Abstract— High temperature is main reason of rutting and Urban Heat Island effect. Thermal resistance wearing course materials are developed to solve that. Instead of common aggregate, sintered clay (size in 0-5 mm) and recycled ceramic (size in 4.75-9.5 mm) are used to improve the thermal resistance performance. The solar radiation simulation system is developed to evaluate mixtures heat resistance effect. Thermal properties are tested by Transient Plane Source method. Volume and mechanics index of mixtures are tested by Marshall experiment. The thermal properties change largely with the use of sintered clay and recycled ceramic. Thermal resistance wearing course materials can isolate heat effectively. The performance of water sensitivity, high-temperature and low-temperature of developed materials are tested. The results show that the thermal resistance wearing course has good performance by choosing proper dosage of sintered clay and recycled ceramic.
Index Term-- thermal resistance wearing course; sintered clay; recycled ceramic; thermal properties
1.0 INTRODUCTION
Rutting is defined as the progressive accumulation of permanent deformation of each layer of the pavement structure under repetitive loading [1]. Problem related to rutting is reported by user agencies in the worlds. The rutting would decrease the performance and life of road. Many factors such as materials, design and construction affect high-temperature performance. The conventional methods improving the high temperature performance by using asphalt SBS modifier, good gradation and controlling construction quality strictly [2-5]. All these conventional methods focus on improving the high temperature performance of HMA.
However, the key reason lead rutting is ignored. As we known, the HMA is easy to absorb and keep heat in sun radiation. The heat makes mixture in high temperature. The research shows that dynamic stability (DS) decrease sharply as exponential rule for each 5°C temperature increment. Therefore the rutting can be controlled effectively by reducing road temperature [6].
In addition, Urban Heat Island (UHI) effect is becoming more serious in urban areas. UHI effects increase the air temperature in summer and lead to the air condition use in big cities. Summer urban heat islands with daytime average air
temperature 2.5°C higher than surrounding rural areas are found throughout the world. UHI effect cause an increase of 1.5-3.0% energy demand for each 0.5°C increment [7]. Another study showed that UHI effect also accelerates the formation of harmful smog which harm to the citizens [8].
UHI effect is mainly caused by the artificiality instead of original vegetation. Asphalt pavement in cities takes a large account (Chicago and L.A. more than 20%) [9]. Some researchers try to change pavement type to reduce pavements temperature. The researches showed that reducing pavements temperature can mitigate UHI effect [10]. Heat reflection coating is developed to decrease the temperature. The researches showed that the coating can lower about 10°C. However the coating costs high about $50/m2 [11, 12]. Recently light color aggregate and discolored asphalt are chosen to decrease pavement temperature by increasing the albedo of pavements [13].
Wearing course is widely used in road maintain to improve the performance. As a function layer, it is an effective way to increase anti-skid and driving comfort.
According to thermodynamics, the object with smaller thermal conductivity has lower balance temperature [14-17]. Sintered clay (size in 0-5 mm) and recycled ceramic (size in 4.75-9.5 mm) have smaller thermal conductivity (about 0.23-0.55 W/m·K). Based on this, the thermal resistance wearing course is developed by using sintered clay and recycled ceramic as partial aggregate. The new wearing course can not only lower temperature and mitigate UHI effectively, but also make use of abandoned ceramic, the construction and demolition wastes (CDW) worldwide.
The main objective of this paper is to develop wearing course with heat resistance effect. Thermal properties of materials are tested by Transient Plane Source method. Heat resistance effect is evaluated by solar radiation simulation system. The road performance, water sensibility, high-performance and low-performance are tested. Considering road performance and heat resistance effect, the proper dosages of sintered clay and recycled ceramic are determined. The results show that thermal resistance wearing course has good performance by choosing proper dosage of sintered clay and recycled ceramic.
Thermal Resistance Wearing Course
Development and Performance
FENG Decheng, ZHANG Xin
School of Transportation Science & Engineering, Harbin Institute of Technology, Harbin, China.
2.0 MATERIALS AND EXPERIMENT
2.1 Materials
Aggregate for thermal resistance wearing course should be equal, clean, firm and a small quantity of needle particle. In this study, granite is chosen as common aggregate. The filler is limestone. Tested by ASTM D3398 and D3744, it satisfies the requirements. The asphalt is PG70-28 modified by 5% SBS.
