Laying concrete mixture

So, ready-mixed concrete. Now it has to be put in the form. Ideal condition laying concrete in the form is filled with concrete forms of the whole space. If you are in the form of reinforcing bars, the concrete mix should envelop all fittings and evenly with no gaps to fill all available space between the walls and form fitting. It does not have to be formed cavity or shell. In some cases, cause the formation of cavities in the concrete may be present in the concrete mix is ​​very coarse aggregate, which wedged between the wall and form fitting. It is therefore very important constant control grain size. The valve must be covered evenly concrete, which protects it against weather conditions or it will oxidize and corrode, and sometimes destroyed. The process is called rusting reinforcement corrosion.

When laying concrete often faced with challenges that are related to the plasticity of concrete. If the concrete mixture has the properties of the liquid, it will be filled in exactly the form in which it is placed. So, we need to make concrete with liquid, for which it must be added a large amount of water. However, the excess water is detrimental effect on the strength of concrete: for all the water that has not entered into a chemical compound with cement remains in the free state in the concrete. It flows or dry, gradually forming voids in concrete. Therefore turns porous concrete and fragile. Hence, it is necessary to introduce a little water! But the low-water concrete is fragile!

How can that be? There is a contradictory task: to easily put concrete mix in the form, you must enter into it a lot of water. On the other hand, the excess water will affect the strength of concrete. So, you need to enter the water is so low to get the biggest strength of the concrete! So, like the old Russian proverb: "pulled nose, tail stuck", "tail pulled - nose stuck."

That's how the builders and have a question about the proper selection of the amount of water in the manufacture of concrete.

The issue remains, and it is very important. The amount of water introduced into the concrete mix should be strictly defined. Modern building science has given into the hands of builders based calculations. They allow you to get high quality concrete mix with a minimum amount of water.

Water flow with the mobility and rigidity of concrete can be determined according to the schedule prof. S. Mironov A, which reflects the dependence of the water demand of a concrete mix of mobility and rigidity.

But what are these two new terms, "mobility" and "rigidity" of concrete? "Mobility" - the ability of concrete to flow under its own weight or due to vibration, and the "stiffness" - is the resistance of concrete mix of mobility. By the degree of mobility of the concrete mix can be tough, ductile and cast. To assess the quality of concrete has been proposed, the term "workability". He characterizes the ability of concrete mixtures are easily stowed in the form of concrete at ensuring a maximum possible density. A maximum density for maximum strength and durability of the structure.

But the term was very arbitrary, since it does not explain the physical meaning of this property.

For the experimental determination of the "workability" of concrete was proposed a number of ways. The most common way to slump and the way vibration table. The first method is the following. Of concrete shaped pattern in the form of a truncated cone of a certain size. Builders use for the metallic form, which is filled with concrete. Beyond that the form is removed, and is so-called. "Cake." Liberated from the form of the concrete mix is ​​flexible enough, so it settles and some spreads. Sludge "cake" after removal from a form and an estimate of the mobility (or workability) concrete. For example, a cone of stiff mixture practically does not settle, wear plastic was allowed to precipitate in the 8 - 12 cm, cast - more than 12 cm Slump independent of clutch material in the mixture and its internal friction. Again new physical concepts? What do they mean? What is their meaning? Recall the mechanics.

Any object lying on the ground, depending on their weight creates a certain pressure on the land. To move it, you need to apply a force and the larger, heavier object. The relationship between the force applied horizontally and parallel to the plane of movement of goods and mass object, called the coefficient of friction. The same forces of friction exists between particles and between the concrete mixture and stand. In addition, the concrete mix has some traction, that is, the internal resistance of the deformation of the mixture. It allows you to freshly prepared concrete held in a vertical position after removal of forms.

Another way to assess the "workability" is a test of the concrete mixture was shaken at the table.

For this truncated cone of concrete free of form, measure the diameter of the cone and the cone of a number of reports of shaking. After that measure the increase in diameter of the melt cone relative to the start.

Although both of the method and have flaws, they do provide an opportunity to assess the workability of concrete. They also allow us to establish the relative amount of energy required to deform the concrete mix and compacted. Therefore, these methods are widely used in construction practice. And yet they do not conclusively identify the behavior of concrete when it is panning. After the concrete mix is ​​behaving in an experimental form of the cone and in different ways!

Дата добавления: 2015-08-27