Vol.17 No.3

Journal of Wuhan Universityof Technology-Mater.Sci. Ed.

Sept. 2002

The Development of Recycling Agent for Asphalt Pavement WU S h a o - p e n g 1'2) H U A N G X i a o - m i n g 1) Z H A O Yong-li 1) 1) Southeast University 2) Wuhan University of Technology ( Received: Oct. 11,2001) Abstract:

A type of recycling agent was developed and its use for modifying used asphalt is described. The results show that the viscosity and three main properties of the aged asphalt were remarkably improved. With 5% 7% content of recycling agent, the main properties of recycled asphalt comported with China GB asphalt standard AH- 70 and the recycled asphalt concrete could be used us high-grade highway. Furthermore, the recycling mechanism of the aged asphalt is discussed. Key words: recycling agent; recyclingasphalt; asphalt concrete; high-grade highway

1 Introduction Recycling agents have been studied since the oil crisis in 1970s. Many kinds of recycling agents have been applied in recycled pavement, and the relevant technologies (including standards and specifications) have been highly developed abroad especially in the USA series of recycling agents have entered into China market since then. Some Chinese institutions such as Shanghai Institute of Civil Engineering, Yunnan Institute of Transportation studied recycling agents in the early 1980s. The main recycling agents were then studied for residue oil pavements, but it is hard to find in current market. Recently, the maintenance work for high - grade highway has quickly increased year by year. It will be significant for the Chinese transportation field to develop a new type of recycling agent for asphalt pavement of high-grade highway An attempt was made to rejuvenate aged asphalt by adding some specific components, which had disappeared from the original asphalt. This method is theoretically feasible. But the literatures indicated it was difficult to find a recycling agent aging asphalt to add it up to original asphalt. The reason is as follows. Firstly, asphalt is difficult to divide into some chemical compositions to suit chemical and engineering properties due to its very complicated chemical structure, which differs from that of oil. At the beginning of SHRP(a research project in US),researchers mm'nly focused on analysis of the compositions, but few practical achievements in performance research were gainedI13. The optimum chemical compositions are still not WU Shao-peng(~:~'~,~):Born in 1965;Prof. ;PhD; Collegeof Transportation, SoutheastUniversity,Nanjing 210096, China;School of MaterialsScience and Engineering,Wuhan Universityof Technology,Wuhan 430070, China

found. Secondly, it is difficuh to synthesize some recycling agent with permanent compositions in technology. Not only the requirement of equipment and technology but the costs were very high. So it is not realized to control the recycling of aging asphalt by chemical composition.

2 Influence of Recycling Agent on Asphalt Hydrodynamics Large quantity literature showed that the effective method to reduce asphalt viscosity is to add low-viscosity composition. In the early of 1980s, some oil industry products, such as lubricant, diesel, engine oil or its mixture were used as recycling agents in our country[2-43 . The main composition of recycling agent in abroad also was low-viscosity oil. In oil industry, two types of different viscosity asphalt were mixing together to gain some viscosity asphalt. This is a kind of asphalt mixture. The progress of aging asphalt's recycling is to add low-viscosity oil, reduces recycling asphalt's viscosity to some degree, renews its pavement performance. Viscosity after mixing was not the simple combination of two types of different asphalt. In order to find out the regular of mixing asphalt' s viscosity, recycling agent A (3600 pa" s) and aging asphalt(4.57 x 105pa" s) were mixing with different ratio, then tested mixing asphalt's viscosity at 60~ Its result was showed as table 1. The data on Curve A is real-testing data. When content of recycling agent was less than 20%, the content and logarithmic viscosity was linear function. When content of recycling agent more than 20%, the curve slow down. Therefore, due to the defect of logarithmic viscosity and the complex hydrodynamics relation ship between the two, there is no reasonable solution to the phenomena. The literature in abroad showed the formula of calcu-

64

Journal of Wuhan Universityof Technology- Mater.Sci.Ed.

lating mixing asphalt's viscosity as followed: Log~mix = alOgT~A +

blogr/s

( 1)

