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Utilization of Waste Asphalt Concrete as Cement-treated Bases for Airport PavementsYoshitaka Hachiya a & Peiwen Hao ba National Institute for Land and Infrastructure Management Ministry of LandInfrastructure and Transport , 1-1, Nagase 3, Yokosuka, 239-0826, Japan E-mail:b Highway College, Chang An University , South Erhuan Road, Middle Section, Xian,Shaanxi, 710064, China E-mail:Published online: 19 Sep 2011.
To cite this article: Yoshitaka Hachiya & Peiwen Hao (2006) Utilization of Waste Asphalt Concrete as Cement-treatedBases for Airport Pavements, Road Materials and Pavement Design, 7:2, 247-260
To link to this article: http://dx.doi.org/10.1080/14680629.2006.9690035
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Road Materials and Pavement Design. Volume 7 – No. 2/2006, pages 247 to 260
SCIENTIFIC NOTE
Utilization of Waste Asphalt Concreteas Cement-treated Bases for AirportPavements
Yoshitaka Hachiya* — Peiwen Hao**
* National Institute for Land and Infrastructure ManagementMinistry of Land Infrastructure and Transport1-1, Nagase 3, Yokosuka [email protected]
** Highway College, Chang An UniversitySouth Erhuan Road, Middle SectionXian, Shaanxi, [email protected]
ABSTRACT. The waste materials produced during the construction or repair of airportpavements are typically of high quality and should be reused. Current specifications,however, may not apply to such usage. This paper describes a series of laboratory tests thatwere performed to investigate the use of waste asphalt concrete in airport pavements,especially stabilized bases. These tests show that recycled cement-treated materials cansatisfy the specifications for airport pavement base courses and subbases. By following well-defined construction procedures, it is possible to use 100% recycled materials in airportpavements. This will effectively utilize huge amounts of waste asphalt concrete.KEYWORDS: Recycling, Waste Asphalt Concrete, Cement-treated Base, Airport, LaboratoryTest.D
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248 Road Materials and Pavement Design. Volume 7 – No. 2/2006
1. Introduction
Japan has enacted a number of environmental laws and regulations designed tofully utilize natural resources and protect the environment. At the same time, thegeneral focus of infrastructure development in Japan has shifted from initialdevelopment and construction to maintenance and repair. In many cases, industrialwaste and by-products are being recycled very effectively.
The waste asphalt concrete generated by scrapping existing pavements has beenreutilized in repairs using hot mix asphalt recycling or cold mix asphalt recycling,either in situ or at a central plant (OECD, 1997). Compared to cold mix asphaltrecycling, hot mix asphalt recycling produces more valuable materials, i.e., theperformance of the recycled asphalt concrete is equal to that of conventional asphaltconcrete (Kandhal et al., 1997).
Two recycling procedures are presently specified for the construction and repairof airport pavements in Japan. The first is hot mix asphalt recycling, i.e., recycledhot mix asphalt concrete for surface courses. The second is cold mix asphaltrecycling, i.e., recycled unbound granular material for bases. Both are produced byusing the central plant mixing method. However, not all of the waste asphaltconcrete can be reused under existing specifications at many airports (Hachiya et al.,2004a). For example, at Tokyo International Airport, a vast area of pavement,including three runways, has been affected, and a huge amount of waste asphaltconcrete has been stockpiled for reuse in new pavements.
With this as background, the authors performed laboratory tests in order todevelop new methods for recycling huge amounts of waste asphalt concrete bymeans of cold asphalt mix recycling for bases (Hachiya et al., 2004c). Cold asphaltmix recycling generally uses bituminous additives (Asphalt Institute, 1983;AASHTO, 1998; Pasetto et al., 2004), the validity of which has been verifiedthrough experiments (Hachiya et al., 2004b). However, to reduce recycling costsand in consideration of available facilities of most asphalt recycling plants in Japan,the authors investigated a recycling method that doesn’t use bituminous additives.
This paper summarizes laboratory studies of cold asphalt mix recycling from theviewpoint of making the best possible use of waste asphalt concrete for bases. First,the mechanical properties of recycled unbound granular materials mixed with wasteasphalt concrete are elucidated. Next, those of recycled cement-treated waste asphaltconcrete are investigated.
