The Le-Chatelier test detects unsoundness due to free Lime only. This method of testing does not indicate the presence and after effect of the excess of magnesia.
As per Indian Standard specification, if the content of magnesia is greater than 3% in cement then Autoclave Test is performed which is sensitive to both Lime and Magnesia.
The Autoclave test is performed as per IS: 4031 Part-3
Apparatus:
- Balance:
The variation on balance in use shall be +/- 1.0 gram per 1000 gram. The permissible value of a new balance shall be half of this value.
- Weights:
Same as in Le-Chatelier Method
- Graduated Glass:
Graduated glass cylinders of 150 ml capacity shall be used. The permissible variation on these cylinders shall be plus or minus one millilitre. The main graduation lines of the cylinders shall be in circles and shall be numbered. The least graduations shall extend at least one-seventh of the way around, and intermediate graduations shall extend at least one-fifth of the way around the cylinder. The graduation lines may be omitted for the lowest 5 ml.
- Moulds:
Moulds of 25 X 25 mm size and 282 mm internal length and other accessories shall conform to IS 10086-1982.
- Autoclave:
The autoclave shall consist of a high-pressure steam boiler equipped with a suitable safety device. The capacity of the heating unit shall be such that with maximum load ( water plus specimens ) the pressure of the saturated steam in the autoclave may be raised to a gauge pressure of 2.1 MPa or to an absolute pressure of about 2.2 MPa, in 1 to 11 hour from the time the heat is turned on. The automatic pressure control shall be capable of maintaining the pressure at 21 ± 01 MPa corresponding to a temperature of 215.7 ± 1.7°C. The autoclave shall be designed to permit the pressure to drop from 21 MPa to less than 0.07 MPa in one hour after the heat supply has been shut off. It shall be equipped with a vent valve for allowing the escape of air during the early part of the heating period and for releasing any steam pressure remaining at the end of the one-hour cooling period. The pressure gauge shall have a nominal dial diameter of 115 mm and shall be graduated from 0 to 4.1 MPa with the scale division of not more than 0.04 MPa. The error in the gauge shall not exceed plus or minus 0.02 MPa at the operating pressure of 2.1 MPa.
Source: ELE International
- Length Comparator:
Changes in the length of the test specimen shall be measured by an apparatus conforming to
IS 9459-1980
.
Preparation of Test Specimens
- Preparation of Mould:
The mould shall be covered with some mineral oil. After the application of oil, the stainless steel or non-corroding metal reference inserts with knurl heads shall be set to obtain an effective length of 250 mm.
- Mixing Cement Paste:
The standard batch of cement paste shall consist of 500 g of cement, mixed with sufficient water to give a paste of standard consistency.
- Moulding Specimens
Immediately following the completion of mixing, the test specimens shall be moulded in one or two layers, each layer being compacted with the thumb or forefinger by pressing the paste into the corners, around the reference inserts, and along the surfaces of the moulds until a homogeneous specimen is obtained. After the top layer has been compacted, the paste shall be cut off flush with the top of the mould and the surface smoothed with a few strokes of the trowel. During the operations of mixing and moulding, the hand shall be protected by rubber gloves.
- Storage of Test Specimen
After the mould has been filled, it shall be immediately placed in a moist closet or a moist room. Specimens shall remain in the moulds in the moist room for at least 24 h. If removed from the moulds before 24 h, they shall be kept in the moist closet or moist room until tested.
The variation on balance in use shall be +/- 1.0 gram per 1000 gram. The permissible value of a new balance shall be half of this value.
Same as in Le-Chatelier Method
Graduated glass cylinders of 150 ml capacity shall be used. The permissible variation on these cylinders shall be plus or minus one millilitre. The main graduation lines of the cylinders shall be in circles and shall be numbered. The least graduations shall extend at least one-seventh of the way around, and intermediate graduations shall extend at least one-fifth of the way around the cylinder. The graduation lines may be omitted for the lowest 5 ml.
Moulds of 25 X 25 mm size and 282 mm internal length and other accessories shall conform to IS 10086-1982.
