How To Prepare Gypsum-Based Self-Leveling Mortar?

What are the material requirements for gypsum self-leveling mortar?

1. Active admixtures: Self-leveling materials can use active admixtures such as fly ash and slag powder to improve the particle gradation and enhance the performance of the hardened material. Slag powder undergoes hydration reactions in an alkaline environment, increasing the structural density and later strength of the material.

2. Early strength cementitious materials: To ensure construction time, self-leveling materials have certain requirements for early strength (mainly 24-hour flexural and compressive strength). Sulfaloaluminate cement is used as an early strength cementitious material. Sulfaloaluminate cement has a fast hydration rate and high early strength, meeting these requirements.

3. Alkaline activators: Gypsum composite cementitious materials can achieve the highest absolute dry strength under moderate alkaline conditions. Quicklime and 32.5 cement can be used to adjust the pH value to create an alkaline environment and promote hydration.

4. Setting accelerators: Setting time is a key performance indicator for self-leveling materials. Both too short and too long setting times are not conducive to construction. Setting accelerators can activate gypsum, accelerate the supersaturated crystallization of dihydrate gypsum, shorten the setting time, and keep the setting and hardening time of self-leveling materials within a reasonable range.

5. Water reducers: To increase the density and strength of self-leveling materials, the water-cement ratio must be reduced. Under the premise of maintaining good fluidity, the addition of water reducers is necessary. The water reduction mechanism of naphthalene-based water reducers lies in the formation of hydrogen bonds between the sulfonic acid groups in the naphthalene-based water reducers and water molecules, forming a stable water film on the surface of the cementitious materials. This facilitates the sliding of material particles, reduces the required mixing water, and improves the structure of the hardened material.

6. Water retention agents: Self-leveling materials are applied to relatively thin substrates and are easily absorbed by the substrate, which may lead to insufficient hydration, surface cracking, and reduced strength. In this experiment, methyl cellulose (MC) is selected as the water retention agent. MC has excellent wettability, water retention, and film-forming properties, preventing water from seeping out and ensuring the full hydration of self-leveling materials.

7. Redispersible polymer powder (hereinafter referred to as polymer powder): Polymer powder can increase the elastic modulus of self-leveling materials, enhance their crack resistance, bond strength, and water resistance.

8. Defoamers: Defoamers can improve the surface performance of self-leveling materials, reduce bubbles during the forming process, and help increase the strength of the materials.