Characteristics of various mortar additives in self-leveling cement


Release time:

2015-07-29

Author:

New Earth Group

Source:

Characteristics of various mortar additives in self-leveling cement

After the cement mortar is mixed with water, there is a gradual dissolution process, which is accelerated by the stirring force applied by the outside world. By tracking the real-time power consumption of mortar mixer, we can understand the dynamic process after mortar and water are mixed. The initial contact between cement and water and the gradual formation of agglomeration state will increase the stirring resistance and the power consumption will increase sharply. Then, with the dispersion of water and dispersant on cement, the stirring resistance decreases, the water is gradually dispersed between cement particles, and the agglomeration state is opened. After the mortar reaches the liquefaction point, the viscosity will drop significantly and tend to stabilize. Shortening the time for the mortar to reach the maximum liquefaction point is the key to improve the pumping efficiency. Shortening the liquefaction time can be achieved in a variety of ways, such as improving the mixing efficiency, increasing the mixing water, using high-efficiency water reducing agents, etc. Under the rated mixing power, increasing the mixing water will greatly reduce the performance of all aspects of mortar, while adding water reducing agent can greatly improve the speed of mortar wetting and dispersion by water, so that the mixing time is greatly shortened, but the dispersion speed will slow down under low water cement ratio. At the same time, the self-leveling mortar formula also has a tackifier to prevent bleeding and segregation, which also needs to be dissolved quickly and take effect. Only by combining the two can a uniform and stable high-flow mortar be formed. The dispersion rate of these two additives determines the mixing time required for self-leveling mortar.
Self leveling mortar is the most complex composition of a special mortar, in order to improve the fluidity of the mortar, water reducing agent is one of the components, different water reducing agent on the mortar dispersion speed also has a big difference. Polycarboxylic acid water reducing agent can be quickly adsorbed to the surface of cement particles, through electrostatic repulsion and space hindrance to disperse the cement particles, with rapid dispersion characteristics, can greatly shorten the mortar from water to maximize the flow of time.
Compared with the traditional manual mixing mortar, continuous mechanized pumping construction can greatly improve the construction efficiency of large area site, but the mixing time of this kind of special mortar pump is shorter, usually only 5-15 seconds. Short mixing time can not give the mortar fully mixed with water time, some additives are not fully dissolved to play a corresponding role. The self-leveling mortar additives are usually up to five or more, the traditional self-leveling mortar in the water mixing and even need a few minutes of "aging" time, in order to ensure that the water reducing agent and tackifier completely dissolved to form a specific mobility and stability. The use of rapid dispersion additives can greatly shorten the mixing time, quickly disperse the cement mortar and stabilize its rheological state, reduce the occurrence of similar problems, and improve the conveying efficiency of the mortar pump.
For self-leveling mortar, the rapid dispersion of water reducing agent to cement is not enough to achieve the best flow state of mortar, because the dispersion process may be accompanied by bleeding and segregation problems, so the formula will add viscosity enhancer to stabilize the viscosity of mortar, so it is also called stabilizer. The thixotropy of the stabilizer cannot be high, otherwise it will affect the fluidity of the mortar, so the type with moderate viscosity and small thixotropy should be selected. Commonly used types, such as low viscosity cellulose ethers, are added in carefully controlled amounts.
As a natural dispersed water reducing agent extracted from milk, casein has been used in self-leveling cement for its good workability and anti-bleeding, but with the high requirements for environmental protection and its low water reduction efficiency, the market share of casein has been declining year by year.
Large-area self-leveling mechanized construction has higher requirements for the workability of mortar. Mortar Tianjianji can greatly shorten the mixing time of mortar, making the rapid and continuous pumping construction easier to control. The function of additives in self leveling mortar can be summarized as follows:
-Low water cement ratio can also quickly disperse cement mortar, open the state of cement agglomeration flocculation;
-It can reduce the power consumption and wear of the stirring paddle, quickly complete the stirring process, and there is no liquidity delay problem;
-Higher water tolerance to prevent bleeding and segregation caused by excessive water;
-Rapid dissolution, reduce the self-leveling surface defects caused by undispersed agglomeration;
-High and low temperature can quickly disperse the effect.
 
自流平水泥

Key words: