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Study on Marshall Design parameters of porous asphalt mixture using limestone as coarse aggregate
Construction and Building Materials 124 (2016) 846–854
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Study on Marshall Design parameters of porous asphalt mixture using limestone as coarse aggregate Bin Xu, Jingyun Chen, Changhong Zhou ⇑, Weiying Wang Dalian University of Technology, No. 2 Road Linggong, Ganjingzi District, Dalian, Liaoning 116024, PR China
h i g h l i g h t s Limestone is used as the coarse aggregate to mold the porous asphalt mixture. The properties of porous asphalt mixture using limestone as coarse aggregate are measured and analyzed. The optimal Marshall molding parameters of porous asphalt mixture using limestone as coarse aggregate is proposed. It provides support for the design and construction of porous asphalt using limestone as coarse aggregate.
a r t i c l e
i n f o
Article history: Received 9 May 2016 Received in revised form 1 August 2016 Accepted 3 August 2016
Keywords: Porous asphalt mixture Marshall Design Method Compaction temperature Number of compactions
a b s t r a c t Porous asphalt pavement is defined as an asphalt concrete with air voids content of around 20% and capable of forming drainage channels inside the mixture. It consists of an open-graded asphalt mixture composed predominantly of embedded-occluded single-sized macadam from interlocking processes, and is also known as porous asphalt mixture. In China, Marshall Design Method for porous asphalt mixture is the most widely used mixture design method for laboratory experimental study at present. The main parameters of Marshall Design Method are compaction work (number of compactions) and compaction temperature, i.e. this method can work out the air voids content meeting the performance requirements under uniform standard compaction work and given range of compaction temperature in practice. However, on account of different climates and traffic volumes, the molding parameters of Marshall Design shall be adjusted correspondingly to satisfy the pavement performance of mixture. For this purpose, limestone, which is of relatively low strength, is used as aggregate in porous asphalt mixture for experimental study, and the feasibility of limestone used in porous asphalt is also analyzed and verified. By analyzing the influences of Marshall molding parameters (compaction temperature and number of compactions) on the air voids content of porous asphalt mixture, the ranges of molding parameters of Marshall Design Method suitable for porous asphalt using limestone as coarse aggregate is found. Through analyzing the influence rules of Marshall molding parameters (compaction temperature and number of compactions) on the properties of porous asphalt mixture (high temperature stability, water stability and low temperature stability), combining with the ranges of molding parameters calculated with air voids content, the molding parameters for the Marshall test specimen applicable to the limestone porous asphalt mixture in Chinese region is proposed. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction Porous asphalt pavement has the technical features of good anti-slipping performance, low noise, restraining water splash and spray on rainy days, mitigating glaring lights when driving on the night and so on, because of the large air voids content contents which is around 20% and permeable skeleton inside the mixture [1,2]. ⇑ Corresponding author. E-mail address: [email protected] (C. Zhou). http://dx.doi.org/10.1016/j.conbuildmat.2016.08.005 0950-0618/Ó 2016 Elsevier Ltd. All rights reserved.
The porous asphalt pavement, developed in 1960s, was mainly applied to improve driving safety on the road surface, and reduce the traffic noise in populous regions and those with dense road network [3]. In the United States (US), open-graded friction course (OGFC) with large air voids content (higher than 15%) was developed to improve the anti-slipping performance of the freeways pavement [4]. In the 1980s, the porous asphalt technique was imported from Europe to Japan. In combination with the local climate and transport conditions, a specific porous asphalt technique was formed and extensively promoted in Japan. The research and application of porous asphalt in China were started in 1980s.
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Now the high-viscosity modified asphalt is mainly adopted as the binder to improve the anti-raveling performance. So far, porous asphalt pavement has been applied in more than ten provinces, and the total length of porous asphalt section is over 300 km. Marshall Design Method was established between the end of 1950s and the beginning of 1960s. The theoretical basis for this method is that the density of test specimen obtained in laboratory with certain compaction energy is equal to the final density of asphalt pavements which have been used for many years [5]. The design concept of asphalt mixture in China’s current Design Specification [6] is: using Marshall Design Method to work out the air voids content which meets the performance requirements under uniform standard compaction power and given range of compaction temperature. However, for the porous asphalt mixtures used in different regions or different conditions, the design method proposed in the Specification [6] is not always applicable, for example, pavements bearing heavy and light traffics require different mechanical strengths of the mixture, and the differences in climatic conditions in the southern and northern parts of China also result in different requirements for high-and-low temperature performance. The Specification [7] indicates that the number of compactions (double-side) for dense graded asphalt mixture in Marshall test design is 75, the numbers of compactions (double-side) for SMA mixture and OGFC mixture are 50, and the compaction temperature is basically 150 °C ± 5 °C; However, it does not show the specific parameters requirements for different climates and different traffic volumes. Most studies have discussed different molding methods of the asphalt mixtures and their physical and mechanical properties difference, for example: Li Hanguang [8] compared various performances between the asphalt mixture fabricated in laboratory with different molding modes and the asphalt test specimens directly ground on the site; Xu Haijing [9] studied the factors which may influence the compaction quality of asphalt pavement; Cao Lintao [10] determined the number of rolling passes of the asphalt pavement required for reaching certain compaction degree from the perspective of energy equivalence on the basis of studying the compaction properties of asphalt mixture. However, there are few researches on the design parameters of the molding method. In this study, the traditional Marshall test method is adopted, and porous asphalt specimens with the same gradation are prepared. The limestone aggregates are collected locally. The influence rules of Marshall Design parameters (number of compactions and compaction temperature) on the high and low temperature stabilities and water stability of molded test specimens are investigated. The compaction effect of porous asphalt mixture is evaluated to provide theoretical basis for the site compaction technology of limestone porous asphalt pavement.
2. Materials and test methods 2.1. Materials 2.1.1. High-viscosity modified asphalt Porous asphalt is different from ordinary asphalt mixture in structure and certain pavement performances: coarse aggregates with large specific gravity are used to form a skeleton-pore structure spatially, which provides high compressive strength. In the meantime, due to small contact area of coarse aggregate in the mixture, ordinary asphalt or common modified asphalt is insufficient to cement the aggregates. High-viscosity modified asphalt is thus required to enhance the bonding effect and eliminate the influences of the small contact area of aggregates on the tensile strength and shear strength of mixture. Existing experimental studies indicate that: he performance of the mixture at
Table 1 Properties of high viscosity asphalt binder. Test item
Unit
Values
Penetration (25 °C, 100 g, 5 s) Softening point Ductility (5 cm/min, 25 °C) Quality loss after thin-film heating test Penetration ratio after thin-film heating test Toughness 60 °C dynamic viscosity
0.1 mm °C cm % % Nm PaS
74 114 103 0.06 78.2 23 215,368
high-and-low temperature can be greatly improved by using high-viscosity modified asphalt, compared with normal modified asphalt materials; it also satisfies the high flaking resistance (the material will not flake even though contacting with water for a long time), and significantly improves the cohesiveness of the mixture particles. The porous asphalt using high-viscosity modified asphalt also shows advantages under high temperature and heavy traffic conditions. The performance indices of high-viscosity modified asphalt are shown in Table 1. 2.1.2. Limestone In porous asphalt mixture, the aggregates shall be uniform, clean and dry. Important properties for coarse aggregates include the content of elongated and flaky particles, crushed stone value and Los Angeles abrasion loss. In this research, taking into account the costs of road materials (the price of basalt purchased from other places is 170 CNY/ton, while the price of limestone produced locally is 85 CNY/ton) and the large output of limestone in certain region, limestone is thus selected as the coarse aggregate of porous asphalt mixture in this research, provided that all properties of the selected limestone meet the relevant technical requirements. The tested performances of limestone are shown in Table 2. 2.2. Gradation The content of coarse aggregate of common porous asphalt mixture (above 4.75 mm) is generally more than 80%. For guaranteeing the performance of porous asphalt mixture, basalt is usually used as coarse aggregates in China, which shows not only excellent mechanical properties but also high price. In this study, basalt aggregate is replaced with limestone, and the aggregate gradation is also adjusted correspondingly, as shown in Table3. In the paper, PA-L is defined as porous asphalt mixture using limestone as coarse aggregate. 2.3. Test design For the Marshall compaction molding, there are two important influence factors: number of compactions and compaction temperature. The experiment design level refers to the specific state or condition of the factors during the experiment. Five levels are used in this experiment: 35, 42, 50, 57 and 65 for the number of compactions, and 125 °C, 135 °C, 145 °C, 155 °C and 165 °C for the compaction temperature. Suppose all these numbers of compactions and compaction temperatures to match with each other
