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46th Engineers’ Day, September 15 The Institution of Engineers (India), A P State Centre
Studies on the Use of Granulated Blast Furnace Slag as
Substitute for Fine Aggregate in Concrete †M V Seshagiri Rao, FIE, Professor, Department of Civil Engineering, JNTUH, Hyderabad.
††Srinivasa Reddy V, MIE, Associate Professor, Department of Civil Engineering, GRIET, Hyderabad.
Suvarna Latha K , Research Scholar, Department of Civil Engineering, JNTUH, Hyderabad.
ABSTRACT
Sustainability and resource efficiency are becoming increasing important issues within today’s
construction industry. The phenomenal rise in the construction activity in the last decade has
contributed to the wide gap between the supply and demand of river sand. A lot of damage has
been caused to the eco-systems by carrying out dredging operations on the sand beds leading to
the depletion of ground water levels in the country. This paper reports the results of feasibility
studies on the use of industrial waste by-product granulated blast-furnace slag (GBFS) as
substitute for fine aggregate in concrete. GBFS is a product of the steel making process. Once
scorned as a useless byproduct, it is now accepted and, often, preferred and specified as it is
known to be a valuable material with many and varied uses. This paper presents result of an
experimental investigation carried out to evaluate effects of replacing natural sand with GBFS on
concrete strength properties. Performance of concrete in which natural sand was replaced with
GBFS, by proportions 10%, 20 %, 30%, 40%, 50%, 60% and 70%, was compared to reference
sample (0% replacement). According to the results, for higher replacements of sand by GBFS,
the concrete become porous and has relatively low compressive strength. It was concluded that
the granulated blast-furnace slag can be used as fine aggregate under some conditions. The study
concluded that compressive strength of concrete improved almost all the percentage
replacements of natural sand by GBFS. The strength improvements were notably noticed at 50%
replacement level. Replacement of 50% natural sand by GBFS results in increase of 28.96 % in
compressive strength, 12.32 % in split tensile strength and 16.70% in flexural strength.
Keywords: Granulated blast furnace slag, sand substitute, alkali aggregate reactivity, slag
concrete, frugal innovation, GBFS.
--------------------------------------------------------------------------------------------------------------------------------------------† FIE - 015739/9 Email:rao_vs_meduri@yahoo.com †† MIE-1463351 Email:vempada@gmail.com
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46th Engineers’ Day, September 15 The Institution of Engineers (India), A P State Centre
INTRODUCTION
It is accepted fact that sand plays a very important role in the production of concrete. The
features of workability, strength and durability are directly dependent on the properties of the
sand used in the making of concrete. According to industry reports, there is a major shift in the
mindset of the construction industry towards exploring substitutes for river sand. Due to decline
in the availability of river sand causes environmental degradation and a threat to the biodiversity,
ban on sand mining is imposed by different states in India. The natural sand, which is available
today, does not contain the fine particles, in proper proportion as required. Presence of other
impurities such as coal, bones, shells, mica and silt etc makes it inferior for the use in cement
concrete. In the present paper, Granulated blast furnace slag (GBFS) as sand replacement in the
production of concrete is studied for suitability as alternative for natural sand.
A. GBFS as a substitute for natural sand –A Frugal Innovation in Civil Engineering
Figure 1: Granulated blast furnace slag (GBFS) as fine aggregate
Blast Furnace Slag is formed when iron ore or iron pellets, coke and a flux (either
limestone or dolomite) are melted together in a blast furnace. When the metallurgical smelting
process is complete, the lime in the flux has been chemically combined with the aluminates and
silicates of the ore and coke ash to form a non-metallic product called blast furnace slag. During
the period of cooling and hardening from its molten state, granulated slag is rapidly cooled by
large quantities of water to produce a sand-like granule conforming to Zone II which is best for
concreting. If granulated slag is primarily ground into a powder to form GGBS (Ground
Granulated Blast Furnace Slag), or Type S slag cement. It is also mixed with Portland cement
clinker to make a blended Type 1S cement. GBFS fine aggregate has qualities like uniformity,
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46th Engineers’ Day, September 15 The Institution of Engineers (India), A P State Centre
cubical shape, impurity free, gradation as per specification, makes it a superior alternative to
natural river sand in the production of concrete.
