Nghiên cứu ảnh hưởng của cốt liệu thô tạo khung đến sự phát triển biến dạng không hồi phục của bê tông nhựa nóng trong điều kiện việt nam TT TIENG ANH

MINISTRY OF EDUCATION AND TRAINING UNIVERSITY OF TRANSPORT AND COMMUNICATIONS DO VUONG VINH STUDY ON THE INFLUENCE OF COARSE AGGREGATES SKELETON FORMING ON PERMANENT DEFORMATION OF HOT ASPHALT CONCRETE IN VIETNAM CONDITION Field of study: Transport engineering Code : 9580205 Speciality: Highway and urban road engineering SUMMARY OF DOCTORAL THESIS HANOI – 2021 This research is completed at: University of Transport and Communications Supervisors: AssocProf.Dr Tran Thi Kim Dang University of Transport and Communications AssocProf.Dr Nguyen Huu Tri Institute of Transport Science and Technology Reviewer 1: ………………………………… Reviewer 2: ………………………………… Reviewer 3: ………………………………… The thesis will be defended before Doctoral-Level Evaluation Council at University of Transport and Communications at ……… day……… month……….year……… The thesis can be read at: National Library of Vietnam Library of University of Transport and Communications AUTHOR’S PUBLICATION LIST Do Vuong Vinh, Tran Thi Kim Dang (2016), “Effects of fillers and fine aggregates on the flexural strength of the asphalt mortars in the hot asphalt mixture”, Transport Journal No 11/2016 Vuong Vinh DO, Thi Kim Dang TRAN (2017) “Effects of fillers and fine aggregates on the shear strength of fine aggregate matrix in hot mix asphalt”, Proceedings of the Eastern Asia Society for Transportation Studies, Vol.11, 2017 Do Vuong Vinh, (2019), “Research on design methods of dense asphalt mixtures that consider the forming a coarse aggregate skeleton”, Transport Journal No 03/2019 Do Vuong Vinh, Tran Thi Kim Dang (2020), “Permanent deformation resistance of dense-graded asphalt mixtures with the aggregate gradation determined by the Bailey method”, Transport Journal No 6/2020 Do Vuong Vinh, Tran Thi Kim Dang (2021), “Content of coarse aggregate creating load-bearing skeleton and its effects on permanent deformation resistance of dense asphalt mixtures”, Transport Journal No 01+02/2021 Do Vuong Vinh, Nguyen Huu Tri (2021), “Internal structure characterization of asphalt mixtures and permanent deformation resistance”, Transport Journal No 03/2021 INTRODUCTION I Research background Asphalt concrete is a material which has been using widely for the pavement of highways, urban roads and expressway in Vietnam as well as on all over the world due to itself advantages However, this pavement also has disadvantage of being sensitive to temperature Shearing strength of asphalt concrete is decreasing at higher temperature results to permanent deformation Wheel rutting currently is one of the most common distresess of asphalt pavement in Vietnam due to heavy traffic and extreme temperature during hot weather Besides quality of component materials, aggregate gradation or the aggregate size distribution is one of the most important factors affecting to performance of the asphalt pavement included permanent deformation An asphalt concrete mixture with a reasonable aggregate size distribution allows coarse particles to interlock to each other and fine particles just enough to insert in the voids between the coarse aggregate not to destroy the coarse aggregate interlocking frame Such type of the mixture could have good coarse aggregate skeleton, to enhance shear strength, means enhance resistance of permanent deformation because of increasing friction between aggregate particles Role of the coarse aggregate skeleton in forming deformation resistance of asphalt mixture has been focused in many international researchs Typical among them are the research to develop Bailey method for aggregate blending for asphalt mixture design, and the one to develop an image analyse tool for evaluating aggregate skeleton structure In Vietnam, some researchers recently have studied the influence of coarseness of aggregate blend on the resistance to deformation and fatigue of asphalt mixtures However, these studies only assessed directly the influence of coarse aggregate content on rutdepth, but still has not considered the role of coarse aggregate skeleton in deformation resistance of the asphalt concrete mixtures Therefore, selected thesis of "Study on the influence of coarse aggregates skeleton forming on permanent deformation of hot asphalt concrete in Vietnam condition" is academic and practical II Research objective Research and propose a method to design a dense-graded asphalt mixture taking into account the formation of a coarse aggregate skeleton, and investigate the influence of aggregate grading and content of coarse aggregate creating skeleton on the permanent deformation resistance of hot asphalt mixtures The study also proposes and determines the internal structural index related to the to permanent deformation resistance of the asphalt mixture using image processing and analysis method Thereby clarifying the role of coarse aggregate skeleton in forming the permanent deformation resistance of asphalt mixture III Reseach contents The thesis contents include: 2 Overview of the influence of aggregates grading and aggregate skeleton on peemanent deformation resistance of asphalt concrete; Research and propose a method of designing aggregates blend of asphalt mixtures taking into account the formation of coarse aggregate skeleton; Experimental study to evaluate the influence of aggregate grading and coarse aggregate skeleton on permanent deformation resistance of asphalt concrete; The internal structure of the asphalt mixture and its to permanent deformation resistance IV Scientific and practical contribution  Research and propose a method to design asphalt mixtures taking into account the coarse aggregate skeleton in order to determine the appropriate aggregate grading and coarse aggregate content for the asphalt mixture with good permanent deformation resistance  Investigate the influence of coarse aggregate content on the permanent deformation resistance of asphalt mixtures with two different aggregate sources in order to determine a reasonable range of coarse aggregate content for the asphalt mixture with good permanent deformation resistance  Study to determine the internal structure of asphalt