Evaporative Cooling Effect of the Pavement Covered with Reused Sanshu Roofing Tiles

Ineko Tanaka Dr.Eng., Manabu Okazaki, Tetsumi Horikoshi Dr. Eng., Yuji Uno Dr. Eng.

Abstract- Sanshu area located in the South of Nagoya City, Japan has been prosperous for the roofing tileindustry. In recent years, this Industry has become environmentally conscious and has partially reused
inferior goods generated during tile-manufacturing process as raw materials for roofing tiles. In addition,
reusing methods of scrap tiles excreted from re-roofing and constructional demolition has been searched.
On the other hand, in Nagoya, the thermal environment of summer is getting worse every year, because theartificial land-covering materials with high-heat capacity and without water permeability, such as asphalt,
became common. In this study, the crushed roofing tile called Kawara ballast, a by-product from Sanshu
roofing tile industry, was considered as material for water-permeable pavement. Its cooling effect from
evaporation through the permeable ground surface would improve the outdoor thermal environment insummer. Experiments on the evaporative cooling effects of the pavement using the ballast were conducted
to determine thermal characteristics of the pavement. The basic characteristics regarding the evaporative
cooling effect of the ballast were experimentally investigated. The water absorption and the water retention
properties were measured for each particle size. The saturated water content was found to be 13.2% and10.5% for particle sizes 1-4mm and 4-10mm respectively. Field measurements were carried out during
summer in Nagoya in a 300m2 site to clarify the thermal behavior of water-permeable pavement with thecrushed tiles. The results were compared with non-water permeable pavement and lawn-covered surface. It
was confirmed that the pavement using the crushed Sanshu tiles is suitable for increasing cooling effect insummer.
1. INTRODUCTION
The thermal environment problem of urban areas in Japan, such as the expansion of heat island insummer, has been getting worse in recent years. Especially Nagoya, located in the center of Japan, shows
the need for cooling-methods in the urban area, because it is remarkably hot in summer (Horikoshi, 1998).
Instead of high thermal capacity materials, such as asphalt and concrete, ground-covering materials having
an evaporative cooling effect are necessary. The use of tree and lawn vegetation is known as one of themethods to improve thermal environment in summer. Because the evaporation and the respiration fromvegetation as well as the ground removes heat as the latent heat from these surfaces and nearby
atmosphere. Regarding the other methods, there is a study by Akagawa who developed the continuation
dampness pavement system (Akagawa 2000) and a study by Shirai who developed a passive cooling wallfor evaporative cooling effect using a new wall brick (Shirai, 1996). In addition, there are several
experiments that examined the influence of different types of ground-covering materials on thermal
environment (Tsutsumi 1998; Ooi 1998; Okazaki 2002). However, the investigated samples and subjective
areas were limited in these experiments. Hence some numerical simulation models have been proposed todesign and evaluate thermal environment, which can simulate the evaporative cooling effect from theground (e.g. Hagiwara et al. 2001). Each numerical simulation model for the evaporative cooling effect has
to depend on the results of the actual measurement. There needs to obtain data regarding the water content
characteristics for the new materials, which have evaporative properties.
On the other hand, Sanshyu area, located in the south of Nagoya, has been traditionally prosperous in
Japan for the roofing tile industry. In this area, large quantities of waste from the tile production process andused roofing tiles are problems. For conservation of local resources, methods for recycling these disposal
tiles have been examined. Disposal tiles from the production process are crushed, what is to be called
Kawara ballast, and part of the material is mixed with clay of raw materials of Kawara. However, the rest of
the ballast and wastes of used roofing tiles still have no utilization. In addition, the absorption ability of theballast, unglazed pottery, is regarded as worth researching.
In this study, we evaluate the evaporative cooling effect of the new pavement using Kawara ballast andconfirm the possibility of its utilization as the passive cooling materials for a pavement. Water absorptive
characteristics of several kinds of Kawara ballast were examined. The thermal characteristics of thepavement were confirmed with the measurement at the outdoor test models in summer. It is worth todeveloping new utilizations of reused materials from local industry in order to contribute to the sustainable
society and to improve the local environment.
2. WATER ABSOPTIVE CHARACTERISTICS OF KAWARA BALLAST
Two kinds of roofing tiles are produced at Sanshu tile industry. One is called Touki Kawara and anotherone is called Ibushi Kawara. Both of them are made of almost the same raw materials, which include 3% of
Kawara ballast, and are baked at around 1100 degrees Celsius. Particle sizes of clay and the process of
producing are different. Touki Kawara is glazed roofing tile and Ibushi Kawara is baked without glaze. It is
made so that the water may not soak into the roofing tiles. But Kawara ballast has unglazed surface and iseasy to be infiltrated by water. There is few data of water infiltration into the ballasts. In order to clarify thecharacteristics of water absorption and water retention of the ballast made from each Kawara, the two
following experiments were carried out:
Kawara ballast is sifted to particle less than 10mm size during the production process of the ballast at
Sanshu

area

(Fig.

