Concrete bleeding and segregation often occur in concrete projects, causing serious impact on the strength, durability and construction quality of concrete.
Bleeding refers to the phenomenon of concrete water floating up from the inside to the outside. Segregation is a special manifestation of bleeding. Bleeding from pumped concrete is often accompanied by bottom grabbing and hardening.
Segregation means that when the cohesion of concrete cannot resist, the coarse aggregate sinks due to gravity, causing the components in the concrete mixture to delaminate. The phenomenon. Concrete segregation is usually accompanied by bleeding.
The main cause of segregation and bleeding
The bleeding and segregation of concrete is mainly due to the The cement slurry has insufficient cohesion, and the concrete has poor segregation resistance and stability. The mix ratio, raw material properties, production and construction technology of concrete are closely related to the bleeding and segregation resistance of concrete.
Porosity
Usually, concrete with large porosity not only has poor strength, but also bleeds. It will also increase accordingly. For example, when the concrete gradation is unreasonable, the sand rate of the concrete is low or the amount of cementitious material is low, and the slurry is too little to fully wrap the aggregate. Workers looking for jobs click
Another example is the small specific surface area of cementitious materials. This undoubtedly provides a convenient channel for free water floating in the concrete. This makes the concrete more prone to bleeding and segregation. At the same time, the increase in porosity will also lead to a decrease in the cohesion of concrete.
Air content
Usually in commercial concrete, when the concrete bleeds, a certain amount is added The air-entraining agent will solve the problem because a good air-entraining agent will introduce high-quality small bubbles into the concrete, and the bubbles can wrap the free water that is moving upward in the concrete and stabilize it around the bubbles.
Furthermore, as the air content increases, the concrete will become denser, and the bubbles will fill the gaps in the concrete, blocking the floating channels of some free water.
Water-cement ratio
When the amount of free water in concrete increases, the water-cement ratio When it is too large, the fluidity of the cement slurry will increase, but the cohesion and water retention will become worse, and it will not be able to withstand the sinking force of the coarse aggregate in the concrete, resulting in bleeding and segregation.
Concrete setting time
The longer the setting time of concrete, the longer it takes for the aggregate to settle The longer it is, the easier it is for bleeding to occur. If cement takes a long time to set, the C3A content is too low. Excessive retarder in the pumping agent will have a great impact on the bleeding of concrete.
Compatibility of admixtures and raw materials
Compatibility of admixtures and raw materials Mainly reflected in the adsorption and dispersion effects of cement particles and admixtures. If the adsorption effect is too strong, the slump loss of concrete will be rapid. If the dispersion effect is too great, bleeding and hardening will occur, such as over-doping of water-reducing agent.
Excessive vibration
When vibration is insufficient, honeycombs and holes will appear in the concrete, which will affect the concrete. strength. However, excessive vibration will aggravate the settling water of the aggregate in the concrete and lead to the phenomenon of bleeding and segregation of the concrete. Bleeding of concrete caused by excessive vibration.
Conclusion
Concrete bleeding and segregation is a common concrete quality problem. Bleeding segregation has a considerable impact on the quality of concrete in all aspects. It will not only cause serious economic losses, but also reduce the service life of concrete.
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