mixtures using image processing and analysis method, and establish correlation between these structural indexes and mechanical parameters indecating permanent deformation resistance of asphalt mixtures From the internal structural indexes, it is possible to basically predict the permanent deformation resistance and preliminarily screen the asphalt mixtures based on the permanent deformation resistance LITERATURE REVIEW Chapter provides an overview of the influence of aggregate grading and coarse aggregate skeleton on permanent deformation properties of asphalt concrete for empirical studies in the following chapters 1.1 Components and internal structure of asphalt concrete 1.1.1 Components of asphalt concrete Asphalt concrete is a mixture which consists of mineral aggregates (coarse aggregate, sand, mineral filler), asphalt binder and additives (if any) that are combined in a reasonable ratio Each component in asphalt concrete plays a certain role and is closely related to each other in order to creat a mixture with sufficient strength and required properties for the operation process 1.1.2 Internal structure of asphalt concrete Structurally, asphalt concrete is a building material of the artificial aggregate type, in which mineral aggregates are adhevise together by an asphalt binder At researched components, the asphalt concrete is considered as a system includes three components [6] (Figure 1.1) - Microstructure consisting of bitumen and mineral filler to form mastic asphalt - Intermediate structure consisting of sand and mastic asphalt to form asphalt mortar - Macrostructure consists of coarse aggregate and asphalt mortar to form asphalt mixture Figure 1.1 Multiscale model for asphalt mixtures Figure 1.6 Effect of coarse aggregate content on compressive strength of AC 1.2 Permanent deformation and permanent deformation distresses of the asphalt pavement 1.2.1 Instability rutting The instability rutting appears on a narrow range along the wheel paths with humps formed on the sides of the rut as shown in Figure 1.7 This rutting is due to the fact that asphalt concrete is “weak”, not enough shear strength to resist the shear stress caused by wheel load in the asphalt concrete layer This kind of rutting is the most common form and mainly occurs in Figure 1.7 Instability rutting on asphalt concrete layers with a depth of Asphalt Pavements about 10cm from the road surface 1.2.2 Strutural Rutting The structural rutting occurs at the wheel paths over a wide range and does not form humps along the wheel track This kind of rutting is due to the accumulation of deformation caused by repetitive loads in the roadbed (or in the sub-base and base layers) during the operation period 1.2.3 Surface/Wear Rutting Wear rutting occurs at the wheel paths on a narrow range and does not form humps along the wheel track This kind of rutting is due to the fact that asphalt layers not archieve requiered density in the construction period 1.3 Test methods for permanent deformation evaluation of asphalt mixtures 1.3.1 Creep tests Creep test is conducted by applying a static load to the asphalt concrere specimen and measuring the resulting permanent deformation The test can be carried out under unconfined or confined conditions Figure 1.12 Typical creep stress and strain relationships 1.3.2 Repeated load tests Repeated load test is conducted by applying a repeated load to the specimen with several thousand repetitions During the test, the cumulative permanent deformation as a function of the number of load cycles is recorded The test can be carried out under unconfined or confined conditions 1.3.3 Simulative Tests Several simulative test methods have been used in the past and are currently being used to evaluate rutting performance of asphalt mixtures Some of these methods include the Hamburg Wheel-Tracking Device, Asphalt Pavement Analyzer, French Rutting Tester (LCPC Wheel tracker), Purdue University Laboratory Wheel Tracking Device 1.4 Studies about the influences of aggregate grading and coarse aggregate skeleton on the resistance to permanent deformation of asphalt mixture 1.4.1 Studies in the world Refer to many previous studies, the report [31] concludes that there is "clear evidence that the aggregate composition of dense graded asphalt mixture has a decisive influence on rutting" In the research record [21] Carpenter and Enockson (1987) reported studies on 32 projects of spreading reinforced wearing course on national highways in Illinois (USA) and concluded as follows: most of the rutting problem can be attributed to the aggregate particle blend of the asphalt mixture The research of the authors Stakston, AD, and Bahia, H (2003) [48] also shown that the rutting resistance of asphalt mixtures mostly depends on the aggregate grading Even the mixtures are made from the good materials, but the aggregate grading are not proper, they may also occur rutting during operating period In some other studies by Chen, J.S., and Liao, M.S (2002) [22]; Krutz, N C., and Sebaaly, P E (1993) [29]; Elliot, R.P., Ford, M.C., Ghanim, M., and Tu, Y.F (1991) [25]; Button, J.W., Perdomo, D., and Lytton, R.L (1990) [20] on the strength of the asphalt mixture, the authors concluded on the influence of the composition material properties For aggregates, it is found that there is a threshold of strength value determined by the nominal maximum aggregate particle size, the strength of the mixture increases when the mix creates contact and interlock between aggregate particles Contact and interlock between coarse aggregates is considered to be the major factor forming the strength of the asphalt mixture, and the mix should be designed with a strong load-bearing coarse aggregate skeleton 1.4.2 Studies in Vietnam The researchs in Vietnam mostly focuses on improvement of permanent deformation resistance by modified asphalt mixtures Vu Phuong Thao (2015) [12] studied the degree of improvement in fatigue resistance and wheel rutting resistance of asphalt mixture made from dispersed fiberglass reinforcement Tran Thi Cam Ha in 2019 [8] assessed the improvement in the resistance to wheel rutting of asphalt concrete using epoxy bitumen There are two local researchs which focused more on the aggregate gradation