Japanese Geotechnical Society Special Publication 8th Japan-China Geotechnical Symposium
Techniques for the effective use of recycled asphalt pavement material as a civil engineering material
Atsuko Sato i), Osamu Hatakeyama ii), Kakuto Morita iii) and Shoji Yokohama ⅳ)
i) Senior Research Eng.,Civil Engineering Research Institute for Cold Region, Hiragishi 1-3, Toyohira-ku, Sapporo, Japan ii) Team Leader Eng., Civil Engineering Research Institute for Cold Region., Hiragishi 1-3, Toyohira-ku, Sapporo, Japan. iii) Research Eng.,Civil Engineering Research Institute for Cold Region, Hiragishi 1-3, Toyohira-ku, Sapporo, Japan ⅳ) Faculty of Engineering, Hokkaido University, Kita 13, Nishi 8, Chuo-ku, Sapporo, Japan
ABSTRACT
From the viewpoint of the effective use of materials and environmental conservation, the recycling of waste materials generated at construction sites has been increasingly required. Asphalt pavement materials that are left after pavement repair are among such waste materials. Thus, for the purpose of effectively using waste asphalt, the applicability of recycled asphalt as a civil engineering material was examined by conducting laboratory tests and the trial construction of embankments. It was found that waste asphalt could be used in embankments and in frost blankets, and could be used for improving unsuitable soil.
Keywords: effective use, recycled asphalt, proceedings, civil engineering material
1 INTRODUCTION removed, the waste asphalt is crushed and sorted for various purposes. This study addresses both asphalt The reuse and recycling of waste construction materials produced at an asphalt recycling plant for reuse materials are actively promoted in civil engineering and asphalt materials cut from waste asphalt herein. works in Japan. Sand and crushed materials produced by Using these materials, laboratory tests and field test were drilling prior to the repair of asphalt pavement are conducted. designated as “specified waste construction materials” pursuant to the Construction Material Recycling Act, 2.1 Laboratory tests and these materials should be recycled. Waste asphalt Laboratory tests were conducted to determine the materials have been effectively used as base course basic physical properties of waste asphalt and to examine materials after crushing, and as materials for hot-mix usability of such waste as a civil engineering material. asphalt used for paving. In some regions, however, more With the aim of checking the usability of waste asphalt waste asphalt is generated than can be effectively as a civil engineering material, basic physical properties utilized, and it has been increasingly difficult for these such as density of soil particles, natural water content, regions to secure final disposal sites of surplus waste particle size distribution, compaction curve, asphalt materials. The recycling and effective use of trafficability, and frost heave susceptibility were these materials will need to be maintained at a high level investigated according to the standards of the Japanese in the future, too. In light of the above, techniques for Geotechnical Society. To identify any hazardous using waste asphalt materials for purposes other than substances that might be contained in waste asphalt and paving are required. Thus, in an effort to expand the that might leach, we measured the elution of cadmium, scope of application of waste asphalt, laboratory tests lead, hexavalent chromium, arsenic, total mercury, and the trial construction of full-scale embankments selenium, boron, and fluorine, which are specified in the were conducted in order to examine techniques for using environmental quality standards. waste asphalt as a civil engineering material for The author considered that waste asphalt could be embankments and frost blankets, and for improving used for improving unsuitable soil, so we investigated unsuitable soil. the strength of compacted waste asphalt and compacted mixtures of waste asphalt and soil. 2 TESTING METHODS 2.2 Field test construction Asphalt chunks and waste asphalt generated from 2.2.1 Construction method pavement repair and drilling work are transported to At three places in Hokkaido (Tomakomai, Sapporo asphalt recycling plants. After the impurities are and Wakkanai), full-scale embankments were built on a