1).

On

these

experiments, two kinds of ballast with

Table 1 Mean saturated water content of Kawara ballast.

different particle were used for bothmeasuring samples of Ibushi Kawara
and Touki Kawara. Each kind of ballast
was divided by particle size from 4mm

Type of material

Touki ballast

Ibushi ballast

Particle size [mm]1-4

4 - 101-4

4 - 10Mean sarturated watercontent (mass by mass)[%]

13.2

10.5

11.7

9.4

to10mm and from 1mm to 4mm.
2.1 WATER ABSORPTION CHARACTERISTICS
To clarify the water absorption characteristics of the ballast, the saturated water content were obtained by
the experiment based on JIS A1203. After 4 kinds of the ballast absorbed water for 24 hours in the artificial

Water content (%)

14
12

Touki ballast 1-4mm

10

Touki ballast 4-10mm

8Ibushi ballast 1-4mm

6

Ibushi ballast 4-10mm

4
2
0
0

Fig. 1 Particles of Touki ballast withless than 10mm.

1

2

3

4

5 6 7
Tim e (h)8910 11 12Fig. 2 Transition of water content of each Kawara
ballast at a 40 degrees Celsius atmosphere.

climate chamber, the weight of these samples were measured. While they absorbed water, the artificial
climate chamber was set at a 20 degrees Celsius temperature and 50% relative humidity. These samples
were dried for 24 hours at 105 degrees Celsius with a constant temperature dryer, and the weight of eachsample was measured again. The saturated water contents of the materials were calculated from the weightof entirely dried samples and the absorbed ones. This process was repeated five times and their meanvalue was adopted.
The average saturated water content of each sample is shown in Table 1. The saturated water content ofTouki ballast was higher than that of Ibushi ballast. In addition, the saturated water content of the small
particle was higher than the large one. The evaporative cooling effect and retaining rainwater ability were
expected for Touki ballast, because its saturated water content is higher.
2.2 DRYING SPEED CHARACTERISTICS
To investigate the water retention characteristics of both Ibushi and Touki ballast, the drying speed of test
samples were observed. These samples were the same as those used in the experiment of chapter 2.1.
The 4 kinds of measuring samples absorbed water for 24 hours in the artificial climate chamber at 20
degrees Celsius and 50%RH. These samples were set in the constant temperature dryer, and their weight
was measured every 30 minutes till they were completely dried.
Fig. 2 shows the results when the dryer temperature is 40 degrees Celsius. Ibushi ballast dried faster than
Touki ballast and large particles of 4-10mm dried faster than small particles. Therefore, continual
evaporative cooling effect should be expected by using smaller particle of Touki ballast.
2.3 PROPOSAL OF PAVEMENT MADE OF KAWARA BALLAST
Touki ballast is suitable for the pavement material because the evaporative cooling effect is expected fromthe results above. The ballast with small particle shows higher performance of absorption and retention ofwater. In addition, the previous investigation of roofing tile ballast (Tsuboi, 2001) indicates that small particle
ballast has low permeability. The following test models covered with the ballast were made to cool theoutdoor space efficiently as follows. Large particles of Touki ballast were placed at the upper part of thepavement as the water permeable and absorptive layer, and small particles were placed at the bottom partof the pavement as the earth-water retaining layer.
3. EVAPORATIVE COOLING EFFECT OF THE KAWARA BALLAST PAVEMENT
3.1 SUMMARY OF FIELD MEASUREMENT
To compare the evaporative cooling effects of the pavement covered with different materials, seven kindsof test models were constructed in the Nagoya Human Science Park, southern part of Nagoya. The fieldmeasurements were conducted in the summer of 2003.
(1) Test Models of Pavement
Seven kinds of test models and their placements are shown in Fig. 3. The dimensions of each test modelare 5m x 5m. The perimeters of the test models
were insulated with foamed polystyrene board of
30mm thickness and also waterproofed as tominimize the influence from the sides. Fig. 4
shows the sections of the test pavement models.
Type 1 and 2 are the models using the ballast.
The structure of Type 1, as shown in Fig. 5, is asfollows; whole roofing tiles stand at intervals of
20mm on the lower layer with relatively smaller
particle than that of upper layer.