Advantages of GBFS
1. It has cubical particle shape which gives high compressive strength
2. It has internal gradation conforming to IS 383 Zone II Fine aggregate
3. Due to its surface texture there is reduction in moisture absorption/lower water cement
ratio
4. higher resistance to an aggressive environments
5. Reduction in wastage and increase in economic value
6. Blast furnace slag fine aggregate does not contain materials that may affect the strength
and durability of concrete, such as chlorides, organic impurities, clay and shells.
7. No alkali-aggregate reactivity is observed.
Blast Furnace slag is a vesicular material with a non-interconnected void structure and high
surface area which can hold moisture. Blast furnace slag does have a sulfur component
depending on the slag source, water percolating through the slag may dissolve the sulfur and
other basic minerals such as calcium. This may cause a rotten egg smell and a white precipitate
formation called GNFS leachate which has no long term impact to the environment and can be
likened to a swamp with decaying organic matter. All slags goes through a magnetic metal
separation process to remove as much of the available metal left from the steel manufacturing
process. The slag processor recycles the recovered metal to the steel mill process. GBFS has less
than 1% iron oxide remaining in the aggregate. Replacing Portland cement with GGBS (ground
granulated blast furnace slag) in concrete mixtures will also help reduce greenhouse gas
emissions because the manufacture of Portland cement emits large amounts of CO2. Highways
built with slag not only resist wear but provide superior protection against skidding. Durability,
fire resistance, strength and quality control all contribute to making GBFS a superior aggregate
in any construction use. Blast Furnace slag offers versatility, high yield; bond and light weight
reduce construction costs.
Production of Blast furnace slag fine aggregate
Slag only just removed from the blast furnace and in a molten state of approximately 1500ºC is
injected with pressurized water, and when cooled rapidly it becomes granulated slag.
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46th Engineers’ Day, September 15 The Institution of Engineers (India), A P State Centre
This granulated slag is then lightly crushed, granularized and regulated for grain shape, after
which solidification-preventing agents are added, producing Blast furnace slag fine aggregate.
Figure 2: General Schematic view of Blast Furnace Slag Production
Applications of GBFS
The use of steel slag as an aggregate is considered a standard practice in many jurisdictions, with
applications that include its use in granular base, embankments, engineered fill, highway
shoulders, and hot mix asphalt pavement. Although the principal use of GBFS is in the
manufacture of slag blended cement and Ground Granulated Blast Furnace Slag, it can be used
as lightweight aggregate where its high fire resistance and insulation properties make it an
excellent aggregate for concrete and masonry units where high fire resistance is required. It can
also be used in geo-polymer concrete, as an additive for glass manufacture, as a lightweight fill
and in engineered fill applications.
B. Emergence of other alternatives for natural sand
1. Manufactured Sand
Across the World there is growing support for the increased use of manufactured sand used in
the production of concrete. The properties of particle shape, consistent gradation and zero
impurities are the reason for the preference by structural consultants and concrete technologists.
The product is produced to IS 383 code standards. The manufactured sand must have cubical
particles or spherical particles which can be generated only from V.S.I. Crushers. Sand
manufactured from any other process/ machine can not have cubical shape.
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46th Engineers’ Day, September 15 The Institution of Engineers (India), A P State Centre
2. Powdered glass
In cities such as Hong Kong, which produce a considerable amount of glass waste, builders use
powdered glass as a substitute for sand. Glass panes and bottles are broken, ground to a suitable
size and processed.
3. Copper Slag
Singapore, which is perpetually short of sand and depends on South-East Asian countries for it,
is looking at copper slag, a by-product of copper production. In the U.S., furnace slag and
moulding sand used in foundries are recycled and used as alternatives. Substitutes such as GBFS
slag are right now in an experimental stage.
EXPERIMENTAL INVESTIGATIONS
Granulated Blast Furnace Slag (GBFS) conforming to Zone –II (It was collected from
Visakhapatnam steel plant) is used as fine aggregate replacing sand in concrete. It is having high
Silica content. It has a higher proportion of the strength enhancing Calcium Silicate Hydrates (C-
S-H).