Bui Ngoc Hung (2016) [10] studied the influence of aggregate grading, aggregate source and bituminous type on wheel rutting depth and fatigue strength of dense-graded asphalt mixture 12.5 and dense-graded asphalt mixture 19 Research are conducted on aggregate gradations within limitation provided in the Decision 858/QĐ-BGTVT, namely very coarse, medium coarse and low coarse The research results showed that wheel rutting resistance of the low coarse-grading mixtures were the lowest, increasing gradually with medium coarse-grading, and the highest with very coarse-grading mixtures for both dense-graded asphalt mixture 12.5 and 19 Tran Danh Hoi (2018) [9] studied the high modulus asphalt mixture using for flexible pavements of high-class road in Vietnam In this study, the author proposed to use the Bailey method to design aggregate grading for high modulus asphalt mixtures 25mm and 31.5mm 1.5 Studies about image analysis methods to determine the internal structure of asphalt mixtures Digital image processing and analysis techniques are effective tools for determing internal structure of asphalt mixes These techniques have been researched and developed by scientists in recent years [39], [43], [58] Internal structure parameters of asphalt mixtures are interested to research include air void, air void distribution, particle shape, orientation and distribution of aggregate particles and contact properties between aggregates Coenen et al (2012) [24] developed an image processing and analysis software to determine the structure of asphalt mixtures - IPAS software Then, Sefidmazgi et al [45] improved the IPAS software to IPAS-2 for determining the contact length, the contact direction of the aggregate particles – the internal structure parameters are related to the rutting resistance of asphalt concrete The research results show that there is a good relationship between the number of contacts, the contact length and the internal structure index (ISI) with the rutting resistance of the asphalt mixture expressed by the FN - Flow Number index In another study in 2013 Shaheen et al [46] also used IPAS-2 software to determine the internal structure of asphalt mixtures The results show that the number of contacts and the contact length have a good correlation with the rutting depth of asphalt concrete determined by the Hamburg Wheel Rut Tester Up to now, in Vietnam, there has been almost no research using image analysis method to determine internal aggregate structure of asphalt concrete and investigate the relationship between these parameters and mechanical parameters that show the rutting resistance of asphalt concrete 1.6 Problem statement The thesis focuses on solving the following issues:  Research and propose a method of designing aggregate blend of asphalt mixtures taking into account the formation of coarse aggregate skeleton;  Investigate the influence of aggregate grading and content of coarse aggregate forming load-bearing skeleton on the permanent deformation resistance of asphalt concrete through wheel rutting test and creep test  Determine the internal structure parameters of asphalt concrete that are believed to be related to the permanent deformation resistance using image processing and analysis methods and establish correlation between these structural indexes and mechanical parameters indecating permanent deformation resistance of asphalt mixtures 1.7 Research methodology Combining between theoretical method and experimental method RESEARCH AND PROPOSE THE METHOD FOR DESIGNING AGGREGATE BLEND OF ASPHALT MIXTURES TAKING INTO ACCOUNT THE FORMATION OF COARSE AGGREGATE SKELETON Chapter research to clarify the role of coarse aggregate skeleton in forming permanent deformation resistance of asphalt mixture, and also studies and proposes a method of designing aggregate blend of asphalt mixtures taking into account the formation of coarse aggregate skeleton - Bailey method 2.1 Principle of strength formation of asphalt mixture and role of coarse aggregate skeleton in forming strength of asphalt mixture 2.1.1 Principle of strength formation of asphalt mixture According to professor NN Ivanop [5], the shear strength of the asphalt mixture depends on two factors including the friction force of mineral aggregates and the adhesive force between the bitumen and the mineral aggregate, and internal cohesive of the bitumen and the interlock between the coarse aggregate particles According to the literature [54], the shear strength of concrete is contributed by mineral aggregates and bitumen The Mohr - Coulomb equation can be used to show how these two materials contribute to the shear resistance of asphalt mixture The shear strength of asphalt mixtures can be improved by mixing the aggregate blend to form contact between coars aggregate particles 2.1.2 The role of coarse aggregate and coarse aggregate skeleton in the strength formation and permanent deformation resistance of asphalt mixtures Aggregate skeleton plays an important role in forming strength and creating stability of asphalt mixture especially in high temperature conditions The asphalt mixture with a good aggregate skeleton will ensure the resistance to rut, reduce deformation, thereby increasing the Figure 2.2 Stress transmission in service life and improving the the aggregate skeleton operation quality To ensure having aggregate interlocks creating coarse aggregate skeleton to resist permanent deformation, it is necessary to design a asphalt mixture with a coarse aggregate skeleton 2.2 Theory of aggregate grading and design methods of asphalt mixtures 2.2.3 Design methods of asphalt mixtures Design of asphalt mixture is an experimental process to select a reasonable aggregate blend and find the optimal bitumen content to satisfy two factors including volumetric properties and mechanical properties Asphalt concrete design methods used commonly in the world such as Marshall and Superpave methods basically follow this principle 2.3 Guidelines for selecting coarse gradings according to Vietnamese specifications Standards and specifications for design, construction and acceptance of asphalt pavements in Vietnam in different stages have addressed the issue of “coarse aggregate” in many ways Decision 