Why prefabricated buildings are so "like" low modulus sealants？

As a building auxiliary material, building sealant plays an important role in the overall waterproof sealing of the building. The assembled building sealant is mainly used for the joint sealing of the assembled PC component to ensure the air tightness, water tightness and overall performance of the assembled building. Assembly building sealant attention to the construction performance of sealant, adhesion, displacement ability, coating performance, in addition, low modulus is also one of the performance of assembly building sealant attention.

1. What is the modulus

In terms of mechanical properties of materials, modulus refers to the ratio of stress and strain of a material under stress. Modulus can be regarded as an index to measure the degree of difficulty for a material to produce elastic deformation. The greater its value is, the greater the stress causing a certain deformation of the material will be, that is, the greater the material stiffness is, that is, the smaller the elastic deformation will be under a certain stress.

And the modulus of sealant, usually refers to its secant tensile modulus. According to GB/T 13477.8-2017 "Test Methods for Building Sealing Materials Part 8: Determination of Tensile Adhesiveness" in the provisions: the sealant is bonded between the surfaces of two parallel substrates and made into specimens; Stretch the specimen to the failure, draw the force-elongation curve, can calculate the secant tensile modulus of sealant. The secant tensile modulus (σ, unit MPa) of each specimen with selected elongation is calculated as follows:

2 the difference between high modulus sealant and low modulus sealant

According to the provisions of the national standard GB/T 14683-2017 "silicone and modified silicone building sealant", the tensile modulus of the product is divided into high modulus (HM) and low modulus (LM) two levels. See the following specifications for the physical and chemical properties of modified silicone building sealant (MS)

According to the regulations, when the sealant is stretched to the corresponding elongation, its modulus at 23 ° C is less than or equal to 0.4Mpa and the modulus at -20 ° C is less than or equal to 0.6Mpa, the sealant can be determined as a low modulus; If any of the conditions is not satisfied, it can only be determined as a high modulus. The elongation varies with the displacement grade. 20 grade sealant products, measured the elongation of 60% of the tensile modulus, and for 25 grade sealant products and above, measured the elongation of 100% of the tensile modulus.

3. Advantages of low modulus sealant

Under normal circumstances, the tensile modulus of the sealant is flexible, the lower the tensile modulus, the softer the sealant is, and the same deformation occurs, the smaller the internal stress; The higher the tensile modulus, the greater the toughness, and the greater the internal stress at the same deformation. In the same deformation joint, the use of low modulus sealant products, the internal stress will be much smaller than the same displacement level of high modulus sealant products. Therefore, it can effectively avoid the cracking of sealant caused by high internal stress. Figure 2: Cracking caused by incorrect use of high modulus sealant in the project.