Thursday, October 7, 2010

ACI - 211 At Our Homes

Abstract: 
 This Technical Note has presented an executive method for concrete placing in small building sites.
Since there is not a mechanized and automatic systems for concrete placing ( Cast - in - place ) in small building sites (included : Batching plant , Batch mixer , Truck mixer , … ) , a contractor utilizes from drum mixer or handling mixer by volume batching method .
In this Technical Note, author has tried to show changing of weight batching to volume batching of concrete materials (cement, water, aggregates) so that weight batching has already obtained by using of ACI-211 (Mix Design).
Therefore, ACI-211 can be used even at our homes.

Introduction: 
In order to execute concrete placing (cast-in-place) at the sites, it needs to be obtained a mix design of concrete.
A mix design of concrete (in accordance with ACI-211) introduces us only the weight batching of cement, water, aggregates.
We can use from weight batching, if we have had a batching plant, batch mixer, truck mixer…
In fact, if we have had a mechanized and automatic system for concrete placing that it is used only in big and large sites.
But we have to use volume batching instead of weight batching in small sites.
In this paper, author has presented a method for changing of weight batching to volume batching.

Main Body of Article Describing work and Results:

In here, we proceed step by step for changing of weight batching to volume batching:
1) We should get the results of simple tests on aggregates as follows:
- Sieve analysis of coarse and fine aggregates
- Free unit weight of coarse aggregate
- Free unit weight of fine aggregate
- Free unit weight cement
2) According to above tests results and tables of ACI-211, we can estimate weight batching of concrete materials.
3) We assume weights batching of concrete materials per one cubic meter of the concrete in according with point (2) are as follows:
- ma Weight of coarse aggregate / 1 m3 concrete
- ms Weight of fine aggregate / 1 m3 concrete
-mc Weight of cement / 1 m3 concrete
- mw Weight of water / 1 m3 concrete
4) So, we should get the volume of a batch that it is available for us and total volume of Drum Mixer should be recognized that it depends on to type of Drum Mixer (It is Standard)
- v1 Volume of an available batch
- v2 Total Volume of Drum mixer (Volume capacity of Drum mixer)
5) According to point (1), we have:
- da Free Unit weight of coarse aggregate

- ds Free Unit weight of fine aggregate
- dc Free Unit weight of Cement
- dw=1000 Kg / m3 Free Unit weight of Water
6) In this step, we can get the volume of each one of the concrete materials for one cubic meter of the concrete:
-va =ma / da The volume of coarse aggregate / 1 m3 concrete
-vs =ms / ds The volume of fine aggregate / 1 m3 concrete
-vc =mc / dc The volume of Cement / 1 m3 concrete
-vw =mw / dw The volume of Water / 1 m3 concrete
-vT = va + vs + vc + vw Sum of concrete materials volumes
7) According to Volume of Drum Mixer, we should calculate the volume of concrete materials for one Drum Mixer batch:
- VIa = v2.va / vT The volume of coarse aggregate / 1 unit Drum Mixer batch
-VIs = v2.vs / vT The volume of fine aggregate / 1 unit Drum Mixer batch
-VIc = v2.vc / vT The volume of Cement / 1 unit Drum Mixer batch
-VIw = v2.vw / vT The volume of Water / 1 unit Drum Mixer batch
8) We should get number of batches:
N = v2 / v1 Number of total batches

9) Now, we can get number of batches for each material of the concrete with using of below formula:
ni = N.VIi / v2
VIi = v2.vi / vT
ni = N.vi/ vT
vT = SUM vi = va + vs + vc + vw
ni = N.vi/ SUM vi
vi = mi / di
ni = N. mi / di SUM mi / di
Where:
- i Each one of the concrete materials (aggregate, cement, water)
- n Number of batches for each material of the concrete
- N Number of total batches
- mi Weight of each one of the concrete material / 1 m3 concrete (According to ACI-211 Tables)
- di Free Unit weight of each one of concrete material

Example:
According to ACI-211 Tables, we have obtained amount of materials per one cubic meter of the concrete as follows:
- ma = 1040 kg
- ms = 830 kg
-mc = 350 kg
- mw = 190 kg
And so, free unit weight of above materials is below cited:
-da = 1470 kg / m3
- ds = 1530 kg / m3
- dc = 1200 kg / m3
- dw=1000 Kg / m3
The volume of Drum Mixer and the Volume of the batch sample are:
- v1= 0.2 * 0.2 * 0.2 = 0.008 m3
- v2 = 0.2 m3
Therefore, we have:
N = v2 / v1 , N = 25 Number of Total batches
Now, we can calculate number of batches for each materials of the concrete. For instance, batches number of coarse aggregate is calculated as follows:


ni = N. mi / di SUM mi / di

na = 25 * 1040 / 1470 (1040/1470 + 830/ 1530 + 350 / 1200+ 190/1000) = 10.2
Conclusion:
 According to previous mentioned matters, we can execute concrete placing by using of ACI-211 or another standard and volume batching method in small sites where there is not any mechanized or automatic system.
Therefore, we can speak about optimum slump, W/C, quality of concrete even in small building sites.
Small building sites could be meant even when we are using of concrete in our homes.
But we should notice, for producing the concrete with high quality, all of aggregates, cement and water should be tested in laboratory before using of them.