2. Study plan
In re-utilizing waste asphalt concrete as unbound base materials, the waste isgenerally mixed with conventional (new) aggregate. Since asphalt concrete isthermally sensitive, the recycling ratio (defined as the amount of waste asphalt
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Utilization of Waste Asphalt Concrete 249
concrete to the total amount of aggregate) has been kept relatively low in order toensure satisfactory performance at higher temperatures. However, as mentionedabove, a huge amount of waste asphalt concrete has been generated, so thepossibility of cold asphalt mix recycling at high recycling ratios must be studied.This is also true of cement-treated waste asphalt concrete.
The mechanical properties of both materials were studied in a series oflaboratory tests. Their target properties were those currently specified for airportpavements that contain only new aggregate. As the mechanical properties ofunbound granular materials and cement-treated materials are specified as modifiedCBR and unconfined compressive strength, respectively, CBR tests and unconfinedcompression tests were conducted. Table 1 shows the current specifications for basecourse and subbase materials for airport pavements (Civil Aviation Bureau – CAB,1999).
Table 1. Specifications of base materials
Material Item Specification Layer *
80 Base (A)
45 Base (C)
30 Subbase (A)Unbound granular Modified CBR
(%)
20 Subbase (C)
2.9 Base (A)
Cement-treated Unconfined compressivestrength (MPa) 2.0
Subbase (A)
Base (C)
* A: Asphalt pavement, C: Concrete pavement.
3. Materials
The materials used in this study are described below. Waste asphalt concrete isdescribed separately from the others.
3.1. Waste asphalt concrete
Waste asphalt concrete from demolition work at Tokyo International Airport wasused for this study. The material was crushed in a recycling plant and separated intothree portions according to size (20-13 mm, 13-5 mm, and 5-0 mm in diameter). Thepassing percentages are shown in Table 2. These were then remixed as shown in
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250 Road Materials and Pavement Design. Volume 7 – No. 2/2006
Table 3 to produce the specified aggregate distribution (CAB, 2001), which wasthen used as recycled aggregate in the laboratory tests that followed. The asphaltcontent was 2.3%, 3.0%, and 6.2% in the 20-13 mm, 13-5 mm, and 5-0 mmdiameter portions, respectively. The penetration of asphalt recovered from therecycled aggregate was 23 (1/10 mm), which meets the requirements of therecycling guidelines (Japan Road Association, 1992).
Table 2. Passing percentages of separated waste asphalt concrete
Passing percentageSieve size (mm)
20 - 13 mm 13 - 5 mm 5 - 0 mm
26.5 100
19.0 94.4 100
13.2 10.0 23.2 100
4.75 0.8 8.6 95.2
2.36 1.2 51.4
0.60 0.6 10.4
0.30 0.4 3.9
0.15 0.3 1.1
0.075 0.1 0.4
Table 3. Composition of separated portions for recycled aggregate
Aggregate size (mm) 20-13 13-5 5-0
Mixing ratio (%) 21.8 39.5 38.7
3.2. Others
The new aggregate that was used as a supplement had a maximum diameter of40 mm as specified in JIS A 5001 (unbound granular aggregate with a maximumdiameter of 40 mm). The new aggregate was mixed into the recycled aggregate inaccordance with the test plan (to be described later). In addition, Portland cementwith the properties specified in JIS R 5210 was used in preparing the recycledcement-treated base materials.
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Utilization of Waste Asphalt Concrete 251
4. Utilization as recycled unbound granular base materials
Mixing recycled aggregate with new aggregate produces a recycled unboundgranular material. To study the applicability of such materials to the bases of airportpavements, several compositions that met the required specifications wereformulated and the resulting materials examined.
Recycled unbound granular materials with five combinations of recycledaggregate and new aggregate were prepared. The percentages of recycled aggregatein the material (recycling ratio) were set at 0%, 25%, 50%, 75%, and 100%. Figure 1shows the gradations of these materials together with the grey area recommended inthe specification (CAB, 2001). The figure shows that the materials with higher ratiosof recycled aggregate barely stay within the recommended range.
0
20
40
60
80
100
0.01 0.1 1 10 100
0255075100
Per
cent
pas
sing
Sieve size (mm)
Recycling ratio (%)
Recommended
Figure 1. Gradations of recycled unbound granular materials
0 25 50 75 1000
2
4
6
8
1.8
1.9
2
2.1
2.2
Recycling ratio (%)
wopt
ρdmax
Figure 2. Results of compaction tests on recycled unbound granular materials
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252 Road Materials and Pavement Design. Volume 7 – No. 2/2006
Compaction tests were conducted on materials with these compositions inaccordance with Method E in JIS A 1210, which specifies that the specimens becompacted in three lifts with 92 drops of a 4.5kg rammer. These tests wereconducted at a temperature of 40oC, which was selected as the worst-case scenarioof pavement construction during a hot summer day. Figure 2 shows the results. Themaximum dry density (ρdmax) decreased as the recycling ratio increased, while theoptimum water content (wopt) varied little. At the higher recycling rates, the recycledunbound granular materials may be difficult to compact because the waste asphaltconcrete is covered with asphalt.
