--- title: "Casting and curing temperature; concreting in Kathmandu" subject: "Concrete Technology and Masonry Structure" chapter: 4 key: "semester_5/concrete_technology_and_masonry_structure:casting-curing-temperature-kathmandu" source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/casting-curing-temperature-kathmandu site: BCT Engineering --- # Casting and curing temperature; concreting in Kathmandu Concrete Technology and Masonry Structure · Chapter 4: Properties of hardened concrete - Asked in: 2064 Jestha (old course) - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/casting-curing-temperature-kathmandu - Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-4 ## Question Explain the influence of casting and curing temperatures on concrete strength and suggest the appropriate method of concreting in Kathmandu. ## Short answer High temperature increases early strength but reduces long-term strength due to non-uniform gel; low temperature gives higher ultimate strength but slows early gain. In Kathmandu, cast in spring/autumn; in winter use warm water, cover, and delay form removal; in summer avoid hot/dry winds, shade, and cure continuously for 7–10 days. ## Answer Casting and curing temperature change the speed of hydration and the final structure of the gel. A high temperature gives high early strength but a lower 28-day and long-term strength (non-uniform gel, coarse pores, drying cracks). A low temperature slows early strength but improves later strength, as the gel forms more densely; near freezing, hydration almost stops and fresh concrete can be damaged by ice. #### Concreting in Kathmandu Kathmandu valley has a temperate climate: mild to warm summers (up to about 30 °C) and cool winters (night temperature 0 to 5 °C in December to January) with fog and little rain in winter. The temperature is mostly favourable, but special care is needed in winter and in the pre-monsoon dry period. 1. **Season:** prefer casting in spring and autumn, between 10 and 30 °C; avoid pouring in the cold early morning of Poush to Magh, or heavy monsoon rain unless protected. 2. **Cement:** OPC 43 or PPC (Nepal Standard), with fresh stock; PPC is acceptable with extended curing. For durable work follow the minimum cement content and maximum w/c of IS 456 Table 5 for the exposure (mild or moderate: w/c 0.50 to 0.55). 3. **Winter:** keep the concrete at 5 °C or higher at placing (IS 456, Cl. 14.1); use warm mixing water, cover with plastic and straw/jute at night, delay formwork stripping, avoid casting if frost is expected. 4. **Summer (dry spells):** cast in early morning or evening, wet the forms, shade, and prevent plastic shrinkage cracking (IS 456, Cl. 14.1). 5. **Curing:** keep moist for at least 7 days for OPC and 10 days for PPC (IS 456, Cl. 13.5.1) with ponding or wet hessian, and use a curing compound where water is scarce. 6. **Mix:** use a water-reducing admixture, keep w/c low, compact properly, and cast cubes cured under site conditions for stripping decisions. Thus normal procedures with attention to cold-night protection and proper curing are enough for Kathmandu. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. High casting temperature versus low casting temperature has what effect on strength? A. High: low early, higher later; low: high early B. High: high early, lower later; low: slower early, better later C. Both give same strength D. High: higher at all ages Answer: B. High temperature gives non-uniform gel and coarse pores; low temperature gives denser gel. (Key point: Temperature effect) 2. Which winter measure is suggested for Kathmandu? A. Keep concrete at 5 C or higher at placing, using warm water and night covers B. Add extra water for workability C. Remove formwork early D. Avoid curing Answer: A. Winter nights near 0-5 C need warm mixing water, covers, delayed stripping. (Key point: Winter practice) 3. Minimum moist curing recommended (IS 456 Cl. 13.5.1)? A. 3 days for OPC and 5 days for PPC B. 14 days for both C. 7 days for OPC and 10 days for PPC D. 1 day for both Answer: C. IS 456 requires at least 7 days for OPC and 10 days for PPC. (Key point: Curing period) 4. In dry warm spells in Kathmandu, one should: A. Cast at noon for fast setting B. Use dry forms C. Add extra water D. Cast in early morning or evening, wet forms and avoid plastic shrinkage Answer: D. Cooler timing, wet forms and shade reduce plastic shrinkage. 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