Self-leveling mortar is a new type of floor material with high fluidity and automatic leveling, which has many advantages over traditional floor materials. According to the main cementitious materials, it can be divided into cement-based and gypsum-based self-leveling. Cement-based self-leveling has high strength and good wear resistance, while gypsum-based self-leveling has small shrinkage and is energy-saving and environmentally friendly. Both have their own strengths. Regardless of the type of self-leveling, water reducing agent is the core additive to achieve high fluidity of mortar.
01
Brief description of the mechanism of water reducer
The water reducer currently used in self-leveling mortar is mainly polycarboxylate Superplasticizer(PCE). Under normal circumstances, inorganic cementitious materials such as cement and gypsum will produce a flocculent structure during the process of adding water and stirring, and a large amount of mixing water will be wrapped inside, resulting in poor slurry fluidity, increased water demand, and reduced strength. After adding polycarboxylate water reducer, the comb-shaped polycarboxylic acid molecules are adsorbed on the surface of the cementitious material particles, and the cementitious material particles are dispersed through electrostatic repulsion and steric hindrance (Figure 1), preventing the formation of flocculent structure, so that the water added to the powder can fully play the role of dispersion medium, thereby improving the fluidity of the slurry and reducing the water demand of the powder. Due to the reduction in the amount of water added, the strength of the slurry after hardening will increase accordingly.
Figure 1 Mechanism of action of polycarboxylic acid water reducer
Water reducer molecules are adsorbed on the surface of cementitious material particles,
charges of the same kind repel each other, dispersing the cementitious material particles
02
Selection of water reducer in self-leveling mortar
Many important properties of self-leveling mortar are closely related to the water reducer used in it, such as initial fluidity, fluidity retention, setting time, etc., so it is very important to choose a suitable water reducer.
Currently, cement-based self-leveling mostly adopts a ternary cementitious material system. The sulfate ions produced by the dissolution of gypsum in the ternary system and the sulfate ions contained in the cement itself compete with polycarboxylic acid molecules on the surface of cement particles for adsorption, which will affect the dispersion of polycarboxylic acid on cement particles and reduce fluidity. In addition, the adsorption capacity of polycarboxylic acid molecules on ordinary silica cement particles and special cement particles is also different. These factors will affect the flow properties of self-leveling mortar. Therefore, the water reducer used in self-leveling mortar needs to have good sulfate tolerance and adaptability to the ternary cementitious material system.
Citric acid is a commonly used retarder in cement-based self-leveling mortar. Citric acid molecules and polycarboxylic acid molecules have obvious competitive adsorption on the surface of cement particles. When citric acid is added to the system, the dispersion effect of ordinary polycarboxylic acid water reducer will be significantly reduced, resulting in poor flow properties. When using specially modified polycarboxylic acid water reducers, the adsorption of water reducers on the surface of cement particles will be greatly reduced due to the influence of citric acid molecules, thus ensuring good dispersion effect and fluidity.
For gypsum-based self-leveling, since the adsorption characteristics of gypsum itself are different from those of cement, there are many factors affecting the dispersion effect, and the applicability requirements for water reducers are also very high.
03
Application of FWD PC-01 water reducer in self-leveling
FWD Newtech FWD PC-01 has specially designed and modified polycarboxylic acid molecules, and the FWD PC-01 water reducer launched by it can play an excellent dispersing effect in both cement-based self-leveling and gypsum-based self-leveling systems.
FWD PC-01 has excellent sulfate tolerance and is less affected by competitive adsorption of sulfate ions in composite systems. It can be widely used in various composite cement-based cementitious material system mortars including ternary systems.
FWD PC-01 is also suitable for pure gypsum cementitious material systems. Its influence on the initial fluidity of pure gypsum-based self-leveling compared with similar competing products on the market is shown in Figure 2. It can be seen that in the pure gypsum-based self-leveling system, FWD PC-01 can give the slurry better fluidity than other water reducers.
Finally, Summary of FWD PC-01 performance characteristics:
High water reduction, excellent fluidity
Improved early strength development
Fast dispersion and adsorption, shortened mixing time
Excellent stability retention, extended slump retention time
Applicable to a wide range of pH values
Excellent compatibility with other admixtures