Three different emulsion residues, such as SS1HP, HFE90, and SS-1VH (trackless), and a base asphalt binder (PG 64-22) are compared to characterize rheological properties by using DSR test. In order to capture the emulsion properties, different frequencies (from 1 to 100 rad/sec at a 10% constant shear rate) and temperatures (from −45°C to 75°C with 15°C increments) were applied. Then, a master curve for shear modulus was plotted for each emulsion. The transition of the HFE90 emulsion from viscous to elastic behavior occurs at lower temperatures, compared to the other materials. This emulsion is known for performing in a wider temperature range as shown in the results. The trackless emulsion presents an elastic behavior at intermediate temperatures. This product is known as having very fast setting and high resistance to shear stresses. The trackless emulsion presents the highest viscous and elastic modulus, followed by the PG 64-22 binder, SS1HP, and HFE90 emulsion. Shear strength test results show a behavior between trackless emulsion and SS1HP similar to the frequency sweep test results performed by DSR.
As the need for new construction for asphalt pavement has been decreased over time, an increased interest in preventive maintenance and rehabilitation has come to the fore. The asphalt emulsion is one of the most effective materials for the preventive maintenance of asphalt pavement. Also, the asphalt emulsion is an ecofriendly material because its construction system does not include heating equipment. For example, chip seals, which are among the most efficient and cost-effective methods utilized by state highway agencies to preserve and rejuvenate existing pavements, are constructed by application of asphalt emulsion and aggregate. The asphalt emulsion is applied as a liquid condition, and then it becomes a residue condition by curing procedure. Therefore, the properties of asphalt residue play a vital role in the performance.
Diverse laboratory tests are usually performed on the asphalt emulsions and their residue. In order to obtain appropriate properties that can be related to field performance, it is critical to obtain an emulsion residue that is representative of the emulsion used in the field.
Takamura [
King et al. [
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Deneuvillers and Samanos [
Bec et al. [
The objective of this study is to characterize rheological properties of three different asphalt emulsion residues and a base binder by using DSR. The results also will be related to the emulsions performance as a tack coat material.
Three different emulsions SS1HP, HFE90, and SS-1VH (trackless) are used in this study. For the sake of time, the RTFO method has been selected to recover emulsion residues. In addition, a base binder with PG 64-22 is also tested. The samples are characterized by using dynamic shear rheometer (DSR) to find their rheological properties such as shear modulus
The dynamic shear rheometer (DSR) is a common device to characterize the elastic and viscoelastic behaviors of asphalt binders as well as asphalt emulsions at high and intermediate temperature. Figure
(a) DSR equipment and (b) schematic of cylindrical specimen.
The emulsion residues are obtained using the Superpave binder test procedures by Marasteanu and Clyne [
This test system consists of parallel metal plates, an environmental chamber, a loading device, and a control and data acquisition and measures the rheological properties of asphalt binder. The test is performed by sandwiching the binder specimen between a fixed plate and a rotated plate on which the torque is applied. The DSR is able to directly apply and measure torque
Note that the shear stress and shear strain are not uniform in DSR testing. Rather, stress and strain are maximum at the sample periphery and zero at the sample center. The maximum stress and strain at the edge of the sample are normally reported in DSR testing, assuming a fixed sample radius and height.
Two important parameters are obtained from the dynamic shear rheometer test on asphalt:
Definition of phase angle.
The complex modulus is a measurement of a binder’s total resistance to deformation and can be divided into two components, such as a real part and imaginary part. The simple relation is shown below:
Additionally, the phase angle can be represented by the following equation:
The shape of the load, which is used in this test, is sinusoidal, and the loading is controlled by two types, such as constant stress and constant strain mode. The complex shear modulus and phase angle are automatically calculated by proprietary computer software. The more detailed procedures for DSR test can be found in ASTM D7175-05 [
Marasteanu and Clyne [
Salomon and Zhai [
Zhai et al. [
Asphalt binder is well-known for
The effects of time and temperature on viscoelastic material behavior can be combined into a single parameter, called
The principle of time-temperature superposition states that the change in a material property (e.g.,
The data at various temperatures are shifted with respect to time until the curves merge into a single smooth function. This behavior allows for the horizontal shifting of the data onto an arbitrarily selected reference temperature curve to form a single curve, the master curve, which is used to describe the constitutive behavior of asphalt binder over a wide range of temperatures and frequencies. The concept of a master curve is illustrated in Figure
(a) Original frequency sweep data at multiple temperatures and (b) shifted frequency data to a reference temperature.
The
The WLF equation is typically used to describe the time-temperature behavior of polymers in the glass transition region. The equation is based on the assumption that, above the glass transition temperature, the fractional free volume increases linearly with respect to temperature. The model also assumes that as the free volume of the material increases, its viscosity rapidly decreases.
The other model commonly used is the Arrhenius equation (
Several trial tests are performed on the sealant samples. Based on these tests the testing frequency is selected to cover a range from 0.1 rad/sec to 100 rad/sec to cover both high and low loading speeds. The applied strain is changed to 0.1% to make sure that the sample does not damage at either low temperature or high frequency. Because of the testing time and instrument limitation, the temperature range also shortened from 15°C to 75°C.
