Flooding refers to the phenomenon of floating slurry caused by bleeding during the period from pouring to the beginning of setting of the pouring material. Bleeding refers to the phenomenon where solid particles sink, water rises, and the castable undergoes settlement and contraction, leading to the precipitation of water on the surface. Float refers to the soft layer material that floats on the surface of the casting material caused by cement bleeding.

What is the effect of bleeding?

A small amount of bleeding is necessary to ensure construction quality, as it indicates that solid particles have settled, and the pouring material has shrunk and become dense. Especially during the vibration molding of low moisture castable, the start of bleeding often indicates that the castable is relatively dense and vibration can be stopped. A small amount of bleeding can also prevent the surface of the casting material from drying too quickly, making it easier for surface finishing.

What are the hazards of bleeding?

A large amount of bleeding is harmful because it weakens the strength of the surface layer of the casting material after hardening, and produces a large amount of easily peeled "powder layer". If the pouring material is poured in layers, if the surface layer is not removed, it will damage the bonding between each layer of pouring material. Some rising water will also aggregate below the aggregate, harden into voids, and form weak bonding zones. The rising water evaporates and leaves a channel for water, reducing the strength and corrosion resistance of the casting material. At the interface with the template, bleeding will take away the cement slurry, leaving only the aggregate, resulting in "sand streaks" and a decrease in strength.

How to prevent excessive bleeding?

The main way to prevent excessive bleeding is to prevent excessive bleeding. The use of water reducing agents and air entraining agent grades to reduce the unit water addition of castables is an effective measure to improve the bleeding performance of castables. The performance of cement and the use of admixtures also have an impact on the water permeability. Improving the fineness of cement by incorporating some finely ground admixtures or ultrafine powders can reduce the bleeding of the casting material.