The Design And Construction Of SAC13 Asphalt Mixture

The highway construction in our country enters into new times, in which High grade highway such as expressway and first class highway give priority since Shenyang-Dalian and Shanghai-Jiading expressway have been set up to be open to traffic in 1988. The total expressway mileage is up to 24,700 kilometers in the period of"tenth five". The newly built highway mileage will be up to 24,000 kilometers till 2010. And the total highway mileage of the national expressway will add up to 65,000 kilometers. The condition of most asphalt pavement is good during the highway set up already. However, the damaged phenomenon of earlier period appeared in some highway asphalt pavement. The data show that aggregate gradation and homogeneity of the material are the two most critical factors that can improve asphalt pavement performance and durability. Therefore,the workers engaged in asphalt pavement have been studying on aggregate gradation design method and construction technology in recent years. Whatever methods are used to design aggregate gradation, asphalt mixture performance must be tested and studied by suitable equipment in laboratory in order to prove that its performance really meets the request. Above all, the gradation has to be tested by engineering practice to verify the performance satisfying the request.Aggregate gradation design and test method of SAC is put forward by academician Qinglin-Sha in recent two years. This method is more superior not only lies that it can calculate the passing quantity of arbitrary sieve pore for coarse and fine aggregate,but also it can adjust aggregate gradation to the structure type needed according to the different category rock class and judge performance of aggregate gradation offered in advance. In combination with actual engineering, the paper deeply studied gradation design and construction technology of SAC13 asphalt mixture, aiming at making this creative result widely used and resolving the insufficiency in the current aggregate gradation design methods. This paper draws main conclusions as follows:(1) According to the amount of coarse aggregate in asphalt mixture and relationship of VCA_DRL,VCADRV and VCA_AC, the criteria using to judge structure type of asphalt mixture is put forward distinctly, that are compact skeleton-dense structure (VCA_AC=VCADRV), general skeleton-dense structure (VCADRV AC≤VCA_DRL) and suspended-dense structure (VCA_AC > VCA_DRL) and skeleton-gap structure (VCA_AC < VCADRV); Based on filled-theory, skeleton formed by coarse aggregate of asphalt mixture when VCA_AC is less than VCADRV. However, SMA aggregate gradation itself is not dense. Denseness of SMA asphalt mixture is achieved by using more asphalt. Consequently, SMA asphalt mixture is extremely sensitive to asphalt content;(2) The methods used to test coarse aggregate deposit density method in loose condition, pestle denseness condition and vibratory denseness condition have some defect in some extent through the analysis result of testing regulations. Aggregate deposit density tested under vibroplatform setting which maintains unaltered is below pestle denseness of 2kg weight and 3min vibration time, through which coarse void is calculated and gained in order to study how skeleton forms;(3) The value of VCADRV and VCA_DRL is definitely influenced by size of container. The bigger is containers diameter, the smaller is their values. If the ratio of the container diameter and the largest diameter of coarse aggregate is more than 10 times, the influence of the size of container for VCA is very little and can be ignored;(4) VCA of coarse aggregate will primarily depends on the nature of aggregate. And there is little correlation with the proportion of each grade coarse aggregate and VCA. In this paper, VCA of seven different gradation fall within positive and minus two times of average value standard deviation;(5) The example in the paper confirm that the correlation coefficient of them is above 0.8761, namely VCA_AC strongly depends on coarse aggregate content of aggregate gradation, and it reduces with the coarse aggregate content increases through analyzing the irrespective many coarse aggregate content of asphalt mixture that is mould by big or small Marshall equipment and the corresponding VCA_AC. Thus, as long as VCA_DRV and VCA_DRL value of coarse aggregate are determined by test when the raw material is selected. Then according to the relation between aggregate gradation VCA_AC and content of the coarse aggregate, coarse aggregate content required by the design asphalt mixture corresponding component types can be calculated. And then every sieve opening passing amount of coarse and fine aggregate is calculated according to SAC aggregate grading design method;(6) Analysis of asphalt mixture intensity form shows that the effect of coarse aggregate in intensity composition shows more distinct with the gradual formation of stable