Silica Fume in Concrete: Advantages, Disadvantages, and Applications

1. Silica smoke (fume)is a by-product of silicon metal or ferrosilicon alloy industry. • The material with an average grain size of 0.1 μm during the reduction of quartz to silicon in electric arc furnaces is collected through bag filters. • The escaping gaseous SiO oxidizes and condenses in the form of extremely fine spherical particles of amorphous silica hence the name silica fume.

2. In particular, ferrosilicon with a 50-per cent content of silicon results in a silica fume with a content of silica of only about 80 per cent. However, steady production of a given alloy results in a silica fume with constant properties. • Typical silica contents are as follows (per cent): silicon metal, 94 to 98; 90 per cent ferrosilicon, 90 to 96; and 75 per cent ferrosilicon, 86 to 90.

3. What is SilicaFume? Silica fume is a byproduct of producing silicon metal or ferrosilicon alloys. One of the most beneficial uses for silica fume is in concrete. Because of its chemical and physical properties, it is a very reactive pozzolan. Concrete containing silica fume can have very high strength and can be very durable.

4. Advantages of Using Silica Fume • High early compressive strength • High tensile flexural strength and modulus of elasticity • Very low permeability to chloride and water intrusion • Enhanced durability • Increased toughness • High electrical resistivity and low permeability

5. Disadvantages of Using SilicaFume • Silica fume concrete shrinkage rate is large • Decreasesworkability • The surface crack caused by wet expansion

6. Silicafumeeffect of freshconcrete • Cement pulp containing silica smoke is more adhesive. Therefore, the possibility of separation of fresh concrete is less. • Decreasesbleeding. • Increases the risk of cracking. • Setting time is extended. • Unit weight of concrete is reduced.

7. SLURRY INFILTRATED MAT CONCRETE(SIMCON)

8. DEFINITION • Providingthefibers as a mat (belowfigure), which is theninfiltratedby a highstrengthslurry, a newtype of HPFRCC, calledSlurryInfiltrated Mat Concrete (SIMCON) can be produced.

9. In the making of SIMCON, the fibres are placed in a “mat form” rather than as discrete fibres. The advantage of using steel fibre mats over a large volume of discrete fibres is that the mat configuration provides inherent strength and utilizes the fibres contained in it with very much higher aspect ratios.SIMCON the aspect ratios of fibres contained in it could well exceed 500

10. GENERAL PROPERTIES • Improve tensile strength • Improveflexualstrength • Improveshearstrength • ExtremelyDuctile • Littleor no corrosion • Increaseenergyabsorptioncapacity • Small cracks

12. SIMCON vs SIFCON • With SIMCON, the same strength and energy absorption capacity can be achievedas with SIFCON at a lower fiber volume . • SIMCON also has other advantages.Stainless steel is used to form the fiber mat, so little or no corrosion will take place.

14. APPLICATION AREAS • Militarystructures or industrial applications requiring high strength and ductility. • Repairand rehabilitation of structures. • Concretemega-structures, such as offshore platforms and solar towers.

15. HIGH STRENGTHCONCRETE

16. Whatis High StrengthConcrete ? • High strengthconcreterequiresqualitycement, aggregateandsuperplasticizeradditiveandsilicafume. Water/cementratio is reduced 0,20. Strength can be increasedto 100 N/mm2. High workability (20 cm slump) and is a specialtype of concretethatprotectsitspumpability. • It is a type of highperformanceconcretegenerallywith a specifiedcompressivestrength of 40 MPaorgreater. Thecompressivestrength is measured on 150-300 mm or 100-200 mm test cylindersgenerally at 56 or 90 daysorsomeotherspecifiedagedependingupontheapplication.

17. Why do weneed High StrengthConcrete ? • To put theconcreteinto service at muchearlierage, forexampleopeningthepavement at 3 days. • Tobuildhigh-risebuildingsbyreducingcolumnssizesandincreasingavailablespace. • Tobuildthesuperstructures of long- spanbridgesandtoenhancethedurability of bridgedecks. • Tosatisfythespecificneeds of specialapplicationssuch as durability, modulus of elasticity, andflexuralstrength. Some of theseapplicationsincludedams, grandstandroofs, marinefoundations, parkinggarages, andheavydutyindustrialfloors. • (Notethathighstrengthconcretedoes not guaranteedurableconcrete.

22. PLASTICIZERS AND SUPERPLASTICIZERS

23. PLASTICIZERS • Generally, theyarewater-reducingadditives in theorder of 5-10%. Theyaremainlyused in C-20 and C-25 concreteclasses. 4 to 1.2% of thecementdosage • Normal plasticizersarebesed on lignosulphonateorhydrocarboxylicacid.

24. SUPERPLASTICIZERS • Generally, the water-reducing additives are 12-25%. They are known in the market as superplasticizers. They are generally used for concrete classes of C-30 and above. They are used between 0.6% and 3% of the cement dosage. • Super plasticizers are usually based on melamine or naphthalene sulphonate.

25. Working Principles of Normal and Super Additives •In these two types of additive, the working function allows the additive to wrap around the grains of the cement and load the grains with negative electric charge, so that the cement grains push each other and prevent their agglomeration. Affects the hydration reactions and changes the surface tension of water by adhering to cement grains.

27. TAKE NOTE THAT HIGH PERFORMANCE CONCRETE MUST BE CONSIDERED FOR EXAMS.