cement quantity for concrete mixing
How to calculate how many 50kg bags of cement for 100 cubic metre of concrete.
Ratio 1:3:6 (Cement:Sand:Aggregate)
Also, how to calculate how many 50kg bags of cement for mortar in 10 square metres of concrete block wall.
Block size =450mm x 225mm x 150mm thick. Mortar ratio = 1:5 (cement: Sand)
With a 1:3:6 mix for 100 cubic meter of concrete you would need 420 x 50kg bags of cement, 56 cubic meters of fine aggregate (sand and gravel passing through a 5mm sieve) and 79 cubic metres of coarse aggregate (gravel retained by a 5mm sieve).
For 10 square meters of concrete block wall, you would need 110 blocks, assuming a mortar bed depth of 10mm and with a mix of 1:5 cement: sand and 10% wastage you would need 1.225 cubic metres of mortar, which would require 0.245 cubic metres of cement and 1.225 cubic metres of sand (the cement sits in the spaces between sand grains and so does not bulk up the sand volume). 245 litres of cement is about 7.5 bags of cement (1 x 50kg bag is 33 litres). If your mortar bed is thicker, increase the quantities in proportion - 12 mm bed would increase cement and sand by 20%.
I have to admit that the cement quantities for concrete are direct from a table in Engineering in Emergencies and so should be accurate. I have done the calcs for mortar from first principles (11 blocks/square metre is a known), bed depth seems ok but could be increased as a factor of safety. If you can get some plasticiser or hydrated lime (not agricultural) to add to the mortar it would be much more workable - use a cement: lime: mortar mix of 1:1:5 so same amount of lime as cement. Make sure the sand is finer for the mortar (sand and not fine aggregate) than the concrete and well washed.
If you need more come back and we'll see if we can give you more details. The RedR book Engineering in Emergencies gives good construction detailing for both concrete and mortar.
Regards, Toby Gould
Thanks for the advice. I followed how you calculated the amount of cement bags for the 100 cubic meters of concrete, by using the data in Engineering in Emergencies Table 19.6. I calculated more conservative quantities by using the following example below 1. Required volume of concrete = 100 m3 2. Estimated volume of dry material = 100 x 1.65 = 165 m3 (includes 10% waste) 3. Mix totals = 1+3+6 = 10 (1:3:6 cement:sand:gravel) 4. Ingredient Volumes: 165 x 1/10 = 16.5 m3 cement, 165 x 3/10 = 49.5 m3 sand 165 x 6/10 = 99 m3 gravel 5. # Bags of cement: 16.5 m3 cement / .0332 m3 per 50 Kg bag = 497 bags of cement (use three bags) Let me know what you think of the above calculation. Your advice on the mortar is very help as well. Can you give more details on how the mortar quantities were calculated from first principles? The standard mortar bed depth used in Southern Sudan is 20mm.
Thanks, Don Lucey
I have found the EiE table fine to work with as is but go with what you find best.
For the mortar I have gone back to my original calcs and revised them:
Blocks SA= 0.45x 0.25 = 0.1125m2 1m2 = 1/0.1125 = 9 + 2 for wastage/corners etc
Assuming bed depth now of 20mm mortar on 2 sides of each block = 0.15 x (0.45+0.225) = 0.10125m2 for each block + 10% wastage = 0.111375m2
20mm bed gives 0.111375x 0.02 = 0.0022275 per block - I had a decimal point wrong here - I apologise I hope it hasn't messed up your calculations
For 10m2 of wall - 110 blocks 0.245m3 of mortar
0.245m3 of mortar at 1:5 gives 0.049m3 (50 litres) of cement and 0.245 m3 of sand
50 litres of cement is 1 1/2 bags
Regards Toby Gould
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