The autoclave shall consist of a high-pressure steam boiler equipped with a suitable safety device. The capacity of the heating unit shall be such that with maximum load ( water plus specimens ) the pressure of the saturated steam in the autoclave may be raised to a gauge pressure of 2.1 MPa or to an absolute pressure of about 2.2 MPa, in 1 to 11 hour from the time the heat is turned on. The automatic pressure control shall be capable of maintaining the pressure at 21 ± 01 MPa corresponding to a temperature of 215.7 ± 1.7°C. The autoclave shall be designed to permit the pressure to drop from 21 MPa to less than 0.07 MPa in one hour after the heat supply has been shut off. It shall be equipped with a vent valve for allowing the escape of air during the early part of the heating period and for releasing any steam pressure remaining at the end of the one-hour cooling period. The pressure gauge shall have a nominal dial diameter of 115 mm and shall be graduated from 0 to 4.1 MPa with the scale division of not more than 0.04 MPa. The error in the gauge shall not exceed plus or minus 0.02 MPa at the operating pressure of 2.1 MPa.
Changes in the length of the test specimen shall be measured by an apparatus conforming to
IS 9459-1980
The mould shall be covered with some mineral oil. After the application of oil, the stainless steel or non-corroding metal reference inserts with knurl heads shall be set to obtain an effective length of 250 mm.
The standard batch of cement paste shall consist of 500 g of cement, mixed with sufficient water to give a paste of standard consistency.
Immediately following the completion of mixing, the test specimens shall be moulded in one or two layers, each layer being compacted with the thumb or forefinger by pressing the paste into the corners, around the reference inserts, and along the surfaces of the moulds until a homogeneous specimen is obtained. After the top layer has been compacted, the paste shall be cut off flush with the top of the mould and the surface smoothed with a few strokes of the trowel. During the operations of mixing and moulding, the hand shall be protected by rubber gloves.
After the mould has been filled, it shall be immediately placed in a moist closet or a moist room. Specimens shall remain in the moulds in the moist room for at least 24 h. If removed from the moulds before 24 h, they shall be kept in the moist closet or moist room until tested.
Procedure:
- Remove the specimen from the moist atmosphere after $24 \pm 1/2 h$ and measure its length and place it in Autoclave at room temperature in a rack in such a way so that all the four sides are exposed to saturation steam.
- There should be enough water in Autoclave to maintain an atmosphere of saturated steam vapour during the entire period of the test. Normally 7 to 10 % of the volume of the autoclave is occupied by water.
- In the starting phase of heating, let the air to escape by opening the vent valve until stream begins to escape.
- After that, the vent valve is closed and the temperature in the autoclave is raised in such a way that gauge pressure of the steam is increased to 2.1 MPa in 1 to 1.25 Hours from the time heat is turned on.
- Maintain this pressure for 3 hours and after this period shut off the heat supply and allow autoclave to cool down at a rate such that the pressure is less than 0.1 MPa after an hour. Dissipate the remaining pressure by partially opened vent valve.
- Open the autoclave and immediately place the specimen in water of temperature more than $90^\circ C$
- Cool the water surrounding the bar by adding cold water so that the temperature of the water lowers to $27 \pm 2^\circ C$ in 15 minutes
- Measure the length of the specimen when it is surface dry.
Calculation
The difference between the lengths measured before and after the autoclaving shall be calculated nearest to 0.01 per cent of the effective gauge length which is the length between the innermost points of the metal insert used as reference points and shall be reported as autoclave expansion of cement.
Autoclave soundness limits for different cements
| Cement | Soundness (%) Max | Cement | Soundness (%) Max |
|---|---|---|---|
| 33 Grade OPC | 0.8 | Slag Cement | 0.8 |
| 43 Grade OPC | 0.8 | Low Heat Cement | 0.8 |
| 53 Grade OPC | 0.8 | Masonry Cement | 1 |
| Sulphate Resisting Cement | 0.8 | OPC Grade 53 S [IRS-T-40] | 0.8 |
| Portland Pozzolana Cement | 0.8 | ||
| Rapid Hardening Cement | 0.8 |
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