Fig. 5 The outdoor surface in Type 1.

GravelFig. 3 Site plan of test models in the test fieldof Nagoya.

Fig. 4 Cross-section of test models andlocations of internal thermocouples(φ= 0.3mm).

Highest air temperature(h=30cm)
Touki ballast(d=30)
Ground(d=90cm)

4500

40

4000

35

3500

30

3000

25

2500

20

2000

15

1500

10

1000

5

500

0

0
8/1

8/8

8/15

8/22

8/29

9/5

Solar radiation (W/m2)

Temperature (℃)

45

9/12

Date

Fig. 6 Outdoor climate and internal temperature of Type 1 from Aug. 1 to Sept. 12.
locations of internal thermocouples(φ= 0.3mm).
The remaining spaces were filled with Touki ballast. Type2 was constructed with only Touki ballast at 60mm
depth. The gravel model was constructed with around 30mm particle sizes of gravel at 60mm depth. Theinter-locking blocks used in this measurement are water permeable and are made of recycled concrete.
They were constructed with 60mm depth on the sand of 20mm depth.
(2) Method of measurement
Fig. 4 shows the positions of waterproofed T-typed-thermocouples placed in the test models. The vertical
distributions of air temperature were measured above the surface of the test models with solar shaded
T-typed-thermocouples at 100cm, 30cm, 10cm and 2cm height. The air temperature and the undergroundlayer temperature of the test models were automatically recorded by data-logger every 10 minutes. The
measurement has been conducted since August 1st., 2003. Wind direction and velocity were obtained fromthe air pollution monitoring system of the Ministry of Environment, which is located 900m distant from thetest field, Those data were utilized and analyzed in the present study. The rainfall data from Nagoya
Meteorological Observatory was also used.
To examine the thermal behavior of the pavement precisely, relative humidity, long wave radiation, winddirection and wind velocity were measured every 30 minutes, and thermographs of the surface of the test
models were measured every hour. This measurement took place on August 22nd., a clear day.
In addition, to determine the water absorption characteristics of the ballast after rainfall, samples of theballast were obtained from the surface, 10cm and 20cm of depth, and from the bottom of Type 1. The watercontent of each sample was measured.
3.2 RESULTS AND DISCUSSION(1) Climate during the field measurement
Fig. 6 shows the outdoor climate, the ballast layer temperature (depth = 30cm) of Type 1 and theunderground temperature at 50cm from the bottom of Type 1. This data was obtained from August 1st. to70Type2: Touki ballast
Asphalt
I.L.blockConcrete

2800

60

2400

50

2000

40

1600

30

1200

20

800

10

400

0

0
5:00

9:00

13:00

17:00
Time

21:00

1:00

Solar radiation (W/m2)

Surface temperature (℃）

Type1: Roofing tile
Lawn
Type1:Touki ballast
GravelFig. 7 Surface temperature of test models and solar radiation on a clear day (Aug. 22).
70 [℃]

60

50

40

30

Fig. 8 Thermograph of test models at noon on a clear day (Aug. 22).
September 12th, 2003. The ballast layer temperature is much more influenced by daily climatic changes
than the underground. The daily range of the ballast layer temperature is less than 2 K.
(2) Surface temperature on a clear day
The surface temperatures of each test model obtained on August 22nd, a clear day, are shown in Fig. 7.
The surface temperatures of Type 1 and 2 remained lower than that of asphalt and higher than that of lawn
during the daytime. The maximum difference of surface temperature between Type2 and lawn was 8K, andbetween asphalt and Type2 was 10K. The surface temperatures of Type1 and 2 gradually decreased along
the time and became closer to the surface temperature of lawn. Especially in Type 2 with only Touki ballast,
there was a drastic drop of the surface temperature around 5 p.m. The surface temperature of Type 2
shifted with the change of the solar radiation because heat capacity of Type 2 with shallower depth is lower
than that of Type 1. It tended to be same for the surface temperature of gravel. This temperature becomes
the same as lawn temperature from 8 p.m. Fig. 8 shows the thermograph of all test models at 12:00 noon on
August 22nd. The surface temperature of Type 1 and 2 indicates the same horizontal distribution with that of

Type1:Surface
Type1:20cm
Type2:Surface

0.025

Type1:10cm
Type1:Bottom
Type2:Bottom

0.02

14

0.015
0.01
Type1:Touki ballast
Type2: Touki ballast
Law nAsphalt

0.005

Water content (%)

Absolute humidity (kg/kg'

16

12
10
8
6
4
2

0

0
6:00

10:00 14:00 18:00 22:00 2:00

8/19

Time

Fig. 9 Absolute humidity over the test models
of Type 1 and 2 on the clear day (Aug. 22).

