What to do about the difficult problems encountered during the use of concrete

If the sand content is slightly low or there are few small stones, how to configure high-cohesion concrete? The following are some problems and solutions that occur during the installation process of concrete:

1. Abnormal solidification of concrete

The concrete batching station solidifies quickly, usually The reasons are that the factory temperature of the concrete is too high, there is too little plaster in the concrete, the water-reducing agent is not suitable for the concrete, the boiling water comes into direct contact with the concrete, etc. It may also happen that the setting time is too long. One situation is that the overall setting is severely retarded, or the demand for water-reducing agent exceeds the normal demand, resulting in excessive retardation of concrete. Most of them are caused by the water-reducing agent, because they are mixed with poor retarding components. Another situation is that some parts are severely retarded. The reasons may include: the post-mixing method of water reducing agent is used, and the concrete mixing station is uneven. When water is released on the spot, the cohesion of the concrete is reduced. Some ingredients in the admixture are not easy to mix evenly, resulting in excessive retardation of the concrete.

2. Concrete has a large slump

When concrete with a higher strength level is configured, a large slump occurs. The reasons may be: the use of carboxylate salts or admixtures with similar characteristics; the water reducing agent contains more retarding components; the mortar mix ratio is not good (such as the sand rate is too small, too many admixtures, etc.). Bleeding in the middle period; there is remaining water in the concrete tank. The first few types of problems can be adjusted through laboratory trial preparation, and the amount of water reduction must be strictly controlled during actual production.

3. Bleeding and segregation of concrete

Bleeding and segregation are common problems in the use of concrete, and preventive measures are generally taken in advance. Increase the sand lifting rate and reduce the mud content in the sand. The effective sand rate can ensure the workability and compressive strength of concrete; add coal ash to improve its water-retaining solubility; the amount of water-reducing agent is too large, and the water-reducing agent strips If there is bleeding component, reduce the water reducing agent or increase the thickening multi-component and air-entraining multi-component in the water reducing agent to improve the cohesion of concrete and avoid bleeding and concrete segregation; it may be due to excessive storage time. The cement clinker part in the concrete has solidified, which promotes the poor water solubility of the concrete. The composite thickening multi-component and early strength multi-component in the water reducing agent.

4. "Salt precipitation" state

Due to changes in external temperature, the internal demand for sodium sulfate (purity higher than 98%) in the concrete exceeds 0.8% of the weight of the concrete. That is to say, surface salt precipitation will occur. The higher the alkali water content of concrete, the more likely it is to cause the above-mentioned situation. The other is related to the setting time of concrete. Early-strength concrete is usually not prone to salt precipitation.

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