Table 2 Performances of limestone aggregate. Test item
Unit
Values
Crushing value Quality loss of Los Angeles abrasion test Bulk specific gravity Water absorption Flat and elongated particle ratio (>9.5 mm)
% %
18.73 29 2.57 0.56 5.46
% %
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Table 3 Gradation of porous asphalt in this study. Mixtures
Passing (by Mass) under different sieve size (mm)/% Limestone
PA-L
AR/% Sand
13.2
9.5
4.75
2.36
1.18
0.6
0.3
0.15
0.075
100
91.6
43.9
12.0
12.0
10.5
7.9
6.2
4.6
3.0
at every level, we will carry out 52 = 25 experiments. Taking into account this complicated operations, the uniform design method [11] is used to design the laboratory experiment, so as to cover the representative combinations with less experiments, and accomplish the analysis and verification of test rules. The experiment design is based on uniform design table, and each uniform design table has a code U n ðqs Þ or U n ðqs Þ: in which, ‘‘U” refers to uniform design, ‘‘n” refers to the number of times of the experiments, ‘‘q” refers to the levels of each factor, and ‘‘s” refers to the number of columns of this table. Adding and not adding ‘‘⁄” on the top right corner of U represent two different types of the uniform design tables, and generally the design with ‘‘⁄” has better uniformity. Each uniform design table is attached with a selection table, which indicates how to select proper column from the uniform design table and the uniformity of the test scheme composed of these columns. The uniform design table used in this research is shown in Table 4, and the selection table of the uniform design table U 5 ð53 Þ is shown in Table 5. Table 5 indicates that Columns 1 and 2 shall be selected for the test if there are two experimental factors, and if there are three experimental factors, Columns 1, 2 and 3 shall be selected. In Table 5, D means the discrepancy of the evenness. And when the discrepancy value is smaller, the evenness is better. The five levels of two factors of the molding conditions are combined respectively, and the experiments are arranged by selecting Columns 1 and 2 in Table 5. The combination results can be seen in Table 6. From Table 6, if Marshall specimen is prepared according to the uniform design method, the combinations of low compaction temperature and small number of compactions or high compaction temperature and large number of compactions may appear; in consideration that the uniform experiment data shall be as representative as possible, the high-and-low combinations of compaction temperature and number of compactions shall be discrete as far as possible. In this case, we properly adjust the combination results of uniform experiment, i.e. the larger and smaller data of temperature and number of times are combined discretely. The preparation conditions of the test specimen achieved are shown in Table 7. In the meantime, based on the requirements of JTG F40-2004 Technical Specification for Construction of Highway Asphalt
Table 4 Uniform design table U 5 ð53 Þ.
1 2 3 4 5
Mineral Powder
16
1
2
3
1 2 3 4 5
2 4 1 3 5
4 3 2 1 5
Table 5 Selection table of uniform design U 5 ð53 Þ. S
Column number
D
2 3
1 1
0.31 0.457
2 2
3
4.6
Table 6 Combination of experiment conditions for compacting Marshall specimens with uniform design method. No.
Compaction temperature/°C
Number of compactions/times
1 2 3 4 5
125 135 145 155 165
42 57 35 50 65
(1) (2) (3) (4) (5)
(2) (4) (1) (3) (5)
Table 7 Combination of actual test conditions for Marshall test specimens. No.
Compaction temperature/°C
Number of compactions/times
1 2 3 4 5 6
125 135 145 155 165 155
42 65 50 35 57 50
(1) (2) (3) (4) (5)
(2) (5) (3) (1) (4)
Pavements [7], a group of standard specimen at 155 °C and with 50 compactions (double-side) are prepared to compare with the other test specimens. By combining the molding conditions of mixture with different compaction temperatures and numbers of compactions, several groups of representative combinations are selected for the research. The high temperature performance, water stability and low temperature stability of the porous asphalt mixture under various molding conditions are to be compared. The inherent laws between the molding conditions and mixture performances are considered to be found out in this way. 2.4. Test methods The performances of porous asphalt to be investigated include: the high temperature stability, water stability and low temperature stability of mixture. In this paper, the air voids content is first analyzed, which is the most critical factor of porous asphalt mixture. Trends of air voids content changing with molding condition are investigated by regression analysis. Comparative analyses are carried out on the following properties of the porous asphalt mixture: 2.4.1. High temperature performance This performance is one of the most important factors for evaluating the asphalt pavement performance. For porous asphalt, high temperature stability is mainly based on the skeleton interlocking effect among the coarse aggregates. As only parameters for Marshall specimens are studied in this research, Marshall Stability Test is adopted for the experimental study of high-temperature performance. Marshall Stability test shall be executed by reference to the test method of T 0709-2011 [12].
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2.4.2. Water stability It is inevitable that the large air voids content structure of porous asphalt tends to suffer the repeated erosion of water, and the asphalt film is liable to peel off from the mineral aggregate surface under the repeated effects of hydrodynamic pressure and vacuum suction and scouring of the vehicle loads. Therefore, the water damage resistance property is crucial to the long-term service life of the pavement. The test methods for evaluating the water stability of mixture in this study include: Cantabro Raveling Test, Marshall Test and Freeze-thaw Split test. The Cantabro test was measured according to T0733-2011 method [12].
2.4.3. Low temperature stability For porous asphalt pavement, crack during the service period is a common problem. Low temperature shrinkage and cracking is very common in regions where the temperature in winter is low, especially in north part of China. It will seriously affect the service life and quality of porous asphalt pavement; therefore, it is necessary to investigate the low temperature performance. In this research, Freeze-thaw Split test is adopted to analyze the changing tendencies of these two indices under different molding conditions, and a molding combination best matching this region is to be selected based on regression analysis, so as to meet the low temperature stability requirements of road. Freeze-thaw Split test shall be executed by reference to the test method of T 0729-2000 [12]. The preparation conditions of the test: firstly immerse the Marshall test into water until saturation, place the water saturated test specimen into a refrigerator at 16 °C for 16 h, then place it into water at 60 °C for 24 h (water bath), and finally saturated in another water bath at 25 °C for 2 h.
3. Result and discussion 3.1. Air voids content Air voids content is one of the most important parameters of porous asphalt mixture, which is generally between 18% and 25% in China, which shall meet the national specification JTG F40-2004 [7]. In order to guarantee the permeability, the minimum air voids content in this research is set at 19%. The standard Marshall specimens are made according to the experiment design requirements. Porosities of the specimens produced at different compaction temperatures and numbers of compactions are measured. Combinations of compaction temperatures and compaction numbers which lead to the required air voids content range between 19% and 25% are to be found. The air voids content test results are shown in Table 8. It can be seen that the air voids content data measured from the tests have certain internal relation with different molding conditions of the specimens. The relation diagram of the compaction temperature, number of compactions and air voids content is plotted by means of Matlab software based on binary linear regression, as shown in Fig. 1.
Fig. 1. The relation diagram of compaction temperature, number of compactions and air voids content.
From the fitting analysis, the relational expression (1) of the air voids content, temperature and number of compactions is obtained:
z ¼ 31:4439 0:0801 x 0:0319 y
ð1Þ
where, z is air voids content, x is compaction temperature, and y is number of compactions. In order to analyze whether the linearity of regression equation (1) satisfies the correlation requirements, residual analysis between measured data and fitting data is carried out. Residual is the difference between the actual observed value and regression estimated value. The residual plot of air voids content, temperature and number of compactions of the porous asphalt mixture is shown in Fig. 2. The residual plot shows the distances of the data residuals to the zero point. If the confidence intervals of residuals include the zero point, the regression model preferably conforms to the original data; otherwise, it will be considered as abnormal point. If all the residuals include the zero point, which indicates that the regression equation (1) can preferably fit the experimental data, the regression equation (1) is considered usable. In JTG F40-2004 [7], 50 times of compactions is required for compaction of Marshall test specimen of OGFC mixture in laboratory. with the regression equation (1), if the air voids content value is fixed at 19%, the numbers of compaction are set as 10, 20, 30, 40 and 50 respectively, the corresponding temperature can be calculated (listed in Table 9). otherwise, if the temperatures are set as 160 °C, 150 °C, 140 °C, 130 °C and 120 °C, the corresponding numbers of compactions are also calculated (listed in Table 9). From Table 9, when the number of compactions increases from 10 (minimum) to 50 (standard requirement), the corresponding temperature decreases from 151.6 °C to 135.6 °C. Equivalently, when increasing one compaction, the temperature will decrease by 0.6 °C, i.e. the decreasing value of temperature is 0.6 °C/ compaction. In the case of analyzing the compaction number,
Table 8 Air Voids content test results of PA-L. PA-L 155 °C 125 °C 135 °C 145 °C 155 °C 165 °C
& & & & & &
50 42 65 50 35 57
compactions compactions compactions compactions compactions compactions
Cf (gross volume relative density)
Ct (theoretical
2.121548 2.053047 2.039657 2.057297 2.049212 2.135554
2.535719
minimum relative density)
VV (air voids content/%) 16.33 19.03 19.56 18.87 19.19 15.78
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Fig. 2. Residual plot of air voids content.