In forma 1, ~,~x - mixing asphalt' s viscosity, r/A - viscosity of asphalt A,/Is -- viscosity of Asphalt B, a - contend of asphalt A, b - contend of Asphalt BCurve B in Table 1 was according to formula 1, which was greatly different from curve A. Formula 1 was based on test data of two types of asphalt' s viscosity, which was only suitable for close viscosity. When contend of ~cycling agent was 20%, viscosity of aging asphalt reduced to 7.02 x 104 pa. s, which was less than ordinary asphalt. The purpose adding recycling agent is to reduce viscosity of aging asphalt. The curve of Formula 2 is as followed, y = - 4 . 0 2 6 x + 5.6301(when x < 0 . 2 ) (2) The curve had no a widespread meaning. When mixing other recycling agent and asphalt, the curve changes greatly. Doing the same test with recycling agent B and Shell asphalt AH - 70 (1.90 x 105pa's), the data and Formula 2 had great difference. 5. 5 5.

point improved obviously with 5% - 11% recycling agent. But prolongation only improved a little, which perhaps was due to higher wax content.

4 Primary Properties of Mixing Recycling Asphalt and Original Asphalt Pavement performance of recycling asphalt mixture could not meet the pavement requirement. In order to improve its pavement performance, new asphalt mixture had to be added. So it was necessary to research their mixture's property standards. The mixture with different percentage of aging asphalt, recycling agent and new asphalt was belonged to mixing asphalt. Aging asphalt with 5 % and 7 % , recycling agent was mixed with new asphalt in different contend, and tested their primary properties. The result was showed as Fig. 2. Viscosity test showed that viscosity changed obviously. Viscosity of recycling asphalt with 5% and 7% recycling agent was 3.23 x 105pa's and 2.16 x 105pa's respectively, new asphalt's

viscositywas 1 . 1 8

y = -4. 0263x + 5. 6301

h~ 105 p a " s .

x

5.44

i

4.9 4.7 4 4.3 4.1 3.9 3.7 3.5

B .

5

5.42 5.40 5.38 5,26 5,34 5.32

~

Sept. 2002

5.30 5.28

0

0.1

0.2

0.3 0.4 0.5 0.6 0.7 content of recycling agent/%

0.8

0.9

1

5.26 5.24

,

,

,

i

i

i

i0

20

30

40

50

60

Fig. 1 Viscositycurve of mixingasphalt

3 Improvement of Aging Asphalt Properties for Recycling Agent The final purpose is not only to reduce aging asphalt' s viscosity, but also improve its pavement performance. The improvement of aging asphalt's properties was comparing with different contend of recycling agent. Experimental result about recycling agent A is showed as Tab. 1. Table 1 The Relationship BetweenPropertiesof Aging Asphalt and the Contlmt of Recycling Content

C~mtofreeydingagent(%) 0 1 3 5 7 9 11 Viscosityof recycling 457 404 323 263 216 179 149 asphalt (60~C,103pa9s) Penetration(O.lmm,25~C) 38.1 50.4 57.2 67.6 79.3 104.6106.5 Prolongation(15~ ,cm) 20 38 55 ,fi7 81 88 96 Softeningpoint/~C 63.1 61.3 58.8 57.2 55.6 54.1 52.7 It was obvious that recycling asphalt's penetration and prolongation were increased, soften point decreased, aging asphalt's properties improved. Kalamayi asphalt AH - 7 0 was used as aging asphalt. Penetration and soften

70

i

i

,

80

90

i00

content of new asphalt/% Fig.2 The relationshipbetweenvicosityof mixing asphalt and content of new asphalt 93 88 83 78 73 68 63 58 100

Pcnea'ationof n e w i

I

I

90

80

70

i

i

I

t

I

60

50

30

10

0

content of new asphalt(%)

Fig.3 Penetrationof recyclingasphalt Experimental result about aging asphalt with 5 % and 7% recycling agent mixing new asphalt was showed as Figs. 3 - 5. Curve A and curve B were respectively for mixing with 5 % , 7% recycling agent in the three figures. Lines were the requirement of relevant standard about Asphalt A H - 70.

