MODIFIED CONCRETE BY USING A WASTE
MATERIAL AS A COARSE AGGREGATE
Abdulkerim H. Ghailan1
ABSTRACT
Natural aggregate is the main source of aggregate used in concrete work in Iraq. Synthetic
aggregate is also used in limited scale around the world. An industrial solid waste is
produced from iron and steel industry. It was physically treated and fully inspected and
incorporated in concrete as coarse aggregate. The concrete mixes were made with three mix
proportions 1:1:2, 1:1.5:3 and 1:2:4. Each mix was made with different water/cement ratio to
cover wide range of workability. In the present work some characteristics of the prepared
mixes are evaluated and discussed. The characteristics include; static modulus of rigidity,
rebound number and chemical resistance towards some acids and salts solutions. For
comparison purposes conventional concrete mixes are prepared and tested. The results
obtained confirmed that the concrete mixes made with the waste material gave higher
modulus of rigidity, higher rebound number and higher chemical resistance towards the
expose acids salts solutions compared with the conventional concrete mixes. The results
obtained insure that the reuse of the waste material gives an approach to solve the pollution
problems that arise from an accumulation of the waste in the site of production, at the same
time, modified properties are added to the concrete. Especially previous investigations
regarding other characteristics revealed that the concrete mixes made with the waste material
possessed superior modified properties.
INTRODUCTION
Concrete is a composite material composed of a coarse granular material (aggregate or filler)
embedded in a hard matrix of material (cement or binder) that fills the space between
aggregate particles and glues them together [1]. The various properties of concrete depend on
the quality and proportion of the constituent materials (cement, aggregate, water and
sometime special additives) [2]. Concrete still is one the most important building material in
the works of civil engineering all over the world. The primary requirements of good concrete
in its hardened state are strength and durability. For this reason a great number of research
projects have been directed towards various factors influencing its strength or causing its
disintegration [3,4]. Since aggregate constitutes the major part of the mix, the more aggregate
in the mix, the cheaper is the cost of the concrete, provided that the mix is of reasonable
workability for the specific job for which it is used. Properties of the coarse aggregate affect
the final strength of the hardened concrete and its resistance to disintegration, weathering,
and other destructive effects [2]. Natural aggregate is the main source of aggregate used in
concrete works in Iraq. Synthetic aggregates are also used to limited scales around the world.
The possibility of using solid waste as an aggregate in concrete has received increasing
attention in recent years as one promising solution to the escalating solid-waste problem. The
1
Professor, Civil Engineering Department College of Engineering, Baghdad University, IRAQ
1
use of solid wastes is not a new concept: industrial waste is the basis of many concrete
admixtures. The use of concrete for the disposal of solid waste has concentrated mostly on
service as aggregates, since this provides the only real potential for the utilization of large
quantities of waste materials. When considering a waste material as a concrete aggregate,
three major considerations are relevant; economy, compatibility with other materials, and
concrete properties. The successful utilization of solid wastes in concrete will depend on
anticipating potential problems and ensuing properties of concrete, and developing uses that
comply with these restraints [1].
In the production of iron, iron ore, iron scrap, and fluxes (limestone and/or dolomite) are
charged into a blast furnace along with coke for fuel. The coke is combusted to produce
carbon monoxide, which reduces the iron ore to a molten iron product. This molten iron
product can be cast into iron products, but is most often uses a feedstock for steel production.
Blast furnace slag is a nonmetallic co-product produced in the process. It consists primarily
of silicates, alumino-silicates, and calcium-alumina-silicates. The molten slag comprises
about 20 percent by mass of iron production. Different forms of slag product are produced
depending on the method used to cool the molten slag. These products include air-cooled
blast furnace slag, expanded or foamed slag, pelletized slag, and granulated blast furnace slag
[5,6]. In state company for iron and steel, an industrial waste by-product, which is commonly
named slag, is produced from the blast furnace of steel. It is produced in relatively large
amounts, formed about 10% mass of the iron produced. Its use is limited and constrained in
the field of road services as road bases. It forms a pollution problem when it accumulates in
the site.
Previous studies [7,8] concerning some characteristics of concrete mixes made from the
industrial unprocessed slag as a coarse aggregate are stated else where. The characteristics
studied were workability, mechanical strength, drying shrinkage and pulse velocity. In this
research some other properties of the concrete mixes made with the industrial unprocessed
slag are inspected and discussed. These include modulus of rigidity, rebound number and
chemical resistance. For the purpose of comparison, conventional concrete mixes are
prepared and inspected similarly.
EXPERIMENTAL WORK
MATERIALS USED:
The materials used in this research work are locally available. The cement used through this
investigation was the Iraqi ordinary Portland cement manufactured by Umm Qasr factory.