Totally 40 points are measured during each test. For some of the samples, it was hard to capture data at low temperature because of brittleness of the samples which may lead to damage or at high temperature because the sample was so soft to bear a shear load.
Figure
(a)
As shown in Figure
Tack coat shear test results.
For PG 64-22 binder, it can be seen that the complex modulus increases as the frequency increases or temperature decreases. For the complex compliance, the behavior is inversed. In other words, it decreases as frequency increases or temperature decreases. The maximum complex modulus obtained for this material was 4,318,000 Pa. Regarding the phase angle, it starts decreasing at a higher rate when the reduced frequency reaches an approximate value of 3,000 rad/s. It occurs at 2.9 rad/s and 15°C for the real frequency.
Similarly, it can be noticed from the shear modulus chart that at low frequencies or high temperatures the material presents a viscous-like behavior since the viscous modules
Considering the prediction of rutting resistance, it is necessary to know the locations where
Figure
(a) Complex modulus, (b) complex compliance master curves, (c) phase angle at 45°C, and (d) complex modulus at each temperature.
(a) Elastic and viscous modulus at 45°C and (b) shift factors at reference temperature (45°C).
For HFE90 emulsion, the complex modulus increases as the frequency increases or temperature decreases as can be seen in Figure
(a) Complex modulus, (b) complex compliance master curves, (c) phase angle at 45°C, and (d) complex modulus at each temperature.
(a) Elastic and viscous modulus at 45°C and (b) shift factors at reference temperature (45°C).
For this material, it can be seen again that for each temperature the modulus increases as temperature decreases and frequency increases. The shift factors for each temperature as well as the WLF coefficients and Arrhenius coefficient are also shown.
For SS1-HP emulsion as for the two previous materials, the complex modulus increases as the frequency increases or temperature decreases as can be seen in Figure
(a) Complex modulus, (b) complex compliance master curves, (c) phase angle at 45°C, and (d) complex modulus at each temperature.
(a) Elastic and viscous modulus at 45°C and (b) shift factors at reference temperature (45°C).
For this material, it can be seen again that for each temperature the modulus increases as temperature decreases and frequency increases. The shift factors for each temperature as well as the WLF coefficients and Arrhenius coefficient are also shown.
For trackless emulsion as for the three previous materials, the complex modulus increases as the frequency increases or temperature decreases as can be seen in Figure
(a) Complex modulus, (b) complex compliance master curves, (c) phase angle at 45°C, and (d) complex modulus at each temperature.
(a) Elastic and viscous modulus at 45°C and (b) shift factors at reference temperature (45°C).
Additionally, it can be seen in Figure
After the results for all the material were shown, it is important to compare at what frequency the crossover point takes place for each material. It was found that for the HFE90 emulsion the crossover point occurred approximately at 4,000 rad/s, which means that for this product the transition from viscous to elastic behavior takes place at lower temperatures comparing to the other three materials. On the other hand, it can be seen from Figure
Viscous modulus for each material at 45°C.
Conversely, crossover point of the trackless emulsion was estimated to happen at less than 100 rad/s, which means that this material will become elastic at intermediate temperatures. Also, this product has the highest viscous modulus compared to the other three materials.
Stiffness ratio (SR) is used to have a better comparison between different emulsions. This stiffness ratio is the modulus (
The SR results for viscous modulus are presented in Figure
SR based on viscous modulus at different frequencies: (a) 0.1, (b) 1, (c) 10, and (d) 100 rad/sec.
Figure
The results from the shear testing on tack coat also show a similar behavior. For a certain shearing speed at low temperatures, trackless emulsion has lower shear strength than SS1HP product and at high temperature tack coat has higher shear strength than SS1HP.
In this study three different emulsion residues, such as SS1HP, HFE90, and SS-1VH (trackless), and a base asphalt binder (PG 64-22) were compared to characterize rheological properties by using DSR test. In order to capture the emulsion properties, different frequencies and temperatures were applied. Then, a master curve for shear modulus was plotted for each emulsion. The results of this study are as follows. The HFE90 emulsion presents the crossover point The trackless emulsion has the crossover point at reduced frequency lower than 100 rad/s. It indicates that the material presents an elastic behavior at intermediate temperatures. This product is known as having very fast setting and high resistance to shear stresses. The trackless emulsion presents the highest viscous and elastic modulus, followed by the PG 64-22 binder, SS1HP, and HFE90 emulsion. At high temperatures trackless emulsion has the highest modulus. Depending on the frequency below a certain temperature, trackless material has the lowest modulus. This temperature gets lower as the frequency decreases. Shear strength test results show a behavior between trackless emulsion and SS1HP similar to the frequency sweep test results performed by DSR.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors would like to acknowledge the financial support from the Korea Institute of Civil Engineering and Building Technology (KICT) under research project “Support for Commercialization of Warm Mix Asphalt.”