Sintered clay Sintered clay is made from clay by powering and calcinations. The size is 0-5 mm, and bulk density is about 500 kg/m3. The surface is dense but void inside. The thermal conductivity is about 0.23-0.55 W/m·K. The other technology index is showed in table I.
Recycled ceramic Recycled ceramic is made of abandoned ceramic by crusher. The size is controlled among 4.75-9.5 mm. The technology index is showed in table I. From the results, fragmentation, lost quantity Q (Los Angeles machine, ASTM C535) and AIV (Impact test, EN 1097-2) are high, so the dosage of ceramic should be controlled. To avoid high content of needle, ceramic should be crushed several times. The adherence is low because of acidity and slippery enamel. To satisfy the requirement, calcareousness is used to modify.
Table I
Technology index for sintered clay and recycled ceramic
Item Results Criterion
Sintered clay
Fragmentation value (%) 19.4 <20
Adherence 4 ≥4
Clay dosage (≥0.075mm) (%) 1.2 ≤3 1h water absorption (%) 6.1 — 24h water absorption (%) 9.5 —
Recycled ceramic
Fragmentation (%) 24.2 ≤26 Lost quantity Q (%) 15.5 ≤28
AVI (%) 21.7 —
Needle (%) 33 ≤15
Adherence ≤3 ≥4
Gradation Refer to the research and experience, the median of SAC-10 is chosen as the design gradation. The designed gradation is showed in Fig.1.
Fig. 1. Design gradation for thermal resistance wearing course
2.2 Thermal properties test
Factors affecting temperature field are external factors (including air temperature, radiation intension, clouds, and wind
speed) and interior factors (including thermal properties, surface albedo and surface emissivity). Thermal properties are thermal conductivity, heat diffusivity, heat capacity. It is very important to get accurate thermal properties in this study.
Transient Plane Source is a transitory method to determine the thermal properties. In the TPS method a round and plane heat source is used. It behaves as a transient plane source working simultaneously as a temperature sensor. This element consists of an electrical conducting pattern of thin nickel foil in the form of a double spiral, inserted between two insulating layers made of polyimide, as depicted in Fig. 2. The TPS element is located between two similar samples with both sensor faces in contact with the two samples surfaces (Fig. 2).
The method was based on the theory developed by Gustafsson. A constant electric power supplied to the sensor results in an increase in temperature
T
t
which is directly related to the variation in the sensor resistanceR
t by the equation:
t
R
T
t
R
01
(1)where
R
0is the disk resistance at the beginning of the recording (initial resistance) and
is the temperature coefficient of resistance of the nickel foil.Assuming an infinite sample and conductive pattern being in the plane of a coordinate system, the temperature rise at a point at time is obtained by solving the equation for the heat conduction, which relates change in temperature with time. In the particular case of sensor geometry, n concentric ring sources, the spatial average
T
ave
can be obtained through the equation:
3/2
10
T
ave
P
D
a
(2) Where P0 is a Bessel function,D
is a geometric function characteristic of the number n of concentric rings, and is the temperature increase of the sensor expressed in terms of only one variable
, defined as
t
/
(3)k
a
2/
(4) Where t (s) is the measurement time from start of transient heating,
is the characteristic time, which depends both on parameters of the sensor and the sample,a
(mm) is the sensor radius and k (mm2/s)is the thermal diffusivity of the sample. The characteristic time needs to be in the range 0.5-1.5 to guarantee that theoretical assumptions are kept, thus the heat flow is an ellipsoid of neither too high nor too low sphericity.Fig. 2. Schematic set-up of the experiments and sensor used
2.3 Heat resistance effect test
By using sintered clay and recycled ceramic as part of aggregate, the mixtures thermal properties changes. Heat resistance wearing course built on surface decrease heat storing in pavement materials, which mitigate rutting and UHI effect. The heat resistance effect is evaluated by solar radiation simulation system showed in Fig. 3, which is developed to simulate pavements in solar radiation environment. The lamp-house is iodine-tungsten light, which has similar spectrum with sun. On the assumption that object has the same temperature in the same radiation energy, the radiant intensity is determined 788 W/m2, and the radiation time is 7 h. The specimen size is 300×300×50 mm. Collect specimen surface and underside temperature.