https://doi.org/10.3208/jgssp.v08.j08 149 trial basis by using waste asphalt and a mixture of waste conditions of soil and waste asphalt. shows the physical asphalt and soil. Each embankment had a height of 1.8 properties of soil mixed with waste asphalt. B is a high m, the crown width of 4.5 m ~ 5.0 m and a slope gradient quality soil with a large cone index when compacted. of 1:1.5. The mixing of waste asphalt and soil, it was However, A and C have a relatively high water content, adjusted in Tomakomai and Sapporo by backhoe bucket, the cone index when compacted is small. For this reason, and in Wakkanai by rotary stabilizer. Waste asphalt or a the runnability of the construction machine cannot be mixture of waste asphalt and soil was spread and roller- ensured. compacted to make each embankment. Each embankment was made up of 6 layers. Each Table 2. Basic characteristics of soil used for mixing test and layer was 30 cm thick, so the upper surface of the sixth mixing conditions of soil and waste asphalt layer was at a height of 180 cm. Construction site Tomakomai Sapporo Wakkanai In Tomakomai, the embankments were built on a 0.5 Sample No. A B C m-high foundation made of gravel with a diameter of Soil particle 3 2.727 2.489 1.949 0~80 mm in order to avoid any effects of deformation density ρs (g/cm ) Natural water due to subsidence induced ground deformation. 68.7 31.9 445.0 content wn (%) In Sapporo and Wakkanai, settlement plates were installed at the bottom of each embankment. In Ground material Volcanic classification SFG Pt Tomakomai, one embankment was built without ash Cone index qc applying roller compaction. 2 57 >2000 31 (kN/m ) Table 1 shows the physical properties of the waste No. of waste asphalt materials tested. The soil particle density of the asphalt to be 5 2 4 waste asphalt materials was 2.465~2.522 g/cm3. These mixed values are lower than the particle density of typical soil Laboratory test ○ - - 3 in Japan: 2.6~2.8 g/cm . The soil particle densities were Field test ○ low partly because asphalt components were adhered to Field test of the soil particles. The natural water content was 4:1,4:2, 8:1,8:2, mixing amount 4:3 2.8~7.4 %. These values are much lower than the values 4:3,4:4 8:4,8:4 of typical soil in Japan, and are close to the water content (As:Soil) of rock. 2.2.2 Survey method Table 2 shows the physical properties of soil mixed Ease of execution was investigated for each with waste asphalt of soil used for mixing test and mixing embankment, and sand replacement was used to measure
Table 1. The basic physical properties of the waste asphalt. Sample No. 1 2 3 4 5 6 7 8 9 10 11 12
Occurrence place Asphalt recycling plants Construction site
Sapporo Wakkanai Tomakomai Naka- Fuka- Collection site Chitose Yakumo Tanno a b a b a b c gawa gawa Soil particle density 3 2.482 2.511 2.501 2.540 2.513 2.482 2.448 2.495 2.465 2.522 2.468 2.475 ρs (g/cm ) Natural water content 2.8 7.4 5.3 2.9 3.3 3.3 1.15 4.3 3.4 2.5 4.2 6.2 wn (%) Maximum particle size (mm) 19 37.5 19 37.5 37.5 - 37.5 26.5 37.5 37.5 37.5 37.5 Grain 2mm- (%) 72.4 85.4 73.5 84.8 85.8 - 92.5 91.0 79.7 94.8 87.3 89.2 size 75 μm-2 mm 10.6 characte (%) 27.5 14.4 26.4 14.7 9.1 - 7.3 8.6 20.1 5.1 12.1 ristics -75m (%) 0.1 0.1 0.5 5.1 - 0.2 0.1 0.2 0.1 0.1 0.2 Consistency limit N.P. N.P. N.P. N.P. N.P. N.P. N.P. N.P. N.P. N.P. N.P. Ground material classification GS G-S GS G-S G-FS - G-S G-S GS G-S G-S G-S Maximum dry 3 1.773 1.842 1.860 1.672 1.764 1.614 - 1.614 1.639 1.612 - 1.718 densityρdmax (g/cm ) Optimum moisture 10.2 11.8 9.1 8.3 9.2 7.9 - 10.8 11.3 5.0 - 7.6 content wopt (%) Cone index qc 1351 >2000 1891 >2000 >2000 1420 - 2491 1478 1163 - >2000 (kN/m2)
