Common Problems and Treatment Measures of Concrete

The quality problems that arise in the construction of concrete projects, the lighter ones affect the beauty, the more serious ones affect the safety of the structure. How to prevent and eliminate quality problems and ensure the safety of the project structure has become a problem that we must take seriously.

Hysteresis bleeding of concrete

Hysteresis bleeding refers to the phenomenon that the concrete initially works to meet the requirements, but after a period of time (for example, 1h), a large amount of bleeding occurs. Reasons and countermeasures for lagging bleeding:

1. The real sand rate is low, and the sand contains too much rock. Increase the sand rate and increase the real sand content.

2. The content of fine particles in the sand is small. Increasing the number of admixtures in concrete and take necessary supplements.

3. Unreasonable stone gradation and single particle size. Increase the sand rate by 2% to 5%.

4. High bleeding rate of cement and admixtures. Replace cement and admixtures; thickening components in admixtures.

5. Fly ash has coarse particles and high carbon content. Replace fly ash.

6. Low-strength grade concrete. Use an air-entraining agent or increase the amount of cementing material.
   

7. High-strength grade concrete. Reduce the admixture content or reduce the retarding components in the admixture.

8. There is water in the tanker. Before loading the ash, turn the mixing tank upside down to drain the water.

9. Unexplained reasons. Change the admixture formula or take the above comprehensive measures.

The concrete site has a larger slump than the exit machine

When preparing concrete with a higher strength level, sometimes the on-site slump may be larger than the machine slump. The reasons may be as follows:

• Use of sulfamate or additives with similar performance.

• There are more retarding components in the admixture or the later reaction is violent.

• Improper mixing ratio (such as low sand ratio, too much admixture, etc.) leads to bleeding in the later stage.

• There is water in the concrete tank.

Solution: The first three types of problems can be found and adjusted through laboratory tests (for slump loss and setting time, etc.). In actual production, the admixture and water consumption should be strictly controlled, and sulfamates should be added. The agent is particularly sensitive to water; for the latter, you can invert the mixing tank before filling to drain the remaining water.

The slump loss in the concrete production process suddenly accelerates. It is suddenly found that the slump loss of concrete is relatively fast during the production process. The possible reasons are:

1. The water-reducing component of the admixture changes.

2. There are few admixtures in the pool, which are early-strength components such as precipitated sodium sulfate.

3. Changes in cement composition, etc.

These problems can be solved by adjusting the components of the admixtures or their dosages.

In the process of concrete pouring, due to the changes of the ground material and the season, the problems encountered are also various. We should do more analysis to find out where the problem lies, and timely take practical and feasible treatment measures to avoid and reduce the occurrence of concrete quality problems and effectively ensure the quality of concrete engineering.

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