Next, modified CBR tests were carried out on these materials at a temperature of40oC, which was selected in consideration of the hot summer daytime condition.Figure 3 shows that the modified CBR decreased as the recycling ratio increased.The maximum recycling ratios given in Table 4 were determined from this figure.To meet the requirement for using as much waste as possible, the recycled unboundgranular materials should be applied to the subbase.
0 25 50 75 1000
20
40
60
80
100Specification
Base(C)
Subbase(A)Subbase(C)
Base(A)
0 100755025
Mod
ified
CB
R (%
)
Recycling ratio (%)
Figure 3. Modified CBR of recycled unbound granular materials
Table 4. Maximum recycling ratio for base courses and subbases
Base SubbaseItem
(A) (C) (A) (C)
Recycling ratio (%) 3 18 28 37
Modified CBR tests were also conducted at 20oC, which is considered thestandard temperature (JRA, 1979). Each material was prepared with the recyclingratio shown in Table 4. The modified CBR decreased as the recycling rate increased,
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Utilization of Waste Asphalt Concrete 253
just as it did at 40oC, as shown in Figure 4. The ratio of modified CBR at 40oC tothat at 20oC decreased as the recycling rate increased. This is due to the differentmechanical properties of the asphalt at these temperatures.
In addition, bases are likely to become soaked from infiltrated rainwater orgroundwater under actual conditions. Thus, the CBR of the materials was measuredafter soaking them in water for 63 days. This test was done in accordance with thetest done on cement-treated materials, which is described later in this study. Asshown in Figure 5, the CBR fell when soaking in water. This trend is morepronounced at the lower recycling ratios.
0
20
40
60
80
100
Base (A) Base (C) Subbase (A) Subbase (C)
2040
Mod
ified
CB
R (%
)
Temperature (oC)
Figure 4. Change in modified CBR with temperature
0
50
100
150
200
250
Base (A) Base (C) Subbase (A) Subbase (C)
20 C (Submerged)20 C (Unsubmerged)40 C (Submerged)40 C (Unsubmerged)
CBR
(%)
o
o
o
o
Figure 5. Change in CBR under water soaked condition
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254 Road Materials and Pavement Design. Volume 7 – No. 2/2006
From the test results obtained in this section, the modified CBR of recycledunbound granular materials was found to decrease as the recycling ratio increased,and the mechanical properties were negatively influenced by both temperatureincrease and submergence in water. Therefore, the amount of waste asphalt concretethat can be used in this way is hardly adequate.
5. Utilization as recycled cement-treated base materials
As another means of increasing the amount of waste asphalt concrete that can berecycled, the authors evaluated recycled cement-treated base materials in whichrecycled aggregate and new aggregate were mixed with Portland cement.
5.1. Basic properties of recycled cement-treated materials
Minimum cement contents of recycled cement-treated materials were determinedfor four combinations of recycled and new aggregate. The percentages of recycledaggregate in the material (recycling ratios) were set at 25, 50, 75 and 100%, as wellas the recycled unbound granular materials.
First, the optimum moisture content was determined through compaction tests.Tests were conducted on materials having several cement contents in accordancewith Method A of JIS A 1210, which specifies that the specimens be compacted inthree lifts with 25 drops of a 2.5 kg rammer. Unconfined compression tests werethen performed at the standard temperature of 20oC on materials with variouscement and predetermined optimum moisture contents.
0 2 4 6 8 10 12 140
2
4
6
8
10 Recycling ratio (%)
Stre
ngth
(MP
a)
Cement content (%)
25 50 75 100
Figure 6. Unconfined compressive strength of recycled cement-treated materials
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Utilization of Waste Asphalt Concrete 255
These tests clarified the relationship between the unconfined compressivestrength and the cement content for the four combinations of materials, as shown inFigure 6. The strength clearly increases as the cement content increases and therecycling ratio decreases. The reason may be because the maximum dry densitydecreases as the recycling rate increases.
Finally, the minimum cement contents required to obtain the specified strengthsdescribed in Table 1 were determined. These are shown in Table 5 (CAB, 1999).This table also shows the optimum moisture contents.