Table 9 Calculation sheet of temperature and number of compactions for the molding test of Marshall test specimen (VV = 19%). Set number of compactions
Table 10 Marshall test results. PA-L
Stability MS (KN)
Flow value FL (mm)
Marshall modulus T (KN/mm)
MS mean value (KN)
155 °C & 50 compactions
12.10 11.98
1.99 1.41
6.08 8.50
12.04
125 °C & 42 compactions
6.77 8.72
1.83 2.08
3.70 4.19
7.74
135 °C & 65 compactions
9.01 7.93
1.59 2.24
5.67 3.54
8.47
145 °C & 50 compactions
9.87 11.39
1.81 1.62
5.45 7.03
10.63
155 °C & 35 compactions
10.82 10.34
1.27 1.62
8.52 6.38
10.58
165 °C & 57 compactions
10.32 10.78
1.24 1.99
8.32 5.42
10.55
Set temperature
Number of compactions
Temperature °C
Temperature °C
Number of compactions
10 20 30 40 50
151.6 147.6 143.6 139.6 135.6
160 150 140 130 120
Negative result 14 39 64 89
when the temperature is 160 °C, the number of compactions is negative, which indicates that the result air voids content is lower than 19% and the temperature is too high. When the temperature decreases from 150 °C to 120 °C, the number of compactions will increase from 14 to 89, equivalently, the number of compactions will increase by 2.5 times with the temperature decreasing by 1 °C, i.e. 0.4 °C/compaction. These two groups of data indicate that the influence of temperature on air voids content is greater than that of the number of compactions. In order to satisfy the compaction of PA-L, the temperature of test specimen shall be within the scope of 140–150 °C, and the number of compactions shall be between 20 and 40. In other words, in order to satisfy the air voids content requirement of porous asphalt, the fabrication of test specimen shall be carried out with 145 ± 5 °C and 30 compactions (average between 20 and 40, double-side). 3.2. Stability of porous asphalt mixture The stability of porous asphalt mixture is evaluated according to the Marshall test results. Two main indices are obtained from the test, i.e. flow value and Marshall stability. The flow value means the deformability of mixture under the effect of external forces, and the stability reflects the load bearing condition of the mixture. The porous asphalt mixture is of special skeleton structure, and is mainly made from coarse aggregates which are mutually interlocked without the protection of filled fine aggregate. The overall
strength of porous asphalt is based on the occlusion of aggregates. JTG F40-2004 [7] shows that the Marshall stability of porous asphalt mixture is the lowest among all types of mixtures, the standard requirement of which is not less than 3.5 kN. Marshall test results are given in Table 10. In order to obtain the mathematical model of the relationship among Marshall stability, compaction temperature and number of compactions, multivariate fitting is performed by Matlab7.0. The generated relation is shown in Fig. 3. Based on the fitting diagram, the regression function of stability, expressed by temperature and number of compactions is obtained:
z ¼ 0:0902 x 0:0175 y 2:3533
ð2Þ
where, z is stability, x is compaction temperature, y is number of compactions. In order to check whether the correlation between regression equation (2) and data meets the requirements, residual analysis of the data is executed. The residual plot is shown in Fig. 4. From the residual plot, the confidence intervals of data all include the zero point, which indicates that the regression
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3.3. Cantabro raveling test
Fig. 3. The relation diagram among compaction temperature, number of compactions and Marshall stability.
equation (2) can preferably meet the original data, and the obtained formula is feasible. From various groups of data, PA-L meets the standard requirements: the maximum value is 12.04 kN, the corresponding preparation condition is 155 °C & 50 compactions; the minimum value is 7.74 kN, the corresponding preparation condition is 125 °C & 42 compactions. The temperature difference of these two groups of data is 30 °C, while the difference of the number of compactions is 8. This indicates that the Marshall stability is more sensitive to temperature rather than compaction number. In most of the cases, the stability mainly concentrates between 10 and 11 kN. The stability is calculated by substituting 145 ± 5 °C and 30 compactions into the Eq. (2). The result is 10.2 kN, which also meet the characteristics of measured data. In this study, the Marshall stabilities of test specimens molded under various conditions all meet the standard requirement [7]. The test results show that there are three values of Marshall Stability ranging between (10 and 11) KN, and the calculated Marshall stability also meet this characteristic. It indicates that the test conditions obtained from the air voids content calculation are feasible.
The raveling test is used for evaluating the stripping and scattering degrees of the aggregates from the road surface under the effect of repeated traffic loads. The representation of raveling test is the mass percentage of the scattered asphalt mixture test specimen after rotating and striking the Marshall standard test specimens for certain times in Los Angeles abrasion testing machine. In this research, limestone is used as the coarse aggregate and porous asphalt mixture is prepared in the laboratory. The Cantabro raveling tests are then carried out to find out the ranges of temperature and number of compactions which meet the standard requirements under various conditions. The raveling test data are summarized in Table 11. Matlab7.0 is used to execute multivariate fitting among the number of compactions, compaction temperature and the raveling value. The trend diagram of compaction temperature, number of compactions and raveling value is generated as shown in Fig. 5. With data fitting analysis, the statistical relation among raveling, compaction temperature and number of compactions is obtained as follow:
z ¼ 65:0288 0:3088 x 0:0160 y
ð3Þ
Table 11 Raveling test results of PA-L. PA-L
Mass before test (kg)
Mass after test (kg)
Dm (kg)
Mean value (%)
155 °C & 50 compactions
1058.6 1079.2
946.2 960.3
112.4 118.9
10.82
125 °C & 42 compactions
1080.5 1108.9
859.6 907.3
220.9 201.6
19.31
135 °C & 65 compactions
1101.2 1112.8
772.7 803.1
328.5 309.7
28.83
145 °C & 50 compactions
1085.6 1099.5
851.9 866.6
233.7 232.9
21.35
155 °C & 35 compactions
1096.5 1072.3
797.7 838.4
298.8 233.9
24.53
165 °C & 57 compactions
1113.1 1108.4
1017.3 1008.9
95.8 99.5
8.79
Fig. 4. Residual plot of Marshall stability.
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compactions is less than that by 35 compactions, which shows that under high temperature, the more the number of compaction is, the better the effect of raveling resistance will be. The compaction temperature and number of compactions are calculated for the case which results the 19% air voids content and the 20% raveling loss (the 20% raveling loss percentage is the upper limit value of raveling value specified in JTG F40-2004 [7]), by combining the raveling loss value formula (3) and the air voids content formula (1) into a binary linear equation set.
20 ¼ 65:0288 0:3088 x ðtemperatureÞ 0:0160 y ðnumber of compactionsÞ 19 ¼ 31:4439 0:08 x ðtemperatureÞ 0:0319 y ðnumber of compactionsÞ Fig. 5. The trend diagram of compaction temperature, number of compactions and raveling value.
