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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of concrete by using crushed rock dust as fine aggregate,” Civil Engineering and

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7. Isa Yuksel, Omer Ozkan, turhan Bilir. (2006), Use of granulated blast furnace slag in

concrete as fine aggregate, ACI materials journal, May-June, pp 203-208.

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