Use of Blast Furnace Slag in Road Construction

By,Nagarjun

Civil departmentNIT,Raichur

CONTENTS

• Introduction

• Experimental Studies

1. Strength development of concretes with slag

2. Stabilization of Expansive Clays with slag

• Use of Blast Furnace Slag in Road Construction• Benefits of slag cement• Summary• References

Introduction10 million tons of blast furnace slag is produced in India

annually as a byproduct of Iron and Steel Industry.

Blast furnace slag is composed of silicates and alumino

silicates of lime .

It is a latent hydraulic product which can be activated

with anyone- lime or Portland cement.

Contd ….

The hydration of granulated blast furnace slag is slower

than that of the ordinary Portland cement(OPC).

A mixture of the blast furnace slag and ordinary

Portland cement will retard the rate of strength

development.

Lime-GBFS mix as alternate binder to cement, and for

its use in mortar, soil stabilization as well as in concrete.

The degree of retardation depends upon the

Contd ….

• Chemical composition of the slag and OPC,

• Percentage of slag,

• Temperature and

• Humidity of the environment.

BFS shows a potential of pozzolanic reaction . When mixed

with Portland cement, And accelerates the hydration of

Portland cement.

The replacement of Portland cement by BFS, up to 70%,

does not have any negative effect on the compressive

strength of concrete after 28 days.

Contd ….

The use of Blast Furnace Slag in Engineered

cementitious composites not only reduces the cost and

increases the greenness, but also improves the workability,

the mechanical properties and the durability.

Contd ….

• Activity and granule size of the slag,

• The quantity and quantity of lime (activator),

• The composition of the bed and the relative

content of binder, and

• The setting conditions.

The use of GBFS in road construction shows that the

strength of the reinforced bed depends on

Experiment

Throughout this investigation, ordinary Portland cement,

ground granulated-blast furnace slag, and fly ash were used

as cementing materials. The coarse aggregate used was a

10 mm maximum size. The fine aggregate was 3 mm

maximum size and it was obtained from the same source of

the coarse aggregate.

Strength development of concrete with Slag

During this study five mixes were used. The first one,

made by using OPC with out any replacement, was used

as the mix control. The second and third mixes had

30%and 50% of the cement replaced by fly ash. The

fourth and fifth mixes had 30% and 50% of cement

replacement with slag. Total aggregate/cementitious materials ratio was 6.0 with

33% of fine aggregates, and

The water/cementitious ratio was 0.55.

• For each temperature 10 standard test cubes

(100xl00xl00 mm) were cast for each of the five mixes.

• The compressive strength was obtained at ages of 1,3, 7,

28, and 90 days for water-cured specimens at 6, 20,35, 60,

and 80ºC.

• Prior to mixing, the mix ingredients were stored at the

temperatures of 6, 20, 35, 60, and 80ºC for at least24 hours.

Fig 1 Compressive strength results of OPC concrete Vs age

• At 6ºC and 20ºC curing temperature OPC concrete

shows greater strength than other concretes up to the age

of 90 days.

Fig. 2 - Experimental and calculated compressive strength results of 30% slag concrete.

Fig3- Experimental and calculated compressive strength results of 50% slag concrete.

Concretes containing slag initially gained strength at a

slower rate than 100% OPC mix. However, at later ages (56

days) the slag mixes did tend towards achieving their

equivalent OPC mix strength.

The compressive strength of concretes subjected to

different temperature is affected by the curing temperature

greatly. In order to predict time-strength development, this

effect should be taken into consideration.

Carino suggested a hyperbolic strength age function that

can account for temperature and time effects on strength

development of concretes cured under isothermal

conditions.fc = k fu ( t - to) 1 +k(t-to)

wherefc = Strength at age t;t o = Age when strength development begins;fu= Ultimate strength;k = Initial slope of the relative strength (fc/fu) versust curve.

Stabilization of Expansive Clays with slag

Preparation of Samples

Soil, sample , was prepared by mixing 85% Kaolinite (Gs

= 2.69) and15% Bentonite (Gs = 2.39) by dry mass. A

preliminary swell test on sample a resulted in 32.90%

vertical swell, indicating a highly expansive soil. To

overcome the swelling potential, ground GBFS (Gs =

2.88), was first added in amounts ranging from 5, 10, 15,

20 and 25% in dry mass to sample A.

And GBFSC (Gs = 2.89) was manufactured by blending

ground GBFS (80%) and ordinary Portland cement (20%)

by mass). GBFSC was added in amounts ranging from 5, 10,

15, 20 and25% in dry mass to sample A.Sample Properties

Hydrometer tests were performed to determine particle

size distribution. The LL, PL, PI, SL , and specific gravity

(Gs) of the samples were determined. The LL, PL and PI of

the untreated and treated samples are given in(Table2 )

Testing Procedure

In this study, the ‘‘Free Swell Method’' was used to

determine the amount of swell. Each specimen was

prepared to 60 g dry mass. 6 ml of water was added to the

sample to obtain 10% water content.

The consolidation ring containing the specimen was placed

in the oedometer after placing filter papers on the top and

bottom of the specimen not to clog the porous stones. An

air-dry porous stone was placed on top of the specimen.

•Dial gauge measuring the vertical deflection was set to

zero.

•The specimen was inundated with water to the upper

surface directly, and to the lower surface through

standpipes.

