The concrete admixture is a chemical substance that is added during the mixing of du concrete, cement paste or mortar, before mixing, or during additional mixing to improve the performance of concrete. In non-special circumstances, the addition amount generally does not exceed 5% of the cement mass.
At present, in response to various special requirements of concrete engineering, many kinds of admixtures that can meet various requirements have been developed, and they can be added to concrete in an appropriate manner to achieve some expected effects. According to the effects of these additives, they can be divided into water reducers, quick-setting agents, retarders, air-entraining agents, waterproofing agents, binders, expansion agents, rust inhibitors, defoamers, mold release agents, coloring agents , Moisture-proof agent, etc.
These concrete admixtures can be divided into four categories according to their main functions:
If it is mixed in too much, it will affect the setting and hardening of the cement, thereby affecting the strength of the concrete.
The addition of water reducing agent will increase the slump of concrete, and excessive addition will cause concrete bleeding or even segregation.
Theoretically speaking, adding a small amount of water reducing agent will only increase the slump without affecting the water-cement ratio, and the strength of concrete will not be affected. But if it is not handled properly, it will definitely affect the intensity.
The impact on strength can be considered from the following aspects:
1) Test block production. The water reducing agent increases the slump of the concrete, and the concrete is easy to cause segregation and bleeding. This requires very high test block production. If the test block is not made properly, the strength will be reduced.
2) Concrete slump. If the slump of the prepared concrete is below 200mm, adding less admixture will have little effect; if the slump is relatively large, above 220mm, the effect of adding admixtures twice will be greater.
3) Adjust the concrete. If the slump of the concrete is too small after being transported to the construction site, admixtures need to be added for adjustment. Better than adding water. But it should be noted that the pouring should be completed quickly, otherwise problems such as pump blockage will occur.