Precast external wall panels are the most widely used form in PC buildings in China. The prefabricated external wall panels have good surface flatness and high overall accuracy, and the thermal insulation and decoration layers of building external windows and facades can be prefabricated directly in the factory, which has won the favor of many developers.
Because the prefabricated external wall is assembled in blocks, it is inevitable to encounter the problem of waterproof treatment of connecting joints, so we must attach great importance to the treatment of waterproof joints of prefabricated external walls. In this paper, several existing waterproof technologies of precast external wall panels are analyzed and introduced, and some problems needing attention in waterproof construction of precast external wall panels are discussed.
First, the waterproof design concept of prefabricated buildings
Waterproof engineering of buildings has always been a very important link in building construction, because the waterproof effect directly affects the future use function of buildings, and houses that often leak water can not meet the living and use needs of users.
We know that water is very mobile and pervasive, so the most important design concept of traditional building waterproofing is to block water, which can enter all the passages in the room and achieve waterproof effect. This concept can still achieve ideal results when used in traditional cast-in-place structures, but it may not be so ideal when used in prefabricated buildings.
Assembled building is to disassemble building structures such as wallboard, column, beam, floor and stairs according to certain specifications, then prefabricate them in the factory and transport them to the site for assembly. Because the components are assembled on site, a large number of assembly joints will be left, which can easily become seepage channels, so prefabricated buildings actually have certain inherent weaknesses in waterproofing. In addition, in some prefabricated buildings, in order to resist the influence of earthquake force, the outer wall panels are designed to be movable within a certain range, and the movable wallboard increases the difficulty of waterproofing the joints of wallboard.
In view of the above factors, the waterproof design concept of prefabricated buildings must be adjusted. We think that for the waterproofing of prefabricated buildings, guiding water is better than blocking water, and drainage is better than waterproofing. To put it simply, it is necessary to consider that some water may break through the external waterproof layer when designing, and guide these broken water into the drainage structure through a reasonable drainage path, so as to be discharged outdoors and avoid further infiltration into the room.
In addition, based on the principle of natural vertical flow of water under the action of gravity, the joints of wallboard are designed into a tongue-and-groove shape with high inside and low outside, and combined with a certain decompression cavity design, water is prevented from climbing backwards into the room through capillary action. In addition to concrete waterproof measures, rubber water stop and multi-component weather-resistant waterproof glue are also adopted to improve the waterproof system of the whole prefabricated wallboard, so that it can really be watertight.
Secondly, several forms of waterproof treatment for joints of precast external wall panels are introduced.
At present, the waterproof forms of precast exterior wall panels are widely used in practical applications as follows:
1. Precast external wall panels (i.e. PCF panels) externally poured and externally hung mainly adopt the waterproof form of external drainage cavity and glued joints, and the inner side relies on the self-waterproof of cast-in-place concrete.
This waterproof form of exterior wall joint is the most widely used form at present. Its advantage is that the construction is relatively simple and fast, but its disadvantage is that the waterproof quality is difficult to control, and sometimes the cavity is blocked. Once the internal concrete cracks, it will directly lead to the waterproof failure of wallboard.
2. The external prefabricated external wall panel adopts closed waterproof form.
There are three main waterproof measures for this wallboard: the outermost side is made of weather-resistant waterproof silica gel with high elasticity, the middle is a decompression space formed by a physical cavity, and the inner side is made of waterproof rubber strips embedded in concrete and squeezed up and down to achieve waterproof effect. A layer of polyurethane waterproof layer is added outside the rubber waterstops at the transverse joints between walls, which is mainly used to block the tiny cracks that may occur when the rubber waterstops are staggered. For rooms or buildings with particularly high waterproof requirements, polyurethane waterproof can be fully constructed inside the rubber water stop. A drainage pipe is arranged on the waterproof silica gel of the external wall at intervals of about 3 layers, which can effectively guide the rainwater seeping into the decompression space to the outside.
The waterproof structure of closed-line waterproof adopts the method of combining internal and external waterproofing without blocking, and its waterproof structure is very perfect, so the waterproof effect is also very good. The disadvantage is that the precision is very high during construction, and the displacement of wallboard can not be greater than 5mm, otherwise the water stop can not be pressed. The weather-resistant waterproof glue used has high performance requirements, not only high elasticity and aging resistance, but also a service life of not less than 20 years. The structural adhesive has high cost and high quality requirements, so it must be constructed by experienced professionals.
