Analysis and Prevention of External Thermal Insulation Cracks in AC Exterior Walls Jianping â–¡Henan Sanjian Construction Group Co., Ltd. Liu Zhixiong Lei Xingjuan External wall thermal insulation system External thermal insulation system consists of interface layer, thermal insulation layer, anti-crack protection layer and decorative layer . Exterior wall insulation is to put the thermal insulation system outside the outer wall, forming a closed thermal insulation shell, effectively blocking the cold (heat) bridge, so that the building to achieve thermal insulation construction methods. For the main structure, due to the existence of the heat preservation system, the effect of the temperature difference is greatly reduced, and the temperature deformation is reduced, which not only protects the structural wall but also contributes to prolonging the life of the structure. However, due to the fact that the external thermal insulation system was placed on the outside of the external wall and directly subjected to various factors from the natural world, Ah proposed a higher requirement for the external wall external insulation system, and the flexibility and weather resistance of the anti-crack protection layer. The external insulation system plays a key role in the crack resistance.
Cause analysis of cracks In external wall insulation, we often pay attention to the insulation of the whole wall, but we neglect the insulation of the parapets, awnings, bay windows, external balconies, deformation joints, etc., and make this part crack or reduce the service life .
In the material transformation of the insulating layer and other materials, because the material density of the insulating layer and other materials differ greatly, it is extremely easy to generate surface cracks in these areas. At the same time, water-repellent treatment should also be considered to prevent moisture from intruding into the heat-insulating system, avoiding the damage of the system caused by freeze-up and affecting the normal service life of the system and the durability of the system.
External cracking and water repellent treatment for external thermal insulation is generally wiping cracking mortar and reinforcing grid cloth is laminated in anti-crack mortar. From the factors of thermal stress resistance of anti-crack protection layer, the thermal insulation layer of the system is generally 2060mm. The anti-crack mortar composite grid cloth is only 35mm thick, and the thermal conductivity of the thermal insulation layer and the thermal conductivity of the anti-crack mortar are quite different. Due to the large thermal resistance of the thermal insulation layer, the heat of the protective layer is diffused into the room through conduction. Therefore, when the temperature difference between day and night and the season outdoor temperature is relatively large, the flexibility of the mortar and the durability of the grid cloth are relatively equivalent. High demand. Another factor is that when using polystyrene board insulation, when the temperature exceeds 70 °C, the polystyrene board will produce irreversible thermal shrinkage deformation, resulting in more severe cracking deformation, this situation is more evident in high-temperature dry areas.
There are deficiencies in the design of the external thermal insulation structure of the cement mortar thick plastering steel wire frame insulation board. This type of external thermal insulation usually uses polystyrene board with a steel wire frame as the main thermal insulation material, divided into two types: steel mesh penetrating polystyrene board and non-penetrating polystyrene board. The steel wire mesh penetrating the polyphenylene steel wire frame polyphenylene plate is fixed on the base structure by pre-cast concrete as a whole and once cast, and the non-penetrating polystyrene board is fixed on the base structure by a mechanical anchoring method. All use 20mm30mm ordinary mortar leveling.
Due to the use of thick plastering cement mortar in this type of system, ordinary cement mortar itself is prone to various shrinkage deformations, and there is a contradiction of short cycle of strength growth and long volume shrinkage cycle. Under constraint conditions, the tensile stress formed when the volume contraction exceeds When the tensile strength of cement mortar, there will be cracks. The main structure under the protection of the thermal insulation layer is less affected by the temperature deformation, and the 2030mm leveling mortar is located on the outside of the polystyrene board with a large thermal resistance and is therefore subject to large deformation due to the influence of the ambient temperature. The cement material on both sides of the polystyrene board is affected by the environmental temperature difference, resulting in a large relative deformation difference, causing cracking.
In addition, due to the flatness of the insulation board, the thickness of the plaster is unevenly distributed, and local cracks and uneven temperature stress cause cracks.
The reason of construction is that the deviation of the verticality of the wall is large, which results in the local super-thickness or ultra-thin insulation layer, and the deformation caused by the temperature stress is of different sizes, so that the anti-crack layer is cracked.
Filling wall and column, beam, plate joints are not densely packed according to specifications.
The grassroots wall cleaning is not clean, so that the insulation layer is not firmly bonded, hollow cracking.
The external insulation at the head was not sealed in accordance with the design requirements. The insulation layer absorbed moisture and caused cracks due to freezing.
Insulation materials, crack-resistance mortars, and grid material differences can also cause cracks.
The bottom layer and window openings are not reinforced by the design along the diagonal and other parts.
Preventive measures The external insulation of the building should be the entire external insulation of the entire building. The external wall insulation should be integrated with the roof insulation to form a closed system. It is recommended to increase the bonding area as much as possible, adopt no cavity, and enhance the wind pressure destruction. And crack resistance requirements.
The selection of thermal insulation materials should be based on the principle of gradual change in the thermal conductivity between the various structural layers. The growth of thermal insulation in the anti-crack layer should be alleviated by the larvae, so that the thermal load and stress caused by the sudden temperature change of the system can be released compared to that of Shaanxi, and the anti-crack layer can be improved. The durability.
As the key reinforcement material of the crack protection layer, glass fiber mesh cloth can effectively increase the tensile strength of the protective layer on the one hand, and can effectively disperse the stress on the other hand, thereby forming a crack resistance. As the outer protective crack resistant mortar of the insulation layer is alkaline, the long-term alkali resistance of the glass fiber grid cloth has decisive significance to the cracks. From the durability analysis, the high alkali-resistant fiber mesh cloth has much better durability than the alkali-free (or alkali-base) mesh cloth. Therefore, when selecting the reinforcing mesh, a high alkali-resistant mesh cloth should be used.
The protective layer must use a special anti-cracking mortar and supplemented with a reasonable reinforcement net, and add a proper amount of fiber to the mortar. The cracking resistance of the anti-cracking mortar is less than 3. If the exterior facing is a tile, it is also used in the cement cracking mortar. Can add steel wire mesh, steel wire mesh spacing should not be too small or too large, the short side of the tile should be covered in at least two holes on the Internet, wire mesh should be used anti-corrosion good hot-dip galvanized steel wire mesh.
Strengthen the quality of the construction of the control of the grass-roots clean-up grass-roots level, the focus is to clean the oil, cleaning floating ash, loose walls and clear wall surface protrusions, in order to ensure that the grass-roots level and the insulation layer firmly.
For those with large deviations in wall verticality, cement mortar leveling should be carried out to ensure that the screed layer is firmly bonded and there is no emptying or cracking phenomenon.
Do a good job of detailing and strengthening the parts, and seal the end of the insulation layer with a waterproof sealant.
Ensure that the ratio of cementitious material and anti-crack mortar is reasonable. We have analyzed and summarized the anti-crack construction technology for exterior wall external insulation, targeted measures have been taken, and the occurrence of cracks has been effectively controlled during construction. A relatively mature construction process has accumulated a wealth of experience. dST
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