Which is the correct permissible limit for solids as per clause 5.4 of IS 456 : 2000?
Water used for mixing concrete and curing must be clean and free from harmful amounts of acids, alkalis, salts, sugar, organic substances, or other impurities that may adversely affect the concrete's strength, durability, or cause corrosion of the reinforcement. The Indian Standard code for plain and reinforced concrete, IS 456 : 2000, specifies certain permissible limits for various impurities in water.
Permissible Limits for Solids in Water for Concrete
According to Clause 5.4 of IS 456 : 2000, the following limits are considered generally acceptable for water used in concrete production. These limits ensure that the water quality does not compromise the properties of the concrete.
Understanding Different Solids and Their Limits
The presence of various types of solids in mixing water can have different impacts on concrete. It's crucial to adhere to the specified permissible limits to maintain the quality and performance of concrete.
| Type of Impurity | Permissible Limit (mg/l) | Notes |
|---|---|---|
| Organic solids | 200 | Higher organic content can interfere with cement hydration and reduce concrete strength. |
| Inorganic solids | 3000 | Excess inorganic solids can affect setting time and strength. |
| Sulphates (as SO3) | 400 | High sulphate content can lead to sulphate attack on concrete, causing expansion and cracking. |
| Chlorides (as Cl-) for Plain Concrete | 500 | Excess chlorides can contribute to efflorescence and, more critically, corrosion of reinforcement in reinforced concrete. |
| Chlorides (as Cl-) for Reinforced Concrete | 1000 | The limit is higher for reinforced concrete due to different considerations, but still critical for corrosion prevention. |
| Suspended solids | 2000 | High suspended matter can affect the workability of concrete and its final strength. |
Analysis of the Given Options
Let's evaluate each option based on the values specified in IS 456 : 2000, Clause 5.4 concerning permissible limits for solids:
- Inorganic 3000 mg/l: As per IS 456 : 2000, the permissible limit for inorganic solids is indeed 3000 mg/l. This aligns with the standard.
- Organic 1000 mg/l: The permissible limit for organic solids in IS 456 : 2000 is 200 mg/l, not 1000 mg/l. Therefore, this option is incorrect.
- Sulphates 2000 mg/l: The permissible limit for sulphates (as SO3) as per IS 456 : 2000 is 400 mg/l, not 2000 mg/l. Thus, this option is incorrect.
- Suspended 500 mg/l: The permissible limit for suspended solids according to IS 456 : 2000 is 2000 mg/l, not 500 mg/l. Hence, this option is incorrect.
Based on the detailed analysis of Clause 5.4 of IS 456 : 2000, the only option that states the correct permissible limit for solids is for Inorganic solids.
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