Oleic acid may be used in the manufacture of:
💧 What is Hydrophobic Cement?
Cement is hygroscopic, meaning it readily absorbs moisture from the atmosphere. This can cause the cement to prematurely hydrate and form lumps, a phenomenon known as "warehouse pack," rendering it useless.
Hydrophobic cement is a special type of cement designed to resist this deterioration. It is manufactured by adding a water-repellent film-forming substance during the final grinding process. This makes it ideal for use in projects located in regions with high humidity or for long-term storage where exposure to moisture is a concern.
📝 Detailed Analysis of the Options
(a) White cement
White cement gets its color from using raw materials that are extremely low in iron oxide and other metal oxides that cause the grey color. Its manufacturing process does not involve oleic acid.
(c) Anti-bacterial cement
This cement contains specific anti-fungal or anti-bacterial agents to prevent the growth of microbes on the concrete surface. This is a different type of additive for a different purpose.
(d) Portland pozzolana cement
PPC is made by blending pozzolanic materials like fly ash with cement clinker. This enhances properties like long-term strength and chemical resistance but doesn't inherently make the cement hydrophobic.
(b) Hydrophobic cement
This is the correct answer. During the final grinding of cement clinker, a small amount (about 0.1% to 0.4%) of a water-repellent substance like oleic acid or stearic acid is added. This acid forms a thin, protective film around each cement particle. This film prevents atmospheric moisture from reaching the particle and causing premature hydration. When the cement is later mixed with aggregates and water in a mixer, the abrasive action of the aggregates breaks this protective film, allowing normal hydration and hardening to proceed.
📊 Common Additives During Cement Grinding
| Additive | Purpose | Resulting Cement Type |
|---|---|---|
| Oleic Acid / Stearic Acid | Imparts water-repellency for storage | Hydrophobic Cement |
| Gypsum (CaSO₄) | Controls setting time (prevents flash set) | All Portland Cements |
| Pozzolanic Materials (Fly Ash) | Improves durability and workability | Portland Pozzolana Cement (PPC) |
💡 Study Tips
- Hydro = Water, Phobic = Fear: The name itself tells you the function. This cement "fears" water until it's ready to be used.
- Think "Raincoat": Oleic acid acts like a microscopic raincoat for each cement particle, keeping it dry until the storm of the concrete mixer arrives.
- Distinguish from Waterproofing: Hydrophobic cement is about protecting the *unmixed* cement powder. Waterproofing compounds are admixtures added to the *concrete mix* to reduce the permeability of the final hardened product.