Concrete Yield-How to figure?

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intensespider Participant Join Date: Nov 2008 Posts: 1	Concrete Yield-How to figure? 11/23/2008 8:48 AM
	Hello all, Please walk this through with me. Im not an engineer but I am interested in solving this problem.My goal is to know how much concrete materials I will use (cement, agg, sand). I have an abundance of all materials here on my site. My slab is 6 inch thick, 5x10 meters. Ive calculated total cubic yards= 10, covert to cubic meters =7.6. So our ratio is 300 kg agg, 200 kg sand, 100 kg cement. I have a Silo full of cement I can take, how much cement to drain for my project? Getting numbers off the web, relative density of water is 1000kg, aggregates are between 2.4-2.9 (say 2.6), Cement is 3.15, water/cement ratio is .40. I found this on the net: V _a = W _L / ( SG ) W _u where V _a = absolute volume, ft ³ (m ³ ) W _L = weight of material, lb (kg) S _G = specific gravity of the material W _u = density of water at atmospheric conditions (62.4 lb/ft ³ 1000 kg /m ³ ) Then, job yield equals the sum of V _a for cement, gravel, sand, and water. Ok so all Relative densities= 6.15 6.15 x (1000kg for water)= 6150 600/ 6150=.097 Is this correct? Im a little confused if I did this correct. The answer would have me almost 1 cubic meter per mix. S0 I would need to drain about 760 kg from my silo? Can someone please hep me?
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#1 "Re: Concrete Yield-How to figure?" by babybear on 11/24/2008 12:53 AM (score 2)

babybear

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Re: Concrete Yield-How to figure?

11/24/2008 12:53 AM

Hello intensespider:

I know you have researched quite a bit already but, have a look at this site. It is very detailed.

The sum of the ingredient volumes will be greater than the volume of concrete, because the sand will fill the voids between the coarse aggregate. The materials normally have 30 to 50% greater volume than the concrete mix; 5 to 10% is allowed for waste and spill. The cement added does not noticeably increase the volume. The above assumptions are used in Example 1 in roughly estimating the amount of ingredients needed. In Example 2, a more accurate method of calculating the amount of concrete obtained from the ingredients is shown.

http://www.fao.org/docrep/S1250E/S1250E08.htm

This is a small part which I think you will find useful.

Let me know if this was of use, or the site of use. I am sure it will be, I am not so sure you will want to figure things out after the work you have down. The piece I pasted above has the amounts (allowing for certain assumptions) which it explains, and you will see the mixes list different ratios of sand, cement and aggregates on the left of the chart.

Table 3.13 Requirements per Cubic Metre for Batching Nominal Concrete Mixes

Proportions by	Cement No. of 50 kg	Naturally moist aggregate¹				Aggregate: cement	Sand to total aggregate
Proportions by	Cement No. of 50 kg	Sand		Stones		Aggregate: cement	Sand to total aggregate
Volume	bags	m³	tonnes	m³	tonnes	ratio	%
1:4:8	3.1	0.46	0.67	0.92	1.48	13.4	31
1:4:6	3.7	0.54	0.79	0.81	1.30	11.0	37
1 5:5	3.7	0.69	1.00	0.69	1.10	10.9	47
1:3:6	4.0	0.44	0.64	0.89	1.42	10.0	31
1:4:5	4.0	0.60	0.87	0.75	1.20	9.9	41
1:3:5	4.4	0.49	0.71	0.82	1.31	8.9	35
1:4:4	4.5	0.66	0.96	0.66	1.06	8.7	47
1:3:4	5.0	0.56	0.81	0.74	1.19	7.7	40
1:4:3	5.1	0.75	1.09	0.57	0.91	7.6	54
1:2:4	5.7	0.42	0.62	0.85	1.36	6.7	31
1:3:3	5.8	0.65	0.94	0.65	1.03	6.5	47
1:2:3	6.7	0.50	0.72	0.74	1.19	5.5	37
1:1:5:3	7.3	0.41	0.59	0.82	1.30	5.0	31
1:2:2	8.1	0.60	0.87	0.60	0.96	4.4	47
1:1:5:2	9.0	0.50	0.72	0.67	1.06	3.9	40
1:1:2	10.1	0.37	0.54	0.75	1.19	3,.3	31

These quantities are calculated with the assumption of sand having a bulk density of 1450 kg/m³ and stone 1600 kg/m³. The density of the aggregate material being 2650 kg/m³.