8/20

8/21

8/22

Time

Fig. 10 Transitions of water content of Touki
ballast of Type 1 and 2 from Aug.19 to 22.

inter-locking blocks. It is around 10 K lower than that of asphalt and gravel. The surface temperature ofconcrete is around 10K lower than that of Type1 and 2. It is considered that the concrete had not dried andcontained moisture because it passed only a few months after concreting. The relative observation about
the test model and other models of concrete will have to be continuously carried out.
(3) Absolute humidity and water content after rainfall
The absolute humidity of each test model obtained on August 22nd at 30cm height is shown in Fig. 9. The
absolute humidity above Type 1 and 2 is not only higher than that of asphalt but also of lawn from noon to
midnight. The water content of the ballast in Type 1 and 2 were measured from August 19th to 22nd after
the rainfall. The precipitation of rainfall from August 14th to 17th was 115mm at the Nagoya District
Meteorological Observatory. The transitions of water content in Type 1 and 2 are shown in Fig. 10. The
water contents of surface ballast in Type 1 and 2 decreased day by day and became absolutely dry after
4days from the rainfall. On the other hand, the water content of internal ballast at 10cm of depth remained
more than 7% after 4days from the rainfall. It indicates a high property of water content of the ballast in theunderground layer. It was also confirmed that there is few differences of the water content property between
Type 1 and 2, even though the depth of Type 1 is about seven times deeper than that of Type 2.
(4) Surface temperature and air temperature after the rainfall
Fig. 11 shows the transitions of the surface temperatures of Type 1, Type 2, asphalt and lawn after therainfall. The surface temperature of Type 1 and 2 fluctuated similar to that of lawn and remained less than
46 degrees Celsius for three days after the rainfall. The temperature of Type 2 reached more than 54
degrees Celsius on August 22nd. As for the transitions of water content in Fig.9, the surface temperatures ofType 1 and 2 were fairly influenced by its water content. Fig. 12 shows the transitions of differential air
temperature at 2cm, 10cm and 100cm of height from the surface of Type 2 and asphalt. There is little
difference at 100cm of height, but some difference at 2cm and 10cm of height. It represents the evaporative
cooling effect by retained water in the ballast as shown in Fig. 10.

Type1:Touki ballast
Type2: Touki ballast
Lawn
Asphalt

3.0

70

2

Surface temperature (℃)

3500
50

3000

40

2500

30

2000
1500

20

1000
10
0
8/19

Solar radiation (W/m )

4000

60

Differential air temperature ( K )

4500

2.0
1.0
0.0
-1.0
-2.0

500
0
8/20

8/21
Date

8/22

Fig. 11 Transitions of surface temperatureof test models after the rainfall.

-3.0
8/19

h=2cm
h=10cmh=100cm

8/20

Date

8/21

8/23

Fig. 12 Transitions of difference between
air temperature over asphalt and Touki
ballast (Type 2).

4. CONCLUSIONSThe pavement using Kawara ballast was examined on its water absorption property and evaporative
cooling effect by using both of the chamber test and the field measurement. It was confirmed that the test
models of the pavement using the ballast had an evaporative cooling effect after the rainfall and the effectremained for a few days. However, this cooling effect was found to be less than the effect of lawn. The
cooling effect of the pavement using only the ballast at 6cm of depth appeared much more effective thanthat of the pavement using whole roofing tiles at the same depth. The application suitability of the reused
Kawara ballast to urban pavement in summer was confirmed.
Our further work will be directed at investigating the influence of the pavement’s cooling effect on thehuman body in summer and at examining the property of rainwater storage to avoid flood in the urban area.
ACKNOWLEDGEMENT
The authors express gratitude to the members of 3R-tile Promotion Societies, Nagoya Urban Industries
Promotion Corporation and Science Park Project Promotion Office of Nagoya City for their cooperation to
the field experiment. This study was supported by a grant from the NITECH 21st Century COE Program“World Ceramics Center for Environmental Harmony”.
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