LIME REACTIVITY TEST OF FLYASH

Method of lime reactivity test of flyash with hydrated lime

This method of testing cover the process of determining the lime reactivity of flyash with hydrated lime, as indicated by the compressive strength of standard mortar test cubes prepared and tested under specific conditions.

Test standard: IS 1727:1967

Test Apparatus lime reactivity test of flyash

  1. Planetary mixer with paddle
  2. Mixing bowl and scrapper
  3. Flow table and its accessories
  4. Tamping rod
  5. Standard hydrated lime
  6. Standard sand
  7. Cube moulds of size 50x50x50mm
  8. Mixing trowel
  9. Weighing balance
  10. Compression testing machine

Sample Preparation for lime reactivity test of flyash

Prepare a standard test mortar by mixing standard hydrated lime, flyash and standard sand in the proportion 1: 2M: 9 by weight.

Where M= Specific gravity of flyash/Specific gravity of standard hydrated lime

Six test cube of size 50x50x50mm shall be casted for the test with estimated quantity of materials suggested below:

Standard Hydrated lime = 150 gms
Flyash = 300 x M gms
Standard sand = 1350 gms

The amount of water required for gauging shall be equal to that required to give a flow of 70± 5% with 10 drops in 6 seconds

Mixing of mortar

Prepare trial test mortar with different percentages of water until the specified flow is obtained. Mixing of the mortar shall be done mechanically by means of planetary mixer. Mixing paddle and bowl shall be dried and placed in the mixing position in the mixer, then introduce the materials into the bowl and mix in the following manner:

  1. All appliances shall be cleaned prior to mixing & temperature of water and the test room at the time of mixing shall be maintained at the temperature and relative humidity of 27±2 °C and 65±5%.
  2. Place all the mixing water in the bowl.
  3. Add the flyash mixture (flyash and standard hydrated lime) to the water and start the mixer & mix at a slow speed of 140 ± 5 rev/min for 30 seconds.
  4. Add the entire quantity of sand slowly over a period of 30 seconds while mixing at slow speed.
  5. Stop the mixer, change to medium speed (285 ± 10 rev/min) & mix for 30 seconds.
  6. Stop the mixer and let the mortar stand for one and half minutes. During the first 15 seconds of this interval quickly scrap down into the batch any mortar that may have been collected on side of the bowl. Then for the remainder of this interval cover the bowl with lid.
  7. Finish by mixing for one minute at medium speed (285± 10 rev/min)
  8. In case requiring a remixing interval, any mortar adhering to the sides of the bowl shall be quickly scrapped down into the batch with the scraper prior to remixing.
LIME REACTIVITY TEST OF FLYASH
Planetary mixer with paddle

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Determination of Flow

  1. Upon the completion of mixing, the mixing paddle shall be shaken to remove excess mortar into the mixing bowl. Wipe the flow table top, clean, dry and place the mould at the centre.
  2. Place a layer of mortar about 25 mm thick into the mould & tamp 20 times with tamping rod.
  3. The tamping shall be sufficient to ensure uniform filling of the mould, then fill the mould to overflow & tamp as specified for the first layer.
  4. Cut off the mortar with the plane surface flush with the top of the mould by drawing the straight edge of the trowel (held nearly perpendicular to the mould) with a sawing motion across the top of the mould.
  5. Wipe the table top and remove any water around the edge of the flow mould. Lift the mould away from the mortar one minute after the mixing operation. Immediately drop the table to a height of 12.5 mm, 10 times in 6 seconds.
  6. Flow is the resulting increase in the average base diameter of the mortar, measured at least four diameters of approximately equispaced intervals expressed as percentage of original base diameter.
  7. If the measured flow is equal to the required flow of 70 ± 5, then proceed for casting of test specimens of size 50x50x50 mm with the test mortar, otherwise repeat the procedure by preparing fresh trial batch of mortar with increase or decrease in water percentage until required flow is obtained.
 LIME REACTIVITY TEST OF FLYASH
Flow Table

Moulding of test specimen

  1. Place the mortar in 50x50x50 mm size cube mould in layer of 25 mm thickness and tamp 25 times with tamping rod.
  2. The tamping shall be sufficient to ensure uniform filling of the mould, then fill the mould to overflow & tamp as specified for the first layer.
  3. Cut off the mortar with the plane surface flush with the top of the mould by drawing the straight edge of the trowel (held nearly perpendicular to the mould) with a sawing motion across the top of the mould.
  4. Cover the surface of the specimen in the mould with a smooth and greased glass plate. Keep the specimens with moulds and cover plate under wet gunny bags for 48 hours.
  5. Remove the specimen from the mould and keep it in the temperature and humidity-controlled chamber at relative humidity of 90-100 % and temperature of 50±2 °C for a period of 8 days.

Testing of specimen

  1. Remove the specimens from the chamber and test for compressive strength after they reach at room temperature. Minimum of 3 specimens to be tested.
  2. The cubes shall be tested on their sides without any packing between the cube and steel plattens of the testing machine.
  3. Load shall be steadily and uniformly applied at the rate of 35 kg/cm²/min
    Calculate the compressive strength by dividing the maximum load with the average area over which the load is applied, which is a measure of lime reactivity of the flyash.
Cube mould

Calculation

The average compressive strength of 3 specimens shall be calculated and reported to nearest 1.0kg/cm².

Limit

Limits as per IS 3812-Part 1, Minimum average strength of flyash cubes should be 4.5 N/mm2

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Founder & Admin of civilengineeringsolution.com, I am a civil engineer working as a Assistant Engineer (QA/QC).

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