3. There is also a joint waterproof form of prefabricated wallboard of external wall called open wire waterproof.
This waterproof form is basically the same as the two waterproof measures of closed-line waterproof, that is, tongue-and-groove decompression space and internal pressure waterproof strip. However, the waterproof measure of open wire waterproof is not sticking, but the curtain-shaped rubber strip with one end embedded in the wallboard and the other end protruding out of the wallboard is overlapped up and down to play a waterproof role. At the same time, stainless steel air guide grooves are arranged on the outside rubber strip at regular intervals to balance the internal and external air pressure and drain water.
The waterproof form of the outermost layer of open wire adopts embedded adhesive tape, which makes the product quality easier to control and check. During construction, workers do not need to glue the outside of the wallboard, which saves construction measures such as scaffolding or hanging basket, which is safer and simpler. The disadvantage is that the requirements for product protection are high. Once the embedded rubber strip is damaged, it is difficult to replace it, and the cost of weather-resistant rubber water stop is high. Open-wire waterproofing is the most advanced form of exterior wall waterproofing joint treatment at present, but it is a patented technology developed by foreign companies. Due to the influence of patent use cost, there are few projects using this technology in China at present.
Third, the construction points of waterproof treatment of precast exterior wall slab joints
At present, the waterproof treatment technology of precast exterior wall slab joints is technically complicated and the construction is difficult. In actual construction, targeted construction schemes and measures should be made according to different joint design requirements of external wall panels. Specifically, the following construction points should be paid attention to in the construction process:
1. Do a good job in product quality inspection before wallboard construction.
The processing accuracy of precast wallboard and the quality of concrete curing directly affect the installation accuracy and waterproofing of wallboard. Before installing the wallboard, it is necessary to carefully check the geometric size and smoothness of the wallboard, whether the concrete on the surface of the wallboard and around the embedded window frame is dense and whether there are through cracks. It is forbidden to use wallboard with unqualified concrete quality.
In addition, we also need to carefully check the installation quality of the embedded adhesive tape around the wallboard, check whether the adhesive tape is embedded firmly, whether the corner parts are damaged, and whether there is concrete slurry leaking into the interior of the adhesive tape, which leads to the hardening and loss of elasticity of the adhesive tape. The rubber strip must be strictly inspected to ensure that there are no defects, and only when there are quality problems can it be hoisted.
2. Strictly control the installation accuracy during wallboard construction, and do a good job of measuring and setting out before wallboard hoisting.
It is necessary not only to set the datum line, but also to set out the position line of the wallboard, so as to facilitate the positioning of the wallboard during hoisting. The precision adjustment of wallboard is generally divided into two steps: coarse adjustment and fine adjustment. The coarse adjustment is to decouple the wallboard in place according to the control line, and the fine adjustment requires that the axis position and verticality deviation of the wallboard be adjusted to the allowable deviation range of the specification, and the actual construction generally requires less than 5 mm
3. During the waterproof construction of wallboard joints, strictly follow the technological process and do a good job in quality inspection of each working procedure.
Glue the outside of wallboard joints in strict accordance with the design process, and the base and reserved cavity must be cleaned with high-pressure air. Carefully check the depth of the backing before gluing, and the thickness of gluing must meet the design requirements. The wallboard in the glued part should be primed to enhance the bonding force between the glue and the concrete wallboard. When gluing is interrupted, construction joints shall be left, with the internal height and external height being low, and the lap joint shall not be less than 5cm.
Polyurethane is used to seal the connecting iron pieces and cross joints on the inner side of wallboard. Because there is no rubber water stop at the iron parts, rust removal and rust prevention of iron parts should be done carefully before polyurethane construction. Polyurethane should be applied tightly, leaving no gaps. After the construction, splash test shall be conducted to ensure no leakage before sealing the cover plate.
4. After the completion of the construction, conduct waterproof effect test, and properly and effectively deal with the leakage problem in time.
After the waterproof construction of wallboard is completed, the water spraying test should be carried out in time to test the effectiveness of waterproof. The focus of water spraying is the cross joint of wallboard, the joint of precast wallboard and cast-in-place structure and window frame. When spraying water, the test parts should be sprayed with fire hose. Externally check whether there is degumming phenomenon in the gluing part, whether the drainage pipe is unobstructed, and carefully observe whether there are watermarks and water marks inside. If a local leak is found, it must be carefully recorded, the cause found out and handled in time. If necessary, polyurethane waterproof material can be added to the inner side of the wallboard to improve the safety factor of leakage prevention.
Fourth, summary.
Prefabricated building is a new technology that is being vigorously promoted in the construction industry at present. From the technical level, by adopting a series of improvement measures, the waterproof performance of its external wall has been effectively guaranteed. I believe that after the above introduction, everyone has a certain understanding of the technical form introduction and construction points of precast external wall panels. Welcome to Zhong Da for more information.
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