What Is Soundness of Cement | Soundness Test of Cement | Le Chatelier Apparatus | Soundness Test On Cement

What Is Soundness of Cement?

The soundness of cement indicates the stability of any cement during the volume change in the process of setting and hardening.

In case the volume change in cement is unstable after setting and hardening, the concrete element will crack, which can affect the quality of the structure or even cause serious accidents, known as poor dimensional stability.

The soundness test of cement determines the expansion of cement after it starts setting. Certain cement has been found to undergo a large expansion after setting causing disruption of the set and hardened mass.

This expansion of cement can cause serious problems for the durability of structures when such cement is used.

The soundness of cement is mainly measured by two methods: EN-196 (1995), which is based on the Le Châtelier test method, and the autoclave test (ASTM-C151, 2015), in which pressure is also applied to the sample.

Significance of Soundness of Cement

The testing of the soundness of cement, to ensure that the cement does not show any appreciable subsequent expansion of prime importance.

The unsoundness is occurring mainly due to an excess lime that could be combined with acidic oxide at the kiln.

This is also due to inadequate burning or insufficient fineness of grinding or thorough mixing of raw materials. It also may occur due to too high a proportion of magnesium content or calcium sulfate content may cause unsoundness in cement.

For this reason, the magnesia content allowed in cement is limited to 6 percent, It can be recalled that to prevent flash setting, calcium sulfate is added to the clinker while grinding. The quantity of gypsum added will vary from 3 to 5 percent depending upon C3A content.

If the addition of gypsum is more than could be combined with C3A, excess gypsum will remain in the cement in Free State.

This high percentage of gypsum leads to an expansion and consequent disruption of the set cement paste.

The unsoundness in cement majorly occurs due to excess lime, excess magnesia, or excessive proportion of sulfates.

The unsoundness effect of cement does not come to the surface for a considerable period of time,

Read More: Setting Time Of Concrete And Method Of Testing

Le Chatelier Test

Therefore, accelerated tests are required to detect them. The soundness of cement is tested by is Le – chatelier’s soundness test.

Different Tests of Cement

The following tests are conducted on cement in the laboratory are as follows:

1. Fineness Test of Cement
2. Consistency Test of Cement
3. Setting Time Test of Cement
4. Soundness Test of Cement
5. Heat of Hydration Test
6. Speicific Gravity Test of Cement
7. Tensile Strength Test
8. Chemical Composition Test

Soundness Test of Cement [ Le chatelier Test ]

IS Code for soundness cement Test is IS:4031-Part 3-1988

Soundness Test Apparatus

1. Le- chatelier mould
2. Cement
3. Glass sheets
4. Mixing pan
5. Trowel
6. Weight

It consists of a small split cylinder of spring brass or other sulfa metal. Le- Chatelier mold is 30 mm in diameter and 30 mm high.

On both sides of the mold are attached two indicator arms 165 mm long with pointed ends.

Water is added to cement as 0.78 P. where P is % of water for standard consistency of cement. Well, a mixed paste is filled in mold and covered with a glass plate on both faces of mold.

Read More: Slump Test – Type Of Slump & Test Method

Procedure Of Soundness Test

The Soundness test of the cementing procedure is as follows,

• The mould and the glass plates are oiled before conducting the test.
• Take 400 grams of cement sample.
• For this test to be performed we need standard consistency of cement. Water is taken as 0.78 x P (Where P is water required for Standard consistency in percentage)
• For example, Standard consistency is 30% of water, then take water percentage for soundness is 0.78 x 30% = 23.4%. So water mixed in 400 gm of cement will be 400 x (23.4/100) = 93.6ml.)
• Make a well-mixed paste of cement and fill in Le- Chatelier mould taking care to keep the edges of the mould gently together during the operation.
• Clean the upper surface and make it smooth and place a small weight over the cover plate.

• Put this assembly quickly in water at a temperature of 27º C + 2ºC and keep it there for 24 hours.
• Take out mould from water and measure the distance between the indicators points as Reading-1.(Suppose it is 2 mm)
• Now, again put this assembly in boiling water for 25 to 30 minutes and keep at boiling for 3 hours. The mould should be in boiled water during this period
• Remove the mould from the water and allow it to cool at room temperature.
• Measure the distance between the indicator points as Reading-2. (Suppose it is 10mm)
• The soundness of cement = (Reading-2) – (Reading-1)

                                   = 10 mm – 2mm

                                   = 8 mm

Read More: What Is Curing Of Concrete And Different Methods Of Curing

The difference between needle readings indicates the soundness of cement. The soundness limit must exceed 10 mm for ordinary, rapid hardening, and low heat Portland cement. If in case the c expansion is more than 10 mm as tested above, the cement is said to be unsound.

The Le Chatelier test has the drawback in that it detects lime-caused unsoundness. This method does not measure unsoundness caused by the presence of an excess of magnesia.

Indian Standard Specification stipulates that cement having a magnesia content of more than 3 percent shall be tested for soundness by Autoclave test which is sensitive to both free magnesia and free lime.

In this test, a neat cement specimen 25 x 25 mm is placed in a standard autoclave and the steam pressure inside the autoclave is raised at such a rate as to bring the gauge pressure of the steam to 21 kg/sq cm in 1 — 1’/4 hour from the time the heat is turned on.

This pressure is maintained for 3 hours, the autoclave is cooled and the length is measured again. The Stream pressure applied eventually accelerates the hydration of both magnesia and lime.

To determine the unsoundness due to excess calcium sulfate there is no satisfactory test is available. But, the amount present can be easily determined by chemical analysis.

FAQs:

Watch Video: Soundness Test of Cement

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