Analysis of mechanical and environmental characteristics of the atomizing
slag to use as a landfill material
Ha Ik. Chunga, Sang Keun. Kimb, Yu. Junc, Won Seok. Changdand Jeong Soo. Parke
a,b,c
Researcher, Korea Institute of Construction Technology
d,e
Researcher, Ecomaister Co. Ltd.
411-712, 2311 Juyeop-dong Ilsan-gu Goyang-shi Gyeonggi-do, Korea
Abstract
The experimental investigations on mechanical and environmental characteristics of the atomizing slag were
conducted to evaluate the effectiveness of the slag to utilize a landfill material. The measured compressive
strength and CBR of the atomizing slag (5:5) and solidated slag samples exceeded the required value of 0.5
kgf/cm2 and 2.5%, respectively. The measured hydraulic conductivity of the atomizing slag and solidated slag
samples ranged from 5.82ⅹ10-6 to 5.96ⅹ10-6 cm/sec. it was observed that atomizing slag (5:5) and solidated
slag had better drainage ability than the granite soil as a typical landfill cover material. The heavy metals
concentrations in the slag leachate were not detected or 1000 order of magnitude lower than the environmental
criteria for Pb, Cu, As, Hg, Cd, Cr, and CN.
Keywords: atomizing slag, solidated slag, landfill material
1. Introduction
Slag is a residual waste product of steel manufacture. The steel slag generated in Korea annually is estimated to
increase to 600 million tons (Lee, 1998). However, landfilling is generally the disposal solution for the byproduct. Therefore, the recycling of slag can be an excellent solution to deal with not only economical but also
environmental concerns regarding the slag disposal issues.
This study aims to evaluate the effectiveness of the recycled steel slag as a landfill material so called alternative
daily landfill cover material. The steel slag used for this study is produced by an atomizing method patented
worldwide (Ecomaister Co.,Ltd.). The atomizing slag so-called PS Ball is a products cut off converter slag by the
atomizing method. The atomizing slag and conventional converter slag are same in its composite by nature in the
converter but compounds of the composite become different because of different method of slag treatment.
Conventional slag cooling slowly in the open yard has composites of CaO, FeO, Fe 2O3 and etc. Currently, sub4mm the atomizing slag are being produced for filter media, ceramic filters, coagulate, construction materials,
abrasives, and desulfurizing agents (Ecomaister, 2003).
In order to utilize the atomizing slag, the physicochemical property of the slag is needed to evaluate prior to the
landfill applications. Thus, the experimental program of the study includes unconfined compressive strength,
California bearing Ratio (CBR), hydraulic conductivity, rainfall drainage, heavy metal leaching, and gas
permeability test.
2. Materials and methods
2.1 Sample preparation
The five types of the samples were prepared: (1) granite soil only; (2) atomizing slag (8:2); (3) atomizing slag
(7:3); (4) atomizing slag (5:5) and (5) solidated slag. Granite soils are widely distributed in subtropical Korea
and currently used for a daily landfill cover material; however, is relatively expensive due to excavation and
transportation cost. The atomizing slag samples were admixed with granite soil sample. The mixing ratios of the
mass of the atomizing slag to the mass of granite soils were 8:2, 7:3 and 5:5, respectively. The solidated slag

Ha Ik Chung, hichung@kict.re.kr, Phone: +82-31-910-0216, Fax: +82-31-910-0211
above refers an admixture of atomizing slag, the recycled sewage sludge and binding additives (cf. 100:100:1 =
mass of atomizing slag : mass of sewage sludge : mass of binding additives).
(a)
(b)
Figure 1. (a) Atomizing slag and (b) SEM (ⅹ15) picture of atomizing slag (Ecomaister, 2003)
2.2 Experimental program
The gravity water contents of the samples were measured by weighing the samples before and after drying in an
oven for 24 hour at a temperature of 110°C. Specific gravity of the atomizing slag sample was estimated
according to the Korean specification method (KS F 2503). Sieve analyses were conducted to investigate grain
size distribution of the slag samples and coefficients of uniformity (D10) and curvature (D60) of the slag were
calculated.
Leaching of heavy metals was examined from a leaching test for the atomizing slag samples according to the
Korean specification for hazardous wastes. The concentrations of Pb, Cu, As, Hg, Cd, Cr and CN in the slag
sample leachates were measured and compared with the maximum concentrations level of the heavy metal. After
demolding the specimen (50 mm diameter and 100 mm thick), the samples from each mix were moist cured in a
fog room for six different periods of time: 3, 7, 14, and 28 days. A conventional compressive strength device
with maximum load of 50 kg and 1mm/min of load rate was used to obtain the compressive strength of the
samples after each curing period (KS F 2314). California Bearing Ratio (CBR) tests were conducted to evaluate
equipment transportability of the atomising slag as a daily landfill cover material (KS F 2320). In order to
investigate capability of atomising slag to transmit water, a saturated hydraulic conductivity was measured using
a constant and falling and head method for curing periods of time 3, 7, 14 and 28 days (KS F 2322). Drainage
from a rainfall event was simulated through the sample (1) to (5). The experiment design enable the continue
monitoring drainage discharge and seepage rate of the atomising slag samples. Gas permeability characteristic of
the slag samples is important in odour and landfill gas migration issues. Gas permeability tests for the atomising
slag samples were designed on the basis of a water vapour transmission test of ASTM E96.
