Superpave沥青混合料设计方法

沥青与沥青混合料课程论文Method for the Design of Superpave Asphalt Mixture院系：土木工程班级：道路2班学号：201301010809姓名：王弘宇2017-01-05Abstract: Based on the brief introduction of the method for the design of Superpave Asphalt Mixture, the differences between Superpave and Marshall Design Method are discussed in the aspects of Molding Method, V olume Calculation and Optimum Asphalt Dosage, by comparing Superpave and Marshall Method for the design of Asphalt Mixture, and give some suggestions on Marshall Method.Key words: highway; asphalt mixture; Superpave Design Method; Marshall Design MethodDue to the rapid increase of traffic volume, tire pressure and axial load, as well as the changes in environment and material, asphalt pavement technology is facing a huge change. A lot of practice has proved that the relationship between Marshall Stability, flow value and the long-term performance of asphalt pavement is not significant, usually the high-temperature rut of the asphalt pavement whose flow value is qualified is still very serious. Asphalt penetration specification that has been used for nearly a century and Marshall Asphalt Mixture design method that has been used for nearly half a century cannot control the destruction of asphalt pavement, Early Damages of a lot of pavements which met the existing norms, designed according to the traditional method still occurred, which cannot be separated with its limitations. Therefore, it is necessary to realize the transition from the traditional empirical method to the road-performance-oriented method so as to prolong the service life of the asphalt pavement.1Brief introduction of Superpave Design MethodStrategic Highway Research Program (SHRP), which was completed in 1993, proposed a method of kneading molding specimens using a Superpave Gyratory Compactor (SGC). This molding method establishes a closer relationship between compaction conditions and traffic conditions, and the compaction process is closer to the compaction effect of actual pavement, reducing the crush of aggregate in the compaction process, the arrangement of the aggregate shape is closer to conditions of actual pavement.Height measurement of the test specimen is an important function of SGC. In compaction process, the density of the specimen can be estimated by the mass of the material, the inner diameter of the test-piece and the height of the specimen. The height is measured by recording the position of the loading head during the experiment, and the compaction properties of the specimen are obtained from these measurements.In Superpave, the compaction level is a function of N, which is the design Gyratory Compaction frequency. The design value of N is used to distinguish the different compaction functions of the design mixture, which is a function of traffic level. Traffic level is expressed by Equivalent Standard Axle Loads (ESALs). Therange of the design values of N is shown in Table 1.The optimum Asphalt-Aggregate Ratio of each asphalt mixture was determined by Superpave V olume Method. First, test an amount of asphalt, and the bulk density of the test specimens was measured by the surface-dry condition method.Table 1. Gyratory Compaction frequency of SuperpaveDesign ESALs/×106roundGyratory Compactionfrequency N/roundApplication of typicalroadInitialvalueDesignvalueMaximumvalue<0.3 6 50 75 Light traffic volume (local/county road)0.3~3 7 75 115 Medium traffic volume (most county roads)3~30 8 100 160 Medium to heavy traffic volume (city street,national highway)≥30 9 125 205 Heavy traffic volume (most interstates,climbing roads)2Comparison of Superpave and Marshall for the design method of Asphalt Mixture2.1Molding MethodCompared with Marshall Compaction Method, the main advantages of SGC gyratory compaction method are: to establish a closer relationship between compaction conditions and traffic volume conditions; the compaction process is closer to the compaction effect of actual pavement; reducing the crush of aggregate in the compaction process; the arrangement of the aggregate shape is closer to conditions of actual pavement; full consideration of the compaction properties of the Mixture, and to establish a relationship according to the compaction properties and the Construction Stability of Mixture as well as the High Temperature Stability of Mixture.Due to the vast expense of a whole set of SGC gyratory compaction equipment, Marshall Compaction instrument is at present widely used in China. In view of this situation, we can learn from SGC compaction method to improve the existing Marshall Compaction Method: It is recommended using large-scale test specimen compaction method for the Mixture which is large particle size, in other words, the mixture is made into a large cylindrical specimen, test it by using the large Marshall Test instrument, and establish the standard of the mechanics index of Marshall Testwhich is suitable for the large-scale standard specimen. The