↑ click above to learn more about "Silicon treasure technology"
Development and advantages of prefabricated buildings
Prefabricated building is a new construction method, which divides the residential building into several units or components. The main components (walls, beams, columns, floors and stairs, etc.) are produced in the factory, and then transported to the construction site. The prefabricated concrete components are assembled and constructed on the site by using the prefabricated technology. The house can be built like a car.
In the residential construction of our country, the concrete structure mostly adopts the cast-in-place system; although the construction method is mature in technology, it also has the problems of high energy consumption, high pollution and low technology content. Assembly building can not only improve the efficiency of construction, but also has more advantages than traditional mode in energy saving, noise reduction, environmental protection and other aspects. Under the guidance of new concepts such as "low carbon economy" and "green building", it has become an inevitable trend to reform the way of housing construction and promote the development of prefabricated buildings in China.
Waterproofing requirements for prefabricated buildings
The waterproof measures of prefabricated exterior wall joints in prefabricated buildings generally adopt the combination of component waterproof and material waterproof. The waterproof sealant is the first line of defense for the waterproof of exterior wall joints, and its performance is directly related to the waterproof effect of the project, which requires the selection of professional and targeted waterproof sealing materials in the implementation of prefabricated buildings.
Waterproof sealant is an important supporting material for prefabricated buildings, and the first line of defense for the waterproof of the exterior wall of prefabricated buildings. Choosing inappropriate waterproof sealant will lead to problems such as debonding, cracking, aging, hardening, etc. (Figure 1), and then wall water leakage, mildew, peeling, insulation layer failure, etc. (Figure 2). Therefore, the quality of waterproof sealant directly determines the quality of prefabricated buildings The service effect, service life and energy saving efficiency of the building.
Figure 1 problems of waterproof sealant
Fig. 2 Effect of failure of waterproof sealant on prefabricated building
According to JGJ 1-2014 technical specification for prefabricated concrete structure and dbj51 / T 038-2015 According to the requirements of the code for design of assembled integral residential buildings in Sichuan Province, the joint sealant of prefabricated exterior wall must have good compatibility with concrete, good displacement ability, waterproof, weather resistant and pollution resistant functions, and the sealant also needs to meet the requirements of corresponding national and industrial standards.
Fig. 3 concrete joint and sealing effect of prefabricated building
Waterproof sealant for exterior wall of prefabricated building
In view of the requirements of the above-mentioned prefabricated building exterior wall waterproof sealant, we have made a comparative analysis of the existing sealant in the market. Common building sealants include silicone sealant (SR), silane modified polyether sealant (MS), polyurethane sealant (PU). Pu is based on polyurethane prepolymer. The main chain consists of C-O bond (bond length 0.136nm, bond energy 339kj. Mol-1) and N-C bond (bond length 0.132 Nm, the bond energy is 284kj. Mol-1); MS is mainly composed of silane terminated modified polyether, and the main chain is composed of a large number of C-O bonds, C-C bonds (bond length 0.154nm, bond energy 348kj. Mol-1) and a small number of Si-O bonds (bond length 0.164nm, bond energy 444kj. Mol-1); Sr is mainly composed of linear polysiloxane, and the main chain is composed of Si-O-Si. Three kinds of sealants are applied in the waterproof sealing of prefabricated buildings with different advantages and disadvantages. The performance comparison is shown in Table 1 below.
According to the analysis of the requirements for the sealing of concrete joints in prefabricated buildings, the sealant shall meet the following requirements in the use process:
01
Caking property
For sealant, the adhesion to the base material is always one of the most important properties, as is the case for the base material used in assembly building. At present, most of the prefabricated building plates used in the market are concrete plates, so the joint sealing materials are required to have good bonding performance to the concrete substrate. For the concrete material itself, it is not easy to achieve the adhesion of ordinary sealant on its surface. The main factors affecting the adhesion are as follows:
1) Concrete is a kind of porous material, the size and unevenness of the holes are not conducive to the adhesion of sealant;
2) The concrete itself is alkaline, especially when the base material absorbs water, it is easy to appear the phenomenon of returning alkali to affect the bonding;
3) During the production of prefabricated building plates in the workshop, release agent will be used, which will lead to poor adhesion between sealant and base material.
In order to ensure the adhesion of the joint sealant to the prefabricated plate, when selecting the prefabricated construction joint sealant, the above factors that affect the adhesion should be taken into account, and a sealant suitable for the concrete substrate should be selected.
Figure 4 Comparison of bonding performance between sealant and concrete
02
mechanical property
The size of concrete joints will move and displace because of the thermal expansion and contraction of concrete slabs with the change of temperature and the slight vibration of buildings. Referring to the corresponding code requirements of prefabricated building, the displacement of the joint shall be considered in the design, and the joint width shall be determined to meet the requirements of the maximum allowable deformation rate of sealant. According to the standards of sealant for construction joints at home and abroad (as shown in Table 2), it can be seen that the mechanical properties of sealant at home and abroad are basically the same.
03
Weatherability
As the service life of the architectural design is generally 50 years, the sealant used between the plate joints has very good weather resistance, meeting the long-term outdoor working conditions. In Japan, Ms adhesive has been used in prefabricated buildings for 40 years, which shows that Ms adhesive can fully meet the outdoor complex conditions and environmental changes. After 1000 hours of UV irradiation, the strength and retention rate of Sibao ms1096 are over 80%, which can fully meet the long-term outdoor working environment.
04
Anti pollution
There are many holes in the surface of precast concrete slab, the plasticizer in common sealant is easy to penetrate into the concrete, causing pollution on both sides of the joint of concrete slab and affecting the appearance of the whole building. The special sealant adopts the internal plasticizing technology, that is, the selected plasticizer can play the role of lubricating and plasticizing on the one hand, and on the other hand, it can participate in the chemical reaction in the later application process of the product, so as to avoid the hidden danger of plasticizer seepage into the hole of the concrete substrate in the later period. In addition, the special primer can play a role of sealing and isolation, which can prevent any possibility from being outside the concrete surface.
05
Finishes
For the current prefabricated buildings, due to the deviation of component size and immature field assembly process, the width of the joint between plates is inconsistent, which affects the appearance of the whole building. It is necessary to brush a layer of paint on the sealant to keep the width of the joint consistent from the outside, so as to ensure the beauty of the whole building. Therefore, the sealant is required to have a certain degree of coating Ornamental. MS glue and polyurethane sealant are widely used in the market due to their good coating ability. However, silicone sealant has low surface energy and poor coating ability. However, it can be used for waterproof joint of fair faced concrete wall without coating and tile back hitting wall.
Figure 5 painting effect of real stone paint on silica ms1096
"Three materials, seven construction" is a popular saying in the industry. Therefore, after selecting good sealant products, standardized construction process is needed to ensure the waterproof and sealing quality of the project.
epilogue
Due to a large number of exterior wall joints in prefabricated buildings, it is necessary to select waterproof sealant to waterproof the exterior wall joints, and the selected waterproof sealant is required to have high elasticity, good adhesion, low modulus, excellent aging resistance, and no pollution to the base material, so the surface finishing operation can be carried out when necessary. After selecting the appropriate waterproof sealant, it is also necessary to follow the standard construction process to prevent the failure of waterproof seal caused by improper operation.
Sibao technology is engaged in intensive cultivation in the field of assembly construction. There are more than 3 million square meters of engineering cases in China, providing high-quality products (Sibao 1068, Sibao 1096 and Sibao 1097l) and engineering contracting services, providing reliable guarantee for the development of the domestic assembly construction industry.
(source: Sibao Technology)
Click "glass industry network" below for more information