858/QĐ-BGTVT introduces a new concept called coarsely graded dense asphalt concrete, with the definition of coarse grading conforming with Table 2.1 and satisfying the passing percent of the control sieve in Table 2.2 2.4 The basis for designing aggregate grading of dense asphalt mixtures taking into account the formation of coarse aggregate skeleton In the traditional asphalt mix design, coarse aggregate are defined as the aggregates retaining on sieve No (4.75mm sieve size), and fine aggregates are the aggregates passing through this sieve With the concept of mixing design to create a coarse aggregate skeleton, coarse aggregates are defined as aggregates having large size and when put into the volumetric block creating voids; fine aggregates are aggregates filling in the voids of coarse aggregates On the basis of this definition, the study of Varik [55] has synthesized the analysis of planar geometry for the shape types of coarse aggregates Considering the fact that the coarse aggregate particles can have different shapes, if we take the average of the calculated rates in all cases, we get the 10 2.7 Conclusion for Chapter - On the basis of 2D geometric analysis of aggregate structure from the point of view of forming the coarse aggregate skeleton, it is possible to propose a sieve size separating coarse and fine aggregates of 2.36mm for asphalt mixtures with maximum nominal particle size of 12.5mm - The Bailey method is an aggregate grading design method that refers directly and according to the principle of ensuring the formation of a coarse aggregate skeleton - With aggregate sources of two rather typical quarries in the North, Thong Nhat quarry - Hai Duong and Sunway quarry - Hanoi, successfully designed the aggregate grading for two asphalt mixture BTNC 12.5 according to the method Bailey, completely satisfying the required aggregate grading according to TCVN 8819: 2011 and basically satisfying the required aggregate grading according to the Decision 858/QD-BGTVT EXPERIMENTAL RESEARCH FOR ASSESSMENT OF THE EFFECTS OF AGGREGATE GRADING AND COARSE AGGREGATE SKELETON ON PERMANENT DEFORMATION OF ASPHALT MIXTURES Chapter investigates the influence of aggregate grading and content of coarse aggregate forming skeleton on the resistance to permanent deformation of asphalt mixtures BTN 12.5 using wheel rutting test and creep test The asphalt mixtures BTN 12.5 are made from two aggregate sources as mentioned above 3.1 Test plan 3.1.1 Materials The materials used to make asphalt mix specimens in the study include: - Coarse aggregate and fine aggregate include different sources as follows: source – limestone in Thong Nhat quarry, Kinh Mon district, Hai Duong province; source – basalt in Sunway quarry, Quoc Oai district, Hanoi city; - Mineral filler: mineral filler is crushed from limestone of Hong Lac enterprise, Hai Duong province; - Bitumen: bitumen 60/70 – Shell Singapore imported by Petrolimex Coarse aggregates, fine aggregates is sieved into separate size groups by standard sieve sets 3.1.2 Selection of asphalt mixtures with typical coarse aggregate skeleton characteristics Each aggregate source, asphalt mixtures of BTN 12.5 with different aggregate grading and coarse aggregate content (d≥2.36mm) were selected in the study In which, with aggregate grading of the mixture CP4 is designed according to Bailey method The aggregate grading of the asphalt mixtures of BTN 12.5 is shown in Table 3.1 and Figure 3.1 11 Figure 3.1 Grading curve of the asphalt mixtures BTN12.5 in the study 3.1.3 Experiment for evaluating permanent deformation properties of the asphalt mixtures Wheel tracking test and creep test were chosen to evaluate permanent deformation properties of asphalt mixtures The wheel tracking test was carried out in water at 50 o C with 20,000 passes The specimen of rectangular plate shape with dimensions of 320x260x50mm is manufactured by roller compaction with content of air voids in accordance with the Decision 1617 Manufacturing specimens and wheel rutting tests were carried out in the LAS-XD 1256 laboratory - University of Transport and Communications The creep test was carried out with a pressure of 200 kPa at 30 o C and 60 o C for hour (3600 s), then unloaded and continued to monitor the strain for 15 (900 s) Marshall specimens with diameter of 101 mm and height of about 63.5 mm is used for creep test The experiment was carried out by Cooper's equipment in the laboratory of Building Materials Devision - University of Transport and Communications Figure 3.2 Wheel tracking test Figure 3.2 Creep test 3.2 Composition design and specimen manufacture 3.2.1 Component material evaluation test Coarse aggregates, fine aggregates, mineral filler and bitumen were tested 12 according to the current specifications of Vietnam in the laboratory LAS-XD 1256, University of Transport and Comunications These materials meet the technical requirements for materials manufacturing asphalt mixtures according to Vietnam's current standards 3.2.2 Design of asphalt mixture composition The composition of asphalt mixtures BTN 12,5 were designed according to the Marshall method in accordance with Vietnamese standards TCVN8820:2011 [2], TCVN 8819:2011 [1] and Decision 858/QD-BGTVT [3] The optimal bitumen content is selected so that the mixture has a air void content of about 4.0%, other technical criteria are in accordance with the specifications 3.2.3 Test specimen production for wheel tracking test and creep test Figure 3.4 Specimens for wheel tracking test Hình 3.5 Specimens for creep test 3.3 Test results – analysis and evaluation of test results 3.3.1 The results and analysis for the wheel tracking test The results of wheel tracking test at 20,000 passes of the mixtures met the precision requirements assessed according to ASTM C670-2015 The wheel tracking rut depths at 20,000 passes of the mixtures are all less than the limit value of 12.5 mm specified in Decision 1617/QDBGTVT Wheel tracking rut depths at 20,000 passes of the mixtures made from Figure 3.19 Resultant chart of rut depth of asphalt mixtures at 20,000 passes aggregates of Sunway quarry are significantly smaller than those made from aggregates of Thong Nhat quarry The mixture CP4 (aggregate grading designed