GGBS
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Transcript of GGBS
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Changing the face of concrete
Avinash Shaw
Department of Civil Engineering
NIT Durgapur
Prof. A. K. Samanta
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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
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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%
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Portland Cement
GBBS
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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
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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.
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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.
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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.
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Durability
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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.
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Appearance
On the left-GGBS usedOn the right-Portland cement
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Appearance
Boyne Bridge M1 motorway(made of
GGBS)
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Powerfloating
As GGBS concrete stays plastic for a longer
time than Portland cement concrete, this
enables the contractor to achieve a very flat
finish.
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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.
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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)
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Strength
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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