cement and chemical admixtures effect of fresh and hard concrete

Chemical Admixture and their Effect on Fresh and Harden Concrete

Muzafar

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Cement

Admixture

Accelerating admixtures

Retarding admixtures

Air-entraining admixtures

Water Reducing admixture/plasticizers

Grouting admixtures

Air detraining admixtures

Gas forming admixtures

Corrosion inhibiting admixtures

Permeability reducing admixtures

Bonding admixtures

Shrinkage Reducing Admixtures

Colouring admixtures

`Fungicidal ,germicidal and insecticidal admixtures

CementLime CaO

(60 - 65 )%

A cement is a binder, a substance that sets and hardens and can bind other materials together

Silica SiO2

(17 – 25 )%

Alumina Al2O3

(3 - 8)% (0.5 – 0.6 )%

Iron oxide Fe2O3

Sulphur trioxide SO3

(1- 2 )%

Magnesia MgO

(0.5 - 4 )%(0.5 – 1.3 )%

Na2O + K2O

Tricalcium Silicate (Alite) C3S 25-50%

Dicalcium Silicate (Belite) C2S 20--45%

Tricalcium Aluminate (Clite) C3A 5-12%

Tetracalcium Alumino Ferrite (Flite) C4AF 6-12%

33 grade 2250 cm2 /g 43 grade 3400+ cm2 /g 53 grade 3400++>> cm2 /g

58(3) 104(90) 122 (13) Cal/g

12 (3) 42(90) 59 (13) Cal/g

212(3) 311(90) 324 (13) Cal/g

69(3) 98(90) 102 (13) Cal/g

Initial strengthFlashflahset

Early Strength

Later Strength(Reaction after 7 days)

Cement

Admixture



Air-Entraining admixtures


Grouting admixtures





Bonding admixtures




ADMIXTURE Admixture are formulated chemical compounds that are used to modify certain properties of concrete.

Admixtures are the material, other than

Cement

Water

Aggregates

Chemical Admixture

These admixture are added to concrete mix before or during mixing of concrete

ADMIXTURE

CHEMICAL

MINERAL

Chemical Admixtures

•Accelerating admixtures•Retarding admixtures•Air-entraining admixtures•Water Reducing admixture/plasticizers•Grouting admixtures•Air detraining admixtures•Gas forming admixtures•Corrosion inhibiting admixtures•Permeability reducing admixtures•Bonding admixtures•Shrinkage Reducing Admixtures•Colouring admixtures•`Fungicidal ,germicidal and insecticidal admixtures

To speed up the rate of development of strength. To keep concrete workable for long time(Enhance workability). To decrease the weight of concrete per cubic meter. To increase the strength of concrete by reducing the water content

To inhibit the corrosion.

To increase the resistance to chemical attack

To enhance the bond between old and new concrete

To produce coloured concrete

Functions of Admixtures

To reduce the cost of concrete construction To achieve certain properties in concrete

To maintain the quality of concrete during the stages of mixing, transporting, placing, and curing To overcome certain emergencies during concreting operations

Reasons for using admixtures are

Cement

Admixture





Grouting admixtures





Bonding admixtures


Coloring admixtures


AcceleratorAccelerating admixtures are added to concrete to increase the rate of early strength development in concrete

Accelerating admixtures also used to speed up the initial set of concrete

C3S + (x)CATALYST(Admixture) = XC3S

XC3S + (Y) = C3S2H3 + (x) + (z)

Accelerator cause a more rapid dissolution of compounds of cement

Mechanism of action is catalytic in nature

The compounds of Accelerating Admixture :

Calcium Chloride CaCl2 ( Most commonly used for plain concrete) Is 7861-1981 maximum 1.5% by mass of cement

Calcium Formate Ca(HCOO)2 (fine powder,less effective than cacl2 and less corrosion to steel)

Fluro silicates and Trietholamine (Remains plastic for less than 10 min, not exceeding 0.2% by mass)

sodium hydroxide (NaOH) and potassium hydroxide (KoH)

Sodium sulfate (Na2So4),

Sodium Chloride (Nacl)

potassium sulfate(K2SO4)

Why Accelerators ?

Earlier removal of formwork.

Reduction of required period of curing

Early placement of structure in service.

Partially compensate for the retarding effect of low

temperature during cold weather concreting.

In emergency repair work.

The Chernobyl disaster (Ukrainian)