In which, z is raveling data, x is compaction temperature, and y is number of compactions. Residual analysis is used to check the correlation between regression equation (3) and data, as shown in Fig. 6. It finds that the confidence intervals of data all include the zero point, which means the residual meets the standard. From Table 11, the raveling value for the compaction of 135 °C & 65 is the worst one. The preparation temperature is the lowest, while the number of compactions is the largest among the four. If the asphalt is of large viscosity, large number of the compactions will destroy the aggregates. Therefore, during practical construction, if the temperature is low, frequent compaction will break the limestone aggregate and affect the road service life. The numbers of compactions at 155 °C and 145 °C are both 50, but the raveling data obtained at 155 °C is better than those obtained at 145 °C. This indicates that temperature has great influence on the molding of test specimen. Comparison between raveling data from 165 °C & 57 compactions and 135 °C & 65 compactions also conforms to this conclusion. At 155 °C, raveling loss for mixture made by 50
The result temperature is 144.4 °C and the number of compactions is 28. In the mathematical model of raveling, the coefficients of temperature and number of compactions are all negative, indicating that the larger the temperature and the number of compactions are, the smaller the raveling value will be. For air voids content analysis, the compaction temperature is set at 145 ± 5 °C, and the number of compactions differs from 20 to 40 (taking the average value of 30). By substituting 145 °C & 30 compactions into the raveling formula and calculate the raveling value, the result air voids content is 19.77%, which is lower than the standard value (20%) in JTG F40-2004. Therefore, it is suggested that the number of times of compaction should be reduced during the construction to prevent the limestone aggregates from being crushed. 3.4. Freeze-thaw split test The research region is a cold region in Northern China, which is also influenced by oceanic climate, the freeze-thaw phenomenon frequently occurred in winter is a serious risk for the asphalt mixture. The freeze-thaw split test reflects the low temperature destruction resistance property of asphalt mixture; the porous
Fig. 6. Residual plot of raveling.
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B. Xu et al. / Construction and Building Materials 124 (2016) 846–854 Table 12 Freeze-thaw split test results of PA-L. PA-L
Maximum load (KN)
Height of test specimen (mm)
Low temperature splitting tensile strength (MPa)
Mean value (MPa)
155 °C & 50 compactions
7.96 7.29
62.95 62.15
0.795 0.737
0.766
125 °C & 42 compactions
5.23 4.93
62.92 64.18
0.523 0.483
0.503
135 °C & 65 compactions
6.08 6.54
62.68 64.35
0.610 0.639
0.624
145 °C & 50 compactions
6.74 6.46
64.54 64.78
0.657 0.627
0.642
155 °C & 35 compactions
8.29 7.54
64.33 64.83
0.810 0.731
0.771
165 °C & 57 compactions
6.91 8.01
63.10 63.86
0.688 0.789
0.738
asphalt mixture has a large number of gaps, the rain and melt snow will freeze in these gaps in winter, freeze-thaw phenomenon will occur repeatedly day and night, and there is also a risk of damage of the internal structure of mixture. The freeze-thaw split test is used for determining the splitting failure of asphalt mixture under specified temperature and loading rate, or the mechanical properties during elastic stage. The freezethaw split test results are shown in Table 12. In order to obtain the mathematical model of the splitting strength and the compaction temperature and number of compactions, multivariate fitting among the number of compactions, compaction temperature and the corresponding splitting strength is carried out, and the trend diagram of compaction temperature, number of compactions and splitting strength is plotted as shown in Fig. 7. The regression formula (4) is obtained as follow:
z ¼ 0:0065 x 0:0007 y 0:2506 Fig. 7. The trend diagram of compaction temperature, number of compactions and splitting strength data.
ð4Þ
In which, z is splitting strength, x is compaction temperature, y is number of compactions. Residual analysis is also conducted for judging the correlation between regression equation (4) and data as given in Fig. 8.
Fig. 8. Residual plot of freeze-thaw splitting strength.
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Table 13 Mean results of laboratory and field tests. Test items
Relative density Air void (%) Raveling Value (20 °C, %)
Laboratory test
Field test
Machine 1#
Machine 2#
LH road
GRJ road
2.063 19.0 17
2.073 18.9 19
2.050 19.7 16
2.060 19.1 13
From the residual plot (Fig. 8), confidence intervals of various data all include zero point, which indicates that the regression equation (4) can preferably meet the original data, and the formula obtained is reasonable. From the mathematical model (Eq. (4)), higher compaction temperature can increase the splitting strength, while larger number of compactions will decrease the splitting strength. Among the test results, the molding of 155 °C & 35 compactions realizes largest splitting strength. When calculating the freeze-thaw splitting strength with fixed combination of compaction temperature (145 °C) and number of compactions (30) by formula (4), the result is 0.686 MPa, which is above the average level and meets the design requirement compared with the test results in Table12. 4. Practice test Porous asphalt mixture using limestone aggregate was applied in several Dalian municipal roads in China. During this period, we carried out laboratory and field examinations for this type mixture. The results are shown in Table 13. Laboratory test results obtained based on the specimen made in lab and the field test results acquired from core samples drilled from pavement after construction (7 days later or more). The results prove that the performance index basically meet the requirement of porous asphalt. 5. Conclusions (1) The porous asphalt mixture with skeleton-pore structure has higher requirements on aggregates in comparison with dense mixtures. In this research, limestone is used as the coarse aggregate to mold the porous asphalt mixture after taking a comprehensive consideration of the economic and social benefits. Even though the crushing value and the content of elongated and flaky particles of the limestone are large, by investigating the high temperature performance, water stability and low temperature stability, it finds that those performances of porous asphalt mixture with limestone as the coarse aggregate all meet the standard requirements. Therefore it considers feasible to use limestone as the coarse aggregate of porous asphalt mixture. (2) From the experimental study on the correlation between the air voids content and Marshall molding parameters (compaction temperature and number of compactions), it finds that the air voids content of porous asphalt will decrease correspondingly with the increase of compaction temperature or number of compactions. Through quantitative back calculation, it shows that the influence of compaction temperature on the air voids content of limestone porous asphalt mixture is greater than that of the number of compactions. (3) The minimum value of Marshall Stability of the mixture is 7.74 KN, which is much larger than the technical requirement specified in the Chinese Standard. By analyzing the
Marshall molding parameters with fixed variables, it can be found that the influence of compaction temperature on the Marshall stability is larger than that of the number of compactions. (4) From the raveling test, it finds that the larger the temperature and the number of compactions are, the smaller the raveling value will be. And the influence of the number of compactions on the raveling loss of porous asphalt mixture is less than that of the temperature. (5) The freeze-thaw split test can reflect the low temperature destruction resistance property of the porous asphalt mixture. The freeze-thaw split test results are presented as: an increasing compaction temperature will enhance the freeze-thaw splitting strength of porous asphalt mixture, and an increasing number of compactions will decrease the freeze-thaw splitting strength of porous asphalt mixture; the number of compactions has the largest destruction influence on the molded test specimen. (6) By analyzing and studying the influences of Marshall molding parameters on the air voids content of porous asphalt mixture, combining with the analysis and verification of the performance indices of porous asphalt mixture (Marshall stability, raveling loss and freeze-thaw splitting strength), it finally works out that the optimal Marshall molding parameters of limestone porous asphalt mixture: compaction temperature is 145 ± 5 °C, and number of compactions is 30.
Acknowledgements This work was supported by the National Natural Science Foundation of China (Grant No. 51208080), and Dalian Science and Technology Project (Grant No. 2010E14SF146, and 2011E13SF047). References [1] Dongwei Cao, Qingquan Liu, Guoqi Tang, Porous Asphalt Pavement, China Communications Press, Beijing, 2009. [2] Mingliang Li, Tyre-Road Noise, Surface Characteristics and Material Properties, Delft University of Technology, Delft, The Netherlands, 2013. [3] J.C. Nicholls, Asphalt Surfacings, E & FN Spon, London, 1998. [4] P.S. Kandhal, R.B. Mallick, Open-Graded Friction Course: State of the Practice, Transportation Research Circular Number E-C005, Transportation Research Board, National Research Council, Washington, D.C., 1998. [5] F.L. Roberts, P.S. Kanho, E.R. Brown, et al. (Hot mixed asphalt mixture materials, mixture design and construction) (Yu Shufan, Trans), Chongqing Communications Technology Research Design Institute Co., Ltd, Chongqing, 2000. pp. 85-87. [6] China Highway Planning and Design Institute, JTG D50–2006, Specifications for Design of Highway Asphalt Pavement, China Communications Press, Peking, 2006. [7] Research Institute of Highway Ministry of Communications, JTG F40–2004, Technical Specifications for Construction of Highway Asphalt Pavements, China Communications Press, Peking, 2004. [8] Hanguang Li, Ying Gao, Determination of asphalt mixture compaction characteristics and number of rolling passes of asphalt pavement, Nanjing: J. Southeast Univ. (2011). [9] Haijing Xu, Analysis of factors influencing the compaction quality of asphalt pavement, Technology and Life, Beijing, 2011. [10] Lintao Cao, Influence of compaction power on gradation, Transp. Sci. Technol. (2003). [11] K.T. Fang, The uniform design: application of number-theoretic methods in experimental design, Acta Math. Appl. Sinica 3 (1980) 363–372. [12] Research Institute of Highway Ministry of Communications, JTG E20–2011, Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering, China Communications Press, Peking, 2011.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Study on Marshall Design parameters of porous asphalt mixture using limestone as coarse aggregate Bin Xu, Jingyun Chen, Changhong Zhou ⇑, Weiying Wang Dalian University of Technology, No. 2 Road Linggong, Ganjingzi District, Dalian, Liaoning 116024, PR China
h i g h l i g h t s Limestone is used as the coarse aggregate to mold the porous asphalt mixture. The properties of porous asphalt mixture using limestone as coarse aggregate are measured and analyzed. The optimal Marshall molding parameters of porous asphalt mixture using limestone as coarse aggregate is proposed. It provides support for the design and construction of porous asphalt using limestone as coarse aggregate.