Table 5. Cement and moisture contents of recycled cement-treated materials
Recycling ratio (%)Layer Item
25 50 75 100
Minimum cement content (%) 3.9 5.7 8.8 12.4Base (A)
Optimum moisture content (%) 5.8 6.7 7.7 6.7
Minimum cement content (%) 2.8 4.2 6.4 8.7Subbase (A)/Base (C) Optimum moisture content (%) 5.3 61. 7.2 6.2
Table 6. Conditions of detailed unconfined compression tests
Item Condition
Curing temperature (oC) 20, 40
Curing time (d) 7, 28, 91
Soaking time (d) 63 (91*)
* Figure in parentheses denotes total curing time.
5.2. Influence of various factors on properties of recycled cement-treatedmaterials
The preliminary test described in the previous section showed that cement-treated materials might be a practical means of utilizing larger amounts of wasteasphalt concrete. To confirm the usage methods, the materials were further testedunder various conditions. The influences of temperature, curing period, and water
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256 Road Materials and Pavement Design. Volume 7 – No. 2/2006
soaking on strength were investigated through detailed unconfined compression testsunder the conditions given in Table 6. Furthermore, durability under repeatedfreeze-thaw and dry-wet cycles was examined by the methods specified by the JRA(1979).
The test results show that the unconfined compressive strength decreases as thecuring temperature decreases. The decrease in unconfined compressive strength dueto the temperature increase (from 20oC to 40oC) was averaged over all testconditions. Figure 7 shows the results, which indicate that the decrease in strengthbecomes more significant as the recycling ratio increases. This might be due to thefact that the recycled aggregate contains asphalt.
25 50 75 1000
10
20
30
40
Stre
ngth
dec
reas
e (%
)
Recycling ratio (%)
Base(A) Subbase(A) / Base(C)
Figure 7. Relationship between the decrease in strength due to temperature increaseand the recycling ratio
7 28 91 -- -- -- -- -- -- -- -- -- -- -- --0
1
2
3
4
5
6
Recycling ratio (%) 25 50 75 100
0 28 917
Stre
ngth
(MP
a)
Curing time (day)
Figure 8. Change in strength with curing time
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Utilization of Waste Asphalt Concrete 257
Next, the influence of the curing time was examined. Figure 8 shows the resultsat 20°C. Three curing durations were applied: 7, 28, and 91 days. The strengthincreased as the curing duration increased, regardless of the recycling ratio.
Figure 9 shows the influence of submerging in water on the unconfinedcompressive strength at a temperature of 20oC. The submerged specimen wasprepared by submerging it for 63 days after curing for 28 days in the dry condition.This was assumed to be the worst possible scenario for water submergence. Theunsubmerged specimen was cured under dry conditions for 91 days but notsubmerged. It was found that submerging the specimen in water caused the strengthto decrease in the lower recycling ratios. This tendency is similar to that of therecycled unbound granular materials shown in Figure 5. Thus, in designing the mixof a cement-treated material, both temperature and water must be taken intoconsideration.
In the repeated freeze-thaw and dry-wet tests, the loss of mass and volume weresmall enough to satisfy the specifications of the Portland Cement Association (JRA,1979).
25 50 75 1000
1
2
3
4
5
6
Stre
ngth
(MP
a)
Recycling ratio (%)
Unsubmerged Submerged
Figure 9. Difference in strength after submerging in water
5.3. Possibility of using cement-treated materials containing 100% recycledaggregate
The above results indicate that recycled cement-treated materials with nosupplements (i.e., 100% recycled aggregate) might be suitable for use in airportpavements. Trials were therefore carried out under actual field conditions. Thevarious factors influencing the unconfined compressive strength were examined,including the material preparation factors (mixing method, mixing time, compactionmethod, and degree of compaction) and various test factors (curing temperature andcuring time). These factors are listed in Table 7.
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258 Road Materials and Pavement Design. Volume 7 – No. 2/2006
Table 7. Preparation of materials and test conditions
Case Mixingmethod
Mixingtime
Compactionmethod
Degree ofcompaction
(%)
Curingtemperature
(oC)
Curingtime(day)
1 Mixer
2 Hand1m
3 15s
4 30s
5 3m
Rammer
6 Gyratory
100
7 92.5
8 95.0
9 97.5
20
10 10
11 30
28
12 7
13
Mixer
1mRammer
100
2091
Figure 10 shows the influence of these material preparation and testing factorson the unconfined compressive strength of asphalt pavement base course materials.In Cases 1, 7, 8, and 9, the strength decreases with the degree of compaction; thestrength at a relative density of 95% is about 70% that at a relative density of 100%.The material must be compacted to a relative density of 94% or more to achieve thespecified strength. The influence of the curing time on the strength is also notable,and matches the test result shown in Figure 8, as seen in Cases 1, 12 and 13.
