The total amount of dissolved salts allowable concentrations in mixing water in order to obtain a good strength concrete in terms of parts per million (ppm) as per IS 456 is __.
Try it first: pick an option, then read the explanation.
Correct answer: D. 15000 ppm
Detailed Explanation: IS 456:2000 Limits for Mixing Water Quality
Water used for mixing concrete must be clean and free from harmful levels of impurities that interfere with cement hydration, impair strength gain, or cause long-term deterioration. IS 456:2000 (Plain and Reinforced Concrete — Code of Practice) is the primary Indian standard governing mixing water quality.
Potable (drinking) water is generally suitable for use in concrete without testing. When non-potable water (groundwater, river water, recycled water) is used, it must comply with IS 456:2000 limits.
Why D (15,000 ppm) is the correct answer:IS 456:2000 sets the maximum total dissolved salts (TDS) limit in mixing water at 15,000 mg/L (15,000 ppm). At this concentration, the combined chemical effect of dissolved salts on cement hydration, setting time, and long-term durability is within acceptable limits. Sea water with ~35,000 ppm TDS clearly exceeds this and must not be used for structural concrete. The other options (2,000; 10,000; 1,000 ppm) do not correspond to the TDS limit in IS 456.
IS 456:2000 Permissible Limits for Mixing Water
| Parameter | Maximum Permitted |
|---|---|
| Total dissolved salts (TDS) | 15,000 mg/L (15,000 ppm) |
| Organic solids | 200 mg/L |
| Inorganic solids | 3,000 mg/L |
| Sulphates (as SO3) | 400 mg/L |
| Chlorides (RCC / prestressed) | 500 mg/L |
| Suspended matter | 2,000 mg/L |
| pH | ≥ 6 (not acidic) |
Key Concepts for Students
- The 15,000 ppm TDS limit covers ALL dissolved salts combined — not any single salt type. Individual salts (chlorides, sulphates) have their own lower separate limits.
- Sea water has ~35,000 ppm TDS — more than double the IS 456 limit — and must never be used for structural RCC.
- Potable water in India typically has TDS < 500 ppm and always meets IS 456 requirements; testing is only required for non-potable sources.
- IS 456 is also the reference for other water quality concerns: sodium carbonates and bicarbonates (affect setting time), and organic matter (impairs hydration).