Vol. 17 No. 3

WU Shao-peng et a/: The Developmentof RecyclingAgent for...

Mixing asphalt's penetration varied between new asphalt and recycling asphalt, which meet the requirement of 60 - 80mm. From Fig. 3, penetration of mixing asphalt can meet the requirement. Requirement of Asphalt AH 70 is not less took at 15~C. For recycling asphalt's prolongation was generally lower. Prolongation was 67cm and 81cm with 5% and 7% recycling agent respectively. So in order to improve mixing asphalt's prolongation, new asphalt must be added. From Fig. 4, only more than 60% new asphalt could meet prolongation requirement. With different content of the three, mixing asphalt soften point could meet the requirement of 4 4 - 54~C about Asphalt A H - 70 on the whole.

140I" 120 ~ 100 80 60

. . . . .

i00

90

80

70

60

50

30

i0

0

65

standard of recycling agent. Secondly, pavement need no harmful to other performance of asphalt. Oil in recycling agent mainly is aromatic and saturant. When oil with more saturant added in aging asphalt, it had bad influence on mixing asphalts properties. More wax content is harmful to" low-temperature and high-temperature performance, which affected pavement service seriously. So recycling agent should be rich in aromatic but less of saturant. Different nations have different standard. Some nations made the range of aromatic content as a rule. Some limited saturant content, some make no requirement. As notional standard, aromatic and saturant content should be included. But the requirement may be relevant loosened for waste oil usage, economic factor, environment factor etc. Thirdly, Recycling agent can effectively postpone service life of recycling asphalt mixture, which require recycling agent have excellent resist-aging ability. Fourthly, no harmful matter to human' s health. When constructional sprigging and hot mixing, flash and smoke do not produced.

content of newasphalt/%

6

Fig.4 Penetrationof recyclingasphalt

55 53 52 51 50 I00

90

80

70

60

50

30

i0

0

contentofnewasphalt/% Fig. 5 Softeningpoint of recycling asphalt

5

Discussions

There is still no standard for recycling agent in our country. Only few units have enterprise standards. At the early of 1980s, many nations such as America, Japan etc. All had made quality standards. Quality standards of hot recycling asphalt mixture had been established in 13th Pacific Ocean Coastal Asphalt Standard Proceeding. In general, the requirement of recycling agent was as following: Firstly, it needs suitable viscosity. Recycling agent was spraying to the old mixture and then mixing together. So recycling agent must be spraying and permeable. In general, the lower viscosity of asphalt is, the stronger permeability it has. Therefore, low-viscosity asphalt is easy to volatilize during mixing and application. SO choosing viscosity must consider fully. Viscosity is the most primary

Conclusions

a) Recycling of aging asphalt firstly to reduce viscosity of old asphalt. Viscosity is one important standard for creating recycling agent. b) Recycling agent, type of asphalt and initial viscosity has a great influence on the regular of recycling asphalt' s viscosity. c) The addition of recycling agent improved the property of aging asphalt obviously. The degree of the improvement related to the percentages of recycling agent. d) The properties had further improvement after mixing recycling asphalt and new asphalt. If the mixture proportion of recycling agent, aging asphalt and new asphalt was moderate, pavement performance of aging asphalt could renew fully.

References 1 O' Neal R I, Gallaway B M. A Review of Pavement Materials Recycling Techniques and Associated [alx)ratory Tests and Evaluation. Epps. Appt. 1976,45:304 - 309 2 Kandhal P S. Asphalt Cold RecyclingTechnologyin Pennsylvania. Appt. 1984,53,618 - 623 3 Lu Weiming, Yan Jiaji. Recycling Technology of Asphalt pavement. Beijing:People's Communications Press of China, 1989 4 Liu Jiapeng,Zhang Xiankang. Study on RecyclingTechnologyfor Used Materials of Asphalt Paverfe.nt.Highway Scienceand Technology of Yunnan, 1995,3:19 - 23