IRC 61 (1975) outlines provisional recommendations for constructing cement concrete pavements in hot environments. It addresses issues like accelerated cement hydration, rapid moisture loss, and early concrete setting by prescribing temperature management, material selection, mix adjustments, and curing techniques to achieve durable pavements in elevated temperature conditions.
Overview
IRC 61 (1975) outlines provisional recommendations for constructing cement concrete pavements in hot environments. It addresses issues like accelerated cement hydration, rapid moisture loss, and early concrete setting by prescribing temperature management, material selection, mix adjustments, and curing techniques to achieve durable pavements in elevated temperature conditions.
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In hot weather concreting, particularly in tropical areas where ambient temperatures may reach 40-50°C, it is crucial to manage the temperatures of concrete ingredients to prevent premature setting and loss of workability. While specific temperature thresholds are not explicitly detailed, the guidelines emphasize cooling materials such as water and aggregates, and maintaining cement temperature as low as possible to extend setting time and facilitate adequate transportation, placement, compaction, and finishing.
The temperature of freshly mixed concrete can be precisely estimated by considering the temperatures and weights of its components using IRC 61’s formula: I = [0.22(Wa ta + We te) + Ww tw] / [0.22(Wa + We) + Ww], where Wa, We, and Ww denote weights of aggregates, cement, and water respectively, and ta, te, tw their temperatures. Addition of ice modifies this formula by accounting for the latent heat of fusion (79.6 cal/gm), enabling better temperature control during mixing.
To manage rapid setting and increased water demand in hot weather, set-retarding and water-reducing admixtures such as calcium ligno-sulphonate, carbohydrates (notably sugar), calcium salts, and metal sulphates of zinc, aluminium, copper, and iron are recommended. For instance, adding 0.05% sugar by cement weight can delay setting by around two hours at 44°C, improving workability and strength while allowing cement savings. Proper dosage and addition to mixing water are essential to avoid adverse effects.
To avoid plastic shrinkage cracking in hot environments, IRC 61 advises immediate covering of freshly placed concrete with wet gunny bags or hessian cloth to retain moisture and reduce evaporation rates, especially when evaporation approaches 2.5 kg/m²/hour. Additionally, using tarpaulins on traveling stands during peak heat hours (11 a.m. to 5 p.m.) offers protection. Early initiation of curing with continuous wetting followed by thorough ponding for at least 28 days is essential. Plastic membrane curing is prohibited, but liquid membranes like sodium silicate may be cautiously used when water is limited.
Batching and mixing should be conducted swiftly to minimize heat generation, ensuring uniformity while utilizing an adequate number of mixers and skilled personnel. Mixers should be painted white externally to limit heat absorption, and blades must be regularly cleaned to maintain performance. Locating batching and mixing units near placement sites reduces transport delays. Use of chilled water or ice in mixing water aids temperature control, provided ice is fully melted to prevent voids. Aggregates should be stored shaded and sprinkled with water to stay cool. Proper planning and equipment availability are critical to avoid delays that exacerbate heat effects.
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