150 the density of each layer. For the purpose of checking the changes in the properties of each embankment over time, 1.9 Soil concrete plates were placed on the embankment crown, Waste asphalt
) 1.7 and the height of each embankment was measured at 3 m c least once a month. To confirm the stability of each / g (
1.5 embankment by revealing the changes in embankment d ρ
y internal strength, the Swedish weight sounding test was t i 1.3 c conducted several times. Air temperatures were n e d
automatically measured at the beginning of each hour. In y
r 1.1
Tomakomai, embankments were cut at 3 years after D construction so that the density could be measured by 0.9 sand replacement and so that the impact acceleration could be measured as a way of understanding the 0.7 strength. 0 10 20 30 40 50 60 Water content w (%) 3 TEST RESULTS Fig. 2. Compaction curves. 3.1 Laboratory test results 3.1.1 Physical properties of the waste asphalt materials can be compacted at optimum water content by slightly adjusting the natural water content. The particle size distribution curve for each waste Tests for assessing the frost heave susceptibility of asphalt type is shown in Figure 1. Although the the waste asphalt were conducted. The test results are maximum particle size varies slightly, all of the shown in Table 3. The frost heave rate at 90 % specimens contained a small fine-grained fraction and compaction was 0.024 mm/h. This value is as low as that are classified as gravel. Waste asphalt has similar grain for commercially available frost blankets. Only two size characteristics. specimens were used for testing, but because the waste asphalt materials used in this study had similar particle 100 characteristics, all these materials had low frost-heave Asphalt recycling plants ) susceptibility and thus can be used for the frost blanket. % Construction site ( 80
e g
a Table 3. Frost heave of waste asphlt. t n
e 60 Sample No. 1 2 c r e
p Degree of compaction (%) 91.0 90.0
s 40 s Frost heave speed (mm/h) a 0.024 0.002 m
g Frost heave ratio (%) 7.9 0.0
n 20 i s s a P 0 The cone index of the waste asphalt materials with 0.01 0.1 1 10 100 natural water content was at least 1000 kN/m2, which Particle size D (mm) suggests that a small self-propelled scraper could operate on an embankment made of waste asphalt materials. Fig. 1. Grain size characteristics. Thus, it was concluded that when waste asphalt is adequately compacted, it can be used as a civil Compaction curves for waste asphalt are shown in engineering material for embankments. Figure 2. A compaction curve of common soil is also For all the waste asphalt materials used in this study, shown in Figure 2. Regarding typical soil, it has been the amount of elution was measured for cadmium, lead, reported that the optimum water content decreases and hexavalent chromium, arsenic, total mercury, selenium, the compaction curve becomes sharper with increases in boron, and fluorine. All measured values satisfied the maximum dry density. In the waste asphalt materials, the environmental quality standards. maximum dry density was not very high, although the optimum water content was lower than that of typical 3.1.2 Strength of mixed soil of waste asphalt and soil. This result indicates that when waste asphalt is unsuitable soil compacted by the application of adequate pressure, the Figure 3 shows the relationship between the ratio of waste asphalt can be used as a ground material that is the mass of waste asphalt to the mass of unsuitable soil lighter than conventional gravel. The optimum water and the cone index when mixing waste asphalt and content was 2.5 %~7.9 % higher than the natural water unsuitable soil. The corn index increased by mixing content (Table 1) in all the waste asphalt specimens used waste asphalt. In the mixed materials, when the mixing in compaction tests. This means that waste asphalt amount (mass ratio) of waste asphalt becomes 1.33, the