according to Bailey method) has the lowest rut depth at 20,000 passes for both aggregate sources This can be seen as an advantage of the Bailey method to select a reasonable content of 13 coarse aggregate The wheel tracking rut depth at 20,000 passes and the content of coarse aggregate forming skeleton (d2.36mm) have a close parabolic relationship (Equation (3.1) and Equation (3.2)) Wheel tracking rut depth is minimum at the coarse aggregate content d2.36 = 64.46% 3.3.2 Results and analysis of creep test results 3.3.2.2 Analysis and evaluation of creep test results a Creep stiffness The results of creep stiffness of asphalt mixtures meet the requirements of precision assessed according to ASTM C670-2015 The analysis shows that the temperature factor and content of coarse aggregate d2.36 have effects on creep stiffness, Figure 3.17 Resultant chart of creep stiffness while the type of rock has no of asphalt mixtures influence on creep stiffness of the mixtures As the temperature increases, the creep stiffness of the mixtures decreases With the mixtures made from aggregates of Thong Nhat quarry, the creep stiffness of the CP4 mixture is highest at both test temperatures With the mixtures made from aggregates of Sunway quarry, the CP1 mixture showed the greatest creep stiffness at both test temperatures Althought the creep stiffness of the CP4 mixture is smaller than that of the CP1 mixture, the difference is insignificant Creep stiffness and content of coarse aggregate forming skeleton d2.36 have a close quadratic relationship as shown in Equation (3.3) Creep stiffness is highest at coarse aggregate content d2.36 = 66.08% b Total strain The results of total strain of the asphalt mixtures meet the requirements of the precision assessed according to ASTM C670-2015 14 The analysis shows that the two factors including temperature and content of coarse aggregate d2.36 have an influence on the total strain, while the factor of rock type does not affect the total strain of the mixtures As the temperature increases, the total strain of the asphalt mixtures Figure 3.19 Resultant chart of total strain of increases With the mixtures asphalt mixtures made from aggregates of Thong Nhat quarry, the total strain of the CP4 mixture is smallest at both test temperatures With the mixtures made from aggregates of Sunway quarry, the CP1 mixture showed the smallest total strain at both test temperatures Althought the total strain of the CP4 mixture is higher than that of the CP1 mixture, the difference is insignificant Total strain and content of coarse aggregate forming skeleton d2.36 have a close quadratic relationship as shown in Equation (3.4) Total strain is smallest at coarse aggregate content d2.36 = 66.24% c Permanent strain The results of permanent strain of the asphalt mixtures meet the requirements of the precision assessed according to ASTM C670-2015 The analysis shows that the three factors including rock type, temperature and content of coarse aggregate d2.36 have an influence on the permanent strain The permanent strains of the asphalt mixtures made from Sunway quarry are smaller than those of the asphalt mixtures made from Thong Figure 3.121 Resultant chart of permanent Nhat quarry As the strain of asphalt mixtures temperature increases, the permanent strain of the asphalt mixtures increases With the mixtures made from aggregates of Thong Nhat quarry, the permanent strain of the CP4 mixture is smallest with both test temperatures With the mixtures made from aggregates of Sunway quarry, the CP1 mixture showed the smallest permanent strain at both 15 test temperatures Althought the permanent strain of the CP4 mixture is higher than that of the CP1 mixture, the difference is insignificant Permanent strain and content of coarse aggregate forming skeleton d2.36 have a close quadratic relationship as shown in Equation (3.5) and (3.6) Permanent strain is smallest at coarse aggregate content d2.36 = 66.23% d Slope of the steady-state portion of creep curve The results of slope of creep curve of the asphalt mixtures meet the requirements of the precision assessed according to ASTM C670-2015 The analysis shows that the three factors including rock type, temperature and content of coarse aggregate d2.36 have an influence on the slope of creep curve The slope of creep Figure 3.121 Resultant chart of slope of creep curve of asphalt mixtures curve of the asphalt mixtures made from Sunway quarry are smaller than those of the asphalt mixtures made from Thong Nhat quarry As the temperature increases, the slope of creep curve of the asphalt mixtures decreases With the mixtures made from aggregates of Thong Nhat quarry, the slope of creep curve of the CP4 mixture is smallest at both test temperatures With the mixtures made from aggregates of Sunway quarry, the CP1 mixture showed the smallest slope of creep curve at both test temperatures Althought the slope of creep curve of the CP4 mixture is higher than that of the CP1 mixture, the difference is insignificant Slope of creep curve and content of coarse aggregate forming skeleton d2.36 have a close quadratic relationship as shown in Equation (3.7) and (3.8) Slope of creep curve is smallest at coarse aggregate content d2.36 = 71.14% 3.4 Conclusion for Chapter - The source of aggregate has the significant effect on the rut depth or the 16 resistance to wheel rutting The asphalt mixtures made from aggregates of Sunway quarry has better resistance to wheel rutting than the mixtures made from aggregates of Thong Nhat quarry With the same aggregate source, the mixture with aggregate composition designed according to Bailey method has the best wheel rutting resistance The rut depth and the content of coarse aggregate forming skeleton have a close quadratic relationship, shown by the empirical regression equations (3.1) and (3.2) with the coefficient R đc = 94.61% It is clear that there exists a coarse aggregate content for minimum rut depth, which is the minimum of the regression equations Wheel tracking rut depth is minimum at the coarse aggregate content d2.36 = 64.46% - Besides the rut depth, the content of coarse aggregate forming skeleton also affects the deformation development, shown by the deformation curve according to the number