The whole quantity was received directly from the factory and stored in a dry place. The
cement is produced according to Iraqi specifications No.3: 1978 [9]. Its physical properties
were tested according to B.S.4450: part 3: 1978 [10]. Chemical analysis of the cement was
according to B.S.4450: part 2:1970 [11]. While for the fine aggregate (sand) the natural sand
from Zubair area was used. It is desert origin sand with angular shape, and yellowish-brown
colour. Its grading conformed to B.S. 882:1973 [12]. The coarse aggregate are of two types:
a. Gravel (Natural coarse aggregate): Crushed natural gravel which was obtained from
Zubair area was used. This type of gravel commonly is usually used in Basrah. Its
2
grading satisfied the B.S. 882.1973 [13]. The maximum size of this gravel was 20 mm,
and the sulfate content was 0.26%.
b. Industrial unprocessed coarse aggregate: The industrial coarse aggregate used in this
study is the waste (air-cooled blast furnace slag) supplied from the State Company of Iron
and Steel (in Basrah Governate). The slag was crushed and screened. Its grading was
modified to conform to B.S.882: 1973 [12]. The maximum size was 20 mm, and the
sulfate content was 0.065%. The physical and chemical properties of the industrial slag
are summarized in Tables (1) and (2) respectively.
The cement and sand were used at air dry condition, but the coarse aggregate was used as
saturated surface dry condition to ensure uniform moisture contents during mixing and avoid
absorbing water from cement, segregation and stiffening before placement is completed [13].
CONCRETE MIXES
Two types of concrete mixes were made, concrete mixes made with natural gravel as a coarse
aggregate (mixes of type A) and concrete mixes made with slag as a coarse aggregate (mixes
of type B). Mix proportions and some physical properties of the prepared mixes are
summarized in Table 3.
TESTS CARRIED OUT
Three tests were carried out, the modulus of rigidity was performed according to B.S.1881:
part (121):1983. For each mix, three cylinders (152x305mm) were used. The rebound test
was performed according to ASTM C805-79:1980. For each mix three cubes (150mm) and
three cylinders (150x300mm) were used. Chemical resistance test was carried out for cube
specimens (100x100x100mm). The specimens were immersed in chemical reagents (5%
sulphuric acid, 10% sodium chloride and 5% hydrochloric acid).
Table 1: Physical properties of the used coarse aggregate
PROPERTY
Shape
Surface texture
Specific gravity
Bulk O.D.
Bulk S.S.D.
App.
Unit mass (kg/m3)
Loose
Tamped
Absorption % (24 hr)
Voids in bulk volume %
Voids in absolute volume %
Abrasion %
3
GRAVEL
angular
smooth
SLAG
irregular
honeycombed
2.42
2.53
2.8
2.7
2.8
3.4
1467
1600
4.15
36.63
58.54
17
1100
1250
7.14
56
127.38
12
Table 2: Chemical composition of the used blast furnace slag
CONSTITUENT
CaO
SiO
Al2O3
MgO
FeO,Fe2O3
MnO
P2O5
%(BY WT.)
47
10
3.4
8
16
5
6
Table 3: Mix proportions, cement content, and density for the prepared mixes A and B
4
RESULTS AND DISCUSSIONS
To study the properties of the concrete made with slag, two types of concrete mixes were
prepared, one by using the industrial waste crushed air-cooled blast furnace slag as coarse
aggregate (type B), the other by using the natural coarse aggregate gravel (type A). Various
mix proportions were selected, as shown in table 3, to cover a wide range of strength and
workability.
Figure 1 shows the relation of 28 days modulus of rigidity and w/c ratio at different
aggregate content. Mixes (B) gives modulus of rigidity higher than those of mixes (A), the
ratio between them is equal to (1.17 as average value). This result is expected because the
concrete made with slag has higher modulus of elasticity and lowers Poisson’s ratio than
gravel concrete [7]. That means that the shear and torsion resistance of mixes (B) is greater
than those of mixes (A). The relationship between the modulus of rigidity and compressive
strength is shown in Figure 2. For similar compressive strength, mixes (B) give a higher
modulus of rigidity than mixes (A).
Figures 3 and 4 show the relationship between rebound number and compressive strength
of 28 days cube and cylinder, respectively. Mixes (B) give a higher rebound number than
mixes (A) with similar compressive strength, due to the high specific gravity, high Los
Angles abrasion, high bond between slag and cement paste [7], and high density of concrete
made with slag compared to gravel concrete.
From these figures, we suggest that with the same mix proportions, the rebound number
of cylinder is less than that of cube for the two types of concrete, that is due to the
compressive strength of the cylinder is less than that of the cube by 20%, and to the
difference in the length.