151 cone index of the mixed soil exceeds 300 kN/m2. When suggests that waste asphalt is a civil engineering material the mixing amount of waste asphalt increases further, the that can be roller-compacted for construction. cone index became bigger. Waste asphalt is a material that can improve unsuitable soil. Table 4. Dry density of embankment. Dry Maximum Degree of >22000 Embankment density dry density compaction 3 3 ～ (g/cm ) (g/cm ) (%) without 1.504 )
2 85 1500 2 compaction
m 1.764 / N 1.787 101 k (
c 2 and B 1.663 1.632 102 q 4 1.842 1.658 111
x 1000 e
d 4:1 1.844 1.660 115
n 2 i
qc=300kN/m 4:2 1.781 1.603 111
e 4 and C n 4:3 1.761 1.585 111 o 500 C 4:4 1.750 1.575 111 5 1.831 1.906 96 8:1 1.716 1.627 106 0 8:2 1.708 1.667 103 0 1 2 3 5 and A 8:3 1.684 1.661 101 Ratio of the mass of waste asphalt to the mass of unsuitable soil 8:4 1.625 1.598 102
Fig. 3. Relationship between the ratio of the mass of waste asphalt to the mass of unsuitable soil and the cone index. 3.2.3 Embankment displacement The settlement of each embankment over time after 3.2 Field test construction construction is shown in Figure 5. Great settlement took 3.2.1 Workability place in the embankments built in Tomakomai in the first summer after construction. Settlement of the At three construction sites, embankments were embankment built by using a mixture of waste asphalt successfully built by spreading and roller-compacting and unsuitable soil was small. Embankment built by waste asphalt or a mixture of waste asphalt and soil using waste asphalt without roller-compaction, exhibited (Figure 4). Thus, waste asphalt is a civil engineering the greatest settlement, followed by Embankment, to material that can be easily used for embankment which roller-compaction had been applied. It can be construction. concluded that both the mixing of soil and roller- compaction helped to reduce settlement. In Sapporo (Figure 5 B) and Wakkanai (Figure 5 C), settlement was also small at the embankments built with a mixture of waste asphalt and soil. The settlement was smaller in the embankmentsin Sapporo and Wakkanai than in the embankments in Tomakomai. This seems to have been caused by the fact that the degree of compaction was higher in the embankments in Sapporo and Wakkanai than in the embankments in Tomakomai. Among the three places, settlement was the smallest in Wakkanai, where air temperatures are cooler than in Sapporo and Tomakomai. Thus, to control the settlement of embankments built with waste asphalt, low temperatures and high degrees of compaction need to be ensured. 3.2.4 Embankment strength versus elapsed time Fig. 4. Construction status The Swedish weight sounding test results are shown 3.2.2 Embankment quality in Figure 6 for embankment in Tomakomai. Regarding The density of the fourth layer in each embankment the number of half-turns per meter, the depth from the immediately after roller-compaction of that layer is crown increased over time after the construction of shown in Table 4. Excluding the embankment that did embankment. Embankment was built in winter, and the not roll, for every embankment, the degree of average monthly temperatures were -10~14 ℃ between compaction exceeds the standard value of 90 %. This late November and late May. Between late November,
152 20 Number of half-turns of per number Nsw Mixture of waste asphalt and soil Load Wsw(kN) (times) Chitose ompaction 0 0.250.50.75 10 200 400 600 10 Chitose without compaction 0.0 0.0 2015.12 )
m 2016.5.10 c
( 0
) t 2016.10. n m ( e 0.5 0.5 n m e w c
-10 o a r l c
p e s i h t
D 1.0 1.0 -20 m o r f h t
A Tomakomai p e
-30 D 2015/12 2016/12 2017/12 2018/12 1.5 1.5 Observation date (Year/ Month) TCohmitaokseomai CCoommppaaccttiioonn 2.0 2.0 20 B sapporo Number of half-turns of per number Nsw Load Wsw(kN) (times) 10 0 0.250.50.75 10 200 400 600 0.0 0.0 )
m 2017.10.4 c
( 0
2017.11.20 t n ) e m m (
e
