Concrete steam curing method in winter

Concrete is the cornerstone of construction. The quality of concrete determines whether the finished building is stable. There are many factors that affect the quality of concrete, among which temperature and Humidity is a big problem. In order to overcome this problem, construction teams usually use steam to cure concrete. The main purpose of using steam is to improve the hardening strength of concrete.

Steam curing of concrete is divided into three categories: , four stages of heating, constant temperature and cooling.

1) Keep the temperature in the shed no less than 5℃ during the static period. After pouring is completed, the steam valve can be opened to start heating after the concrete has finally set?

2) The heating rate should not exceed 10℃/h. The temperature should be measured every 30 minutes. According to the temperature changes, increase or decrease the valve steam release amount to adjust the heating rate

p>3) The constant temperature is controlled below 45℃, and the constant temperature curing time is determined by testing according to the component demoulding strength requirements, concrete mix ratio and environmental conditions

4) The temperature in the middle part of the structure shall not exceed 60°C at constant temperature. It is monitored through a temperature sensor buried in the concrete. When the temperature of the concrete is too high, the steam supply to the steam curing shed is stopped to reduce the temperature inside the shed, but the temperature inside and outside the concrete should be ensured. The temperature difference shall not be greater than 15℃

5) The cooling rate during the cooling stage shall not be greater than 10℃/h. ?

6) The temperature of each part inside the cover should be as consistent as possible, and the temperature difference should not be greater than 15°C.

Winter concrete steam curing method - Steam curing is a thermal curing process that uses a mixture of saturated steam and air as the medium to heat up the concrete.

Several common concrete steam curing methods

The capillary tube method is to make many grooves on the inner surface of the concrete formwork, and the grooves are covered with iron sheets to form a capillary tube formwork. Pass steam into the groove to heat the concrete evenly. This method uses less steam, has a short heating time, is uniform and easy to control. However, the equipment is more complex and is suitable for vertical structure wall columns and other projects.

Steam ventilation method inside the structure: When pouring concrete, embed rubber pipes inside the structure, fill the pipes with water in advance to expand them, or embed steel pipes (coated with isolation agent on the outside). After the concrete has a certain strength, the pipe is pulled out to form reserved channels inside the concrete. Insert a short pipe into one end of the tunnel and pass steam into the pipe to heat the concrete. When the concrete reaches the required strength, drain the condensed water from the hole and pour the mortar into the hole. When the strength of prestressed concrete reaches the design strength of 75 or above, the holes should be grouted after tensioning the steel bars and the reserved holes should be closed.

The diameter of the embedded pipe is 13~50mm and does not require thermal insulation. However, when the outdoor temperature is lower than -10℃, the concrete surface should be appropriately covered with thermal insulation material, and the temperature of the steam flowing into the hole should be Control at 30~60℃.

Tests have proven that after curing for 72 hours at a temperature of 30 to 40°C or 36 hours at a temperature of 40 to 60°C, the concrete strength can reach 80% of the design strength. This method is simple to construct and saves steam, but the heating temperature is uneven, the temperature is difficult to control, and dehydration is easy to occur. Suitable for heating prefabricated columns, beams, hollow slabs and other components.

In the steam curing method, attention should be paid to the heating and cooling speeds, which must not exceed the requirements in Table 5-12.

The steam used in the steam curing method should be low-pressure saturated steam (pressure <0.07 MPa) to maintain appropriate temperature and humidity. The temperature of steam passing through concrete prepared with ordinary cement cannot exceed 80°C, and the temperature of steam passing through concrete prepared with slag cement can be 85 to 95°C.