Concrete Bleeding Meaning

Bleeding is also a kind of segregation. Before the concrete is poured, the suspended solid particles in the fresh concrete sink under the action of gravity. When the water retention capacity of the concrete is insufficient, a layer of water will appear on the surface of the newly poured concrete. This phenomenon is called Bleeding.

Bleeding will destroy the internal uniformity of the coagulation. The mixing water will carry a part of the fine particles in the cement and aggregates when it rises to the upper surface of the coagulation, causing the surface of the concrete to form a layer of floating slurry with large water content, resulting in surface concrete lose and porous, the strength is reduced. When the laitance layer loses water and thickens and loses fluidity, but the strength is not developed enough to resist the tensile stress caused by settlement or plastic shrinkage, cracks will occur on the surface of the concrete. Kingsun concrete plasticizer can be used to improve concrete workability.

The rise of bleeding creates many bleeding channels in the concrete with less cement content. At the same time, the coarse aggregate particles sink gradually to reach solidity and stability, and a water-rich cement laitance is formed under the coarse aggregate particles. After the laitance loses water after precipitation, it becomes a void and porous low-strength cement stone, also under the steel A weak laitance layer is also formed due to internal bleeding, so the bonding force between concrete and steel bars is weakened under the steel bars. Bleeding causes the surface concrete to be loose and weak, easy to be carbonized and increases the risk of corrosion of steel bars in the concrete.

The high water-cement ratio of the laitance layer will form a porous and weak surface after evaporation. The floor or pavement is easy to dust after the laitance layer is formed. The road surface is easy to expose due to the weak surface wear, so the surface treatment and finishing are very important. When there is bleeding on the concrete surface, the finishing process must not be carried out. This is a basic law. After tamping and initial leveling, wait until the bleeding is over and evaporate, and then use a spatula to press and smooth again. Premature wiping will cause surface defects, premature foaming will seal the surface before bleeding stops, and the accumulation of bleeding water and air under the thin surface will cause peeling or thin layer shedding.

Insufficient fine sand content in concrete, too coarse cement particles, too little cement consumption, or too much water consumption for concrete are prone to bleeding. In addition, the application of cement with a long initial setting time and the addition of a retarder will prolong the bleeding time. Bleeding phenomenon.

The correct choice of concrete mix ratio can control bleeding to a large extent, such as reducing the maximum particle size of coarse aggregates and using small slump concrete as much as possible. If you use large slump concrete, you need to add superplasticizers. In order to reduce the water consumption, increase the fine grain material in the concrete, and so on. To reduce bleeding, the following methods can be used:(1) Use finely ground cement.(2) Increase the amount of cement. Under the same water consumption, the bleeding of the rich mix concrete is less than that of the lean concrete.(3) Use fly ash or other pozzolanic materials.(4) There should be enough fine particles in the sand or increase the amount of sand used.(5) Air-entraining agents should be considered when bleeding is serious. The disconnected bubbles generated by the air-entraining agents are like increasing the fine-grain composition, cutting off the bleeding channel, reducing water consumption, and increasing workability.

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