How to prevent cracks in bulk concrete?

Prevent large volumes of concrete.

Control measures for crack generation: Kinah.

1. Priority is given to the use of slag cement with low heat of hydration to mix concrete, and the appropriate use of retarding water reducer.

2. On the premise of ensuring the design strength grade of concrete, appropriately reduce the water-cement ratio.

Reduce the amount of cement used.

3. Reduce the mold temperature of concrete, and control the temperature difference between the inside and outside of concrete (when the design is not required, it should be controlled within 25 degrees).

4. Cover the concrete with thermal insulation and moisturizing materials in time.

5. The cooling water pipe can be pre-embedded in the foundation of the potato, and the circulating water can be introduced to force the temperature generated by the heat of hydration of the concrete.

Cement produces a lot of heat in the hydration process, which is a large volume of concrete.

The main ** of internal heat. Due to the large cross-sectional thickness of large-volume concrete, the heat of hydration is not easy to dissipate inside the structure, so that the temperature inside the concrete increases. Min Li.

The maximum temperature inside the concrete, most of which occurs in 3 5d after pouring, when the temperature difference between the inside of the concrete and the surface is too large, temperature stress and temperature deformation will occur. The temperature stress is proportional to the temperature difference, and the larger the temperature difference, the greater the temperature stress. When the tensile strength of concrete.

When it is not enough to resist this temperature stress, temperature cracks begin to develop. This is the main reason why large-volume concrete is prone to cracks.

The crack control measures for bulk concrete are as follows:

On the premise of ensuring the design strength grade of concrete, the water-cement ratio should be appropriately reduced and the amount of cement should be reduced; Timely cover the concrete with thermal insulation and moisturizing materials; Control the temperature difference between the inside and outside of the concrete; Carry out the suspected secondary plastering work to reduce the surface shrinkage cracks.

Concrete cracks are due to the physical structure changes of concrete structures due to the action of internal and external factors, and cracks are the main reasons for the reduction of bearing capacity, durability and waterproofness of concrete structures.

1. Prevention and control measures for concrete cracks:

1. When the concrete mix ratio is designed to be widened, the unit water consumption of concrete should be reduced as much as possible under the condition of ensuring that the concrete has good workability.

2. Add structural reinforcement to improve crack resistance, and the reinforcement should be small diameter and small spacing. The reinforcement ratio of the full section should be in between. Stress concentration should be avoided due to structural abrupt changes, and strengthening measures should be taken in the weak links that are prone to stress concentration.

Dark sorghum is set at the edge of the crack to improve the reinforcement ratio of the part. Improve the ultimate tensile of concrete.

3. In the structural design, the climatic characteristics of the construction should be fully considered, and the post-pouring joints should be reasonably arranged, and the spacing between the post-pouring joints should be 20-30m under normal construction conditions. The retention period is generally not less than 60 days. If the specific conditions of construction cannot be met, design changes can also be made temporarily according to the specific situation.

4. Strictly control the quality and technical standards of concrete raw materials, select low-hydration thermal cement, and minimize the mud content of coarse and fine aggregates (below 1). Control the brightness and ash ratio of concrete, reduce the slump of concrete, and reasonably add plasticizers and superplasticizers.

5. Adopt comprehensive measures to control the initial temperature of concrete, concrete temperature and temperature change. The pouring time of cracks caused by temperature difference should be arranged at night as much as possible to minimize the initial setting temperature of concrete.

6. During the daytime construction, it is required to set up a simple sunshade device in the sand and stone yard, or cover it with a wet sack, and spray cold water on the aggregate if necessary. When concrete is pumped, straw bags are placed on the horizontal and vertical pump pipes and cold water is sprayed.

7. According to the characteristics of the project, the later strength of concrete can be used, which can reduce water consumption, heat of hydration and shrinkage. Compensating shrinkage concrete technology. For high-strength concrete, medium-heat micro-expansion cement should be used as much as possible, mixed with ultra-fine mineral powder and expansion agent, and high-efficiency superplasticizer should be used.

Through the test, fly ash is mixed, and the dosage is 15%-50%.

1. The pouring method of concrete can be layered and continuously poured or continuously poured, leaving no construction joints, and should meet the following requirements:

1) The paving thickness of the concrete should be determined according to the depth of the vibrator used and the workability of the concrete. When pumping concrete is used, the paving thickness of the concrete is not more than 600 mm; When non-pumped concrete is used, the concrete is paved with a thickness of no more than 400 mm.

2) For layered continuous pouring or push-type continuous pouring, the interval between layers should be shortened as much as possible, and the second layer of concrete must be poured before the initial setting of the first layer of concrete. The maximum interval between layers does not exceed the initial setting time of the concrete. When the interval between layers exceeds the initial setting time of concrete.

This elevation should be considered as a construction joint.

2.When pouring concrete in layers in the construction of large-volume mixed tartard concrete, the treatment of horizontal construction joints should meet the following requirements:

1) Remove the slurry, weak concrete layer and loose stones on the pouring surface, and evenly expose the coarse aggregate;

2) Before pouring the upper layer of concrete, rinse the dirt on the surface of the concrete with pressurized water and fully moisten, but there can be no water;

3) For non-pumped low-fluidity concrete, grouting measures should be taken when pouring the upper layer of concrete.

3.The mixing and transportation of concrete must meet the requirements of continuous pouring construction and minimizing the temperature of concrete out of the tank, and should meet the following requirements:

1) When pouring large-volume concrete in the hot season, the concrete batching plant should take shading and cooling measures for the sand and gravel aggregate;

2) When using pumped concrete construction, concrete mixer trucks should be used for concrete transportation, and the number of concrete mixer trucks should be full of the requirements of continuous concrete pouring of Qingji.

Crack control measures for large-volume concrete: select slag cement with low heat of hydration, reduce the amount of cement, reduce the temperature to control the temperature difference, pre-embed cooling water pipes, and set up post-pouring belts.

1. Choose slag cement with low heat of hydration.

Priority is given to concrete mixed with slag cement with low heat of hydration, and appropriate use of retarding superplasticizer.

2. Reduce the amount of cement.

On the premise of ensuring the design strength grade of concrete, the amount of cement is reduced. Shouqing.

3. Reduce the temperature and control the temperature difference.

Reduce the temperature of the concrete mandowel and control the temperature difference between the inside and outside of the concrete (when the design is not required, control the temperature difference between the inside and outside within 25 degrees Celsius). Timely maintenance of concrete covering envy celery, bright temperature, moisturizing materials.

4. Pre-embedded cooling water pipe.

Cooling water pipes can be embedded and circulating water can be introduced to bring out the heat inside the concrete, carry out artificial heat conduction and monitor the temperature regularly.

5. Set up the post-pouring belt.

According to the design drawings and specifications, the post-pouring belt can be set to reduce the external stress and temperature stress, which is conducive to heat dissipation and reduce the internal temperature.