Determination of Alkali Aggregate Reactivity of GBFS
IS 2386 part 7 -1963 covers a chemical method to determine the potential reactivity of
aggregates with alkalis present in portland cement concrete as indicated by the amount of
reaction during 24 h at 80ºC between 1M NaOH solution and the aggregate that has been
crushed and sieved to pass a 300-micron IS sieve and be retained on a 150-micron IS sieve. The
solution is then filtered and analyzed for the content of dissolved silica (Sc) and reduction in
alkalinity (Rc) both of which are plotted on a standard graph defining areas of innocuous,
deleterious, and potentially reactive aggregates.
Alkali-silica reaction (ASR) is a chemical reaction between alkali ions (Na+ and K+) a
hydroxide ions (OH-) in the concrete pore solution, generally derived from the portland cement,
and silica (SiO2), generally occurring in the aggregate. The reaction produces a hydrous alkali-
silica gel. Formation of the gel alone does not cause cracking, rather cracking occur when the gel
adsorbs water and swells. The swelling causes expansion. It often results in pressures greater
than the concrete can withstand and so produces cracks in the concrete. Aggregate reactivity
depends directly on the alkalinity (typically expressed as pH) of the solution in the concrete
pores. This alkalinity generally primarily reflects the level of water-soluble alkalis (sodium and
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46th Engineers’ Day, September 15 The Institution of Engineers (India), A P State Centre
potassium) in the concrete. Innocuous aggregates show either little or no reduction in alkalinity
or a very high reduction in alkalinity accompanied by little silica dissolution.
TEST RESULTS AND DISUCSSIONS
Table 1: Physical Properties of GBFS and Natural Sand
GBFS Natural Sand
Apparent specific gravity 2.71 2.69
Water absorption 1.75% 1.0%
Loose bulk density 1520 kg/m3 1630 kg/m3
Compacted bulk density 1793kg/m3 1800 kg/m3
Porosity 15.2% 14.5%
Aggregate Crushing Value
(ACV)34.5% 33.6%
Aggregate Impact Value (AIV) 15.45% 16.22%
Fineness Modulus 2.65 2.21
Table 2: Chemical Properties of GBFS
Constituent Percent
Sio2 34.4
Al2O3 21.5
Fe2O3 0.2
CaO 33.2
MgO 9.5
P2O5 0.54
SO3 0.66
Passing 90 micron 80%
The above results revealed that its specific gravity, bulk density, porosity, water absorption, silt
content, the impact value and the aggregate crushing value showed satisfactory performance.
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46th Engineers’ Day, September 15 The Institution of Engineers (India), A P State Centre
Table 3: Particle Size Distribution for GBFS (Zone – II)
S.No IS Sieve DesignationPercentage Passing of Zone II Sand Grading Limits
for Zone II SandNatural Sand GBFS
1 4.75 mm(No.4) 94.75 100 90-100
2 2.36 mm(No.8) 88.5 99.4 75-100
3 1.18 mm(No.16) 71.25 87.9 55-90
4 600 μ (No.30) 42.5 42.9 35-59
5 300 μ(No.50) 11.5 12.9 8-30
6 150 μ(No.100) 1.75 0 0-10
Particle Size Distribution of GBFS Fine Aggregate
4.752.36
0.6
0.3
0.15
1.18
0
20
40
60
80
100
120
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
IS Seive Size
Per
cen
tag
e P
assi
ng
Figure 3: Gradation Curve of GBFS Fine aggregate
Table 4: Workability Test Results
% GBFS Slump (mm) Compacting Factor
0
(Reference Mix)85 0.87
10 86 0.89
20 92 0.91
30 90 0.84
40 94 0.88
50 95 0.89
60 85 0.89
70 76 0.87
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46th Engineers’ Day, September 15 The Institution of Engineers (India), A P State Centre
The result of the workability tests presented in Table indicates that an increase in percentage of
GBFS replacement does not affect workability slumps and compacting factors much.
