Bulking of sand
(i) The increase in volume of sand due to moisture content is called bulking. Fine sands bulk more than coarse sands. Fully saturated sand occupies the same volume as dry sand. So, an easy way of determining the bulking of sand is by finding the decrease in volume of the given sand when fully saturated .
(ii) With volume batchings if bulking of moist sand is not accounted, we may batch less sand than required. So if the bulking is 25 % the instead of 2 parts ( boxes) of dry sand for one part of cement, we may actually batch only 2 / 1.25 = 1.60 parts of dry sand for one part of cement. To avoid this we should actually batch 2 x 1.25 = 2.50 boxes of moist sand to get 2 boxes of dry sand
(iii) Effect on yield: As shown in the earlier example , when bulking is not accounted for in proportioning a mix by volume then use of moist sand will result in less quantity of sand than calculated. This decrease in batch quantity of sand will reduce the yield of concrete per bag of cement.( yield is defined as the volume of concrete produced per bag of cement) . As an example consider the following case. Mix proportion of 1:4 by volume with water cement ratio 0.55 is used . Initially there is no bulking of sand since sand is dry. Assume loose density of coarse aggregate is 1400 kg/[censored] and its specific gravity as 2.80. Sand has a dry loose density of 1450 kg/[censored] and a specific gravity of 2.65. Assume specific gravity of cement as 3.15. First calculate the yield of concrete per bag of cement by absolute volume method.
(i) The increase in volume of sand due to moisture content is called bulking. Fine sands bulk more than coarse sands. Fully saturated sand occupies the same volume as dry sand. So, an easy way of determining the bulking of sand is by finding the decrease in volume of the given sand when fully saturated .
(ii) With volume batchings if bulking of moist sand is not accounted, we may batch less sand than required. So if the bulking is 25 % the instead of 2 parts ( boxes) of dry sand for one part of cement, we may actually batch only 2 / 1.25 = 1.60 parts of dry sand for one part of cement. To avoid this we should actually batch 2 x 1.25 = 2.50 boxes of moist sand to get 2 boxes of dry sand
(iii) Effect on yield: As shown in the earlier example , when bulking is not accounted for in proportioning a mix by volume then use of moist sand will result in less quantity of sand than calculated. This decrease in batch quantity of sand will reduce the yield of concrete per bag of cement.( yield is defined as the volume of concrete produced per bag of cement) . As an example consider the following case. Mix proportion of 1:4 by volume with water cement ratio 0.55 is used . Initially there is no bulking of sand since sand is dry. Assume loose density of coarse aggregate is 1400 kg/[censored] and its specific gravity as 2.80. Sand has a dry loose density of 1450 kg/[censored] and a specific gravity of 2.65. Assume specific gravity of cement as 3.15. First calculate the yield of concrete per bag of cement by absolute volume method.
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ReplyDeleteIs it possible for concrete yield to be affected by bulking of sand or can concrete yield be affected by wrong calculation or estimation of moisture content.
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ReplyDeleteWe have to consider bulkage in crush sand also? If it’s yes, then what is the procedure ?
Effect of bulking of sand in volumetric proportion of mortar and concrete
ReplyDeleteBLUNKING AND EFFECT ON STRENGTH
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