Analyze the reference formula of gypsum-based self-leveling mortar and the influence of different admixtures on gypsum mortar

December 28 10:48 2020

Using desulfurized gypsum as the base material, analyze the formula design of desulfurized gypsum-based self-leveling mortar. The customer currently uses gypsum powder as dihydrate desulfurized gypsum. The current formula is as follows:

36% of desulfurized gypsum powder, 32% of slag powder, 28% of sulphoaluminate cement, 4% of alkaline activator; accelerator accounts for 0.9% of the total mass of basic ingredients, and superplasticizer accounts for 0.6% of the total mass of basic ingredients , Latex powder accounted for 0.8% of the total mass of the basic ingredients, water retention agent accounted for 0.08% of the total mass of the basic ingredients, and defoamer accounted for 0.05% of the total mass of the basic ingredients.

The dihydrate desulfurized gypsum itself has no self-hardening property and does not produce strength. However, a certain fineness of powdered dihydrate gypsum can undergo hydration reaction with active mineral materials under suitable excitation conditions to generate hydraulic water with a certain strength. According to this mechanism, desulfurized gypsum is a favorable condition for powdery materials. The undisturbed gypsum without any pretreatment is prepared by adding suitable excitation materials and active mineral materials in an appropriate proportion to make gypsum composite cementitious materials. The hydration reaction is fully carried out under the conditions of, and the hydraulic hydration products mainly composed of ettringite and hydrated calcium silicate are generated. The solubility of these hydration products in water is extremely low. The gypsum composite cementing material prepared by this method It not only has higher strength than general construction gypsum, but also has the characteristics of hydraulic cementitious material, has a higher softening coefficient and better water resistance.

The following explains the effect of different admixtures on the performance of desulfurized gypsum mortar:

1. Cement and lime have a retarding effect on desulfurization plaster gypsum, and lime has a better effect on prolonging the setting time of desulfurization plaster gypsum than cement.

2. When cement and lime are compounded with desulfurization plaster gypsum, the effect on the strength of desulfurization plaster gypsum is better.

3. Using slag and fly ash as a composite cementing material to be added to the desulfurization plastering gypsum can better improve the operability of the desulfurization plastering gypsum, and improve the early strength, cohesion, and water resistance. To achieve the use under humid environment conditions, it is necessary to add an appropriate amount of cement and lime as its alkaline activator to make the cementitious material play a better role.

The main factors affecting the water resistance of gypsum products are the amount of cement and blast furnace slag. The primary and secondary relationship that affects the 24h water absorption rate of the product is: the mixing amount of cement, blast furnace slag, quicklime and fly ash. For the water resistance of gypsum products, a better ratio is blast furnace slag: cement: fly ash: quicklime = 1:1:3:1.

For the flexural strength of gypsum products, the content of blast furnace slag is still the main factor affecting its strength. Among them, the primary and secondary order affecting the dry flexural strength of products is blast furnace slag, quicklime, cement and fly ash. The primary and secondary order that affects the 2h flexural strength of gypsum products is blast furnace slag, quicklime, fly ash, and cement. Considering the strength loss of the product after water resistance, it is concluded that the optimal ratio of the flexural strength of the product is blast furnace slag: quicklime: fly ash: cement = 1:1:2:1.

For the compressive strength of gypsum products, the content of quicklime is the most important factor. The primary and secondary order that affects the compressive strength of the product after 2h is immersed in water: quicklime, cement, blast furnace slag, fly ash, taking into account the loss of strength after water resistance, the optimal ratio of its compressive strength is quicklime: cement: blast furnace slag: Fly ash = 1:2:1:2.

General speaking:

(1) The water resistance and mechanical properties of gypsum products mixed with active admixtures are enhanced. Therefore, it is a simple and feasible way to modify gypsum products with active admixtures.

(2) After mixing the same amount of active admixtures: the products with better water resistance are blast furnace slag and cement composite products. The improvement of its mechanical properties is not much different, and both have a positive promoting effect. In contrast, the effect of adding cement is better.

(3) The proportions of the four active admixtures: quicklime, cement, blast furnace slag, and fly ash are 1% quicklime, 3% cement, 3% blast furnace slag, and 5% fly ash.

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