Why do prefabricated buildings favor low-modulus sealants?

As a bonding material in the building sealing system, sealant plays an important role in the overall waterproof sealing of the building, and in the field of prefabricated buildings, it is no exception. Prefabricated building sealant is mainly used for joint sealing of assembled PC components. When selected, users often pay attention to construction performance, adhesion, displacement ability and other parameters. Among them, low modulus is also one of the performance characteristics of prefabricated building sealant.

So why is low-modulus sealant so popular in prefabricated buildings?

1.What is modulus?

From the mechanical properties of the material, the modulus refers to the ratio of stress and strain in the stress state of the material. The modulus can be regarded as an index to measure the difficulty of elastic deformation of a material. The greater the value, the greater the stress that causes a certain deformation of the material, that is, the greater the stiffness of the material, that is, the smaller the elastic deformation occurs under a certain stress. The modulus of the sealant usually refers to its secant tensile modulus. The sealing adhesive is bonded between the surfaces of two parallel substrates to make a specimen; The shear tensile modulus of sealant can be calculated by drawing the force-elongation curve after the specimen is stretched to failure.

2.The difference between high 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 two sub-levels: high modulus (HM) and low modulus (LM). According to the regulations, when the sealant is stretched to the corresponding elongation, its modulus is less than or equal to 0.4MPa at 23℃ and less than or equal to 0.6MPa at -20℃, the sealant can be determined as a low modulus; If any condition is not satisfied, it can only be judged as a high modulus. The elongation varies with different displacement levels. For grade 20 sealant products, determine the tensile modulus of 60% elongation, and for grade 25 and above sealant products, determine the tensile modulus of 100% elongation.

3.Advantages of low modulus sealant

Under normal circumstances, the tensile modulus indicates the flexibility of the sealant, the lower the tensile modulus, the softer the sealant, and the smaller the internal stress when the same deformation occurs. The higher the tensile modulus is, the greater the internal stress is when the same deformation occurs. In the same deformation of the glue joint, the use of low modulus sealant products, the internal stress will be much smaller than the same displacement grade of high modulus sealant products. Therefore, it can effectively avoid the cracking of sealant caused by large internal stress.

Secondly, the small internal stress means that the sealant has a small force on the surface of the bonded substrate. The surface of traditional materials such as aluminum and glass is relatively dense, but for the relatively loose surface of prefabricated concrete components, cement mortar, autoclaved aerated concrete slabs and other materials, the low modulus has great advantages, which can greatly reduce the probability of material surface stripping.