framework, from less than 85% contribution rate of suspended dense structure of up to 85% of general skeleton-dense structure and up to 90% of compact skeleton-dense structure;(7) The aggregate gradation design of three different specification-SAC13,SAC20 and SAC25 verifies SAC aggregate gradation design and test method are simple, flexible and strongly applicable, and are generalized and applied expediently. Examples in this paper provide a model for design method for the user;(8) By testing dynamic split test parameters of common asphalt mixture surface course (SAC composed of three types, AC, SMA, SUP) under different temperature, the value scope of dynamic indirect tensile stiffness modulus and relational expression of modulus along with temperature changing are gained. As it has good correlation between temperature and modulus, modulus in different and standard temperature can be deduced by the tested temperature, which is proposed for reference in design. This provides a convenient condition for test conditions and has better practical value;(9) Asphalt mixture dynamic modulus drops distinctly as the temperature increases. Among three SAC aggregate gradation, the dynamic modulus SAC1 of compact skeleton-dense structure sensitivity to temperature is least with temperature changing. General skeleton-dense structure SAC2 is the second. Suspended dense structure SAC3 is largest. And compared with AC, SMA, SUP, SAC1 and SMA are closer and better than AC and SUP. SAC2 is between AC and SUP, SAC3 is the worst(10) Through test study on pavement performance of three composing types asphalt mixture which are designed by SAC aggregate gradation method and AC SMA, SUP asphalt mixture which are commonly used. The results show:①Compared with asphalt mixture which takes asphalt mixture of hydrated lime as filler instead of slag filler cement as filler, high temperature resistant permanent deformation capacity is high, the anti-aging performance is low and water stability performance of the same grading is lower. But the low temperature performance can not be determined;②High temperature resistant permanent deformation capacity is classified from high to low as follows: compact framework dense structure, the general framework dense structure, suspended dense structure judging by the indexes of high temperature resistant permanent deformation capacity corresponding to rutting test, SGC test and GTM test;③It is more reasonable to use permanent deformation value and deformation speed in rutting test together to evaluate high temperature resistant permanent deformation capacity. And evaluation index is more effective by extending test time of wheel rutting;④In hypothermia bending test, prepared methods of sample will greatly influence the largest bending strain and bending stiffness modulus of asphalt mixture destruction in low-temperature. Relational rules for prepared methods of sample should be added in test methods;⑤The results of hypothermia bending test and dynamic indirect tensile test modulus differ obvious. Therefore, asphalt mixture low temperature performance is very difficult to evaluate. The effectiveness of asphalt mixture low-temperature performance index evaluation should be taken into accout;⑥The results of residual stability test and freeze-thaw split test show simultaneous that asphalt mixture water stability of three SAC aggregate gradation which are designed by the same methods is classified from high to low as follows: compact framework dense structure SAC1, the general framework dense structure SAC2, suspended dense structure SAC3. However, residual stability of them is less than AC, SMA and SUP. Only the splitting freeze-thaw test intensity ratio of SAC1 is higher than all other grading;⑦The initial structure depth of framework dense structure asphalt mixture is deep and decay slowly. And the initial structure depth of suspended dense asphalt mixture is low and decay fast. However, the structure depth decays faster than that of SAC due to the special structure of SMA;⑧The order of asphalt mixture anti-aging performance when fillers are the same is: suspended dense structure is greater than general framework dense structure, and the latter is greater than the compact framework dense structure;(11) Compact performance of compact framework dense structure is comparative to SMA and SUP and general framework dense structure SAC2 is comparative to SAC3, asphalt mixture of AC grading is compacted easily by synthetically considering compact performance parameters gained by asphalt mixture gyration curve;(12) Samples are made by different compaction methods of GTM, SGC and Marshall Compaction when asphalt content is equal. Bulk density of SGC is largest, bulk density of GTM take the second place, bulk density of Marshall compaction is the least. The corresponding size parameters (Va., VMA) parameters of SGC is the least, the size parameters of GTM times takes the second place, the size parameters of Marshall compaction