of loaded wheel passes Mixtures with a high content of coarse aggregate quickly reach the steady state, where the deformation rate is small, which is considered the starting point of the sideways trend of the curve - From the creep test results, the characteristics of creep curve include: total strain (%), permanent strain (%), slope of creep curve (%/s) and creep stiffness (MPa) were synthesized to analyze and evaluate influencing factors The analysis results show that the rock type factor has no obvious effect on creep stiffness and total strain, but effects on permanent deformation and slope of creep curve While, factors of temperature and content of coarse aggregate forming skeleton influence all characteristics of creep curve The parameters of creep test have close relationships with the coarse aggregate content and temperature, shown by the experimental regression equations from (3.3) to (3.8) with R adj > 69 % These empirical regression equations show the quadratic relationship between the parameters of creep test and the coarse aggregate content forming skeleton It can be clearly seen that there exists values of coarse aggregate content for extremum of creep parameters: maximum creep stiffness; minimal total deformation and permanent strain; minimum slope of creep curve The content of coarse aggregate forming skeleton (d≥2.36mm) for the maximum creep stiffness, minimum total strain and permanent strain and minimum slope of creep curve range from 64.24% to 71.14%, the average of 66.92% INTERNAL STRUCTURE OF ASPHALT MIXTURE AND PERMANENT DEFORMATION RESISTANCE Chapter determines aggregate structure indexes of the asphalt mixtures by IPAS-2 software - a specialized image processing and analysis software for asphalt mixture From the test results and image analysis results, it is expected to find out the relationship between the aggregate structure indexes and the content of coarse aggregate forming skeleton and the correlation between the aggregate structure indexes and the mechanical parameters expressing the 17 permanent deformation resistance of the asphalt mixture 4.1 Image analysis method for determination of the internal structure of asphalt mixture 4.1.1 Characteristic indicators for the internal structure of asphalt mixtures The internal structural indexes of asphalt mixtures are interest to research including air void content, air void distribution, particle shape, orientation and distribution of aggregate particles and contact properties between aggregates In which, the internal structural indexes are believed to represent the permanent deformation resistance of the asphalt mixture including the number of contact, the length of the contact, the direction of contact between the aggregates 4.2 IPAS-2 software – image processing and analysis software for determination of the internal structure of asphalt mixtures 4.2.1 Introduction of IPAS-2 software IPAS-2 (Image Processing and Analysis System) software was developed by the University of Wisconsin - Madison and the Michigan State University to process and analyze images for determination of the internal structure of asphalt mixtures The cross-section images of asphalt concrete used for analysis are digital images obtained by digital Figure 4.2 Interface of IPAS-2 software cameras or scanners – very common devices today The software can determine some internal structural properties of the concrete such as the orientation of the aggregate particles, the segregration of the aggregates, as well as the structural parameters for assessment of the contact between the aggregates such as the number of contact, the contact length, the contact direction The IPAS-2 software interface is shown in Figure 4.2 4.2.2 Principle of analysis method for determination of the internal structure of asphalt mixtures by IPAS-2 software The RGB color image is converted to the gray scale image because there is a significant difference between the color intensity of the aggregate particles and the color intensity of the mastic and air voids in the gray scale image Then the threshold filtering algorithm is used to separate the aggregate particles out mastic and air void Separated images were used to determine the internal structure of the asphalt mixtures To increase image quality for phase separation, filtering techniques were used in IPAS-2 software 4.2.3 Analysis of the internal structure of asphalt mixtures by IPAS-2 The process of image analysis for determination of the internal structure of the 18 asphalt mixtures by IPAS-2 software is shown in Figure 4.5 Figure 4.5 Steps for analysis of the structure of the asphalt mixture by IPAS-2 The processing of digital images in IPAS-2 software is shown in Figure 4.6 4.2.4 The aggregate structure parameters in asphalt mixtures determined by IPAS-2 software - Contact and determination of contact lines: two aggregate particles are considered to be in contact when the distance between their perimeter pixels is less than a predetermined value This distance is chosen so as to not significantly affect the total number of contacts in the image (0.2 mm in this study) Figure 4.6 Diagram of the image The contact line between the two processing in IPAS-2 software aggregate particles is made up of pixels located in the middle of each pair of perimeter pixels of the two aggregates The number of contact is determined when there is contact between two aggregates and there is only one contact between two adjacent aggregates - The orientation of contact between aggregates: is characterized by the angle between the normal of the contact line and the horizontal axis (the axis being perpendicular to the direction of force) The interlock between aggregate particles can be determined more precisely by the Figure 4.14 Contact lines and Internal Structure Index (ISI) – a orientation in a asphalt mixture parameter determined from the contact length and contact orientation according to Equation (4.1): Where N is the number of contacts in the aggregate skeleton, Contact length i and AA Ci are the contact length and angle of the i-th contact, respectively 19 4.3 Apply IPAS-2 software for analysis of the internal structure of asphalt mixture 4.3.1 Specimen preparation for analysis of the internal