Fly Ash And Steel Slag In Road Construction Engineering Essay

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ABSTRACT

The generation of slag and fly-ash is so high during production of iron and steel. Accumulation of these waste materials is now becoming a major concern. Road construction is one such sector where these can be utilized in bulk. In road construction, nearly all country use these material to replace natural aggregates, either for blanket courses, bases or sub bases. The 15% FlyAsh and15%SteelSlagmix is optimum mix in road construction respectively.15%SteelSlagmix is ecomomical and stonger than 15%FlyAshmix These things are discussed in full length paper.

Key Words:- Design of road, Air cooled slag, GBFS, Steel making slag and Fly-ash, optimum mix, Hard Murum.

INTRODUCTION

Today, several million tones of iron and steel are being produced in our country by the various steel plants. The production of steel is, however, always associated with other wastes like, flyash, fluedust, blast furnace slag etc.

The generation, handling and safe disposal of these wastes is now a grave concern in the country. Road construction is one such sector where it can be utilized in bulk.

This material can be used in the sub bases and bases of road works as extensive tests have been carried out and it is establish that slag meet all the requirements set forth by Ministry of Road Transport and Highways (MORTH).

Typical Characteristics of By Products

Air Cooled Slag:- Air Cooled Blast Furnace Slag ( commonly known as BF slag) is produced by putting the molten slag into a pit where it is allowed to cool in slowly in open air. Crystallization takes place in resulting in materials, like, a fine-grained igneous rock. Because of its similarity to igneous rock, it has found extensive use as concrete aggregate, road surfacing stone and road base course material. When air cooled blast furnace slag is crushed and clean, its physical properties make it particularly suitable as an aggregate, both coated and uncoated. Typical values of the steel slag aggregate and fly ash as obtained from steel plant in MIDC area Jalna and thermal power station parli (v) respectively are given in Table-1.

Table 1: Geotechnical Properties of Fly Ash and SteelSlag

Sr. No.

Property

Flyash SteelSlag

1.

Specific gravity

2.01 3.2-3.4

2.

Particle size analysis : %

Gravel content

-

Sand content (4.75 to 0.075 mm)

12.45

Silt and clay content (below 0.075mm)

87.55

3.

Atterberg's limits : %

Liquid limit

41 43

Plastic limit

Non plastic

Plasticity index

Non plastic

4.

Maximum dry density gm/cm3

1.392 1.541

Optimum moisture content %

15.93% 12.57%

5.

California Bearing Ratio value % (soaked)

2.2 7

In road construction, nearly all countries use granulated blast furnace slag to replace natural aggregates, either for blanket course, bases or sub-bases. It is used exactly in the same way as course or medium sand

Steel Making Slag: Steel making slag is produced during manufacturing of steel. To produce steel, it is necessary to further refine molten iron to remove carbon and make additions of materials such as, maganese, silicon, chrome and titanium. This refinement stage imparts the properties, such as, strength, hardness, toughness, and flexural strength.

Steel slag is relatively non-porous and consequently makes a high density stone of high crushing strength. Its composition is approximately half time, the other two main constituent is silica and iron oxide. Fresh steel slag is not recommended as the change in volume due to the presence of dicalcium silicate, or the hydration of particles of burnt dolomite (lime) may affect the stability of slag however, the weathered steel slag stockpiled for more than a year, generally do not exhibit any volume instability.

Table 2: Effect of Steel Slag Addition on California Bearing Ratio for Gravel (Hard Murum) and Modified soils

Sr.

No.

Property

HM + steel slag

HM : SS-0

HM:

SS -1

HM :

SS -2

HM :

SS -3

HM:

SS -4

Proportion HM: steel slag

100:00

95:5

90:10

85:15

80:20

1

California bearing ratio %

18.93

30.

39

41

45

Figure 1: Effect of Steel Slag Addition on California Bearing Ratio for Gravel (Hard Murum) and Modified Soils

Table 3: Effect of fly ash Addition on California Bearing Ratio for Hard Murum and Modified Soils

Sr.

No.

Property

HM: steel slag

HM:

SS-0

HM-:SS-1

HM- :

SS-2

HM-SS-3

HM- :SS-4

Proportion HM: steel slag

100:00

95:5

90:10

85:15

80:20

1

California bearing ratio %

18.93

29.00

38.03

39.94

41.37

Figure 2: Effect of fly ash Addition on California Bearing Ratio for Gravel ( Hard Murum) In Subbase .