In contrast, the mixing method and mixing time have scarcely any effect on thestrength, as seen in Cases 1 through 5. The compaction method also has little effect,as shown by Cases 1 and 6. Since 100% compaction was applied in these cases, it isclear that the degree of compaction is much more important than the other factorsfor achieving the specified strength. In addition, the influence of the curingtemperature is unclear when these results are compared with the test results shownin Figure 7 as the temperature was set here between 10 and 30oC.
The above-mentioned influence of the various factors on the compressivestrength is similar to that of the materials used for the subbase in asphalt pavementsand the base course in concrete pavements, as shown in Figure 11. This means that100% recycled cement-treated materials can be utilized in the base courses andsubbases of airport pavements. However, the compaction methods must beappropriately specified in order to achieve the required properties.
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Utilization of Waste Asphalt Concrete 259
1 2 3 4 5 6 7 8 9 10 11 12 130
1
2
3
4
5
6
Spec.
Stre
ngth
(MP
a)
CaseFigure 10. Influence of base sample preparation and testing factors on strength
1 2 3 4 5 6 7 8 9 10 11 12 130
1
2
3
4
5
Spec.
Stre
ngth
(MP
a)
Case
Figure 11. Influence of subbase sample preparation and testing factors on strength
6. Conclusions
Various means of reusing a huge amount of waste asphalt concrete for bases inairport pavements were studied through a series of laboratory tests. The results aresummarized below:
– Recycled unbound granular materials can be used in airport pavements.However, the mechanical properties of the recycled unbound granular materials arenegatively influenced by both temperature increase and submergence in water. Theamount of waste asphalt concrete that can be used as recycled unbound granularbase material is rather small;
– Recycled cement-treated materials satisfy the specifications for base courseand subbase materials to be used in airport pavements, regardless of the recyclingratio. However, the minimum cement content increases as the recycling ratio
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increases, and the strength falls when the temperature increases or when thematerials are submerged in water. The cement-treated base material can use a largeamount of waste asphalt concrete;
– With a well-defined construction procedure, it should be possible to use 100%recycled cement-treated materials in airport pavements. This would enable muchlarger amounts of waste asphalt concrete to be re-utilized.
7. Bibliography
AASHTO-AGC-ARTBA Joint Committee (AASHTO), “Cold Recycling of AsphaltPavements”, Task Force 38 Report, March 1998.
Asphalt Institute (AI), Asphalt Cold-Mix Recycling, Manual Series No. 21 (MS-21), February1983, 68 p.
Civil Aviation Bureau, Ministry of Land, Infrastructure and Transport (CAB, MOLIT),Manual for airport pavement design, 1999 (in Japanese).
CAB, MOLIT, Specifications for civil engineering works in airports, 2001 (in Japanese).
Hachiya Y., Himeno K., Hao P., Tsubokawa Y., “Application of recycled asphalt concrete inairport pavement surface courses”, 3rd Eurasphalt & Eurobitume Congress, May 2004,p. 22-30.
Hachiya Y., Matsuzaki K., Tsubokawa Y., Yuasa K., Hayano K., Akimoto H., FullReutilization of Pavement Construction Wastes in Airports, Technical Note of NILIM,No. 176, June 2004 (in Japanese).
Hachiya Y., Matsuzaki K., Tsubokawa Y., Yoshinaga K., Geshi H., “Utilization of abolishedasphalt concrete in bases of airport pavements”, Journal of Pavement Engineering, Japansociety of civil engineers, Vol. 8, December 2004, p. 117-124 (in Japanese).
Japan Road Association (JRA), Manual for test methods of pavements, 1979 (in Japanese).
JRA, Technical guide to plant-recycling of pavement materials, 1992 (in Japanese).
Kandhal P.S., Mallick R.B., Pavement Recycling Guidelines for State and LocalGovernments, FHWA-SA-98-042, December 1997.
Organisation for Economic Co-operation and Development (OECD), Recycling Strategies forRoad Works, 1997.
Pasetto M., Bortolini G., Scabbio F., Carta I., “Experiments on Cold Recycling with FoamedBitumen or Bituminous Emulsion and Cement”, 3rd Eurasphalt & Eurobitume Congress,May 2004, p. 494-503.
Received: 17 February 2005Accepted: 26 September 2005
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