Basics of Concrete (4) Composition and Mixing Concrete

Concrete mortar is planned such that the resulting concrete can be easily done in a cost as low as possible, of course.
Concrete must have a high workabilitas, have higher cohesion properties when in a state of plastic (not hardened), so that the concrete produced quite strong and durable.
Mortar (mixed) concrete should consider the environment in which the concrete will stand, for example on the waterfront environment, or heavy loads, or extreme weather conditions.

Proportional
Reminder: Concrete is a mixture of cement, fine and coarse aggregate, water and additives.

Different composition of the raw materials of concrete affects the properties of concrete produced in the end. This division is usually measured in units of weight. Measurement based on volume can in fact also, and more done on a small scale construction, such as houses.

CEMENT
If the cement content is increased, the strength and durability of concrete will also increase. Cement (with water) will form a paste that will bind the aggregate ranging from the largest (coarse) to the most subtle.

WATER
Conversely, additional water will actually reduce the strength of concrete. Water is used to dissolve the cement. Water also makes mortar become cohesive, and easier to work (workable).

WATER-CEMENT RATIO
Commonly referred to w / c ratio of water to cement ratio alias. If w / c ratio is even greater, strength and durability of concrete to be reduced. In certain environments, the water-cement ratio is limited to a maximum of 0:40 to 0:50 depending on the nature of corrosive or sulphate content in that environment.

AGGREGATE










If fine aggregate is too many, then adukannya will appear "sticky", thin, "soft", such as have no power. And after compaction, the top of the mortar will tend to "empty" aka no aggregate.

Conversely, if the coarse aggregate too much, adukannya will look rough, rocky, looks brittle (fragile). This aggregate will appear on the surface after compacted.

Mixing
Concrete must be mixed and stirred well so sement, water, aggregate, and additives can be dispersed evenly in the mortar.

Concrete is usually mixed with machine. There are mixed in the field (site), there also are mixed before being taken to the field, or to say ready-mix.

For ready-mix concrete, measuring has been measured in a batch plant, then mixed and loaded into trucks. During the journey continues to play drums so that the concrete had not set in concrete in the drum. Kan strange if such taxable loss is then hardened concrete in the drum. Sometimes, in the way, it could be because the old on the street, hot weather, or run track, the temperature rise in the drum so the water evaporates. This condition is sometimes "tricked" by including a large chunk of ice blocks into the drum, so that moisture can be maintained. Hmm .. plus if a straw, we can drum truck labeled "Fresh Juice Concrete" .. : D

While the concrete was mixed in the field usually use a machine called MOLEN (something like a kind of fried banana). When mixing in the field, the aggregate first inserted into the barrel (molen), followed by a final sand and cement. Everything in certain quantities in accordance with the desired strength of concrete.

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There was saying goes: Do not use a shovel to measure concrete mortar to molen! (Though this is often done): D
The size measure is usually expressed in units of weight, while the shovel was not able to measure weight. Do not let the mortar 1:2:3 ratio is defined as one shovel of cement, 2 shovels of sand and three shovels of gravel (aggregate). Of course the result (quality) obtained will be different. Unless there is a shovel that can be advanced as well as measuring weight of cargo.
When all ingredients (except water) are already entered, moleh rotated so that all the ingredients mixed. She's supposed to, if there is no sand visible invisible, meaning it is evenly adukannya. That's when adding water little by little.

Molen has the capacity (in volume). Mixing too full also ineffective because the mixing process will take longer. Molen should be filled to taste first, then if it is finished, the entire contents of molen poured into a container while before it was carried or cast into the formwork. When mixing concrete transported (casted), molen can work again to make the next mortar. As soon as the first mortar was poured all, molen was already finished making the second mortar, so there's no delay when molen work.

Well, for a very small scale, concrete can be mixed using a shovel. Must be done in a flat and clean (ie free of twigs, leaves, trash, and other nuisance material). Gravel, sand, and cement mixing / mixed first, then made like a mound, and at its peak made like a lake dug to retain water. If the mortar is mixed in the container sides are sealed so that water could be dammed, do not bother to make a mound, just pour water into the container. :)

In closing, we will provide tables of weight composition of cement, sand, and gravel, and water volume needed to make 1 m3 of concrete with a certain quality.
Quality Concrete Cement (kg) Sand (kg) Gravel (kg) Water (liter) w / c ratio
4.7 MPa (100 K) 247 869 999 215 0.87
8.9 MPa (125 K) 276 828 1012 215 0.78
12.2 MPa (150 K) 299 799 1017 215 0.72
5.14 MPa (175 K) 326 760 1029 215 0.66
9.16 MPa (200 K) 352 731 1031 215 0.61
3.19 MPa (225 K) 0:58 215 1047 371 698
7.21 MPa (250 K) 0:56 215 1039 384 692
24.0 MPa (275 K) 0:53 215 1026 406 684
4.26 MPa (300 K) 0:52 215 1021 413 681
8.28 MPa (325 K) 0:49 215 1006 439 670
2.31 MPa (C 350) 448 667 1000 215 0:48

Reference tables:
SNI DT - 91-0008 - 2007 The calculation mode Unit Price Concrete Work, by the Department of Public Works.