Lime Reactivity (LR) of Pozzolana

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Scope

This method of test covers the procedure for determining the reactivity of the pozzolana with hydrated lime.

Why should we perform Lime Reactivity Test

Pozzolana is basically a silica rich non-cementing material. Reactive silica while react with lime and water develops a contentious property.

Thus LR test allows us to know how much does this pozzolana is reactive with lime or it is usable or not. 

Reaction of Pozzolana with Lime and Water

CaO + SiO2 + 2H2O → Ca(OH)2 + H4SiO4 [i.e. Calcium Hydroxide and Silicic Acid]

Ca(OH)2 + H4SiO4 → CaH2SiO4·2 H2O

i.e. CH + SH → C-S-H Gel [which is responsible for strength development]

Sampling

As per IS : 3535

Temperature and Humidity

 

Temperature

Relative Humidity

Moulding Room

27 ± 2 °C

Not less than 65%

Dry Material

Water

Apparatus

  1. Cube Moulds - 50 ± 0.1 mm
  2. Balance (1000g, Least Count - 1g)
  3. Mixing Apparatus
  4. Flow Table
  5. Tamping Rod
  6. Gauging Trowel (IS : 10086)
  7. Measuring Cylinder ( 100ml)

Procedure

  1. Clean appliances should be used for mixing.
  2. The dry material of the standard test mortar shall be Lime, Pozzalana and Standard Sand in proportion 1:2M:9 by weight

    M = ( Sp. Gravity of Pozzalana / Sp. Gravity of Lime )

  3. The amount of water for gauging shall be equal to that required to give a flow of 70±5% with 10 drops in 6 seconds.
  4. The following quantities of materials are suggested for preparation of mortar for 6 test specimens
    • 150 g       -    Hydrated Lime 
    • 300 x M   -    Pozzolana 
    • 1350 g     -    Standard Sand
  5.  
 
  1. Mix the water to dry cement thoroughly by Gauging Trowel. Gauging time should be 3 to 5 minutes.
  2. Take a Vicat Mould (IS : 5513) resting on a non-porous plate.
  3. And, fill the Vicat Mould with this paste.
  4. Smoothen the surface of the paste, making it level with the top of the mould.
  5. Shake the mould slightly to expel the air.
  6. Place the test block in the mould, together with non-porous resting plate, under the rod bearing the plunger of the Vicat Apparatus.
  7. Lower the plunger gently to touch the surface of the test block, and quickly release.
  8. Allow it to sink into the paste.
  9. Plunger should penetrate to a point 5 to 7mm from the bottom of the Vicat Mould.
  10. If not, again repeat the procedure with another quantity of water.

Calculation

        Normal Consistency (P) = (Weight of Water) / (Weight of Cement)  x 100

    (Express the result to the first place of decimal - As per IS : 4031, Clause 6.1 )

Precaution

  1. Clean appliances shall be used.
  2. In filling the mould, the operator’s hand and the blade of gauging trowel should alone be used.
  3. The gauging time shall be counted from the time of adding water to the dry cement until commencing to fill the mould.

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