Concrete in place stacked

In place of the concrete mixture is placed in the formwork of wood and metal shields, the appropriate form of the future design. In the formwork set steel frame - fitting.

Fresh concrete mix in place as quickly as possible is desirable and without interruption. We know that the hardening of the concrete depends on the chemical reaction of cement with water. A key role in this will be played by the heat and water! Therefore, in the winter, when temperatures warmed formwork, and immediately after the concrete shield and insulated mats and the top, the exposed surface of the concrete. We have already said that Russia has developed and put into practice ways of winter concreting. The most effective of these are methods thermos, electric heating and paroprogreva.

By way thermos concrete hardens under "cloud" - a layer of insulating material (ash, sawdust, kamyshita etc.). These materials do not conduct heat. Therefore, the concrete mix is ​​almost loses heat that it was in production. In addition, the hardening cement also produces heat.In many cases, the amount of heat is sufficient to cool down during the concrete has acquired the necessary strength. This strength allows raspalublivat, construction, no longer afraid of freezing. In this case, after thawing, the concrete does not collapse. Way thermos is the most economical and simple. For its implementation does not require special equipment. But this method is only applicable when concreting massive structures as thin designs very quickly cooled.

If in a timely manner thermos not achieve the required strength of the concrete, it is recommended to use artificial heating of concrete electric shock or steam. Electric heating is that the fresh concrete injected metal electrodes through which an electric current. Electrical resistance of a freshly prepared concrete, laid in the formwork increases as the concrete has set. The electric current flowing through the concrete, it will cause heating and hardening: The more resistance, the higher the voltage. Concrete temperature

should be no higher 60є C. When making concrete structures as electrodes using rebar.

Paroprogreva way is the following. In the inside of the mold is cut channels, and through them pass steam. You can also make a double casing and input pairs between its walls. Sometimes steam is passed through pipes laid in the concrete. Heat the concrete up to 50 - 80є C. Due to high temperatures, which are created when paroprogreve concrete, and under favorable conditions of moisture accelerates concrete hardening significantly: for example, in two days you can get such strength that reaches the concrete after the seven-day curing under normal conditions. Paroprogrev concrete requires large additional costs. It's his fault. Method paroprogreva recommended for thin-walled structures.

The "cold" CONCRETE

All applications can require additional costs and equipment. Can not we do without them? Can you force the concrete to harden in the winter, it is not warming? It turns out you can, if you enter into the concrete mixture additives - chemical hardening accelerator. These additives are calcium chloride, ammonium chloride, chlorinated water, as well as aqueous solutions of sodium chloride and hydrochloric acid.

What is the role of these supplements? They lower the freezing point of water and accelerate the decomposition of minerals, which are part of the cement. Due to the action of these additives concrete accelerated maturation. Poi using chemical hardening accelerator is required to heat or the water aggregates. Therefore Takao concrete called cold concrete. Such concrete harden and acquire strength at low temperatures.However, chlorine compounds are corrosive reinforcement. Therefore, the cold concrete is used only for non-reinforced concrete structures, paving, facing slopes, etc. The structures that are running dynamic loads (foundations for hammers, derricks, etc.) to apply a cold concrete prohibited!

As well as concrete, manufactured by heating, cold concrete raspalublivayut only after a specified period of hardening. Until the concrete has reached 50% of its design strength, it must be protected from freezing.

Дата добавления: 2015-08-27