3. Results and discussion
3.1 Material property of the atomizing slag
3.1.1 Engineering property
The determined value of specific gravity was higher than that of typical sand. It was observed that the
compressive strength and hardness of the slag were two times higher than those of sands. Absorption ratio of the
slag was significantly lower than that of typical sands. The shape of the slag produced by atomizing process is
generally spherical according to the calculated coefficient of uniformity. The measured water content of the slag
ranged from 0.79 to 0.98% (See Table 1).
Table 2 presents the measured density of the atomizing slag and solidated samples. Each of the samples was both
lightly and heavily compacted. The density of atomizing slag samples mixed with granite soil and solidated
samples were somewhat lower than that of the typical atomizing slag
The grain size distribution plays a key role in determining engineering property, such as density, permeability,
and shear strength, of coarse materials. According to the grain size distribution analysis measured by a sieve
process, the slag samples, the estimated D10 and D60 were 0.46 mm and 1.36 mm, respectively. The calculated
coefficient of curvature, Cg, ranged 1.01 to 1.06. The grain distribution of the slag samples was good and the size
and shape of the sample was uniform (See Table 3).
Table 1. Property index of atomizing slag
specific gravity hardness (Hv)
3.54
Absorption
(%)
strength
(kg/cm2)
uniformity
water content
(%)
0.1
223
1.22
0.79 - 0.98
500 - 700
Table 2. . Measured density of atomizing slag and solidated samples
atomizing slag
compaction
3
density (g/cm )
atomizing slag (5:5)
Solidated
lightly
Heavily
lightly
heavily
lightly
heavily
2.30
2.34
1.22
2.06
1.40
1.64
Table 3. Grain size characteristics of atomizing slag samples (8:2, 7:3 and 5:5)
Sample I.D.
atomizing (8:2)
atomizing (7:3)
atomizing (5:5)
average
D10 (mm)
D30 (mm)
D60 (mm)
Cu
Cg
0.43
0.77
1.30
3.02
1.06
0.50
0.85
1.30
2.60
1.11
0.45
0.77
1.30
2.89
1.01
0.46
0.80
1.30
2.84
1.06
3.1.2 Leaching test
As shown in Table 3, the atomizing slag consists of CaO, Fe2O3 and SiO2. Table 3 shows he chemical
constituent of the samples. According to the result of leaching test, the heavy metal concentrations of the slag
leachate were lower than maximum concentration level based on Korean standard for hazardous wastes. Table 5
indicates the concentrations of Pb, Cu, As, Hg, Cd, Cr and CN from the collected leachate samples of atomizing
slag and solidated.
Table 4. Chemical constituent of typical atomizing slag
Weight (%)
atomizing slag
CaO
14 to 63
Fe2O3
22 to 45
SiO2
10 to 20
MgO
6 to 10
FeO
<3
Al2O3
<5.5
Table 5. Summary of the leaching test
Analyte
atomizing
a
MCL
(unit: ppm)
(8:2 & 7:3)
b
Pb
< 3.0
N.D.
Cu
< 3.0
N.D.
As
< 1.5
N.D.
Hg
< 0.005
N.D.
Cd
< 0.3
N.D.
Cr
< 1.5
N.D.
CN
< 1.0
N.D.
a
MCL refers to maximum concentration level
b
N.D. denotes no detection
atomizing (5:5)
Solidated
0.001
0.007
0.001
N.D.
N.D.
0.002
N.D.
N.D.
0.08
0.02
N.D.
N.D.
0.02
N.D.
3.2 Atomizing slag as a landfill material
3.2.1 Unconfined compressive strength
As shown in Figure 2, the unconfined compressive strengths of the granite soils, atomizing slag (5:5) and
solidated (atomizing slag + sewage sludge) were higher than the required strength of 0.5 kgf/cm2. According to
the Korean specification for a landfill cover material, the ultimate compressive strength required for workability
and transportability is equal to 0.5 kgf/cm2 in the landfill applications. The atomizing slag samples (8:2) and
(7:3) would not be suitable for a landfill cover material (c.f. 8:2 = mass of atomizing slag : mass of granite soil).