a r t i c l e
i n f o
Article history: Received 9 May 2016 Received in revised form 1 August 2016 Accepted 3 August 2016
Keywords: Porous asphalt mixture Marshall Design Method Compaction temperature Number of compactions
a b s t r a c t Porous asphalt pavement is defined as an asphalt concrete with air voids content of around 20% and capable of forming drainage channels inside the mixture. It consists of an open-graded asphalt mixture composed predominantly of embedded-occluded single-sized macadam from interlocking processes, and is also known as porous asphalt mixture. In China, Marshall Design Method for porous asphalt mixture is the most widely used mixture design method for laboratory experimental study at present. The main parameters of Marshall Design Method are compaction work (number of compactions) and compaction temperature, i.e. this method can work out the air voids content meeting the performance requirements under uniform standard compaction work and given range of compaction temperature in practice. However, on account of different climates and traffic volumes, the molding parameters of Marshall Design shall be adjusted correspondingly to satisfy the pavement performance of mixture. For this purpose, limestone, which is of relatively low strength, is used as aggregate in porous asphalt mixture for experimental study, and the feasibility of limestone used in porous asphalt is also analyzed and verified. By analyzing the influences of Marshall molding parameters (compaction temperature and number of compactions) on the air voids content of porous asphalt mixture, the ranges of molding parameters of Marshall Design Method suitable for porous asphalt using limestone as coarse aggregate is found. Through analyzing the influence rules of Marshall molding parameters (compaction temperature and number of compactions) on the properties of porous asphalt mixture (high temperature stability, water stability and low temperature stability), combining with the ranges of molding parameters calculated with air voids content, the molding parameters for the Marshall test specimen applicable to the limestone porous asphalt mixture in Chinese region is proposed. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction Porous asphalt pavement has the technical features of good anti-slipping performance, low noise, restraining water splash and spray on rainy days, mitigating glaring lights when driving on the night and so on, because of the large air voids content contents which is around 20% and permeable skeleton inside the mixture [1,2]. ⇑ Corresponding author. E-mail address: [email protected] (C. Zhou). http://dx.doi.org/10.1016/j.conbuildmat.2016.08.005 0950-0618/Ó 2016 Elsevier Ltd. All rights reserved.
The porous asphalt pavement, developed in 1960s, was mainly applied to improve driving safety on the road surface, and reduce the traffic noise in populous regions and those with dense road network [3]. In the United States (US), open-graded friction course (OGFC) with large air voids content (higher than 15%) was developed to improve the anti-slipping performance of the freeways pavement [4]. In the 1980s, the porous asphalt technique was imported from Europe to Japan. In combination with the local climate and transport conditions, a specific porous asphalt technique was formed and extensively promoted in Japan. The research and application of porous asphalt in China were started in 1980s.
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Now the high-viscosity modified asphalt is mainly adopted as the binder to improve the anti-raveling performance. So far, porous asphalt pavement has been applied in more than ten provinces, and the total length of porous asphalt section is over 300 km. Marshall Design Method was established between the end of 1950s and the beginning of 1960s. The theoretical basis for this method is that the density of test specimen obtained in laboratory with certain compaction energy is equal to the final density of asphalt pavements which have been used for many years [5]. The design concept of asphalt mixture in China’s current Design Specification [6] is: using Marshall Design Method to work out the air voids content which meets the performance requirements under uniform standard compaction power and given range of compaction temperature. However, for the porous asphalt mixtures used in different regions or different conditions, the design method proposed in the Specification [6] is not always applicable, for example, pavements bearing heavy and light traffics require different mechanical strengths of the mixture, and the differences in climatic conditions in the southern and northern parts of China also result in different requirements for high-and-low temperature performance. The Specification [7] indicates that the number of compactions (double-side) for dense graded asphalt mixture in Marshall test design is 75, the numbers of compactions (double-side) for SMA mixture and OGFC mixture are 50, and the compaction temperature is basically 150 °C ± 5 °C; However, it does not show the specific parameters requirements for different climates and different traffic volumes. Most studies have discussed different molding methods of the asphalt mixtures and their physical and mechanical properties difference, for example: Li Hanguang [8] compared various performances between the asphalt mixture fabricated in laboratory with different molding modes and the asphalt test specimens directly ground on the site; Xu Haijing [9] studied the factors which may influence the compaction quality of asphalt pavement; Cao Lintao [10] determined the number of rolling passes of the asphalt pavement required for reaching certain compaction degree from the perspective of energy equivalence on the basis of studying the compaction properties of asphalt mixture. However, there are few researches on the design parameters of the molding method. In this study, the traditional Marshall test method is adopted, and porous asphalt specimens with the same gradation are prepared. The limestone aggregates are collected locally. The influence rules of Marshall Design parameters (number of compactions and compaction temperature) on the high and low temperature stabilities and water stability of molded test specimens are investigated. The compaction effect of porous asphalt mixture is evaluated to provide theoretical basis for the site compaction technology of limestone porous asphalt pavement.
2. Materials and test methods 2.1. Materials 2.1.1. High-viscosity modified asphalt Porous asphalt is different from ordinary asphalt mixture in structure and certain pavement performances: coarse aggregates with large specific gravity are used to form a skeleton-pore structure spatially, which provides high compressive strength. In the meantime, due to small contact area of coarse aggregate in the mixture, ordinary asphalt or common modified asphalt is insufficient to cement the aggregates. High-viscosity modified asphalt is thus required to enhance the bonding effect and eliminate the influences of the small contact area of aggregates on the tensile strength and shear strength of mixture. Existing experimental studies indicate that: he performance of the mixture at
Table 1 Properties of high viscosity asphalt binder. Test item
Unit
Values
Penetration (25 °C, 100 g, 5 s) Softening point Ductility (5 cm/min, 25 °C) Quality loss after thin-film heating test Penetration ratio after thin-film heating test Toughness 60 °C dynamic viscosity
0.1 mm °C cm % % Nm PaS
74 114 103 0.06 78.2 23 215,368
high-and-low temperature can be greatly improved by using high-viscosity modified asphalt, compared with normal modified asphalt materials; it also satisfies the high flaking resistance (the material will not flake even though contacting with water for a long time), and significantly improves the cohesiveness of the mixture particles. The porous asphalt using high-viscosity modified asphalt also shows advantages under high temperature and heavy traffic conditions. The performance indices of high-viscosity modified asphalt are shown in Table 1. 2.1.2. Limestone In porous asphalt mixture, the aggregates shall be uniform, clean and dry. Important properties for coarse aggregates include the content of elongated and flaky particles, crushed stone value and Los Angeles abrasion loss. In this research, taking into account the costs of road materials (the price of basalt purchased from other places is 170 CNY/ton, while the price of limestone produced locally is 85 CNY/ton) and the large output of limestone in certain region, limestone is thus selected as the coarse aggregate of porous asphalt mixture in this research, provided that all properties of the selected limestone meet the relevant technical requirements. The tested performances of limestone are shown in Table 2. 2.2. Gradation The content of coarse aggregate of common porous asphalt mixture (above 4.75 mm) is generally more than 80%. For guaranteeing the performance of porous asphalt mixture, basalt is usually used as coarse aggregates in China, which shows not only excellent mechanical properties but also high price. In this study, basalt aggregate is replaced with limestone, and the aggregate gradation is also adjusted correspondingly, as shown in Table3. In the paper, PA-L is defined as porous asphalt mixture using limestone as coarse aggregate. 2.3. Test design For the Marshall compaction molding, there are two important influence factors: number of compactions and compaction temperature. The experiment design level refers to the specific state or condition of the factors during the experiment. Five levels are used in this experiment: 35, 42, 50, 57 and 65 for the number of compactions, and 125 °C, 135 °C, 145 °C, 155 °C and 165 °C for the compaction temperature. Suppose all these numbers of compactions and compaction temperatures to match with each other
Table 2 Performances of limestone aggregate. Test item
Unit
Values
Crushing value Quality loss of Los Angeles abrasion test Bulk specific gravity Water absorption Flat and elongated particle ratio (>9.5 mm)
% %
18.73 29 2.57 0.56 5.46
% %
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Table 3 Gradation of porous asphalt in this study. Mixtures
Passing (by Mass) under different sieve size (mm)/% Limestone
PA-L
AR/% Sand
13.2
9.5