Mixing

Mechanical mixing is the best way of mixing concrete. Batch mixers with a tilting drum for use on building sites are available in sizes from 85 to 400 litres. Power for the drum rotation is supplied by a petrol engine or an electric motor whereas the tilting of the drum is done manually. The pear-shaped drum has blades inside for efficient mixing. Mixing should be allowed to proceed for at least 2.5 minutes after all ingredients have been added. For small scale work in rural areas it may be difficult and rather expensive to get a mechanical mixer.

Table 3.14 Mixing Water Requirements for Dense Concrete for Different Consistencies and Maximum Sizes of Aggregate

Maximum size of aggregate³	Water requirement 1/m³ concrete
	1/2- 1/3	1/3- 1/6	1/6 -1/2
	High workability	Medium workability	Plastic consistency
10mm	245	230	210
14mm	230	215	200
20mm	215	200	185
25mm	200	190	175
40mm	185	175	160

³ Includes moisture in aggregate. The quantities of mixing water are maximums for use with reasonably well graded, well-shaped, angular coarse aggregate.

Good luck.

__________________
Take it easy, bb. >"HEAR & you FORGET<>SEE & you REMEMBER<>DO & you UNDERSTAND"<=$=|O|=$=>"Common Sense is Genius dressed in its Working Clothes"<>[Ralph Waldo Emerson]

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Anonymous Poster	#2 Re: Concrete Yield-How to figure? 11/24/2008 7:41 PM
	A couple of things, you must determine the dry weight of each component and the water content msut be added in as if you added water to the mix. Also it seems like you are using the density for the aggregate not the bulk weight, 2.6 g/cc would be the typical density for a solid siliceous mineral rock, which is a weight of 162 pcf, but the bulk weight for aggregate might be less than about 150 pcf. Your Dry bulk weight should be more like 2.0 to 2.4 g/cc. Cement is traditionally estimated at a bulk weight hydrated of only 150 pcf, about 2.4 g/cc. Loose the bulk weight will be lower. In materials applications assume that you use γ instead of S_gxW_uin most calculations. You must always consider the void space of the material being used.
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babybear Guru Join Date: Jun 2008 Location: USA/Europe Posts: 4547 Good Answers: 68	#3 In reply to #2 Re: Concrete Yield-How to figure? 11/24/2008 8:12 PM
	Hello Guest, The sum of the ingredient volumes will be greater than the volume of concrete, because the sand will fill the voids between the coarse aggregate. The materials normally have 30 to 50% greater volume than the concrete mix; 5 to 10% is allowed for waste and spill. This is the first few lines I sent in. As you can see it refers to the volumes being lager before mixing. Which I think is something you kind of say? You make some fair points. But after a couple of mixes you start to get an idea of how 'wet' you want or need to mix to be and add just enough water to reach that consistency. Of course you could do it the 'easy' way and order a ready-mixed load! But with regard to the OP, he has very little to mix and from the size, it sounds like he is making a home garage floor, or slab to later assemble the pre-formed garage on? Not 'rocket science' really. Take care OK. __________________ Take it easy, bb. >"HEAR & you FORGET<>SEE & you REMEMBER<>DO & you UNDERSTAND"<=$=\|O\|=$=>"Common Sense is Genius dressed in its Working Clothes"<>[Ralph Waldo Emerson]
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#1 "Re: Concrete Yield-How to figure?" by babybear on 11/24/2008 12:53 AM (score 2)

You might be interested in: Cement Boards, Cement Tiles, Cement, Concrete and Mortar

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