What to pay attention to in the construction of large volume concrete

1. Article 1 of the Technical Regulations for Concrete for Building Structures (JGJ3-2002) stipulates that the difference between the internal temperature and the surface temperature of large-volume concrete, and the difference between the outer surface of concrete and the ambient temperature should not exceed 25 degrees Celsius;

2. Try to reduce the temperature of concrete into the mold;

3. After the concrete is poured, it should be covered with moisturizing and thermal insulation within 12 hours;

4. The curing period of waterproof concrete is at least 14 days; Large-volume concrete must be plastered twice to reduce surface shrinkage cracks;

Large-volume concrete pouring often adopts the method of inclined plane layered pouring layered vibrating

When pouring, the concrete flows naturally and forms an inclined plane, and when the concrete vibrates, it gradually moves up from the lower end of the pouring layer. When pouring in layers, it should be ensured that the lower and upper layers of concrete should be poured before the initial setting of the lower layer of concrete. And when vibrating the upper layer of concrete, the vibrating rod is inserted into the lower layer 5 cm, so that the upper and lower layers of concrete are better combined.

The division of responsibility for pouring large-volume concrete should be done with the ready-mixed mixing plant, and the concrete mix ratio and trial matching should be done with the mixing plant, and the number of concrete tankers and transportation routes should be determined.

Main measures for crack control in bulk concrete:

1. It is preferable to mix concrete with low-hydration hot cement, and appropriately use retarding water reducer and micro-expansion agent to reduce the impact of volume shrinkage of large-volume concrete, so as to reduce the possibility of concrete cracking.

2. On the premise of ensuring the design strength of concrete, appropriately reduce the water-cement ratio and add an appropriate amount of fly ash to reduce the amount of cement.

3. Reduce the temperature of concrete into the mold, control the temperature difference between the inside and outside of the concrete (when there is no design requirement, control it within 25 degrees Celsius), such as reducing the temperature of the mixing water, washing the aggregate with water to cool down, avoiding exposure to the sun, etc.

4. Properly set up the post-pouring belt to reduce the external stress and temperature stress, which is also conducive to heat dissipation and reduce the internal temperature of the concrete.

5. The surface must be wiped twice to reduce the surface shrinkage cracks, and the moisturizing cover and insulation maintenance should be carried out immediately after.

6. The cold water pipe can be pre-embedded, and the internal heat of the concrete can be brought out through circulating water for artificial heat conduction.

One infusion forming.

Maintenance. The formwork is firm and cannot be out of shape.

Use low-splash heat cement, such as fly ash cement.

Optimize gradation and reduce cement usage.

Use coarse aggregates.

Circulating cold water pipes are buried inside the concrete.

Reduce the temperature of concrete into the formwork. There are more ways to do it.

Strengthen temperature control during construction.

Sectional, layered continuous pouring is adopted. The thickness of each layer is not more than 30, and the interval is not exceeded.

Cover maintenance. The following provisions should be met when pouring in blocks:

a.The blocks should be reasonably arranged, and the flat cross-sectional area of each block should be less than 50m2;

b.The height of each block should not exceed 2m;

c.The vertical joint surface between the blocks should be parallel to the short side of the foundation plane and perpendicular to the long side of the cross-section;

d.The vertical joints between the upper and lower adjacent layers of concrete should be staggered to make the rubbing interface, and be treated according to the construction joints.

Large-volume concrete should refer to the following methods to control the heat of hydration of concrete:

a.The amount of cement is reduced by improving the gradation of aggregates, reducing the water-cement ratio, mixing mixtures, adding admixtures, and participating in flakes.

b.Dam cement, slag cement, fly ash cement or low-grade cement with low hydration heat;

c.Reduce the thickness of the pouring layer to speed up the heat dissipation of concrete;

d.Concrete materials should be avoided from sunlight exposure to reduce the initial temperature.

What problems should be paid attention to when building large-volume concrete: cold joints should not be left in concrete pouring. Ensure that the handover time of pouring is controlled before the initial setting.

Ensure that the vibration is compact, strictly control the vibration time, moving distance and insertion depth, and strictly prevent leakage vibration and over-vibration. Ensure the concrete** and make sure that there are no cold joints. Concrete vibration should be timely, and at the same time no vibration leakage, but not over-vibration to prevent segregation.

Test the temperature difference between the inside and outside of the concrete on time. Adjust the water flow rate of the cooling pipe in time according to the temperature difference regulations.

Temperature control measures for bulk concrete (materials):

Choose medium and low heat cement varieties to make full use of the later strength of commercial concrete.

Add admixtures.

Coarse and fine aggregate selection.

Control the machine temperature and pouring temperature of commercial concrete.

Temperature control measures for large-volume concrete works (construction):

1. The temperature rise value of the concrete pouring body on the basis of the mold temperature should not be greater than 50.

2. The temperature difference between the surface of the concrete pouring block (excluding the equivalent temperature of concrete shrinkage) should not be greater than 25.

3. The cooling rate of the concrete pouring body should not be greater than.

4. The temperature difference between the surface of the concrete pouring body and the general atmosphere should not be greater than 20.

5. Before the construction of large-volume concrete, various pre-construction preparations should be made, and contact the local meteorological stations and stations to grasp the recent meteorological conditions. If necessary, the corresponding technical measures should be added, and in the winter construction, it should also meet the current national standards for concrete winter construction.