Effect of hydrophobic raw materials on performance of cement-based joint sealant

LI Sha WANG Yi-heng SHI Chun-zhi

Abstract: Through experiment, this paper compares the effects of hydrophobic type rubber powder instead of common type rubber powder, and common type rubber powder with silicone water repellent, and investigates the effects on the mechanical properties and hydrophobic properties of cement-based joint sealant. The results show that the water-repellent rubber powder and the water-repellent agent will reduce the flexural and compressive strength of the sealant, and the effect of the water-repellent agent on the strength is more obvious. The water-repellent rubber powder can significantly reduce the amount of water absorbed by the sealant, but it cannot improve the impermeability. The water-repellent agent can improve the water absorption and impermeability at the same time.

1 Foreword

The Chinese economy has shifted from a high-speed growth stage to a high-quality development stage. People are pursuing the comfort and happiness of life, and naturally have higher requirements for their living and working environment. The high expectations and requirements for construction have promoted the unprecedented prosperity of the development of building decorative materials. The use of cement-based grouts in conjunction with decorative materials such as tiles and stone not only directly affects the decorative effect of the wall surface, but may even cause rainwater to enter the wall through the grout, resulting in wall leakage. Therefore, cement The base joint sealant has also developed from a general type to an improved type with low water absorption. Common water-repellent raw materials include water-repellent rubber powder and silicone water repellent, both of which are widely used in polymer waterproof mortars, polymer insulation mortars, and other products. This study mainly examines the use of water-repellent rubber powders instead of ordinary rubbers. Adding two solutions of silicone water repellent to powder and ordinary rubber powder, it affects the mechanical properties and water repellency of cement-based joint grout.

2 Test conditions
2.1 Raw materials fortesting

a.PW52.5 White cement: Albo Portland (Anqing) Co., Ltd., whiteness greater than 87, 28d flexural strength 8.5MPa, 28d compressive strength 55.9MPa;
b. Heavy calcium powder: Hebei Yanxi mineral product processing plant, 200 mesh and 325 mesh, whiteness greater than 85;
c. Redispersible powder: German WACKER, ordinary type 5044N, hydrophobic type 8034H;
d. Silicone water repellent: Dow Corning, USA SHP50.


2.2 Test method
After the preliminary trials, the amount of various raw materials in the cement-based joint grout has been basically determined. The same mix ratio is now fixed. The mix ratio parameters are shown in Table 1, and ordinary 5044N rubber powder and hate are used. Water-based 8034H rubber powder and ordinary 5044N rubber powder are added with three solutions of silicone water-repellent agent, and the test pieces are mixed, formed, and cured in accordance with the requirements of “Ceramic Wall and Floor Tile Sealant” (JC / T1004-2006) and standardized. Testing of flexural compressive strength, flexural compressive strength and water absorption after freeze-thaw cycles under test conditions. Impermeability test, mass loss rate and strength loss rate after freezing and thawing are measured and calculated in accordance with “Standard for Test Methods for Basic Performance of Building Mortar” (JGJ / T70-2009).

Test mix ratio parameter / kg / m

3 Results and discussion
3.1 Mechanical properties
Figure 1 shows the flexural strength and compressive strength curves of the cement-based joint sealant samples of the three schemes under standard test conditions and after 25 freeze-thaw cycles. The specific values, quality, and strength loss The calculation results are shown in Table 2.

Flexural and compressive strength curve chart 2 Strength test results

As shown in Figure 1, all three samples meet the requirements for the joint sealant to have a flexural strength greater than 2.50 MPa and a compressive strength greater than 15.0 MPa under standard test conditions and after freeze-thaw cycles. Or adding a hydrophobic agent to ordinary rubber powder will reduce the flexural and compressive strength of the caulking agent, and the effect of the hydrophobic agent on the strength is more obvious. This shows that the polymer film formed by the reaction between the silicone hydrophobic agent and water. The aspect improves the hydrophobicity of the cement mortar, but also prevents the cement from hydrating to a certain extent and reduces the strength. Observe the sample specimens after the freeze-thaw cycle. The surface of the specimens of ordinary rubber powder A1 and hydrophobic rubber powder A2 will peel and peel, but the sample A3 with hydrophobic agent does not change significantly before and after freezing and thawing. The quality loss rate is significantly reduced.


3.2 Hydrophobic performance
Figure 2 shows the water absorption and impermeability pressure curves of the three cement-based joint sealants.

Water absorption and impermeability pressure curve

As can be seen from Figure 2, in the water absorption measurement test, the A1 sample using ordinary 5044N rubber powder only meets the ordinary type in 30 minutes less than 5g and 240min less than 10g in “Ceramic Wall and Floor Tile Sealant” (JC / T1004-2006)- Cement-based joint sealant requirements, while the A2 sample using hydrophobic 8034H rubber powder and the A3 sample with water-repellent agent reached 30 g not exceeding 2.0 g and 240 min not exceeding 5.0 g of low water absorption-improved cement cement Requirements; in the impermeability test, the impermeability pressure of the A1 and A2 samples is the same, and the impermeability of the A3 sample is significantly improved. It can be seen that when hydrophobic rubber powder is used instead of ordinary rubber powder, the surface polarity of the micropores in the joint filler can be improved to reduce the water absorption, but in a water environment with a certain pressure, it is impossible to prevent water pressure from entering the sample. The interior of the channel does not improve the impermeability of the grout. In the highly alkaline environment of cement slurry, the hydrophobic organic functions of silane hydrolyze to form highly reactive silane hydroxyl groups, and the silane hydroxyl groups continue to irreversibly react with the hydroxyl groups in the cement hydration products to form chemistry. Combined, so that the silane is firmly fixed on the surface of the hole wall of the cement mortar. Because the hydrophobic organic functional groups are directed toward the outside of the pore wall, the surface of the pores acquires water repellency, so it brings a long-lasting, integrated hydrophobic effect to the joint filler.

4 Conclusion

The test results show that both the hydrophobic rubber powder and the water-repellent agent will reduce the flexural and compressive strength of the caulk, and the effect of the water-repellent agent on the strength is more obvious; the hydrophobic rubber powder can obviously replace the ordinary rubber powder. Decreasing the water absorption of cement-based joint grouts, but it cannot improve its impermeability. The addition of a hydrophobic agent in ordinary rubber powder can simultaneously improve the water absorption and impermeability of cement-based joint grouts.┬áIn practical applications, the price of water repellent is much higher than that of water-repellent rubber powder. Therefore, according to the customer’s specific requirements for the performance of cement-based joint sealants, comprehensive consideration of the cost of raw materials can be used to choose a formulation.

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