4.75
2.36
1.18
0.6
0.3
0.15
0.075
100
91.6
43.9
12.0
12.0
10.5
7.9
6.2
4.6
3.0
at every level, we will carry out 52 = 25 experiments. Taking into account this complicated operations, the uniform design method [11] is used to design the laboratory experiment, so as to cover the representative combinations with less experiments, and accomplish the analysis and verification of test rules. The experiment design is based on uniform design table, and each uniform design table has a code U n ðqs Þ or U n ðqs Þ: in which, ‘‘U” refers to uniform design, ‘‘n” refers to the number of times of the experiments, ‘‘q” refers to the levels of each factor, and ‘‘s” refers to the number of columns of this table. Adding and not adding ‘‘⁄” on the top right corner of U represent two different types of the uniform design tables, and generally the design with ‘‘⁄” has better uniformity. Each uniform design table is attached with a selection table, which indicates how to select proper column from the uniform design table and the uniformity of the test scheme composed of these columns. The uniform design table used in this research is shown in Table 4, and the selection table of the uniform design table U 5 ð53 Þ is shown in Table 5. Table 5 indicates that Columns 1 and 2 shall be selected for the test if there are two experimental factors, and if there are three experimental factors, Columns 1, 2 and 3 shall be selected. In Table 5, D means the discrepancy of the evenness. And when the discrepancy value is smaller, the evenness is better. The five levels of two factors of the molding conditions are combined respectively, and the experiments are arranged by selecting Columns 1 and 2 in Table 5. The combination results can be seen in Table 6. From Table 6, if Marshall specimen is prepared according to the uniform design method, the combinations of low compaction temperature and small number of compactions or high compaction temperature and large number of compactions may appear; in consideration that the uniform experiment data shall be as representative as possible, the high-and-low combinations of compaction temperature and number of compactions shall be discrete as far as possible. In this case, we properly adjust the combination results of uniform experiment, i.e. the larger and smaller data of temperature and number of times are combined discretely. The preparation conditions of the test specimen achieved are shown in Table 7. In the meantime, based on the requirements of JTG F40-2004 Technical Specification for Construction of Highway Asphalt
Table 4 Uniform design table U 5 ð53 Þ.
1 2 3 4 5
Mineral Powder
16
1
2
3
1 2 3 4 5
2 4 1 3 5
4 3 2 1 5
Table 5 Selection table of uniform design U 5 ð53 Þ. S
Column number
D
2 3
1 1
0.31 0.457
2 2
3
4.6
Table 6 Combination of experiment conditions for compacting Marshall specimens with uniform design method. No.
Compaction temperature/°C
Number of compactions/times
1 2 3 4 5
125 135 145 155 165
42 57 35 50 65
(1) (2) (3) (4) (5)
(2) (4) (1) (3) (5)
Table 7 Combination of actual test conditions for Marshall test specimens. No.
Compaction temperature/°C
Number of compactions/times
1 2 3 4 5 6
125 135 145 155 165 155
42 65 50 35 57 50
(1) (2) (3) (4) (5)
(2) (5) (3) (1) (4)
Pavements [7], a group of standard specimen at 155 °C and with 50 compactions (double-side) are prepared to compare with the other test specimens. By combining the molding conditions of mixture with different compaction temperatures and numbers of compactions, several groups of representative combinations are selected for the research. The high temperature performance, water stability and low temperature stability of the porous asphalt mixture under various molding conditions are to be compared. The inherent laws between the molding conditions and mixture performances are considered to be found out in this way. 2.4. Test methods The performances of porous asphalt to be investigated include: the high temperature stability, water stability and low temperature stability of mixture. In this paper, the air voids content is first analyzed, which is the most critical factor of porous asphalt mixture. Trends of air voids content changing with molding condition are investigated by regression analysis. Comparative analyses are carried out on the following properties of the porous asphalt mixture: 2.4.1. High temperature performance This performance is one of the most important factors for evaluating the asphalt pavement performance. For porous asphalt, high temperature stability is mainly based on the skeleton interlocking effect among the coarse aggregates. As only parameters for Marshall specimens are studied in this research, Marshall Stability Test is adopted for the experimental study of high-temperature performance. Marshall Stability test shall be executed by reference to the test method of T 0709-2011 [12].
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2.4.2. Water stability It is inevitable that the large air voids content structure of porous asphalt tends to suffer the repeated erosion of water, and the asphalt film is liable to peel off from the mineral aggregate surface under the repeated effects of hydrodynamic pressure and vacuum suction and scouring of the vehicle loads. Therefore, the water damage resistance property is crucial to the long-term service life of the pavement. The test methods for evaluating the water stability of mixture in this study include: Cantabro Raveling Test, Marshall Test and Freeze-thaw Split test. The Cantabro test was measured according to T0733-2011 method [12].
2.4.3. Low temperature stability For porous asphalt pavement, crack during the service period is a common problem. Low temperature shrinkage and cracking is very common in regions where the temperature in winter is low, especially in north part of China. It will seriously affect the service life and quality of porous asphalt pavement; therefore, it is necessary to investigate the low temperature performance. In this research, Freeze-thaw Split test is adopted to analyze the changing tendencies of these two indices under different molding conditions, and a molding combination best matching this region is to be selected based on regression analysis, so as to meet the low temperature stability requirements of road. Freeze-thaw Split test shall be executed by reference to the test method of T 0729-2000 [12]. The preparation conditions of the test: firstly immerse the Marshall test into water until saturation, place the water saturated test specimen into a refrigerator at 16 °C for 16 h, then place it into water at 60 °C for 24 h (water bath), and finally saturated in another water bath at 25 °C for 2 h.
3. Result and discussion 3.1. Air voids content Air voids content is one of the most important parameters of porous asphalt mixture, which is generally between 18% and 25% in China, which shall meet the national specification JTG F40-2004 [7]. In order to guarantee the permeability, the minimum air voids content in this research is set at 19%. The standard Marshall specimens are made according to the experiment design requirements. Porosities of the specimens produced at different compaction temperatures and numbers of compactions are measured. Combinations of compaction temperatures and compaction numbers which lead to the required air voids content range between 19% and 25% are to be found. The air voids content test results are shown in Table 8. It can be seen that the air voids content data measured from the tests have certain internal relation with different molding conditions of the specimens. The relation diagram of the compaction temperature, number of compactions and air voids content is plotted by means of Matlab software based on binary linear regression, as shown in Fig. 1.
Fig. 1. The relation diagram of compaction temperature, number of compactions and air voids content.
From the fitting analysis, the relational expression (1) of the air voids content, temperature and number of compactions is obtained:
z ¼ 31:4439 0:0801 x 0:0319 y
ð1Þ
where, z is air voids content, x is compaction temperature, and y is number of compactions. In order to analyze whether the linearity of regression equation (1) satisfies the correlation requirements, residual analysis between measured data and fitting data is carried out. Residual is the difference between the actual observed value and regression estimated value. The residual plot of air voids content, temperature and number of compactions of the porous asphalt mixture is shown in Fig. 2. The residual plot shows the distances of the data residuals to the zero point. If the confidence intervals of residuals include the zero point, the regression model preferably conforms to the original data; otherwise, it will be considered as abnormal point. If all the residuals include the zero point, which indicates that the regression equation (1) can preferably fit the experimental data, the regression equation (1) is considered usable. In JTG F40-2004 [7], 50 times of compactions is required for compaction of Marshall test specimen of OGFC mixture in laboratory. with the regression equation (1), if the air voids content value is fixed at 19%, the numbers of compaction are set as 10, 20, 30, 40 and 50 respectively, the corresponding temperature can be calculated (listed in Table 9). otherwise, if the temperatures are set as 160 °C, 150 °C, 140 °C, 130 °C and 120 °C, the corresponding numbers of compactions are also calculated (listed in Table 9). From Table 9, when the number of compactions increases from 10 (minimum) to 50 (standard requirement), the corresponding temperature decreases from 151.6 °C to 135.6 °C. Equivalently, when increasing one compaction, the temperature will decrease by 0.6 °C, i.e. the decreasing value of temperature is 0.6 °C/ compaction. In the case of analyzing the compaction number,
Table 8 Air Voids content test results of PA-L. PA-L 155 °C 125 °C 135 °C 145 °C 155 °C 165 °C
& & & & & &
50 42 65 50 35 57
compactions compactions compactions compactions compactions compactions
Cf (gross volume relative density)
Ct (theoretical
2.121548 2.053047 2.039657 2.057297 2.049212 2.135554
2.535719
minimum relative density)
VV (air voids content/%) 16.33 19.03 19.56 18.87 19.19 15.78
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Fig. 2. Residual plot of air voids content.