are the largest. The higher is coarse aggregate content, the smaller is the gap between them. And results gained are contrary to some research results in exists;(13) Adjustment of grading in construction process validates the applicability of SAC aggregate grading design method. Particularly test methods of VCADRF and VCA_AC are validated flexible once again. Responding construction course to which should be paid more attention is proposed. And consistency of aggregate grading is ensured and the quality of asphalt concrete pavement is improved at the same time;(14) The tracking and observing data of test section show that initial deformation of asphalt mixture which is designed by SAC aggregate gradation design method develops very fast. But the reduce degree of deformation rate with continuous load is less than AC grading, which is same with the research conclusion in laboratory. But the permanent deformation at present is equivalent to it and requires to be observed further. In addition, the structure depth and the friction coefficients of the asphalt mixture designed by SAC aggregate gradation design method are both far larger than and AC. However the roughness degree is the same as AC.It can be drawn from the conclusions above that new SAC13 designed by SAC aggregate gradation design and test possesses technical and economic characteristics as follows: Va is small and adjustable and not easily to suffer water damage. It also has the following advantage: strong high temperature resistance to permanent deformation capability, deep structure depth, and good skid-resistant. Also, it is easily to be compacted. The asphalt content is smaller and can save investment etc.Aiming at the key index of determining asphalt mixture structure type and SAC aggregate grading design method coarse aggregate VCA, the paper proposes vibroplatform recommended in specification, VCA_DRV test method is determined in condition of 2kg weight and 3min vibration time. And this can avoid the influence of different personnel operating to test data. Reference for the revision of test methods is provided. VCA_AC reduce along with coarse aggregate content of aggregate gradation increasing is proposed and relationship between VCA_AC and coarse aggregate content is established. When VCA_DRL and VCA_DRV of raw materials test are determined, coarse aggregate content of different component asphalt mixture can be calculated through the relationship between coarse aggregate content and VCA_AC. The passing quantity of sieve pore for coarse and fine aggregate can be calculated by SAC aggregate gradation design method. Thereby, primary grading is gained and tested by VCADRF and VCA_AC, and design steps of final grading which is produced and used are finally determined. Correspondingly, it can provide theoretical basis for selecting coarse aggregate content. Standards for determining asphalt mixture structure type are proposed: compact framework dense structure (VCA_AC=VCA_DRV), general framework dense structure (VCA_DRVAC≤VCA_DRL), suspended dense structure (VCA_AC>VCA_DRL) and framework gap structure (VCA_ACDRV). The concept is clear and can well be used to predict asphalt mixture performance. And at the same time, it is expressly confirmed that denseness of SMA asphalt mixture is achieved through using excessive asphalt. Consequently, SMA is extremely sensitive to asphalt content.Tracking observation of test sections on which SAC grading design method systematically studied and applied combination with the practical engineering firstly have confirmed that asphalt concrete designed by SAC aggregate gradation design test method has better engineering practicality. And provide mode for popularization and application of design method. The applied skill of VCA_AC aggregate gradation test method is proposed in this paper. After aggregate grading which is tested by VCADRF test method meet requirements and when Va which is calculated by the selected specimen density meet 3%-4% of design requirement, VCA_AC test of the aggregate gradation is determined to meet requirements for the structure type, and this makes the method more simple and flexible. The error scope of passing quantity of different sieve pore is proposed and this can assure the consistency of asphalt mixtures.In addition, rutting test time should be properly extended. And the permanent deformation and deformation rate are both used to evaluate the asphalt mixture high-temperature resistance to permanent deformation. In low temperature bending test, considering the great influence of prepared methods of sample to the largest bending strain and bending stiffness modulus of asphalt mixture destruction in low-temperature, relational rules for prepared methods of sample should be added in test methods. The sample short-term aged in condition of 163℃, 4h oven. The discuss of evaluation method and test index for pavement performance above provides some suggestions for the revision of test methods.