Fig. 3. Schematic set-up of solar radiation simulation system
Table II
Surface temperature indoor and outdoor (°C)
Outdoor Indoor
time Temperature(°C) radiation
time(h) Temperature(°C)
9:00 40.2 0 27.4
10:00 46.6 1 50.1
11:00 57.4 2 57.6
12:00 60.6 3 62.3
13:00 65.5 4 65.4
14:00 64.3 5 68.8
15:00 62.5 6 69.6
16:00 60.6 7 69.9
The system is validated by indoor and outdoor test. The same specimen was tested by the system indoor and in solar radiation outdoor. Table II shows the result. From table II, the highest temperature appears at 13:00 outdoor test and at 7 h indoor test. Temperature at 7 h indoor is about 4.4 °C higher than the temperature at 13:00 outdoor. The reason is the system indoor without heat convection by wind. The system is developed to
simulation solar radiation in the hottest season, so the difference in highest temperature is receivable.
3.0 RESULTS AND DISCUSSION
3.1 Marshall experiment
Five dosages of sintered clay and recycled ceramic, 0, 20%, 40%, 60% and 80% are chosen to instead same volume of common aggregate. The optimum asphalt ratio for sintered clay and recycled ceramic wearing course is determined by Marshall experiment. The results of the different dosages are showed in table III.
Because of high water absorption, mixtures with sintered clay need more asphalt. For volume index, with the increase of sintered clay and recycled ceramic, the bulk density decrease, VV reduces first and increase lately, and VFA changes contrarily. For mechanics index, materials with sintered clay have higher stability than common materials. Materials with recycled ceramic have lower stability than common materials. Because sintered clay is used as fine aggregate, that has little affect on mixture structure. The recycled ceramic used as coarse aggregate is fragile. It becomes weak part in mixture structure. Flow value change without rules. So in the materials design, the dosage of recycled ceramic should be controlled strictly.
Table III
Results of Marshall experiment for sintered clay and recycled ceramic wearing course
Item HMA Sintered clay HMA Recycled ceramic HMA
Dosage
(%) 0 20 40 60 80 20 40 60 80
Asphalt
ratio (%) 4.5 4.8 5.4 6.0 6.6 4.8 5.1 5.7 6.0
Bulk density
(g/cm3) 2.51 2.28 2.01 1.77 1.47 2.43 2.38 2.30 2.23
VV (%) 4.0 4.4 4.3 4.5 6.7 4.8 3.9 3.9 4.2
VFA (%) 73.3 75.8 70.6 69.3 57.9 69.9 74.9 76.0 75.2
Stability
(KN) 10.6 10.8 12.5 12.4 12.2 9.00 8.73 8.01 9.02
Flow value
(0.1mm) 31.9 27.8 35.6 26.1 28.5 31.2 21.4 28.0 25.2
3.2 Thermal properties test
properties of binder and aggregate are both decreased.
(a)
(b)
Fig. 4. Results of thermal properties of sintered clay and recycled ceramics wearing course mixture
3.3 Heat resistance effect test
Test surface and underside of specimen temperature for different type mixtures. The results are showed in Table IV. The results indicate that with the increase of sintered clay and recycled ceramic, the surface temperature increases appreciably which is contrary to thermal properties. This can be explained by the fact that the high conductivity allows the heat gain form radiation at the surface to be transferred away rapidly and consequently absorbed into the ground, which acts as a heat sink [22]. But the high heat capability makes low underside temperature. The underside temperature decreases evidently. The lower underside temperature means the mixture in cool environment. Compared with common mixture (0% dosage), the 20% dosage temperature difference increase from 3.2 °C and 3.5 °C to 7.1 °C and 8.5 °C respectively. It means that sintered clay and recycled ceramic can isolate heat effectively. While dosage of sintered clay and recycled ceramic increase up to 60%, temperature difference increase slowly. The isolation heat effect is prominent in some dosage. Considering other performance, the dosage of sintered clay and recycled ceramic should be controlled strictly.
Generally, the highest shearing stress appears in 5 cm below pavement surface. It is benefit to mitigate rutting by decreasing temperature in that depth. Research [6] shows that Dynamic Stability is affected largely by temperature. Fig. 5 shows the
relation between AC mixtures DS and temperature of three types asphalt A, B and C. DS decreases largely for each 5 °C temperature increase on the threshold of 40 °C.
Table IV
Results of lower temperature experiment (°C)
Item
Dosage
0 20
% 40 %
60 %
80 %
Sintered clay
Surface 69.
