Asphalt concrete is a typical rheological material, which is hard brittle at low temperature and reflects soft plastic facture at high temperature; the temperature has a great influence on the mechanical properties of asphalt concrete. In order to eliminate the environmental pollution caused by hot asphalt construction, cationic emulsified asphalt can be used. This paper transforms the temperature control system for static and dynamic triaxial test equipment, which has achieved static and dynamic properties of emulsified asphalt concrete under different temperatures, and researched the temperature sensitivity of emulsified asphalt concrete materials including static stress-strain relationship, static strength, dynamic modulus of elasticity, damping ratio, and so on. The results suggest that (1) temperature has a great influence on the triaxial stress-strain relationship curve of the asphalt concrete. The lower the temperature, the greater the initial tangent modulus of asphalt concrete and the higher the intensity; the more obvious the softening trend, the smaller the failure strain of the specimen and the more obvious the extent of shear dilatancy. When the temperature is below 15.4°C, the temperature sensitivity of the modulus and strength is stronger significantly. (2) With the temperature rising, the asphalt concrete gradually shifts from an elastic state to a viscoelastic state, the dynamic modulus gradually reduces, and the damping ratio increases. When the temperature is above 15.4°C, the temperature sensitivity is obviously stronger for the dynamic elastic modulus and damping ratio. (3) The static and dynamic properties of asphalt concrete are very sensitive to the temperature. The test temperature should be made clear for the static and dynamic tests of asphalt concrete. The specimen temperature and the test ambient temperature must be strictly controlled.
Asphalt concrete is made of asphalt, aggregate, filler, and other cement together to form a synthetic material, is the material more and more widely used in transportation and water conservancy projects, and has an important social and economic value. In order to eliminate the shortcomings of traditional hot asphalt construction heating and environmental pollution, we consider the use of nonheated emulsified asphalt. For the porosity and short storage time of the conventional emulsified asphalt concrete, as well as the difficult to have the fatigue strength, surface closure requirements, and other deficiencies, the use of cationic emulsified asphalt was considered.
Highway traffic load, seasonal difference, climate difference, cold area and hot zone, sunshine and reservoir water temperature differences, and other factors have the impact of asphalt concrete engineering properties [
Based on the static and dynamic triaxial test of emulsified asphalt concrete under different temperatures, this paper has researched the temperature sensitivity of static stress-strain relationship, static strength, dynamic modulus of elasticity, and damping ratio for emulsified asphalt concrete materials. Also, it provided the basis for temperature reliability evaluation of material with emulsified asphalt concrete.
We used cationic emulsified asphalt in this test, and the solid content is 52%. The density is 1.01 g/cm3, penetration is 95.5 mm, ductility is 160 cm, and the softening point is 43.2°C. The mineral aggregate is crushed dolomite; the padding is ore powder of dolomite and PO42.5 cement. The mix proportion of asphalt concrete test is shown in Table
The mix proportion of asphalt concrete.
Asphalt-aggregate ratio (%) | Aggregate gradation (%) | |||||
---|---|---|---|---|---|---|
10–20 | 5–10 | 3–5 | 0.075–3 | Cement | Mineral powder | |
mm | ||||||
6.7 | 10 | 21 | 25 | 38 | 3 | 3 |
The mixture ratio of aggregates and fillers is preliminarily determined by the dense skeleton stacking test [
Relation curve of Marshall stability and asphalt-aggregate ratio.
Relation curve of flow value and asphalt-aggregate ratio.
Relation curve of porosity and asphalt-aggregate ratio.
The mixing material is treated with microwave before compaction, so that the emulsified asphalt is completely demulsified and the water in the emulsified asphalt is evaporated by maintaining the temperature at 120∼130°C. The molded specimen is subjected to a static test on a triaxial apparatus. There is no drainage during the test, and the use of body variable measurement is required rather than an external body. Temperature has a great influence on the mechanical property of the asphalt concrete, so we need to control the sample temperature in the process of the triaxial test. The temperature of the asphalt concrete triaxial test is controlled by the copper coiled tube between the inside wall and outside wall of the pressure chamber. The copper coiled tube is filled with freezing liquid, and it is circulating all the time. And a temperature sensor is placed inside the pressure chamber to monitor the water temperature. The thermostat solenoid valve controls the water temperature to keep ±0.5°C range of the test temperature [
The static triaxial temperature control system.
The specimens are molded by using the compaction method. The asphalt concrete whose mix proportion is shown in Table
The typical stress-strain and volumetric strain-strain relationship of the asphalt concrete are shown in Figures
The relationship between stress and strain (
The relationship between volumetric strain and strain (
Asphalt concrete is a typical rheological material, and the temperature has a significant impact on its mechanical properties. Figure When the temperature is under 15.4°C, the stress-strain relationship curves are grossly softening, and the temperature has a great influence on the initial tangent modulus and the failure strain. But when the temperature is over 15.4°C, the stress-strain relationship curves show hardening type, and it significantly reduced the temperature sensitivity of initial tangent modulus and failure strain. At low temperatures (5.4°C), the initial phase of the stress-strain relationship curves for the asphalt concrete is steeper, It means the initial tangent modulus is greater, and the softening phenomenon is more obvious, especially when the cell pressure is low, and the corresponding failure strain is small (<5%). But at higher temperature conditions (25.4°C), the asphalt concrete shows hardening phenomenon, the failure strain is increased by 7%, and the initial tangent modulus significantly reduced compared to that at lower temperature. It is only 25% of low modulus or less. As the temperature decreases, the steeper the initial stages of asphalt concrete stress-strain curve are, the higher the initial tangent modulus is. The lower the temperature is, the more obvious the softening phenomenon is and the smaller the failure strain of the sample is.
