Soundness test of cement determines ...........
🔊 What is Soundness and Why Does it Matter?
Soundness is the ability of hardened cement paste to retain its volume after setting. A cement that is "unsound" will undergo a delayed, excessive expansion, which can cause cracking and lead to the disintegration of the structure.
This expansion is primarily caused by the slow hydration of excessive amounts of uncombined ingredients left over from the manufacturing process, namely free lime (CaO) and magnesia (MgO). The soundness test is designed to detect the potential for this harmful expansion.
📝 Detailed Analysis of the Options
(a) quality of free lime
This is the correct answer. The soundness test, particularly the Le Chatelier's test, directly measures the expansion of a cement paste due to the presence of excess, uncombined (free) lime. By checking for this expansion, the test effectively determines if the quantity of free lime is within acceptable limits, thus ensuring the "quality" of the cement in terms of its volume stability.
(b) ultimate strength
This is incorrect. Strength, whether early or ultimate, is determined by crushing mortar cubes in a Compression Testing Machine.
(c) durability
While soundness is a critical aspect of durability, the term "durability" is very broad, covering resistance to weathering, chemical attack, abrasion, etc. The soundness test only measures one specific factor related to durability: volume stability due to free lime/magnesia.
(d) initial setting
This is incorrect. The initial setting time is determined using the Vicat apparatus, which measures the time it takes for the paste to lose its plasticity.
📊 Soundness Test Methods
| Test Method | Apparatus | Detects Unsoundness due to... |
|---|---|---|
| Le Chatelier Test | Le Chatelier's Apparatus | Free Lime (CaO) only |
| Autoclave Test | Autoclave (high-pressure steam vessel) | Both Free Lime (CaO) and Magnesia (MgO) |
💡 Study Tips
- Soundness = Volume Stability: The core concept is checking if the cement will expand dangerously after it hardens.
- Free Lime is the Culprit: The main cause of this expansion is unburnt, free lime. The test's purpose is to find this.
- Le Chatelier for Lime: Remember that the standard Le Chatelier test is specifically for detecting expansion due to free lime.
- Autoclave for Both: The Autoclave test is more comprehensive and can detect expansion from both free lime and magnesia.