structure by IPAS-2 AC specimens for analysis of the internal structure were fabricated with the designed composition by Marshall compaction The specimens has the same dimensions as the common Marshall specimens with diameter of 101.6mm and height of about 63.5mm The specimens is cut vertically by a specialized stone cutter Each specimen was cut at positions dividing the sample into pieces with cross-sections as shown in Figure 4.15 Then digital images of the cross-sections of the specimens are obtained by the scanner 4.3.2 The results of determining the internal structure of AC by IPAS-2 Internal structure indexes of asphalt mixtures are determined including number of contact, contact length, ISI structure index Since the dimensions of each section are different, the value of each sample is a weighted average of the areas of the six sections The internal structure indexes of each mixture are the average of the samples The single test results of the number of contact, contact length, and ISI structure index of the concrete mixtures meet the requirements for precision assessed according to ASTM C670-2015 4.4 Analysis and evaluation of the results of the internal structure indexes of asphalt mixtures determined by IPAS-2 software 4.4.1 ISI structure index The analysis shows that the coarse aggregate content factor d2.36 has an effect on the ISI structure index, while the rock type factor has no effect on the ISI index of the mixtures The mixture CP4 has the largest ISI structure index with both aggregate sources There is a close quadratic Figure 4.16 Resultant chart of ISI relationship between the ISI structure index of asphalt mixtures structure index and the content of coarse aggregate forming skeleton d2.36 as 20 shown in Equation (4.2) ISI structure index is largest at coarse aggregate content d2.36 = 66.93% 4.4.2 Contact number index The analysis shows that both factor including the rock type and the content of coarse aggregate d2.36 have an influence on the contact number index The contact number index of the asphalt mixtures made from Sunway quarry are higher than those of the asphalt mixtures made from Thong Figure 4.19 Resultant chart of contact number index of asphalt mixtures Nhat quarry The mixtures CP4 have the highest contact number index with both aggregate sources There is a close quadratic relationship between the contact number index and the content of coarse aggregate forming skeleton d2.36 as shown in Equation (4.3) and (4.4) Contact number index is largest at coarse aggregate content d2.36 = 64.84% 4.4.3 Contact length index The analysis shows that the content of coarse aggregate d2.36 has an influence on the contact length index, while the rock type factor does not affect the contact length index The mixtures CP4 have the higgest contact length index with both aggregate sources Figure 4.21 Resultant chart of contact length index of asphalt mixtures There is a close quadratic relationship between the contact length index and the content of coarse aggregate forming skeleton d2.36 as shown in Equation (4.5) Contact length index is largest at coarse aggregate content d2.36 = 62.50% 21 Comment: - The results show that mixtures CP4 with aggregate grading designed according to Bailey method have the largest structure indexes of contact number, contact length and ISI index with both aggregate sources - The aggregate structure indexes determined by image analysis and the content of coarse aggregate forming skeleton (d ≥ 2.36mm) have a close quadratic relationship (shown from Equation (4.2) to Equation ( 4.5)) There exists a coarse aggregate content for the largest structure indexes 4.5 Relationship between structure indexes and the mechanical parameters expressing the permanent deformation resistance of the asphalt mixture 4.5.1 Relationship between structure indexes and wheel tracking rut depth The relationship between the wheel rut depth at 20,000 loaded passed and the internal structure indexes of the asphalt mixture is shown in Figure 4.23 The results show that the wheel rut depth has a quite close relationship with the aggregate structure indexes of asphalt mixtures in both aggregate sources Wheel rut depth tends to decrease as the number of contacts, contact length and ISI structure index increase 4.5.2 Relationship between structure indexes and creep properties of asphalt mixture at 60 o C The strength of bitumen decreases when temperature increases, and the role of aggregate and aggregate skelton in resistance to deformation will be more evident at high temperature Therefore, creep properties of the asphalt mixture at 60 o C including total strain, permanent strain and creep stiffness were selected to establish correlation with aggregate structure indexes The correlation between the aggregate structure indexes and creep stiffness, total strain, and permanent strain at 60 o C of the asphalt mixtures is shown from Figure 4.24 to Figure 2.26 The results show that the aggregate structure indexes have a quite good relationship with creep test parameters As the number of contacts, contact length and ISI structure index increase, creep stiffness tends to increase, total strain and permanent strain tend to decrease 22 4.6 Conclusion for Chapter - The internal structure indexes of the asphalt mixtures have a close correlation with the coarse aggregate content as shown in the empirical regression equations from (4.2) to (4.5) with R adj > 74% The empirical regression relationship between the internal structure indexes and content of the coarse aggregate forming skeleton has a quadratic function Therefore, it is clear that there exists a content of coarse aggregate forming skeleton for the highest internal structure indexes - The content of coarse aggregate forming skeleton (d≥2.36mm) for the largest internal structure indexes ranges from 62.50% to 66.93%, average of 64.76% The mixtures with aggregate blending designed by Bailey method have the highest aggregate structure indexes This result confirms the advantage of Bailey method in designing a mixture with a good bearing aggregate skeleton - The structure indexes of the bearing aggregate skeleton determined by image analysis have a close correlation with the wheel rut depth as well as the