Pozzolanic or Mineral Admixtures and its Types and Uses according to IS 456:2000

What are Admixtures  

Admixtures are used to improve the quality of concrete used at site and which admixtures will be used at site will depends upon the structure/building because different admixtures have different characteristics according to which they will be used.

Mineral admixtures 

• These are usually added to concrete in larger amounts to alter the workability of fresh concrete
• It maintain the water content in concrete while pouring at site and resist thermal cracking
• it helps to resist alkali-aggregate expansion
• it allow concrete after settle down to fight against sulfate attack

Mineral Admixtures can be

•  Natural materials
• Processed natural materials
• Artificial materials

 

Types of Mineral Admixtures: 

1.Pozzolanas :

Pozzolanic or Pozzolanas are finely divided materials which are added to concrete to obtain specific engineering characteristics/properties.

They are also called ‘Supplementary Cementing Materials’ Mineral because admixtures are not only the inert fillers but they actually react (hydrate) along with the cement.

• Manufacturing:
  

Pozzolanic or Mineral admixtures are basically derived from other substances, not chemically manufactured. 

 Types of Pozzolanas:

👉Fly ash(pulverized fuel ash):

It maybe used as part replacement of Ordinary Portland Cement provided uniform blending with cement is ensured and it conforming to Grade 1 of IS 3812

👉Silica Fume: 

It increases compressive, tensile, flexural and impact strengths and decreases permeability and bleeding of concrete.  

silica fumes is a by product of manufacture of silicon, ferrosilicon or the like from quartz and carbon in electric arc furnace

it is normally used in proportion of 5-10 percent of the cement content of mix.   

 👉 Rice husk ash:  

Rice husk ash is produced by burning rice husk and large proportion of silica.To achieve amorphous state as other admixtures it maybe burnt at controlled temperature.

 We need to ensure water demand,shrinkage,uniformity and performance while using rice husk.  

 👉Metakaoline:  

It maybe used pozzolanic material in concrete and it usually obtained by calcination of pure or refined kaolintic clay.

 Its fineness: 700-900 m2/kg  

 

2.Ground Granulated Blast Furnace Slag: 

 Ground granulated blast furnace slag obtained by grinding granulated blast furnace slag conforming to IS 12089.