Table 4: Typical Physical Properties of Steel Slag

Specific Gravity

3.2-3.4

Aggregate Crushing Value

20%

Aggregate Impact Value

14%

Los Angels Abrasion value

20%

Water Absorption(Per cent by mass)

1-1.6

Flakiness Index

6-8%

Angularity number

7-9

SOIL TREATMENT FOR IMPROVED SUB-GRADE/SUB-BASE:

As per MORTH specification, clayey soil having plasticity index more than 8 are required to be treated and stabilized before road is constructed. Such soil can very well be treated with another steel plant waste material, i.e., Fly-ash to improve plasticity index, liquid limit, plastic limit and CBR values to acceptable limits and further more.

For construction of Dankuni stockyard of SAIL, flyash was extensively used to improve sub grade CBR value from a low value of 2 to 30. Quantity of fly ash required for this work was 2,00,000 m3 (approximate). To improve CBR value further, slag along with fly-ash can be mixed with weak soil.

Sub-Bases (Non-Bituminous):

Clauses 401.2.1 and 403.2.1 of MORTH specification 2001 permit use of crushed slag in sub bases. Table 400-1 and 400-2 for granular sub-base materials, required CBR values of minimum 30, 35 and 20 for grades-I, II and III types of materials respectively. Tests conducted on mixed of air-cooled slag, S.M.S. slag and granulated slag reveal CBR values ranging from 80 to 100. Hence, use of steel plant slag would give far more strong bases than the conventional materials. The road pavement thickness is design as per IRC: 37-2001, which gives a curve correlating pavement thickness with CBR values and traffic volume/ classification. As per the CBR values of base go up,.required pavement thickness goes down.

Hence, if slag is utilized as sub-base material having higher CBR values, the required pavement thickness of road pavement would go down substantially resulting into strong, durable and economical roads.

Water Bound Macadam (WBM) Sub-Base:

Clause 404.2.1 of MORTH specification 2001 permits crushed slag to be used as coarse aggregate for WBM works. Clauses 404.2.2 and 404.2.3 of the same specification gives details of physical and chemical requirements of crushed slag to be used as coarse aggregate in WBM works, which is described in Table-5.

Table 5: Proceedings of IRAM-2003, August 22-23,2003

Sr. No

Description

Requirement

Actual

B.F.

S.M.S.

1.

Los Angeles value

40% Max. limit

30%

10%

2.

Aggregate Impact Value

30% Max. limit

22%

10%

3.

Crushing value

30% Max. limit

25%

17%

4.

Combined Flakiness and Elongation Indices

30% Max. limit

Slag can be crushed to suitable sizes to meet this requirement

5.

Sulphur content

02% Max limits

0.8%

5.

Water Absorption

10% Max. limits

03% •

6.

Unit Weight

1120kg/m3(min)

1500 kg/m3

Central Road Research Institute, New Delhi have conducted exhaustive studies on physical and chemical properties of steel plant slag and have found that they meet all the requirements as stipulated in MORTH specification, 2001. In SAIL, air-cooled slag and fly-ash have been used in the stockyards located at Bokaro, Bhilai, Dankuni, etc. for road construction work where the pavement has to withstand very heavy axle load and tyre pressure upto 12.5 kg/cm2 because of steel movement. This material has also been used extensively for road works in peripheral development areas around Bokaro steel plant excellent result.

From the above, it is very clear that all types of road can be successfully designed and constructed with aste material from steel plants, like, fly-ash and slag.

Cost of road construction per km for subgrade soil with 15% steel slag mix

1. Pavement composition ref …. Annex B

Plate 2 of IRC 37-2001 (page 31)

Bituminous surfacing - 135 mm (40mm BC + 95 mm DBM)

Granular Base - 250 mm (WBM)

Sub Base - 340 mm (granular base) …Annex D

In case fly ash is used in sub grade in place of soil, CBR value of sub grade will very easily increased to 9from 4.

For the above example required pavement thickness works out to 570 mm refer (fig 2 of IRC 37 2001). Page 9, Annex A in place of 725 mm. hence pavement composition would be as follows

Plate 2 of IRC 37-2001 (page 35) …. Annex C

a)

Bituminous surfacing

120 mm (40 mm BC + 80 mm DBM)

b)

Road base

250 mm WBM

c)

Sub base

200 mm Granular base (Refer Annexure-E)

Saving in DBM

15 mm

Saving in sub base

140 mm

Saving in cost for a 3.75 m wide and 1000 m long road

DBM

0.015 ' 3.75' 1000 =

56.25 rn3® .3745.00

Moorum

0.14 ' 3.75 ' 1000 =

525m3@. 152.08

Total saving

Hence saving per meter of road length = 290.00

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Figure 3 : Typical Cross Section of Village Road (VR)

CONCLUSIONS

It can therefore be concluded that steel industry waste product is suitable and economical material for use in the road construction.

Steel slag is easily available and has higher CBR value than fly ash hence saving is excess than fly ash use.

The optimum mix is 15% steel slag mix in subgrade and in subbase for road construction.

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