Unconfined Compression Strength (kgf/cm2)
3.50
3.00
granite soil
atomizing slag (5:5)
atomizing slag (7:3)
atomizing slag (8:2)
solidated
2.50
2.00
1.50
1.00
Unconfined compression strength criteria
0.50
0.00
0
5
10
15
20
25
30
Time (day)
Figure 2. Unconfined compressive strength of the samples
3.2.2 California Bearing Capacity (CBR)
A landfill cover material should be met the required CBR of 2.5% according to the Korean standard (Korean
Highway Corporation). As shown in Figure 3, both the CBR of the atomizing slang and solidated exceeds the
standard CBR of 2.5%.
14
12
CBR (%)
10
8
6
4
CBR criteria
2
0
granite soil
atomizing slag
(5:5)
solidated
Figure 3. Measured CBR of the granite soil, atomizing and solidated slag samples
3.2.3 Hydraulic conductivity
The hydraulic conductivity of a landfill cover material is currently not defined in the Korean specification;
however, the hydraulic conductivity of clay soils, ranging from 1ⅹ10-5 to 1ⅹ10-6 cm/sec has conventionally
used for that of a landfill cover material. Figure 4 shows the measure hydraulic conductivities of the samples.
The atomizing and solidated slag samples have a reasonable hydraulic conductivity range as a daily landfill
cover material.
7.E-06
7.E-06
permeability (cm/sec)
6.E-06
6.E-06
5.E-06
5.E-06
granite soil
atomizing slag (5:5)
4.E-06
solidated
4.E-06
3.E-06
0
5
10
15
20
25
30
Time (hrs)
Figure 4. Measured hydraulic conductivity of the granite soils, atomizing and solidated slag
3.2.4 Simulation of rainfall drainage
According to the rainfall drainage simulation, the atomizing slag (5:5), solidated and granite soils had an
excellent drainage ability as a cover material (See Figure 5)
75
drainage (%)
70
65
granite soil
atomizing slag (5:5)
60
atomizing slag (7:3)
atomizing slag (8:2)
55
solidated
50
0
0.5
1
1.5
2
2.5
3
3.5
Time (hrs)
Figure 5. Measured rainfall drainage of the granite soils, atomizing and solidated slag samples
3.2.5 Gas permeability
As shown in Table 6, the measured gas permeability of the atomizing slag and solidated slag ranged from 69 to
74 g/h/m2, which is lower than that of granite soil samples. The atomizing slag and solidated slag can effectively
resist against landfill gas migration and manage odour issues.
Table 6. Summary of gas permeability
Sample I.D.
Gas permeability (g/h/m2)
Gas transmission factor
Granite soils
Solidated
Atomizing (8:2)
Atomizing (7:3)
Atomizing (5:5)
100.43
73.7
68.7
71.4
74.2
0.64
0.47
0.44
0.46
0.47
5. Conclusion
Material property tests, geotechnical index tests, and leaching tests for granite soils and atomizing slag were
conducted in order to evaluate the effectiveness of atomizing slag to use a daily or intermediate landfill cover
material. The compressive strength, bearing capacity and drainage of the atomizing slag and solidated were
reasonably satisfied with the required criteria for a landfill cover material. In addition, heavy metals in the
atomizing slag were not detected in comparison with the environmental guide. Accordingly, the atomizing slag
can be a cost-effective and environmentally friendly landfill cover material. The results of assessment for the
atomizing slag for a landfill cover are as follows:
1.
2.
3.
4.
5.
The measured compressive strength and CBR of the atomizing slag (5:5) and solidated slag samples ex
ceeded the required value of 0.5 kgf/cm2 and 2.5%, respectively. However, the atomizing slag (8:2) an
d atomizing slag (7:3) were not satisfied with the criteria.
The measured hydraulic conductivity of the atomizing slag and solidated slag samples ranged from 5.8
2ⅹ10-6 to 5.96ⅹ10-6 cm/sec. In comparison with the hydraulic conductivity of clay and clayey sand, 1
ⅹ10-5 to 1ⅹ10-6 cm/sec, the atomizing and solidated slag indicated reasonable hydraulic conductivity
as a cover material.
As a result of the rainfall drainage test with the 50 mm-rainfall intensity , it was observed that atomizin
g slag (5:5) and solidated slag had better drainage ability than the granite soil as a typical landfill cover
material. In addition, the curing periods did not affect the drainage ability of the atomizing and solidat
ed slag samples
The measured gas permeability of the atomizing and solidated slag ranged from ranged from 69 to 74 g
/h/m2 and gas transmission factors ranged from 0.44 to 0.64 as well. The gas transmission of the slag w
as similar to that of the granite soils used for a conventional landfill cover.
According to the leaching tests for the slag samples, the heavy metals concentrations in the slag leachat
e were not detected or 1000 order of magnitude lower than the environmental criteria for Pb, Cu, As, H
g, Cd, Cr, and CN.
References
Ecomaister, co. Ltd. 2003. http://ecomaister.com/
Lee, Yong Soo, 1998, Recycling of Sewage sludge as a liner and covering material in waste landfill sites, Korean
ground engineering institute paper Vol. 13. No. 4, pp. 5 -11 (in Korean).