SOUNDNESS TEST OF CEMENT BY AUTOCLAVE



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  • IS: 4031 (Part-3): 1988


APPARATUS REQUIRED FOR THE TEST:-
  • Cement Autoclave
  • Balance
  • Length Comparator
  • Graduated glass cylinder
  • Modulus: 25×25×280 mm (internal length)
  • Thermometer


Soundness Test of Cement by Autoclave
Autoclave


PROCEDURE OF THE TEST:-
  1. The method shall be thinly covered with mineral oil. After this operation the reference insert shall be set to obtain an effective gauge length of 250 mm.
  2. A cement paste shall be formed taking 800 g of cement with sufficient water to give a past of standard consistency.
  3. Immediately after the mixing the test specimen shall be moulded in one or two layers, each layer being compacted with the thumb pressing the paste into corners.
  4. After the top layer has been compacted the paste shall be cut off flush with the top of the mould.
  5. During the operating the mixing & moulding the hand shall be protected with rubber gloves.
  6. After the mould has been filled, it shall be immediately placed in moist cabinet for at least 24 hours.
  7. After (24 ± 1/2) hours the specimen shall be removed from the moist cabinet, measure for length (L1) & shall be placed in the autoclave at room temperature.
  8. The autoclave shall contain enough water to maintain an atmosphere of saturated steam vapour during the entire period of the test.
  9. To prevent air to escape from the autoclave during the early portion of the heating period the vent value shall be lift steam being to escape.


10. The value shall then be closed & the temperature of the autoclave shall be raised at such rate as will bring the gauge pressure of the steam to 2.1 MPa in (1 to 1¼) hrs. & maintained for three hours.

11. At the end of three hours, the heat supply shall be shut off & the autoclave cooled at the rate such that the pressure shall be less than 0.1 MPa at the end of the hour.

12. The autoclave shall be less than be opened & the test specimen immediately placed in water at a temperature above 90 °C.

13. The water surrounding the bars shall be than cooled at a uniform rate by adding cold water so that the temperature of water shall be lowered to 25°C to 29°C in 15 minutes.

14. The water surrounding the specimen shall then be maintained at 25°C to 29°C in 15 minutes when the specimen shall be surface dried & their lengths measured again.

15. Measure the length (L2of the specimen when it is surface dry.


CALCULATIONS AND REPORTING:-
The difference in lengths (L1 – L2) of the test specimen before & after autoclave shall be calculated to the nearest 0.01% of the effective gauge length & shall be reported as  autoclave expansion of cement.

i.e.  Soundness of cement = L1 – L2,
Where,
L1 = Length measured after curing for a period of 24 hours in a moist room.
L2 = Length measured after completion of autoclave test.
A contraction (negative expansion) is indicated by prefixing a (–) sign to the percentage expansion reported.


Type/Name Of cement
Reference Indian Standard
Expansion of Soundness %, (max.)
OPC (33)
IS:269-1989
0.8
OPC (43)
IS:8112-1989
0.8
OPC (53)
IS:12269-1987
0.8
Rapid Hardening Cement

IS:8041-1990

0.8
Low Heat Cement
IS:12600-1989
0.8
Portland Pozzolana Cement
IS:1489-1991(part 1)

0.8
PSC
IS:455-1976
0.8
SRC
IS:12330-1988
0.8
Masonry Cement
IS:3466-1988
1.0
IRS-T-40
Railway standards
0.8
Super Sulphated Cement

IS:6909-1990

Not specified
High Alumina Cement
IS:6452-1976
Not specified


TECHNICAL DISCUSSIONS :-
  • Volume expansion in cement mortar or in cement concrete is caused by the presence of unburnt lime (CaO), dead burnt MgO and also CaSO₄.
  • By Autoclave method we only find out presence of unburnt lime (CaO) and magnesia (MgO).
  • Magnesia content allowed in cement is limited to 6%.
  • Indian standard specification stipulates that cement having a magnesia content of more than 3% shall be tested for soundness by Autoclave test which is sensitive to both free magnesia and free lime.
  • No satisfactory test is available for deduction of unsoundness due to an excess of calcium sulphate. But it can be easily determined by chemical analysis.