4 70.0 72.8 73.2 72.9
Underside 66.
2 62.9 63.1 60.3 59.4 Temperature difference 3.2 7.1 9.7 12.9 13.5
Recycled ceramic
Surface 69.
4 69.7 70.5 70.8 71.0
Underside 65.
9 61.2 59.3 58.7 58.2 Temperature difference 3.5 8.5 11.2 12.1 12.8
Fig. 5. Relation between AC mixtures DS and temperature of three types asphalt A, B and C
3.4 Road performance
Wearing course generally about 2-5 cm thickness, is used in road maintain to improve pavement performance. Although in the design it is not included in road structure, the road performance water sensibility, high-temperature and low-temperature are tested.
Water sensibility The water sensibility is tested by AASHTO T283-98. Residual stability (RS) and Tensile strength ratio (TSR) are used to evaluate the water sensibility. They can be calculated by (5) and (6):
RS=MS1/MS (5)
TSR=RT2/RT1 (6) where RS is the residual stability, MS1 is the Marshall stability for dipped in water 48 h, MS is the Marshall stability for dipped in water 0.5 h, RT1 is the indirect tensile strength without freeze-thaw cycles, RT2 is the indirect tensile strength with freeze-thaw cycles. The results are showed in table V .
For sintered clay mixtures, RS increases with the dosage 0 to 20%, and decreases with the dosage 40% to 80% but still satisfy requirements. TSR decreases with the increase of sintered clay. For recycled ceramic mixtures, RS increases with the dosage 0 to 20% and decreases slightly with the dosage 40% to 80%. TSR
ceramic mixture has better water sensibility than sintered clay mixture.
Table V Results for water sensibility
Item Dosage (%) 0 20 40 60 80
Sintered clay
RS (%) 91.9 98.2 91.9 86.4 84.2
TSR (%) 88.5 84.0 80.8 69.7 50.2 Recycled
ceramic
RS (%) 95.6 98.8 96.7 95.6 89.9
TSR (%) 90.9 93.7 96.6 86.5 78.4 High-temperature performance The high-temperature performance is evaluated by wheel tracking test (AASHTO T324), the results are showed in Fig. 6. For sintered clay and recycled ceramic mixtures, with increasing the dosage, the dynamic stability (DS) decreases. Compared with sintered clay mixtures, DS of recycled ceramic mixtures decreases hugely. When the dosage of recycled ceramic is 80%, the DS can not satisfy the requirement (≥2400). In materials design, the recycled ceramic should be controlled strictly.
Fig. 6. Results for high temperature performance
Fig. 7. Results for low temperature performance
Low-temperature performance The low-temperature performance is evaluated by ASTM D1423, and the results are showed in Fig. 7. For sintered clay mixture, the flexural modulus decreases hugely with the increase of dosage. For recycled ceramic mixture, the flexural modulus changes slightly. The results show that sintered clay mixture has more effect on low-temperature performance than recycled ceramic.
4.0 CONCLUSIONS
From the test results and discussion, the following conclusions are drawn:
1) Using sintered clay and recycled ceramic instead partial aggregate decrease thermal conductivity and thermal diffusivity effectively. Changing in mixtures decreases pavement work temperature. That is in favor of mitigating rutting and UHI effect.
2) Sintered clay has obvious effect on water sensibility and low-temperature performance, by contraries to high-temperature. Thermal conductivity and thermal diffusivity decrease more than 50% at least dosage (20%). Considering performance and isolation heat effect, the optimum dosage is between 30-40%.
3) Recycled ceramic has obvious effect on water sensibility and high-temperature performance, by contraries to low-temperature. Thermal conductivity and thermal diffusivity decrease more than 30% at least dosage (20%) of crushed ceramic. Recycled ceramic wearing course mixture is better in water sensibility and low-temperature performance. But the high-temperature performance is much worse. Considering performance and heat resistance effect, the optimum dosage is between 40-60%.
4) The recycled ceramic is a kind of construction and demolition wastes (CDW) worldwide, make use of the materials is useful for solving the lack of construction materials and protecting environment. The new thermal resistance wearing course can magnitude UHI effect and save energy by reducing the heat absorption.
5) In this paper only one widely used gradation is chosen to test the performance. More gradations should be considered in further research. The new materials still in experiment should be observed in field for a long time.
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