Table 9 Calculation sheet of temperature and number of compactions for the molding test of Marshall test specimen (VV = 19%). Set number of compactions
Table 10 Marshall test results. PA-L
Stability MS (KN)
Flow value FL (mm)
Marshall modulus T (KN/mm)
MS mean value (KN)
155 °C & 50 compactions
12.10 11.98
1.99 1.41
6.08 8.50
12.04
125 °C & 42 compactions
6.77 8.72
1.83 2.08
3.70 4.19
7.74
135 °C & 65 compactions
9.01 7.93
1.59 2.24
5.67 3.54
8.47
145 °C & 50 compactions
9.87 11.39
1.81 1.62
5.45 7.03
10.63
155 °C & 35 compactions
10.82 10.34
1.27 1.62
8.52 6.38
10.58
165 °C & 57 compactions
10.32 10.78
1.24 1.99
8.32 5.42
10.55
Set temperature
Number of compactions
Temperature °C
Temperature °C
Number of compactions
10 20 30 40 50
151.6 147.6 143.6 139.6 135.6
160 150 140 130 120
Negative result 14 39 64 89
when the temperature is 160 °C, the number of compactions is negative, which indicates that the result air voids content is lower than 19% and the temperature is too high. When the temperature decreases from 150 °C to 120 °C, the number of compactions will increase from 14 to 89, equivalently, the number of compactions will increase by 2.5 times with the temperature decreasing by 1 °C, i.e. 0.4 °C/compaction. These two groups of data indicate that the influence of temperature on air voids content is greater than that of the number of compactions. In order to satisfy the compaction of PA-L, the temperature of test specimen shall be within the scope of 140–150 °C, and the number of compactions shall be between 20 and 40. In other words, in order to satisfy the air voids content requirement of porous asphalt, the fabrication of test specimen shall be carried out with 145 ± 5 °C and 30 compactions (average between 20 and 40, double-side). 3.2. Stability of porous asphalt mixture The stability of porous asphalt mixture is evaluated according to the Marshall test results. Two main indices are obtained from the test, i.e. flow value and Marshall stability. The flow value means the deformability of mixture under the effect of external forces, and the stability reflects the load bearing condition of the mixture. The porous asphalt mixture is of special skeleton structure, and is mainly made from coarse aggregates which are mutually interlocked without the protection of filled fine aggregate. The overall
strength of porous asphalt is based on the occlusion of aggregates. JTG F40-2004 [7] shows that the Marshall stability of porous asphalt mixture is the lowest among all types of mixtures, the standard requirement of which is not less than 3.5 kN. Marshall test results are given in Table 10. In order to obtain the mathematical model of the relationship among Marshall stability, compaction temperature and number of compactions, multivariate fitting is performed by Matlab7.0. The generated relation is shown in Fig. 3. Based on the fitting diagram, the regression function of stability, expressed by temperature and number of compactions is obtained:
z ¼ 0:0902 x 0:0175 y 2:3533
ð2Þ
where, z is stability, x is compaction temperature, y is number of compactions. In order to check whether the correlation between regression equation (2) and data meets the requirements, residual analysis of the data is executed. The residual plot is shown in Fig. 4. From the residual plot, the confidence intervals of data all include the zero point, which indicates that the regression
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3.3. Cantabro raveling test
Fig. 3. The relation diagram among compaction temperature, number of compactions and Marshall stability.
equation (2) can preferably meet the original data, and the obtained formula is feasible. From various groups of data, PA-L meets the standard requirements: the maximum value is 12.04 kN, the corresponding preparation condition is 155 °C & 50 compactions; the minimum value is 7.74 kN, the corresponding preparation condition is 125 °C & 42 compactions. The temperature difference of these two groups of data is 30 °C, while the difference of the number of compactions is 8. This indicates that the Marshall stability is more sensitive to temperature rather than compaction number. In most of the cases, the stability mainly concentrates between 10 and 11 kN. The stability is calculated by substituting 145 ± 5 °C and 30 compactions into the Eq. (2). The result is 10.2 kN, which also meet the characteristics of measured data. In this study, the Marshall stabilities of test specimens molded under various conditions all meet the standard requirement [7]. The test results show that there are three values of Marshall Stability ranging between (10 and 11) KN, and the calculated Marshall stability also meet this characteristic. It indicates that the test conditions obtained from the air voids content calculation are feasible.
The raveling test is used for evaluating the stripping and scattering degrees of the aggregates from the road surface under the effect of repeated traffic loads. The representation of raveling test is the mass percentage of the scattered asphalt mixture test specimen after rotating and striking the Marshall standard test specimens for certain times in Los Angeles abrasion testing machine. In this research, limestone is used as the coarse aggregate and porous asphalt mixture is prepared in the laboratory. The Cantabro raveling tests are then carried out to find out the ranges of temperature and number of compactions which meet the standard requirements under various conditions. The raveling test data are summarized in Table 11. Matlab7.0 is used to execute multivariate fitting among the number of compactions, compaction temperature and the raveling value. The trend diagram of compaction temperature, number of compactions and raveling value is generated as shown in Fig. 5. With data fitting analysis, the statistical relation among raveling, compaction temperature and number of compactions is obtained as follow:
z ¼ 65:0288 0:3088 x 0:0160 y
ð3Þ
Table 11 Raveling test results of PA-L. PA-L
Mass before test (kg)
Mass after test (kg)
Dm (kg)
Mean value (%)
155 °C & 50 compactions
1058.6 1079.2
946.2 960.3
112.4 118.9
10.82
125 °C & 42 compactions
1080.5 1108.9
859.6 907.3
220.9 201.6
19.31
135 °C & 65 compactions
1101.2 1112.8
772.7 803.1
328.5 309.7
28.83
145 °C & 50 compactions
1085.6 1099.5
851.9 866.6
233.7 232.9
21.35
155 °C & 35 compactions
1096.5 1072.3
797.7 838.4
298.8 233.9
24.53
165 °C & 57 compactions
1113.1 1108.4
1017.3 1008.9
95.8 99.5
8.79
Fig. 4. Residual plot of Marshall stability.
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compactions is less than that by 35 compactions, which shows that under high temperature, the more the number of compaction is, the better the effect of raveling resistance will be. The compaction temperature and number of compactions are calculated for the case which results the 19% air voids content and the 20% raveling loss (the 20% raveling loss percentage is the upper limit value of raveling value specified in JTG F40-2004 [7]), by combining the raveling loss value formula (3) and the air voids content formula (1) into a binary linear equation set.
20 ¼ 65:0288 0:3088 x ðtemperatureÞ 0:0160 y ðnumber of compactionsÞ 19 ¼ 31:4439 0:08 x ðtemperatureÞ 0:0319 y ðnumber of compactionsÞ Fig. 5. The trend diagram of compaction temperature, number of compactions and raveling value.
In which, z is raveling data, x is compaction temperature, and y is number of compactions. Residual analysis is used to check the correlation between regression equation (3) and data, as shown in Fig. 6. It finds that the confidence intervals of data all include the zero point, which means the residual meets the standard. From Table 11, the raveling value for the compaction of 135 °C & 65 is the worst one. The preparation temperature is the lowest, while the number of compactions is the largest among the four. If the asphalt is of large viscosity, large number of the compactions will destroy the aggregates. Therefore, during practical construction, if the temperature is low, frequent compaction will break the limestone aggregate and affect the road service life. The numbers of compactions at 155 °C and 145 °C are both 50, but the raveling data obtained at 155 °C is better than those obtained at 145 °C. This indicates that temperature has great influence on the molding of test specimen. Comparison between raveling data from 165 °C & 57 compactions and 135 °C & 65 compactions also conforms to this conclusion. At 155 °C, raveling loss for mixture made by 50
The result temperature is 144.4 °C and the number of compactions is 28. In the mathematical model of raveling, the coefficients of temperature and number of compactions are all negative, indicating that the larger the temperature and the number of compactions are, the smaller the raveling value will be. For air voids content analysis, the compaction temperature is set at 145 ± 5 °C, and the number of compactions differs from 20 to 40 (taking the average value of 30). By substituting 145 °C & 30 compactions into the raveling formula and calculate the raveling value, the result air voids content is 19.77%, which is lower than the standard value (20%) in JTG F40-2004. Therefore, it is suggested that the number of times of compaction should be reduced during the construction to prevent the limestone aggregates from being crushed. 3.4. Freeze-thaw split test The research region is a cold region in Northern China, which is also influenced by oceanic climate, the freeze-thaw phenomenon frequently occurred in winter is a serious risk for the asphalt mixture. The freeze-thaw split test reflects the low temperature destruction resistance property of asphalt mixture; the porous
Fig. 6. Residual plot of raveling.