The relationship between stress and strain. (a)
The results of failure strain.
|
Failure strain (%) | |||
---|---|---|---|---|
100 | 300 | 700 | 1000 | |
5.4 | 2.66 | 5.89 | 10.1 | 13.3 |
15.4 | 5.34 | 12.2 | 17.1 | 20.0 |
25.4 | 10.1 | 18.6 | 20.0 | 20.0 |
The triaxial test
|
|
|
|
|
|
|
---|---|---|---|---|---|---|
5.4 | 2096.0 | 0.202 | 0.888 | 0.594 | 0.143 | 0 |
15.4 | 738.2 | 0.212 | 0.890 | 0.529 | 0.090 | 0 |
25.4 | 500.5 | 0.202 | 0.897 | 0.481 | 0.040 | 0 |
The temperature also has a great influence on the volumetric strain of asphalt concrete. Figure
The relationship between volumetric strain and strain under different temperatures. (a)
The asphalt concrete has a peak point under low temperature and low cell pressure. It takes the peak point as the asphalt concrete strength if the peak appears during the test, but if peak does not appear, it takes the partial stress which corresponds to the axial strain of 20% as asphalt concrete strength. Figure
The relationship between destruction deviator stress and temperature.
Figure
Mohr’s stress circles of triaxial tests of asphalt concrete. (a)
Triaxial test strength parameters.
|
|
Φ (°) |
---|---|---|
5.4 | 462.5 | 27.5 |
15.4 | 268.2 | 28.6 |
25.4 | 292.5 | 21.5 |
The comparison of the triaxial test strength at different temperatures are shown in Figure
Triaxial test strength comparison of normal asphalt and cationic emulsified asphalt concrete. (a)
Triaxial test failure strain comparison of normal asphalt and cationic emulsified asphalt concrete. (a)
The test material is the same as the static triaxial tests. The triaxial test of asphalt concrete is performed on the dynamic triaxial apparatus, and the specimen size is Φ101 mm ×
The temperature control system.
The asphalt concrete triaxial tests conducted three groups test at three different temperatures of 5.4°C, 15.4°C, and 25.4°C, and the trial confining pressures are 300 kPa, 600 kPa, 900 kPa, and 1200 kPa. Specimens are put in water bath at a constant temperature which is the test temperature for 24 hours before the test and then installing the specimen on the dynamic triaxial apparatus. The pressure chamber is filled airless with water at the test temperature, while the water is starting to circulate in the copper tube. After installation, the sample is applied at ambient pressure and the drain valve is opened to let the specimen be in contact with the atmosphere. After it is applied, it should be maintained at a constant pressure for 30 minutes before starting the dynamic test. The dynamic load is sinusoidal and vibrates five times under each load, and the vibration frequency is 1 Hz.
Under the same temperature conditions, when the dynamic strain of asphalt concrete materials is 10−4∼10−3, the elastic modulus variation is small (the modulus change does not exceed 16.3% at the same temperature, the same confining pressure, and the same consolidation ratio), and the damping ratio is also small (≤0.11); it is substantially an elastic deformation phase. The dynamic stress-dynamic strain backbone curve of asphalt concrete basically showed a linear relationship. The dynamic strain has little influence on the dynamic modulus, and it can fit the dynamic stress-dynamic strain backbone curve of the asphalt concrete triaxial test by a straight line through the origin [
The backbone curves of the dynamic triaxial test (
The dynamic modulus results.
|
Stress ratio | Dynamic modulus (MPa) | |||
---|---|---|---|---|---|
300 | 600 | 900 | 1200 | ||
5.4 | 1.5 | 578 | 645 | 680 | 732 |
15.4 | 1.5 | 539 | 604 | 652 | 671 |
25.4 | 1.5 | 381 | 515 | 580 | 614 |
Figure
The relationship between dynamic modulus and temperature.
Figure
The relationship between damping ratio and dynamic strain.
The damping ratio results.
|
Stress ratio | Damping ratio | |||
---|---|---|---|---|---|
300 | 600 | 900 | 1200 | ||
5.4 | 1.5 | 0.061 | 0.049 | 0.044 | 0.037 |
15.4 | 1.5 | 0.072 | 0.060 | 0.045 | 0.040 |
25.4 | 1.5 | 0.094 | 0.074 | 0.063 | 0.052 |
Figure
The relationship between damping ratio and temperature.
The researches presented in this paper can be summarized as follows: When the temperature is under 15.4°C, the stress-strain curves are substantially softening, and the temperature has a great influence on the initial tangent modulus and the failure strain. While the temperature is over 15.4°C, the stress-strain curves are substantially hardened, and the temperature sensibility of initial tangent modulus and the failure strain is significantly reduced. At low temperature, the initial tangent modulus is large and the softening phenomenon is obvious, especially when the confining pressure is low, and the corresponding failure strain is small; while at the high temperature conditions, asphalt concrete is hardened, failure strain increases largely, and initial tangent modulus relatively decreases compared to that at low temperature. When the pressure and the temperature decreases, the body change curves gradually transform into dilatancy, especially at low temperatures and low confining pressure, almost no shear contraction; the volumetric strain of the same axial strain is different because of temperature. When the temperature is under 15.4°C, the temperature sensibility of static strength and modulus is significantly stronger, but when the temperature is over 15.4°C, the temperature sensibility of dynamic modulus is strong, which is contrary to the law of static modulus. When the temperature increases from 5.4°C to 15.4°C, the cohesion of the static strength indicator drops sharply, but the angle of internal friction of static strength index has little difference; while the temperature increases from 15.4°C to 25.4°C, the cohesion of the static strength indicator has little difference; however, the angle of internal friction of static strength index drops largely.
The authors declare that they have no conflicts of interest.
This research was financially supported by the National Natural Science Foundation of China (Grant nos. 51309028 and 51378403).