific gravity > 1.0, 3. With rubber asphalt properties that are better than the current standard specifications, hotmix asphalt mixtures that are more resistant to deformation and rutting will be produced. Combination with mixing aggregate (coarse, medium and fine) which has better properties requirements (abrasion, surface roughness, absorption, etc.) will result in higher and stiffer marshal stability of hotmix mixture so that it can withstand excessive vehicle loads.