What Are Tar Sands?

Asphalt sand is a kind of sand commonly found in oil and gas fields. Because it is wrapped with heavy oil such as petroleum, it has only been used as a road building material for a long time. It is a natural mixture containing asphalt, water, sand, clay and other substances. It is a colloidal black substance, which can be used to produce liquid fuel. Ordinary oil sands contain about 12% asphalt.

Tar sand is also called thick oil sand or oil sand.It is a sedimentary rock containing asphalt or other heavy oil.The basic composition of asphalt sand is sand, clay, heavy oil, water, and a small amount of minerals. The sand and clay content in typical asphalt sand accounts for 70% to 80%, moisture content is less than 10%, and oil content is about 0 to 18%. Tar sands are one of the unconventional reservoirs, and their reserves are much larger than the proven reserves of conventional oil. The world's tar sand reserves are estimated to be 15 500 × 10t, of which 19% are recoverable reserves. The reserves of conventional crude oil are only 3 137.7 × 10t, and 877.7 × 10t has been produced. The remaining reserves can still be recovered for 65 years. It is expected that in the next 10 years, global conventional crude oil production will decrease, and heavy crude oil resources such as tar sands with abundant reserves have attracted the attention of the international community. Canada has already extracted a large amount of heavy oil and asphalt and gradually replaced traditional crude oil. In the new round of national oil and natural gas resource assessment work initiated by China, asphalt sand is also included in the evaluation scope. Asphalt sand will be one of the main sources of liquid fuel in the future and an important supplement to traditional crude oil _.

Asphalt sand is very different from conventional oil and natural gas, and it is difficult to be extracted by ordinary petroleum extraction methods in the original state, and special treatment is required. According to the differences in the storage depth of tar sands, the mining of tar sands can be divided into two categories: in-situ mining methods and surface mining methods. The in-situ mining method collects and pumps out the asphalt by reducing the viscosity of the asphalt by heating or using chemical agents and other special methods. It mainly involves thermal recovery technology, chemical technology and cold recovery technology; the surface mining method is to extract asphalt sand by open-pit mining. And then use hot water washing, solvent extraction and coking process to recover heavy oil from it. Various mining technologies of tar sands resources are reviewed in a comprehensive manner, their advantages and disadvantages and their application scopes are discussed, the main engineering examples are introduced, and some promising research directions in tar sands mining technology are proposed.

Dynamic Shear Creep Characteristics of Asphalt Sand

Asphalt sand is an asphalt mixture composed of mechanical sand, ore powder and asphalt with a particle size of less than 2.36 mm. Analyzing the viscoelastic properties of asphalt sand helps to understand the complex mechanical behavior of asphalt sand and asphalt mixtures. The research on the meso-mechanics of the aggregates and the analysis of the mechanical properties of the finer aggregate asphalt sand are of great significance. Researchers at home and abroad mainly use discrete element technology, finite element method and digital image processing technology to fine-tune the asphalt mixture. Observe the mechano-mechanical characteristics, in which obtaining accurate creep sand mechanics parameters is one of the key factors to ensure the reliability of meso-mechanical analysis results. In addition, asphalt sand is used in road pavement joint maintenance, piezoelectric material preparation and bridge deck paving The viscoelastic mechanical properties that are also applied under the working conditions are of significance for the evaluation of asphalt sand performance and construction applications. The study of the properties of asphalt sand has shifted from simple strength analysis to more complex creep mechanical behavior studies in static mechanical test conditions. The creep model of tar sand is established, and the creep behavior of tar sand is fully analyzed. However, because the dynamic mechanical behavior of the material can better reflect the mechanical properties of the material under use conditions, the dynamic viscoelastic test method has become one of the most effective means to effectively simulate the deformation characteristics of the road surface under dynamic load to characterize the asphalt performance. A large number of studies have used dynamic shear rheometers to analyze the rheological properties of asphalt, and have obtained very effective research data. Hou Hangjian et al. Used a rheometer to apply static shear load on asphalt horseshoe fat, analyzed the effect of temperature on the viscoelastic parameters of horseshoe fat, but did not specify the method for forming asphalt sand. Static load was applied during the test; M ITCHELL et al. Studied the fatigue properties of asphalt sand using a dynamic shear rheometer. Zhang Yanshuang et al. Used a dynamic shear rheometer to test the low-temperature relaxation properties of asphalt sand under different aging conditions. It can be seen that dynamic mechanical testing has become an important method for the analysis of asphalt sand performance. To this end, this study uses a DHR (disco-ery hybrid rheometer) dynamic shear rheometer, independently developed asphalt sand molding and test fixtures for several asphalt mixtures. The dynamic shear creep curve of asphalt sand was tested, and the Burgers model was used to fit and analyze the viscoelastic parameters of several asphalt mixtures.

Raw materials and ratio design

1.1 Raw materials

The test uses 70 # matrix asphalt, SBS modified asphalt and rubber asphalt. The asphalt test results are shown in Table 1. The ores are made of andesite sand.

