Changing the face of concrete

Avinash Shaw

Department of Civil Engineering

NIT Durgapur

Prof. A. K. Samanta

Ground-Granulated Blast-

furnace Slag

Sometimes, also referred to as

GGBFS

Obtained by quenching molten

iron slag from a blast furnace

in water or steam, dried and

ground into a fine powder

Chemicals Present in GGBS

CaO 30-50%

SiO2 28-38%

Al2O3 8-24%

MgO 1-18%

MnO 0.68%

TiO2 0.58%

K2O 0.37%

N2O 0.27%

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Portland Cement

GBBS

What are its physical properties?...

Particle size - 0.1 to 40 microns

Specific Surface Area – 400-600 m2/kg

Relative Density – 2.85-2.95

Bulk density –Loose - 1.0–1.1 tonnes/m3

Vibrated - 1.2–1.3

tonnes/m3

pH (T = 20 °C in water) – 9 to 11

M a i n l y t w o u s e s

Production of quality-improved slag

cement, namely Portland Blast Furnace

Cement (PBFC) and High-Slag Blast-

Furnace Cement (HSBFC)

Production of ready-mixed or site-

batched durable concrete.

Durability

• Provides protection against both sulphate attack and chloride attack.

• Effectively replaced Sulfate-Resisting Portland Cement (SRPC) on the market for sulfateresistance because of its superior performance and greatly reduced cost

• Useful against chloride attack in reinforced concrete in marine environments and in road bridges where the concrete is exposed to splashing from road de-icing salts.

Durability

• use of GGBS in such instances will increase the life of the structure by up to 50% had only Portland cement been used, and precludes the need for more expensive stainless steel reinforcing.

• also routinely used to limit the temperature rise in large concrete pours, which prevents the occurrence of micro cracking.

Durability

Appearance

• The near-white color of GGBS cement permits architects to achieve a lighter colour for exposed fair-faced concrete finishes, at no extra cost.

• Also produces a smoother, more defect free surface, due to the fineness of the GGBS particles.

• GGBS cement prevents the occurrence of efflorescence, the staining of concrete surfaces by calcium carbonate deposits.

Appearance

On the left-GGBS usedOn the right-Portland cement

Appearance

Boyne Bridge M1 motorway(made of

GGBS)

Powerfloating

As GGBS concrete stays plastic for a longer

time than Portland cement concrete, this

enables the contractor to achieve a very flat

finish.

Strength

• GGBS cement has a higher ultimate strength than concrete made with Portland cement.

• Higher proportion of the strength-enhancing calcium silicate hydrates (CSH) than concrete made with Portland cement only, and a reduced content of free lime, which does not contribute to concrete strength.

• Doubles its 28-day strength over a period of 10 to 12 years.

Strength

GGBS % 7 day 28 day 56 day

0 32 42 43

20 30 43 45

35 27 43 47

50 23 40 44

Typical strengths of 35 N concrete (N/mm2)

Strength

Sustainability

• GGBS is a by-product of steel manufacturing process, its use in concrete is recognized by LEED.

• It significantly reduces the embodied CO2 of the structure.

Working with GGBS Concrete

• Fresh concrete containing GGBS has better mobility characteristics, arising from the consistent fineness and particle shape of the GGBS powder, and from its slightly lower relative density.

• The smoother surface texture and glassy surface of GGBS particles also helps to improve workability.

Placing, Compacting and Pumping

• Easier to place the concrete into formwork and easier to compact by mechanical vibration.

• Less liable to segregation during transport and handling.

• Pumping is also easier, due to the slightly lower relative density and better flow characteristics.

Water Demand

• Less of the mixing water(3–5% lower) is adsorbed onto the surface of the GGBS particles, as they are smoother and glassy.

The rate of early age strength gain of GGBS concrete is greatly improved by higher curing temperaturesA temperature increase from 20 to 40°C is sufficient to increase the early strength GGBS concrete by a factor of two to four.

This graph illustrates that as the in-situ curing temperature increases, any delay in strength development that may arise as a result of increasing the % of GGBS may be negated by the increase in temperature.

Water in GGBS concrete takes slightly longer to combine chemically to form hydration products, thus making GGBS concrete a little more sensitive to poor curing.For GGBS contents of up to 60%, curing periods as recommended in IS 326 and BS 8110 for Portland cement concretes are sufficient. For higher GGBS contents, these periods may need to be extended.