n 0.5 0.5 c -10 w a Asphalt only l o p r s Asphalt:Soil=1:0.25 c
i e D Asphalt:Soil=1:0.5 h t
-20
Asphalt:Soil=1:0.75 m 1.0 1.0 o r f
Asphalt:Soil=1:1 h t
-30 p e
2017/7 2018/1 2018/7 D Observation date (Year/ Month) 1.5 1.5
Sapporo 20 2.0 2.0 C Wakkanai Fig. 6. The Swedish weight sounding test results. 10
) 120 m Mixture of waste asphalt and soil c ) (
0
%
t Chitose ompaction ( n
e
c Chitose without compaction m D
e 110
c
a -10 Asphalt only n l o p i s t
i Asphalt:Peat=8:1 c D Asphalt:Peat=8:2 a -20 p 100
Asphalt:Peat=8:3 m o c
Asphalt:Peat=8:4 f o
-30 e 90 2017/7 2017/11 2018/3 2018/7 2018/11 e r
Observation date (Year/ Month) g e D 80 Fig. 5. Deformations of embankment over time. 0 30 60 90 120 Depth from the crown (cm) when the embankment was built, and late May, temperatures were relatively low. Even during that Fig. 7. Degree of compaction of embankment. period and also in the year after construction, the strength of embankment, built with waste asphalt, compaction was roughly the same at different depths, increased. although it was high at the depth of 30 cm from the The degrees of compaction for the three years after crown. In embankments and, the degree of compaction the construction of the embankments in Tomakomai are was higher at greater depths. shown in Figure 7. In embankment, the degree of It is likely that the lower part of the embankments
153 built by using waste asphalt is subject to great settlement crushed stone (in Japanese) from the load imposed by the upper part. 3) Japanese Geotechnical Society (2009): “Test method for frost The relationships between the impact acceleration heave measurement” in the Japanese Standards and and the depth from the crown are shown in Figure 8. The Explanations of Labora-tory Tests of Geomaterials (in Japanes) impact acceleration remained almost the same at 4) Ministry of the Environment http://www.env.go.jp/kijun different depths in Embankment A in Tomakomai. In /dt1.html Embankments B and C, the impact acceleration 5) Ministry of Land, Infrastructure, Transport and Tourism increased with increase in the depth from the crown. This http://www.mlit.go.jp/sogoseisaku/recycle/index.html (in result is consistent with the increase in the degree of Japanese). compaction shown in Figure 7. Embankments built with 6) Ministry of Land, Infrastructure (2014): Transport and Tourism: FY2012 Construction By-product Survey Results Reference waste asphalt differ from soil embankments in that Material (in Japanese). settlement takes place in the former but not in the latter.
Mixture of waste asphalt and soil
) 160 I Chitose ompaction ( Chitose without compaction G
n o i
t 120 a r e l e c
c 80 a
t c a p
m 40 I
0 0 30 60 90 120 Depth from the crown (cm)
Fig. 8.Impact acceleraition of compaction of embankment.
4 SUMMARY A study was conducted with the aim of effectively utilizing waste asphalt as a civil engineering material. A series of tests revealed the following. 1. Waste asphalt can be used for constructing embankments. Although the soil particle density, natural water content, and other physical properties of waste asphalt differ from those of typical soil, waste asphalt can be roller-compacted to increase its density and strength. Because no hazardous substances are released from waste asphalt, it can be utilized as an embankment material. 2. The strength of a mixture of waste asphalt and unsuitable soil is higher than the strength of the soil alone, and the strength of the mixture increases over time. Thus, unsuitable soil can be improved by adding waste asphalt. Embankments built with improved soil are stable. 3. To control the settlement of embankments built with waste asphalt, it is necessary that the degree of compaction be high and that air temperatures be low.
REFERENCES 1) Hokkaido Development Bureau (2019): Specifications for Road and River Construction Work (in Japanese) 2) Japanese Industrial Standard (1995): JIS A 5001-1995, Road
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