creep characteristics When the aggregate structure indexes determined by image analysis increase, the wheel track rut depth tends to decrease, creep stiffness tends to increase, total strain and permanent strain tend to decrease 23 CONCLUSIONS Conclusions The thesis has some new contributions in terms of science and practice Scientific contributions The concept of "content of coarse aggregate forming skeleton" has been introduced in the study to find out and confirm the relationship between this criterion of the aggregate blend and the permanent deformation properties of the asphalt mixture Research and successfully apply Bailey method in designing the aggregate grading of asphalt concrete Study and successfully apply image analysis method using IPAS-2 software to analyze the cross-section of asphalt concrete specimens, determine the criteria: ISI structure index, number of contact, contact length Research to demonstrate the relationship between the aggregate structure indexes obtained from image analysis and the content of coarse aggregate forming skeleton, and the relationship between them and the permanent deformation characteristics of asphalt concrete Practical contributions Conduct an experimental research program by wheel tracking test and creep test with 10 asphalt mixture BTN 12.5mm having different content of coarse aggregate forming skeleton (d≥2.36mm), and it has been demonstrated that the content of coarse aggregate forming skeleton has an effect on the resistance to permanent deformation of asphalt concrete Conduct experimental research and prove that the asphalt mixtures with aggregate composition designed according to Bailey method have the lowest wheel rut depth at 20,000 loaded passes, the largest creep stiffness, and the smalest total strain, permanent strain and creep slope Establish experimental correlations between the wheel rut depth, creep stiffness, total strain, permanent strain, creep slope of the asphalt mixtures BTN 12.5 and the content of coarse aggregate forming skeleton as shown in equations from (3.1) to (3.8) These correlations are quadratic functions with high coefficients of determination expressing the close correlations, indicating that there exists a range of coarse aggregate content for the best permanent deformation resistance With the results of this initial study, it can be seen that the content of coarse aggregate forming skeleton (d≥2.36mm) of the asphalt mixtures BTNC 12.5mm for the best permanent deformation resistance ranges 65%  5% (i.e from 60% to 70%) Use IPAS-2 software to analyze cross-sectional images of asphalt mixtures and determine the aggregate structure indexes including ISI structure index, number of contacts, contact length of the asphalt mixtures BTN 12.5mm Researche and establish correlation between aggregate structure indexes and 24 the mechanical parameters expressing the permanent deformation resistance of asphalt mixtures The results show that there exists a fairly close linear relationship between them When the ISI structure index, number of contacts, and contact length increase, the wheel rut depth tends to decrease, creep stiffness tends to increase, total strain and permanent strain tend to decrease Establish experimental correlations between the aggregate structure indexes obtained from image analysis and the content of coarse aggregate forming skeleton as shown in equations from (4.2) to (4.5) These correlations are quadratic functions with high coefficients of determination expressing the close correlations, indicating that there exists a range of coarse aggregate content for the highest aggregate structure indexes With the results of this initial study, it can be seen that the content of coarse aggregate forming skeleton (d≥2.36mm) of the asphalt mixtures BTNC 12.5mm for the best aggregate structure indexes ranges 65%  5% (i.e from 60% to 70%) The results from the study of analyzing cross-section images of the asphalt concrete specimen using IPAS-2 software also show the possibility of using this method and structure indexes in evaluating the quality of the asphalt mixture Image analysis results show that asphalt mixtures with aggregate composition designed by Bailey method have the highest aggregate structure indexes This result confirms the advantage of the Bailey method in designing the asphalt mixture with a good bearing aggregate skeleton Recommendations and directions for further study - Expand the scope of research with aggregates in some other typical quarries and the asphalt mixtures BTNC 19 - a type of asphalt mixture commonly used for the binder course in asphalt concrete pavement in Vietnam - Carry out experiments to evaluate the permanent deformation of asphalt mixture using the confined repeated load test - the test having a good simulation of the actual bearing conditions of the asphalt concrete pavement - Investigate the influence of the content of coarse aggregate forming skeleton d≥2.36mm on the fatigue resistance of the asphalt mixture in order to find a range of coarse aggregate content for a good asphalt mixture in both resistance to permanent deformation and fatigue - Study the relationship between the aggregate structure indexes and the permanent deformation resistance as well as other mechanical properties of the asphalt mixtures with the other nominal maximum particle size and some other aggregate sources - Study and develop an image processing and analysis software to determine volumetric properties and aggregate structure of asphalt mixtures, and apply analysis method of image analysis for drilled specimens from the pavement to assess the asphalt mixture quality ... 1.2.1 Instability rutting The instability rutting appears on a narrow range along the wheel paths with humps formed on the sides of the rut as shown in Figure 1.7 This rutting is due to the fact... road surface 1.2.2 Strutural Rutting The structural rutting occurs at the wheel paths over a wide range and does not form humps along the wheel track This kind of rutting is due to the accumulation... operation period 1.2.3 Surface/Wear Rutting Wear rutting occurs at the wheel paths on a narrow range and does not form humps along the wheel track This kind of rutting is due to the fact that asphalt