relationship between the times of compaction and the design traffic volume is established to make the compaction standard more reasonable.2.2The Method of Volume CalculationThe volume calculation of Superpave Design Method is different from traditional Marshall Method. The former takes into account the issue of aggregate asphalt absorption, using a four-phase system (air, absorbed asphalt, effective asphalt and aggregate) to calculate the volume; the latter uses a three-phase system (air, asphalt and aggregate), without considering the situation of aggregate asphalt absorption. Since the aggregates composing the asphalt mixture have different numbers of voids, they absorb a certain amount of the asphalt binder during the mixing, spreading and use of the asphalt mixture. The asphalt absorbed by mineral aggregate generally does not affect the strength of the asphalt mixture, so the volume index calculated by Superpave Design Method is more realistic.2.3Optimum Asphalt DosageThe advantage of Superpave Design Method is to ensure that there is a 4% voidage of the mixture, but the voidage is sometimes small in the final selection of the amount of asphalt by Marshall Method, which may cause Early Damages.3The superiority of Superpave design system1)It is more realistic than the traditional empirical method to select the asphaltbinder according to the local climatic conditions and traffic volume, trafficconditions, which is more rational use of materials.2)Selecting aggregate structure according to the control point and the restrictedarea, the volume index of the mixture can meet the design requirements moreeasily.3)Using SGC to mold asphalt mixture can be more realistically than MarshallMethod to compact the mixture to the condition that road construction can,and it is able to identify potentially unstable mixture, to avoid early damageto the road.4)When Gyratory Compaction is adopted, different gyratory compaction timescan be used, the change of voidage can be predicted after long-term load, andto find the problems in time, which can provide reference for thedetermination of gradation.5)Gyratory Compaction uses a large test specimen with a diameter of 150 mm.Aggregates with large grain size can be evenly distributed throughout thespecimen, reducing the variability of the test results of the Marshall specimendue to the small size.4Design of Superpave Asphalt Mixture4.1Selection of raw materials1)Selection of Asphalt BinderDetermine the PG grade that the asphalt binder should meet according to the local climatic conditions and traffic volume, traffic conditions, select the appropriate asphalt binder.2)Selection of aggregateThe main aggregate tests are shown in Table 2.4.2Selection of GradationIn order to introduce the design method of Superpave Asphalt Mixture more concretely, this paper designs with 3 grads (see Table 3). A total of 109 rotations were carried out in the test, which were suitable for the highways of medium to heavy traffic volume. The calculated volume index of the asphalt mixture is shown in Table 4.At the same time, the specimens AC－13 with the Asphalt-Aggregate Ratio of 5.4%, SMA－13 with 6.0%, OGFC－13 with 3.0% were molded, measured the Residual V oidage of the specimens after rotating and compacting 160 times by SGC. The Residual V oidage of the specimens was 2.9%, 2.7% and 13.0% respectively, which met the requirements.Table 3. Three gradations used in the designType of MixturePercentage of mass passing through the following sieve openings (mm)/% 26.5 19 16 13.2 9.5 4.75 2.36 1.18 0.6 0.3 0.15 0.075AC－13 100 100 100 93.0 68.0 46.0 27.0 23.0 15.0 13.0 9.0 8.0 SMA－13 100 100 100 95.0 62.5 27.0 20.5 19.0 16.0 13.0 12.0 10.0 OGFC－13 100 100 100 93.3 67.8 23.0 13.8 10.2 8.1 6.3 5.1 4.1Table 4. Determination results of Asphalt Mixture volume indexType of Mixture OptimumAAR/%Bulk Density/g·cm-3VV/%VMA/%DPVF A/%AC－13 5.4 2.293 3.9 15.3 1.2 75.0 SMA－13 6.0 2.215 3.8 16.1 1.5 77.8 OGFC－13 3.0 2.490 14.1 －－－TechnicalStandardmeasured measured 4.0 ≥14 0.8~1.6 65~754.3Selection of Optimum Asphalt DosageAccording to the selected gradation, the different asphalt dosages are selected, then Gyratory Compaction specimen is made according to the viscosity-temperature curve, evaluate the volume index related to the mixture, then determine Optimum Asphalt Dosage. See Figure 1.Figure 1. Determination of Optimum Asphalt DosageNote: V mm－the volume of paving asphalt mixture without void; V sb－the volume of mineral aggregate (calculated by bulk density); V ba－the volume of absorbed asphalt binder; V se－the volume of mineral aggregate (calculated by effective density); V mb－the bulk volume of compacted asphalt mixture; V fa－the filled with asphalt; V a－the void volume.4.4Validation of mixture1)The validation at maximum compaction levelSuperpave specifies a maximum compaction of 98% at the maximum compaction level, to prevent the designed mixture being compacted excessively during