Table 5: Alkali Aggregate Reactivity by Chemical Method as per IS 2386 part 7 -1963
Reduction in alkalinity 23 millimoles/litre
Silica dissolved 1 millimoles/litre
As per IS 2386 part 7 -1963 - aggregate is determined to be innocuous in nature means not
harmful for use in concrete (non reactive)
Table 6: Strength Studies of Ordinary Grade (M20) GBFS Concrete
Percentage
replacement
of natural
sand by GBFS
Compressive
strength
MPa
Percentage
increase
w.r.t
reference
mix
Split
tensile
strength
MPa
Percentage
increase
w.r.t
reference
mix
Flexural
Strength
MPa
Percentage
increase
w.r.t
reference
mix
0%(Reference Mix)
26.45 - 2.03 - 5.81 -
10% 28.31 7.03 2.11 3.94 5.86 0.86
20% 30.42 15.01 2.14 5.42 5.99 3.10
30% 31.23 18.07 2.22 9.36 6.21 6.88
40% 32.61 23.29 2.23 9.85 6.45 11.02
50% 34.11 28.96 2.28 12.32 6.78 16.70
60% 33.97 28.43 2.22 9.36 6.5 11.88
70% 30.11 13.84 2.04 0.49 6.21 6.88
In case of sand replaced GBFS concrete, an increase in the compressive strength of cement is
observed to be nearly 29 % for 50% replacement of sand by GBFS in Ordinary (M20) grade
concrete. It is observed that there is consistent increase in the strength of concrete when partial
replacement of natural sand by GBS. The sharp edges of the particles in GBFS provide better
bond with cement than rounded particles of natural sand resulting in higher strength up to
optimum 50% replacement.
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46th Engineers’ Day, September 15 The Institution of Engineers (India), A P State Centre
0
5
10
15
20
25
30
35
Str
eng
th(
MP
a)
0% 10% 20% 30% 40% 50% 60% 70%
Percentage of natural sand replacement by GBFS
Compressive Strength
Split Tensile Strength
Flexural Strength
Figure 4: Variation of Strengths with percentage of replacements
Therefore it is feasible to use GBFS as sand replacement as long as designer is aware of the
effects of the different combinations on the hardened and rheological properties. GBFS generally
offers higher compressive strengths than natural aggregates due to increased cement paste bond
because of the angularity and vesicular surface area characteristics of slag. GBFS Concrete
mixes revealed an increase of up to 28.96 % in compressive strength, 12.32 % in split tensile
strength and 16.70% in flexural strength as a result of replacement of natural sand by GBFS at
50% replacement due to optimum reaction with optimum filler capacity.
CONCLUSIONS
From the study of the technical feasibility of using GBFS as fine aggregate in the production of
ordinary grade concrete. The following conclusions can be drawn:
1. The research suggests the use of GBFS as fine aggregate in concrete production.
2. The addition of GGBFS as sand replacement yielded an increased compressive, split
tensile and flexural strengths by nearly 29%, 13% and 17 % respectively.
3. The recommended percentage replacement of natural sand by GBFS is 50%.
4. GBFS has a potential to provide alternative to natural sand and helps in maintaining
the environment as well as economical balance. Non-availability of natural sand at
reasonable cost, forces to search for alternative material. The GBFS is found to have
good gradation and nice finish, which was lacking in natural sand. This had been
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46th Engineers’ Day, September 15 The Institution of Engineers (India), A P State Centre
resulted in good cohesive concrete. This GBFS fine aggregate is considered as an
ideal for concrete.
5. In respect of the above conclusions, it could be said that granular slag replacement
level of 50 % had increased the packing density of concrete which resulted in reduced
w/c ratio, increased strength properties of concrete mix. The rough cubical particles
of granular slag had also improved the bond and adhesion strength.
One possibility is the utilization of industrial by-products and waste materials in making
concrete, which will lead to a sustainable concrete design and a greener environment
REFERENCES
1. "Techniques for preventing solidification of blast furnace slag fine aggregate"
Annual Collection of Papers on Concrete Engineering, Vol. 26, No.1, 2004
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furnace slag fine aggregate for concrete"- Collection of Papers from the 140th Lecture by
the Iron and Steel Institute of Japan, Vol. 13, No.4, p.851, 2000
3. M. Nadeem and A. Pofale, "Utilization of Industrial Waste Slag as Aggregate in Concrete
Applications by Adopting Taguchi’s Approach for Optimization," Open Journal of Civil
Engineering, Vol. 2 No. 3, 2012, pp. 96-105. doi: 10.4236/ojce.2012.23015.
4. I. Yuksel, O. Ozkan and T. Bilir, “Use of Granulated Blast Furnace Slag in Concrete as
Fine Aggregate,” ACI Materials Journal, 2006, pp. 203-208.
5. Nagraj, T. S., “Proportioning concrete mixes with rock dust as fine aggregate,” Civil
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concrete as fine aggregate, ACI materials journal, May-June, pp 203-208.
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