Laboratory Comparison of SBS and PROpolymer MA123 Modified Asphalt Mixture

Abstract
In order to enhance the properties of asphalt mix, especially rutting resistance in Iraq due to high temperature, different modifier types have been adopted. Recent studies have shown that in Iraq, the polymer in the form of SBS is highly effective and gives good results in resistance to rutting and other defects. However, its use increases the cost of asphalt concrete and its difficulty storing, leading to the investigation of alternative polymers that should be more reasonable than the SBS polymer. This study examined a polymer named PROpolymer MA123 to measure its applicability to modified asphalt mix. For this purpose, the Asphalt mix was modified with 0.5% of PROpolymer MA123 from asphalt weight. The results showed that applying the new alternative polymers resulted in equal or better performance than the SBS-modified samples.

Material
This study used 70/100 neat bitumen grade supplied by Gazprom company. To measure the bitumen characteristics, some conventional tests have been conducted for the base bitumen, such as penetration and softening point tests. Table 1 shows the test results according to the GOST (Russian standard) specification. The PMB samples were prepared using two polymers, SBS and PROpolymer MA123. The asphalt mixture compositions are demonstrated in Table 2.

Methods
Density Test
The principle of the method is to determine the average density of samples made in the laboratory or selected from the structural layers of road pavements, taking into account the pores in within the pavement. In this test method, samples are weighed in air then immersed for 30 minutes in a vessel with water having a temperature of (20 ± 2) ° C, so that the water level in the vessel is at least 20 mm higher than the surface of the samples, after that the samples are weighed in water.
Residual Porosity
The aspect of the test method is to determine the volume of pores present in a compacted mixture. The residual porosity of asphalt samples V, %, is determined based on the previously established average and true densities.
Compressive Strength
In this method, the samples are tested at different temperatures using water bath like (50 ± 2) °С, (20 ± 2) °С or (0 ± 2) °С. The temperature (0 ± 2) °C is achieved by mixing water with ice. Samples from hot mixes are kept at a given temperature for 1 hour in water. The sample taken from the water bath is placed in the center of the lower plate of the press, then the upper plate is lowered and stopped above the level of the sample surface by 1.5-2 mm. After that, the press motor is turned on and the sample is loaded.
Shear Resistance
The loading rate of the samples for both compression schemes is the same which is equal to (50.0 ± 1.0) mm / min. Before testing, the samples and the crimping device are kept for 1 hour at a specified temperature (50 ± 2) °C in water. The sample taken from the water bath is installed in the center of the lower press plate in the first compression scheme or in the lower part of the crimping device in the second compression scheme. During the test of the sample, the maximum reading of the force meter is recorded, which is taken as the breaking load. At the same time, with the help of the displacement indicator, the ultimate deformation corresponding to the breaking load or the beginning of the yield stage is measured.

Results and Dicussion
The obtained results are shown in Figures 2-6.

The average density of the four compositions, which ranges from 2.39 to 2.44, varies slightly (Figure 2). The outcomes demonstrate that adding SBS polymer to the mixture for the second compositioncauses the density value to drop significantly. The addition of PMB to the mixture resulted in a reduction in compaction efficiency. Compared to a typical mix, the mixtures have a lower density due to the PMB's elastic characteristic. On the other hand, the PROpolymer MA123 is applied as a modification to the mixture may cause the density to increase compared to the other compositions.

It is evident from the observed data that the residual porosity results for the three compositions are within the accepted ranges (Figure 3). The loss of adhesion or cohesion is the primary cause of water damage. Compared to the other compositions, composition No. 3 had somewhat higher water saturation. This would suggest that the sample with the PROpolymer MA123 would show greater adhesion and cohesiveness than the characteristics of samples at low temperatures.

All compositions' compressive strength at 60 °C is above the minimum standard limit (Figure 4). The inclusion of MA123 in composition No.3 yielded a higher compressive strength compared to the conventional mixture (No.1). The addition of PMB (combination No.2) increased compressive strength due to the increase in viscosity of the bitumen as the utilized elastomeric polymer (SBS) forms discrete particles in the bitumen and its function as a thickener. Based on the above result, PROpolymer MA123 (composition No.3) showed better behavior than other compositions.

Composition No. 1 has a low internal friction coefficient compared to the other compositions (Figure 5). The findings, however, are all still over the minimal threshold (min. 0.89). The internal friction coefficient of the asphalt mixes was raised by adding PROpolymer MA123 to composition No. 3. This shows that PROpolymer MA123 has a high internal friction coefficient due to its high concentration. Internal friction angle is significantly influenced by bitumen viscosity as well. High viscosity PROpolymer MA123 causes the particles to interlock more closely, increasing the internal friction angle of the modified asphalt mixture.

All mixtures produced a cohesion value greater than the minimum demanded (minimum 0.3 MPa) (Figure 6). The control sample (composition No. 1) showed the lowest cohesion compared to the other compositions. The cohesiveness value significantly increased due to the PROpolemer MA123's inclusion in composition No. 3.

Conclusion
The purpose of the study is to use several conventional tests to compare the PROpolymer MA123 and the SBS polymer. The results of the study can be summed up as follows:

1. Results show good porosity; water damage due to adhesion/cohesion loss. Composition No. 3 has higher water saturation, indicating better adhesion/cohesiveness.
2. All compositions meet the minimum compressive strength standard at 60 °C. Composition No. 3 with MA123 has the highest strength.
3. Composition No. 1 has low internal friction but still meets the threshold. Adding PROpolymer MA123 to Composition No. 3 increases internal friction.
4. All mixtures exceed the minimum cohesion requirement. Composition No. 1 has the lowest cohesion, while No. 3 with PROpolymer MA123 has the highest.