1.2 Mixing ratio design

In order to make the gradation of asphalt sand and asphalt mixture have a good correspondence in this study, in order to provide a reference for the study of the meso-mechanics of asphalt mixture, AC20-1, AC20-2 and SM A16 were first designed. This kind of gradation, the gradation curve is shown in Figure 1. According to the passing percentage of aggregates below 2. 36 mm in 3 grades, the asphalt sand grades corresponding to the 3 grades are determined as shown in Figure 2. 70 # asphalt, SBS modified asphalt and rubber asphalt and AC20 -1 grade were used for Marshall compaction tests to determine that the asphalt content (mass fraction) was 4.1%, 4.5% and 5.0%, respectively; 70 # asphalt and AC20-2 and SM A16 grades were subjected to Marshall compaction tests to determine that the amount of asphalt was 4.4% and 5.7%, respectively. According to the literature [18], SM A16 was blended with high-quality fibers in an amount of 0.3% (mass fraction). Then according to the formula B in Appendix B of [19]. 6. 8-1 and Formula B. 6. 8-2 Calculate the proportion of asphalt that is absorbed and used by the aggregate and the effective asphalt content in the asphalt mixture (the thickness of the asphalt film used in the calculation process is 8 m), and then use the 0. 075 mm through rate and The ratio of the effective asphalt amount is used to calculate the powder-to-rubber ratio. Based on the principle of constant powder-to-rubber ratio, the asphalt content in the tar sands, that is, the amount of asphalt in the tar sands, can be calculated to obtain the mix ratio of the tar sands. A total of 7 tar sands are used, as shown in Table 3. Among them, 70 # asphalt and AC20 -1 gradation were used, and the amount of asphalt was fluctuated by 0.3%. The influence of the amount of asphalt on the viscoelastic parameters of asphalt sand was analyzed.

2 Design of dynamic shear creep test of tar sand

2.1 Asphalt sand test piece forming method

This study refers to the design of the tar sand molding device with reference to the Marshall compactor, because the maximum particle size of the tar sand is 2. 36 mm, the corresponding asphalt mixture is AC20, and the maximum particle size is 19 to 26. 5 mm, which is the largest The particle size difference is about 10 times. The similarity design is performed according to the proportion of geometric dimensions. The Marshall compactor is reduced by 10 times. The compaction device of tar sand is designed to form test pieces that can be used for DHR testing. First, use a mixing pot to mix not less than 100 g of mortar each time, and take samples according to the maximum theoretical density and sample size. The size of the shaped asphalt sand sample in this study is a cylinder with a diameter of × height = 6 mm × 40 mm. The sampling quality is about 12 g. After the tar sand was loaded into the mold, it was inserted and tamped, and the front and back sides were compacted 75 times. After molding, it is released for cooling. In order to verify the feasibility of the molding method, the relative bulk volume densities of the mortar specimens formed by this method and the rotational compaction mortar specimens were compared. The test results show that the relative density of the gross volume of the # 1 mortar in Table 3 formed by this method is 1. 981, and the relative density of the gross volume of the rotary compacted test specimen is 1994, the difference is only 0.7%, so the The molding method is feasible. It can be seen that the dynamic shear creep curve of asphalt sand under different working conditions is obviously different. The gradation type, asphalt variety, asphalt dosage and test temperature all have significant effects on the shear creep curve of asphalt sand. It can be seen from Fig. 6 that the shear creep deformation speed of the asphalt sand corresponding to SM A16 asphalt mixture is very fast, and it shows obvious three-stage deformation characteristics within 180 s test time, and obvious accelerated instability deformation appears. In the stage, at 140 s, the shear creep strain reached 300, while the corresponding asphalt mortar's shear creep strain for AC-type asphalt mixtures was only 0.2 to 1.2. The analysis may be due to SM A16 asphalt mixture asphalt. The mortar contains a large amount of mineral powder and a large amount of bitumen, and the content of 2.360 0.075 mm grains of machine sand is very small. The mixed asphalt mortar is difficult to have a skeleton effect when deformed at high temperature, so it is sheared. Creep speed is faster.

2.2 Dynamic shear creep test method

Before carrying out the shear creep test of tar sand, use AB glue to bond the two ends of the test piece to the fixed terminal. After the AB glue is completely cured, install the test piece on the DHR tester for testing. The test piece is installed in the test. Load 5 N forward and hold for 20 s to eliminate the gap between the fixture and the test piece terminals. In this study, the shear creep tests of tar sands at different temperatures were carried out at 45, 60, and 75 ° C. After the temperature reached the test temperature, the test was continued for 30 minutes. Related research shows that the shear strength of asphalt sand is about 400 kPa. A stress ratio of about 75% is selected for the test. The test stress is set to 300 kPa and the data acquisition time is 180 s. Shear creep is collected in real time during the test. Strain and load time data.

3 Conclusion

In this study, DHR was used to perform dynamic shear creep tests on asphalt sand, and the Burgers model was used to fit the shear creep curve. The viscoelastic parameters of asphalt sand under this mechanical mode were analyzed, and the following test conclusions were obtained:

(1) The test temperature, the amount of asphalt, the type of asphalt and the gradation type have a great impact on the dynamic shear creep characteristics of asphalt mortar. The higher the temperature and the greater the amount of asphalt, the greater the dynamic shear creep speed of asphalt sand. The SM-A16 asphalt mixture has a fast shear creep deformation rate, and the rubber asphalt sand has the best shear creep resistance.

(2) Regardless of gradation, the dynamic shear test law of tar sands has a good correlation with the general rules of rut resistance of asphalt mixtures corresponding to tar sands, which can be used as a basis for evaluating rut resistance of asphalt mixtures.

(3) The correlation coefficient obtained by fitting the dynamic shear creep curve of asphalt sand using the Burgers model is high. Different temperatures, asphalt usage, asphalt types, and grading types all have significant effects on the parameters of the Burgers model. SM A16 asphalt sand has poor transient deformation resistance against high-speed loads, rubber asphalt sand has good transient deformation resistance, and AC asphalt sand has strong resistance to unrecoverable residual deformation.

(4) The relaxation modulus of asphalt sand was calculated by fitted Burgers model parameters. Compared to AC asphalt mixtures, the relaxation modulus of SM A16 asphalt sand is very small. The relaxation modulus data can provide data for the numerical simulation of asphalt sand. stand by. ^[2]