Chemical resistance test results of the two types of concrete mixes immersed in different
selected solutions for 28 days are shown in Figures 5, 6, and 7. The alkaline binder hydrated
cement is reactive towards acids. Sulfuric acid attacks the concrete, the reaction is seemed to
be accompanied by the removal of soluble reaction products so that the weight change
decreases with increasing the immersed period as shown in Figure 5. The decreasing in the
weight change for concrete made with slag is less than that for gravel concrete, but the
absorption of concrete made with slag exposed to sulfuric acid is more than gravel concrete,
that means the durability of concrete made with slag higher than that of gravel concrete.
In the case of hydrochloric acid attack, the weight change of specimens increased with
increasing the period of immersion. This behavior may be attributed to the formation of
insoluble reaction products, which deposit on concrete surface. The rate of weight change
increment reaches a maximum within about 7 days as shown in Figure 6, and then remains
approximately constant. The behavior which may be due to the action of deposits as
protectors preventing further reactions to be continued Similar behavior was observed with
NaCl as shown in Figure 7. The higher gain in weight for mixes (B) is attributed to the higher
porosity and absorption ability of the slag. However, the visual observations of the examined
specimens indicated that mixes (B) are more chemical resistant than that of mixes (A). The
tough surface of mixes (B) was less affected compared to mixes (A) during the immersion
period.
5
18.0
1 : 1 : 2
Modulus of rigidity(GPa)
Mix A
Mix B
16.0
14.0
12.0
10.0
0.40
0.44
0.48
0.52
W/ C ratio (by wt.)
14.0
Modulus of rigidity (GPa)
1 : 1.5 : 3
Mix A
Mix B
12.0
10.0
8.0
0.48
0.52
0.56
0.60
W/ C ratio (by wt.)
12.00
Modulus of rigidity(GPa)
1 : 2 : 4
Mix A
Mix B
10.00
8.00
6.00
0.60
0.64
0.68
0.72
W/ C ratio (by wt.)
Figure 1: Modulus of rigidity–W/C ratio relationship for the two types of
concrete mixes with different mix proportions. (at age of 28 days)
6
18.0
Mix A
Mix B
Modulus of rigidity (GPa)
16.0
14.0
12.0
10.0
8.0
6.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
Compressive strength(MPa)
Figure 2: Modulus of rigidity – compressive strength relationship
for the two types of concrete mixes
30
Mix A
Mix B
28
Rebound number
26
24
22
20
18
16
14
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
Copressive strength (MPa)
Fig. (3):- Rebound number– compressive strength of cube relationship for the two
typescompressive
of concrete mixes.
Figure 3: Rebound number–
strength of cube relationship
for the two types of concrete mixes.
7
26
Mix A
Mix B
24
Rebound number
22
20
18
16
14
12
10.0
15.0
20.0
25.0
30.0
35.0
40.0
Copressive strength (MPa)
Fig.4:
(4):Reboundnumber–
number– compressive
strength
of cylinder
relationship
for the
Figure
Rebound
compressive
strength
of cylinder
relationship
two
types
of
concrete
mixes.
for the two types of concrete mixes.
0.0
Mix A
Change in weight (%)
-1.0
Mix B
-2.0
-3.0
H2So4 (5%)
-4.0
-5.0
0
5
10
15
20
25
30
Time (days)
Fig. (5):-Chemical resistance of the two types of concrete immersed in H2So4 (5%) for 28
days.
Figure 5: Chemical resistance
of two types of concrete
immersed in H2So4 (5%) for 28 days.
8
10.0
Change in weight (%)
8.0
6.0
4.0
NaCl (10%)
2.0
Mix A
Mix B
0.0
0
5
10
15
20
25
30
Time (days)
Figure 6: Chemical resistance of the two types of concrete immersed in NaCl(10%) for 28 days.
Figure 6: Chemical resistance of the two types of concrete
immersed in NaCl(10%) for 28 days.
5.0
Change in weight (%)
4.0
3.0
2.0
HCl (5%)
1.0
Mix A
Mix B
0.0
0
5
10
15
20
25
Time (days)
Figure 7: Chemical resistance of two types of concrete
immersed in HCl (5%)
for 28 days.
9
30
CONCLUSIONS
From the test results obtained in this study, it is approved that mixes with slag aggregate
compromise higher modulus of rigidity, higher rebound number and higher durability
compared with those made of gravel. The results confirmed that the cheap industrial slag
adds more modified properties in the concrete mixes and this candidate the use of this
material as coarse aggregate for high strength concrete.
REFERENCES
Mindess, S. and Young, J. F. “Concrete” Prentice-Hall, 1981.
Edward G., Nawy “Reinforced concrete” Prentice-Hall, 1985.
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DANPAT RAI & SONS, 2nd Ed. 1981.
Mineral Commodity Summaries 193. Bureau of Mines, U. S. Department of the Interior,
Washington, DC, 1993.
Witold,Gutt, Cchem, (B.S.6699.1992) Specification for ground granulated blast slag for use
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B.S.4450, “Tests of physical properties of cement”, British Standards Instit. part 3, 1978.
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