For the construction of thin R.C.C. structures the type of cement to be avoided is .........
🏗️ Requirements for Thin R.C.C. Structures
Thin R.C.C. structures, such as shells, domes, or precast panels, have a high surface area to volume ratio. This means they lose heat to the environment very quickly. The heat generated by cement hydration is crucial for strength development, especially at early ages and in colder weather.
Therefore, for thin sections, a cement that gains strength reasonably fast is preferred. A cement with very slow strength gain would be disadvantageous, as it would require the formwork to be kept in place for a longer period, slowing down construction.
📝 Detailed Analysis of the Options
(a) ordinary Portland cement
This is a general-purpose cement and is perfectly suitable for thin R.C.C. structures. It provides a good balance of strength gain and heat generation.
(b) rapid hardening cement
This cement is actually ideal for thin R.C.C. structures. Its high rate of early strength gain allows for quick removal of formwork, which is often a key requirement in such constructions.
(c) low heat cement
While not the best choice, it is the *second* most likely to be avoided. Its primary purpose is for mass concrete (like dams) to prevent cracking from excessive heat. Using it in thin sections would result in very slow strength development, but it's not the primary answer here.
(d) blast furnace slag cement
This is the correct answer to be avoided. Blast Furnace Slag Cement (BFSC) has a lower heat of hydration and a slower rate of early strength gain compared to Ordinary Portland Cement. This slow development is a significant disadvantage for thin structures, which need to gain strength quickly to become self-supporting and to counteract rapid heat loss. The properties of BFSC (low heat, high long-term durability, chemical resistance) make it ideal for mass concrete or marine structures, but unsuitable for thin sections where speed is often critical.
📊 Cement Suitability for Thin R.C.C. Sections
| Cement Type | Early Strength Gain | Heat of Hydration | Suitability |
|---|---|---|---|
| Rapid Hardening Cement | Very High | High | Excellent / Ideal |
| Ordinary Portland Cement | Good | Moderate | Good / Suitable |
| Low Heat Cement | Low | Very Low | Poor / To be avoided |
| Blast Furnace Slag Cement | Low | Low | Poor / To be avoided |
💡 Study Tips
- Thin Sections Need Speed: Remember that thin structures need to gain strength quickly. Therefore, cements with slow strength gain are undesirable.
- Low Heat = Slow Strength: Generally, cements with low heat of hydration (like Low Heat Cement and BFSC) also have slow early strength development.
- BFSC is for Mass, Not Thinness: Associate Blast Furnace Slag Cement with large, massive structures where controlling heat is important, not thin structures where generating heat and gaining strength quickly is needed.