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Metakaolin - measuring the total quantity of fixed Calcium Hydroxide (Chapelle test modified) Referring to the French norm NF P 18-513, Annexe A

1. Principle

The measure of the fixed quantity of calcium hydroxide on pozzolanic materials helps to define their
pozzolanic activity.
1 g metakaolin is reacted with 2 g CaO in 250 ml of water (free of CO2). The non reacted lime is then measured
and the result expressed in mg Ca(OH)2 fixed by the metakaolin.
A blank experiment is done symmetrically without metakaolin

2. Equipment

This consists of:
     - heated stirrer with a Teflon magnet
     - thermometer (scaled from 0 to 100°C)
     - cooling column
     - Erlenmeyer in stainless steel with smooth inner surface (volume of 750 ml)
     - tap with 2 holes
            o one for the cooling column
            o one for the thermometer
     - balance e=0,1 mg
Metakaolin - chapelle test modified
3. Reagents

     - calcium carbonate for analysis
     - distilled water without CO2. Prepare the water by passing it over an ion exchange resin.
       Use this water for all reactions.
     - Saccharose for analysis
     - Hydrochloric acid (decinormal)
     - Indicator solution: 0,1 % phenolphthalein in 50% alcohol solution

4. Working method

     - the apparatus id regulated to a temperature of 90°C
     - weigh exactly 1 g of metakaolin in powder form into the dry clean Erlenmeyer
     - use a calibrated pipette to add 250 ml of the above water
     - add about 2 g of CaO exactly weighed
     - prepare the CaO the following way:
            o weigh 3,6 g of CaCO3 in a platinum crucible with known tare
            o calcine for about 30 minutes at 1000°C
            o weigh and verify that the LOI (loss on ignition) be 44%
     - place the stirrer in the Erlenmeyer
     - place the tap with the thermometer and the cooling column and homogenise the content of the Erlenmeyer
     - place the apparatus on the heated stirrer and start heating
     - verify that the temperature gets to 85°C±5
     - stir and heat for 16 hours
     - cool to room temperature
     - add to the Erlenmeyer 250 ml saccharose solution freshly prepared (60 g saccharose dissolved in
       water give exactly 250 ml solution)
     - stir for 30 minutes on the magnetic stirrer. Filter about 200 ml take out 25 ml with a calibrated pipette.
     - Make the same proceeding without metakaolin

4.1. Titrating the solution

     - titrate with a burette using the HCl 0,1N solution using the phenolphthalein as indicator

5. Calculations


     - V1 (ml) is the volume of 0,1N HCl necessary for the 25 ml of solution obtained by the blank sample
     - V2 (ml) is the volume of 0,1N HCl necessary for the 25 ml of solution obtained by the reaction of
       the metakaolin

The titration reaction is:

CaO + 2HCl → CaCl2 + H2O
Ca(OH)2 + 2 HCl → CaCl2 + H2O

Check of the blank reaction

56 ⁄ 2 x V1 must be under 1000
Trial with metakaolin:

Mg of Ca(OH)2 fixed = 2 x V1 - V2 x 74 x 1000
                                               V1        56

6. Results

The results are expressed in mg Ca(OH)2 fixed by the metakaolin

7. Precision

The results should have a variation of 10%.


Newchem GmbH, Flamminggasse 79, Baden, Austria –