the transport operation period, which results in permanent deformation.Because the traffic volume corresponding to the compaction effect that the compaction at the maximum compaction level represents is much larger than the design traffic volume, excessive compaction does not occur.2)Water Sensitivity AssessmentThe test specimens are required to be compacted to a voidage of approximately 7% and tested for indirect tensile strength. The water sensitivity is the ratio of the indirect tensile strength of the specimens in conditioned group to the indirect tensile strength of the specimens in the comparative group to evaluate the water sensitivity of the mixture.5Problems in the design of Superpave Asphalt MixtureAlthough the design of Superpave Asphalt Mixture has been recognized around the world, its research of design system is far from enough. The design of Superpave Asphalt Mixture is designed by volume and inspection by weight. However, the method of measuring the bulk density, the apparent density, the packing density or the maximum density of aggregates and mixtures and the measurement result have important influence on the volumetric design. In addition, the current design system of Superpave Asphalt Mixture does not use any mechanical test method to evaluate the asphalt dosage and the performance of asphalt mixture. The design system of Superpave Asphalt Mixture is entirely dependent on experience for the determination of aggregate gradation, which cannot provide necessary methods to designers. These are the problems to be solved in designing Superpave Asphalt Mixture.6Discussion1)Superpave level Ⅰdesign method is the volume design method, the correctcalculation of volume index is very important. For the voidage, it should becalculated by the bulk density and the measured maximum theoreticaldensity measured by Saturated Surface-dried Method. When the measuredtheoretical density is not feasible, different formulas should be used fordifferent aggregates. At the same time, the value VMA, VF A, DP, Compactionand other indexes should be paid attention, too.2)Gyratory Compaction method is more stable than Marshall Compactionunder the condition of different asphalt dosage, that is to say, the change ofasphalt content has less effect on Gyratory Compaction, but the impact onMarshall Compaction is more obvious. This is due to the different effects ofGyratory Compaction and Marshall Compaction. Gyratory Compactionresulting in rubbing rolling effect for the mixture in the process of test, whichis conducive to the dislocations between aggregates, so that the aggregateshave a rearrangement process. The mechanical action and asphalt ofGyratory Compaction are both the reasons for the constantly dense aggregate.However, in Marshall Compaction process, the stone dislocations will be fewwhen the asphalt content is insufficient, which is not conducive to thegeneration of aggregate rearrangement, only when the asphalt contentincrease relative movement of the aggregate can occur. So the influence ofasphalt content on Marshall Compaction Specimen is greater than that onGyratory Compactor.3)The research of Superpave in China has started in only recent ten years.Therefore, it is necessary to deepen the research on Superpave design andanalysis system. The conclusion of this research needs to be further deepened,tested and perfected. In the future the following areas can be considered inresearch:a)Establishing the relationship among PG classification and traditionalpenetration and viscosity classification, and the issue to choose asphaltbinder under the conditions of climatic and traffic in China.b)The reasonableness of SGC Gyratory Compacting Parameters should bestudied from theoretical and practical compaction.c)Influence of the DP on the strength of Asphalt mortar.d)Influence of Fine Aggregate Content on Asphalt Mixture.7Conclusion1)Comparing the Molding Method, V olume Calculation and Optimum AsphaltDosage of Superpave and Marshall Method for the design of Asphalt Mixture, and Marshall Design Method is improved by referring to the design methodof Superpave Asphalt Mixture, which makes it closer to the actual situationof asphalt pavement.2)The design of Superpave Asphalt Mixture adopts three gradations; it studiesthe site compaction characteristics of asphalt mixture and ensures therequirement of the voidage at each gyratory frequency of the asphalt mixture.3)The disadvantages of the design method of Superpave Asphalt Mixture arepointed out, and suggestions for the research direction of the design ofSuperpave Asphalt Mixture are put forward.Reference:[1]张登良. 沥青与沥青混合料. 北京：人民交通出版社, 1993[2]江苏省交通科学研究院. 高性能沥青路面Superpave技术实用手册. 2002. 5[3]贾渝. 高性能沥青路面superpave技术实用手册[M]. 江苏：江苏交通科学研究院[4]JTG F40－2004, 公路沥青路面施工技术规范[S][5]AASHTO Designation: MP2-02 Standard Specification for Superpave V olumetricMix Design[6]Joseph F.Goode 等. A New Graphical Chart for Evaluating Aggregate Gradation.Journal of AAPT. 1962。