•A seating pressure of at least 1 kPa applied by the weight

of top porous stone and load plate until primary swell is

complete.

Free Swell(%)= 100 dH/H

Where dH is the change in the initial height of the specimen.

H is the original height of the specimen.

•As soon as the specimen was inundated, swelling began. The

specimen was allowed to swell freely.

•Dial gauge readings showing the vertical swell of the

specimen were recorded until the swell stopped.

• Reduces the LL

• Raises the SL and

• Reduces the PL of the soil.

Discussion of Test Results

The LL, PI, SL and clay content (CC) results can be used to

explain the swell results as follows:

The addition of GBFS (or GBFSC) to the expansive clay:

• Reduces the CC and a corresponding increase in the

percentage of coarse particles.

Use of blast-furnace slag's as

• Sand and gravel for the construction of road beds,

• Basic filler in asphalt–concrete mixtures for the

construction of road and airport coatings,

• Unroasted cement (binder) for reinforcing roadways and

• Preparing slow-setting concrete.

Use of Blast Furnace Slag in Road Construction

• Road construction has different requirements in terms of

both production and operation, calling for different properties

of the Portland cement.

• In particular the fast setting of concrete with considerable

heat liberation tends to create an internal stress state,

• Reduces the crack resistance of the concrete

• To reduce the stress, temperature seams must be

introduced in the plate.

• Temperature seams are usually introduced at intervals of

4–6 m;

• By contrast, slag binders composed mainly of

granulated slag and activators consist of slow-setting low-

basicity silicates C2S (75–85%),which results in slow

setting.

•Unroasted slow-setting binder largely meets the

requirements of road construction.

•Slow setting of the binder is convenient .Hence, materials

with slow-setting binder will retain their thixotropic

properties for a long period.

•This means that material may be applied and worked over

more than 2–3 km at a time, without loss of quality., the

granular composition of the filler

• The interaction of bitumen with blast-furnace slag is

intense, on account of physical, mechanical, chemical,

electrostatic, and diffusional processes.

• Therefore, the adhesive binders at the boundary of the

bitumen–mineral material are strong and stable under the

action of atmospheric factors.

• In addition, the hydraulic activity of the BFS facilitates

prolonged setting of the material and the acquisition of

additional strength, which compensates the increased

porosity of the asphalt concrete.

• Slag is basic filler in asphalt–concrete mixtures for the construction of road coatings.Such coatings ensure

• Rapid drainage of water from the surface and hence

increase road safety during rainstorms,

• By reducing aquaplaning and increasing wheel adhesion to

the road.

• At night, when the headlights are turned on, there is less

reflective glare from the road surface, with improvement in

visibility for the driver

It is recommended for the construction of all roads in

residential areas, so as to

• . Increase road safety,

• Reduce noise, and

• Improve the comfort and visibility of drivers.

This recommendation may also be extended to road

sections with sharp horizontal curves

Benefits of slag cement:

• Improved concrete workability

• Enhanced finish ability

• Lower permeability

• Improved resistance to aggressive chemicals

• Increased compressive and flexural strengths

• Lighter color

The significant advantages of granulated blast furnace slag binder are

• GBFS binder with 7.5 percent gypsum can be used for

making mortars,

• Stabilization of soils and

• making concrete mixes for use in road bases and composite

pavements

SUMMARY• At low, normal and elevated curing temperatures, fly

ash and slag concretes developed strength more slowly

than OPC concretes• Slag concretes behaved similarly to OPC concrete

after 28 days of age.

• The strength age relationship is described more

accurately by using the hyperbolic power function.

• Slag cement can enhance concrete pavement by

improving workability in the plastic state.

• Increasing strengths and reducing permeability in the

harde ned state. • The increasing limestone powder and BFS contents lead to

a smaller average loaded crack width

•blast-furnace slag is a long-acting binder, which facilitates

the solidification of materials used for road construction,

thereby increasing the carrying capacity and durability of

road and runway coatings

REFERENCES•O.Eren, (2002). “Strength development of concretes with

ordinary Portland cement, slag or fly ash cured at different

temperatures”, Department of Civil Engineering, Eastern

Mediterranean University, Gazimagusa, Kibris, Mersin 10,

Turkey, vol 35,page no.536-540

•J. Zhou , S. Qian , M. G. Sierra Beltran G. K. van Breugel

“Development of engineered cementitious composites with

limestone powder and blast furnace slag” Microlab, Faculty of

Civil Engineering and Geosciences,Delft University of Technology,

Delft, The Netherlands

•S V Srinivasan,” Use of blast furnace slag and fly-ash in road

construction”Indian highways. Vol. 21, no. 11 (Nov. 1993)

•Erdal Cokca , Veysel Yazici , Vehbi Ozaydin” Stabilization of

Expansive Clays Using Granulated Blast Furnace Slag (GBFS) and

GBFS-Cement”, Department of Civil Engineering, Middle East

Technical University, 06531 Ankara, Turkey

•B.A.Asmatulaev.R.B.Asmatulaev,A.S.Abdrasulova,”Use Of Blast-

Furnace Slag in Road construction”, Dortrans Kazakh Scientific-

Research and Design Institute, Almaty, Kazakhstan,AK Kazzhol,

Kazakhstan,Vol 37 p.no 722-725