Silica Fume & Ground Granulated Blast Furnace Slag | Effect of silica fume GGBFS on fresh concrete

Lecture-16: Silica Fume, Effect of Silica Fume on fresh concrete, Effect of Silica Fume on Hardened concrete, Uses of Silica Fume, Ground Granulated Blast Furnace Slag (GGBFS ), Effect of GGBFS on fresh concrete by Dr K Mohan;
Dr K Mohan is an internationally renowned and an acclaimed cement scientist. He is a former Director General of National Council for Cement and Building Materials (NCCBM).
He holds a Ph.D. degree in Cement Chemistry from University of Aberdeen, Scotland, U.K
Silica Fume:
• Silica fume, also called condensed silica fume or micro silica, is a finely divided residue produced during the manufacture of silicon or ferro-silicon alloys by electric arc furnaces at temperature of over 2000oc.
• It is a very fine pozzolanic material composed of ultrafine, amorphous glassy sphere. It has at least 85 % SiO2.
• It is extremely fine with particle size less than 1 micron and with an average diameter of about 0.1 micron, about 100 times smaller than average cement particles.
• It has specific surface of about 20,000 m2/ kg, as against 230 to 300 m2/ kg in case of OPC.
• The efficiency of silica fume depends upon its mineralogy and particle size distribution. The extremely fine particle size, large surface area and high content of highly reactive amorphous silica give silica fume the super pozzolanic properties.
• Silica fume, being extremely finely divided, fills the voids between cement particles and make the concrete very dense.
• Silica fume has become one of the necessary ingredients for making high strength and high performance concrete.
• Silica fume is covered under IS: 15388 - 2003.
 Available Forms: Silica fume is available in the following forms:
• Undensified forms with bulk density of 200 - 300 kg/m3.
• Densified forms with bulk density of 500 - 600 kg/m3.
• Micro-pelletised forms with bulk density of 500 - 600 kg/m3.
• Slurry forms with density 1400 kg/m3. Slurry is produced by mixing undensifiedmicrosilica powder and water in equal proportions by weight. Slurry is the easiest and most practical way to introduce microsilica into the concrete mix.
Effects of Silica Fume on Fresh Concrete:
• Water demand increases in proportion to the amount of silica fume added. The increase in water demand of concrete containing silica fume will be about 1 % for every 1 % of cement substituted. (Therefore, 20 mm maximum size aggregate concrete, containing 10 % silica fume, will have an increased water content of about 20 litres / m3. Measures can be taken to avoid this increase by adjusting the aggregate grading and using superplasticizers).
• Addition of silica fume will lead to lower slump but more cohesive mix.
• Silica fume make the fresh concrete sticky in nature and hard to handle.
• There is large reduction in bleeding and concrete with silica fume could be handled and transported without segregation.
• Concrete containing silica fume can have plastic shrinkage cracking and therefore, sheet or mat curing should be considered.
• Silica fume produces more heat of hydration at the initial stage of hydration. However, the total generation of heat will be less than that of reference concrete.
Effects of Silica Fume on Hardened Concrete:
• Increases ultimate strength gain.
• Lowers permeability of concrete.
• Increases durability of concrete.
• Resistance against frost damage (freeze - thaw cycle).
• Reduces alkali aggregate reaction.
• Reduces steel corrosion.
• Reduces sulphate attack.
• Modulus of elasticity of microsilica concrete is less than concrete without microsilica at the same level of compressive strength.
Uses of Silica Fume:
• To conserve cement.
• To produce ultra high strength concrete of the order of 70 to 120 MPa.
• To increase early strength of fly ash / slag concrete.
• To control alkali aggregate reaction.
• To reduce sulphate attack and chloride associated corrosion.
Indian Scenario: The following are some of the major projects where silica fume is used in large quantity:
• Kaiga and Rajasthan Nuclear Power Project.
• Tarapur Atomic Power Project.
• J. J. Hospital Flyover.
• Bandra - Worli Sea link Bridge at Mumbai.
• NathpaJhakri Hydroelectric Power Project.
Ground Granulated Blast Furnace Slag
• Granulated blast furnace slag is a waste industrial by - product obtained during the production of iron.
• Ground granulated blast furnace slag is a non-metallic product consisting essentially of silicates and aluminates of calcium and other bases.
• The molten slag is rapidly chilled by quenching in water to form a glassy sand like granulated material.
#SilicaFume #GroundGranulatedBlastFurnaceSlag #usesofsilicsfume #mineraladmixture #Cementpdm #Admixture #Concretetechnology #Civillecture

[@valipasha7683]

Sir can v use silica fume as acrlrator

[@rohanbhandari4084]

sir, Silica fume is a by-product of the manufacture of ferrosilicon and silicon metal alloys. Is it directly collected and used or some kind of processing is done by collecting company ? Please shar your number

[@Ayushtariyal]

Sir can we use GGBS as partial replacement in concrete for cement?

[@bhaveshparmar4204]

Sir ham india me rahte to apni maatru bhasa ma samjye to sabhi log samj sakhte heee🙏🏻

[@cementpdm]

It will come Hindi also..soon

[@feedmyego8874]

sir, is there a maximum % of GGBS that is to be used or can contractors use 40 or 50% to save money on cement? and what is the effect on strength and durability of structure if more GGBS is used.. thanks.

[@manjunathdarshanr2335]

Sir is fumed silica and silica fume are same?

[@Crazyengineerrr]

Kya sir
Pd to hm bhi sakte hai

[@mohitsomani1531]

Sir can we use GGBS in Fly Ash Bricks manufacturing process? Waiting for your guidance and early response

[@cementpdm]

Yes definitely

[@mohitsomani1531]

@@cementpdm Thank you for reply. What could be the adequate ratio to use GGBS in Fly Ash Bricks. Kindly help