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B. Xu et al. / Construction and Building Materials 124 (2016) 846–854 Table 12 Freeze-thaw split test results of PA-L. PA-L
Maximum load (KN)
Height of test specimen (mm)
Low temperature splitting tensile strength (MPa)
Mean value (MPa)
155 °C & 50 compactions
7.96 7.29
62.95 62.15
0.795 0.737
0.766
125 °C & 42 compactions
5.23 4.93
62.92 64.18
0.523 0.483
0.503
135 °C & 65 compactions
6.08 6.54
62.68 64.35
0.610 0.639
0.624
145 °C & 50 compactions
6.74 6.46
64.54 64.78
0.657 0.627
0.642
155 °C & 35 compactions
8.29 7.54
64.33 64.83
0.810 0.731
0.771
165 °C & 57 compactions
6.91 8.01
63.10 63.86
0.688 0.789
0.738
asphalt mixture has a large number of gaps, the rain and melt snow will freeze in these gaps in winter, freeze-thaw phenomenon will occur repeatedly day and night, and there is also a risk of damage of the internal structure of mixture. The freeze-thaw split test is used for determining the splitting failure of asphalt mixture under specified temperature and loading rate, or the mechanical properties during elastic stage. The freezethaw split test results are shown in Table 12. In order to obtain the mathematical model of the splitting strength and the compaction temperature and number of compactions, multivariate fitting among the number of compactions, compaction temperature and the corresponding splitting strength is carried out, and the trend diagram of compaction temperature, number of compactions and splitting strength is plotted as shown in Fig. 7. The regression formula (4) is obtained as follow:
z ¼ 0:0065 x 0:0007 y 0:2506 Fig. 7. The trend diagram of compaction temperature, number of compactions and splitting strength data.
ð4Þ
In which, z is splitting strength, x is compaction temperature, y is number of compactions. Residual analysis is also conducted for judging the correlation between regression equation (4) and data as given in Fig. 8.
Fig. 8. Residual plot of freeze-thaw splitting strength.
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Table 13 Mean results of laboratory and field tests. Test items
Relative density Air void (%) Raveling Value (20 °C, %)
Laboratory test
Field test
Machine 1#
Machine 2#
LH road
GRJ road
2.063 19.0 17
2.073 18.9 19
2.050 19.7 16
2.060 19.1 13
From the residual plot (Fig. 8), confidence intervals of various data all include zero point, which indicates that the regression equation (4) can preferably meet the original data, and the formula obtained is reasonable. From the mathematical model (Eq. (4)), higher compaction temperature can increase the splitting strength, while larger number of compactions will decrease the splitting strength. Among the test results, the molding of 155 °C & 35 compactions realizes largest splitting strength. When calculating the freeze-thaw splitting strength with fixed combination of compaction temperature (145 °C) and number of compactions (30) by formula (4), the result is 0.686 MPa, which is above the average level and meets the design requirement compared with the test results in Table12. 4. Practice test Porous asphalt mixture using limestone aggregate was applied in several Dalian municipal roads in China. During this period, we carried out laboratory and field examinations for this type mixture. The results are shown in Table 13. Laboratory test results obtained based on the specimen made in lab and the field test results acquired from core samples drilled from pavement after construction (7 days later or more). The results prove that the performance index basically meet the requirement of porous asphalt. 5. Conclusions (1) The porous asphalt mixture with skeleton-pore structure has higher requirements on aggregates in comparison with dense mixtures. In this research, limestone is used as the coarse aggregate to mold the porous asphalt mixture after taking a comprehensive consideration of the economic and social benefits. Even though the crushing value and the content of elongated and flaky particles of the limestone are large, by investigating the high temperature performance, water stability and low temperature stability, it finds that those performances of porous asphalt mixture with limestone as the coarse aggregate all meet the standard requirements. Therefore it considers feasible to use limestone as the coarse aggregate of porous asphalt mixture. (2) From the experimental study on the correlation between the air voids content and Marshall molding parameters (compaction temperature and number of compactions), it finds that the air voids content of porous asphalt will decrease correspondingly with the increase of compaction temperature or number of compactions. Through quantitative back calculation, it shows that the influence of compaction temperature on the air voids content of limestone porous asphalt mixture is greater than that of the number of compactions. (3) The minimum value of Marshall Stability of the mixture is 7.74 KN, which is much larger than the technical requirement specified in the Chinese Standard. By analyzing the
Marshall molding parameters with fixed variables, it can be found that the influence of compaction temperature on the Marshall stability is larger than that of the number of compactions. (4) From the raveling test, it finds that the larger the temperature and the number of compactions are, the smaller the raveling value will be. And the influence of the number of compactions on the raveling loss of porous asphalt mixture is less than that of the temperature. (5) The freeze-thaw split test can reflect the low temperature destruction resistance property of the porous asphalt mixture. The freeze-thaw split test results are presented as: an increasing compaction temperature will enhance the freeze-thaw splitting strength of porous asphalt mixture, and an increasing number of compactions will decrease the freeze-thaw splitting strength of porous asphalt mixture; the number of compactions has the largest destruction influence on the molded test specimen. (6) By analyzing and studying the influences of Marshall molding parameters on the air voids content of porous asphalt mixture, combining with the analysis and verification of the performance indices of porous asphalt mixture (Marshall stability, raveling loss and freeze-thaw splitting strength), it finally works out that the optimal Marshall molding parameters of limestone porous asphalt mixture: compaction temperature is 145 ± 5 °C, and number of compactions is 30.
Acknowledgements This work was supported by the National Natural Science Foundation of China (Grant No. 51208080), and Dalian Science and Technology Project (Grant No. 2010E14SF146, and 2011E13SF047). References [1] Dongwei Cao, Qingquan Liu, Guoqi Tang, Porous Asphalt Pavement, China Communications Press, Beijing, 2009. [2] Mingliang Li, Tyre-Road Noise, Surface Characteristics and Material Properties, Delft University of Technology, Delft, The Netherlands, 2013. [3] J.C. Nicholls, Asphalt Surfacings, E & FN Spon, London, 1998. [4] P.S. Kandhal, R.B. Mallick, Open-Graded Friction Course: State of the Practice, Transportation Research Circular Number E-C005, Transportation Research Board, National Research Council, Washington, D.C., 1998. [5] F.L. Roberts, P.S. Kanho, E.R. Brown, et al. (Hot mixed asphalt mixture materials, mixture design and construction) (Yu Shufan, Trans), Chongqing Communications Technology Research Design Institute Co., Ltd, Chongqing, 2000. pp. 85-87. [6] China Highway Planning and Design Institute, JTG D50–2006, Specifications for Design of Highway Asphalt Pavement, China Communications Press, Peking, 2006. [7] Research Institute of Highway Ministry of Communications, JTG F40–2004, Technical Specifications for Construction of Highway Asphalt Pavements, China Communications Press, Peking, 2004. [8] Hanguang Li, Ying Gao, Determination of asphalt mixture compaction characteristics and number of rolling passes of asphalt pavement, Nanjing: J. Southeast Univ. (2011). [9] Haijing Xu, Analysis of factors influencing the compaction quality of asphalt pavement, Technology and Life, Beijing, 2011. [10] Lintao Cao, Influence of compaction power on gradation, Transp. Sci. Technol. (2003). [11] K.T. Fang, The uniform design: application of number-theoretic methods in experimental design, Acta Math. Appl. Sinica 3 (1980) 363–372. [12] Research Institute of Highway Ministry of Communications, JTG E20–2011, Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering, China Communications Press, Peking, 2011.