Overview

In the soundness test a specimen of hardened cement paste is boiled for a fixed time so that any tendency to expand is speeded up and can be detected. Soundness means the ability to resist volume expansion.

Apparatus

Measuring Instruments

NAME	CAPACITY / RANGE / SIZE	ACCURACY / LEAST COUNT
Autoclave	1000C (min)	10C
Length comparator	IS:9459	0.02 mm
Measuring cylinder	150 ml	1 ml
Balance	1000 g	1 g
Mould	25*25*282 mm (IS:10086)

Other Apparatus

Enamel tray, trowel

Procedure

1. Thinly cover the mould with mineral oil. Then attach the reference points so as to get an effective length of 250 mm.
2. Take 500 g of cement and mix with sufficient water to give a paste of standard consistency.
3. After mixing fill the mould in one or two layers by pressing the paste into corners by thumb. Smoothen the top layer by trowel.
4. After completion of preparation of the mould, store it in a moist room for a period of 24 hours.
5. After 24 ± ½ hrs after moulding, remove the specimen from the moist atmosphere, measure its length (L₁) and place it in the autoclave at room temperature in a rack so that the four sides of each specimen is exposed to saturated steam vapour during the entire period of test.
6. To permit air to escape from the autoclave during the early portion of the heating period, left the vent valve open until steam begins to escape.
7. Then close the vent valve and raise the temp of the autoclave at such a rate, so as to make the gauge pressure of the steam to 2.1 N/mm² in 1 to 1.5 hrs from the time heat turned on. This pressure is maintained for 3 hrs.
8. After 3 hrs switch off the autoclave, and let it be cooled at the rate so as to make the pressure less than 0.1 N/mm² in one hour and bring it to atmospheric pressure by opening vent valve.
9. Then remove the specimen from autoclave and place it in water maintained at a temp of 900C. Then cool the water to 27±2⁰C in 15 minutes. Dry the surface of the specimen and measure its length (L₂).

Calculation

Soundness of cement=L₁-L₂,

Where,

L₁=Length measured after curing for a period of 24 hrs 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.

• Note ::In the event of cement failing to comply with the specified requirements, a further test should be made from another portion of the same sample in manner described above, but after aeration (done by spreading out to a depth of 75 mm at a relative humidity of 50 to 80% for a total period of 7 days).
  

Precautions

• Length L₁ and L₂ should be measured accurately
• The temp of autoclave should be raised and lowered gradually.

Standard Specifications

Type/Name Of cement	Reference Indian Standard	Expansion ,%,(max.)
OPC (33)	IS:269-1989	0.8
OPC (43)	IS:8112-1989	0.8
OPC (53)	IS:12269-1987	0.8
Rapid hardening	IS:8041-1990	0.8
Low heat cement	IS:12600-1989	0.8
Super sulphated	IS:6909-1990	Not specified
Portland pozzolana	IS:1489-1991(part 1)	0.8
PSC	IS:455-1976	0.8
High alumina cement	IS:6452-1976	Not specified
SRC	IS:12330-1988	0.8
Masonry cement	IS:3466-1988	1.0
IRS-T-40	Railway standards	0.8

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.

Test Standard Reference

• IS:4031(Part 3):1988-Methods of physical tests for hydraulic cement (Determination of soundness)