Problems and Countermeasures in the Construction of Lightwei

Plastering gypsum is a material for plastering the surface of interior walls and ceilings of buildings. It is a replacement product of traditional cement mortar. It is made of building gypsum as the base material and supplemented by optimized performance materials and a variety of additives and aggregates. Air-hardening plastering material. As a new type of interior wall plastering material, plastering gypsum has the characteristics of light weight, fire resistance, thermal insulation, sound absorption, high strength, no shrinkage, not easy to crack, and convenient construction. It has been widely recognized and promoted by the market. The plastering plaster is firmly bonded to the base layer, which can avoid the hollowing, cracking, and falling off of the cement mortar plastering surface. The plastering plaster is especially suitable for plastering aerated concrete walls.

 

1. Advantages of plastering plaster

(1) Strong adhesion

Due to the addition of a variety of polymers, its water retention is good. Plastering gypsum can bond well with almost all kinds of wall substrates. The effect is especially obvious for aerated concrete walls. There is no need to brush any interface agent when plastering. Since the plastering plaster has micro-expansion, it can effectively inhibit the shrinkage and cracking of the plaster, and the wall plaster layer will not appear hollow, cracked, and peeled off.

 

(2) It has a decorative effect

Plastering plaster walls are dense and smooth without dusting, non-toxic, odorless, non-cracking, high strength without shrinkage, elegant appearance, and achieve high-level plastering effects.

 

 

 

 

 

 

(3) Good flame retardancy

After the plastering gypsum is condensed, there is a large amount of crystal water. In the event of a fire, a large amount of crystal water in the gypsum is released, and the vapor formed prevents the spread of the flame. At the same time, a large amount of heat is absorbed during the entire dehydration process, thereby improving the fire resistance.

 

(4) Good thermal insulation

Plastering gypsum hardened body is a porous material, and the thermal conductivity is 30% of concrete products and 45% of clay bricks under the same thickness. At the same time, the plastering plaster can effectively prevent the transmission of sound waves after curing, and the effect of the compartment is good.

 

(5) Convenient construction

Plastering gypsum has good workability and water retention. After adding water and mixing evenly on site, it can be directly applied to the wall for plastering. The operation is free, the labor intensity is low, and the material consumption is low.

 

(6) Save construction period

The plastering gypsum plaster layer sets and hardens quickly, and the curing cycle is short. The entire hardening and strength compliance process is only 1-2d, and the construction period can be shortened by about 70% compared with traditional cement mortar.

 

 

 

 

 

(7) It has good breathing function.

Plastering gypsum can form tiny honeycomb breathing holes during the hardening process, which can automatically absorb moisture when the indoor environment is relatively humid. Under the opposite conditions, it can automatically release the stored water, repeatedly circulate, control the indoor humidity within a suitable range, and create a good and comfortable living environment for the occupants

    

(8) Favorable for winter construction.

Plastering gypsum has the characteristics of early strength and rapid setting, construction is not restricted by seasons, especially in winter (above -5℃), it can still be constructed, and its hydration speed will not be significantly slowed down due to low temperature, as long as the mixing water does not freeze It can be plastered, and it is a good material for indoor plastering construction in winter.

 

2. Discussion on the application of desulfurized semi-hydrated gypsum to plaster gypsum

 

Desulfurized gypsum is processed into semi-hydrated gypsum and applied to plaster gypsum. There should be no problem in theory, but unsatisfactory results have appeared in practical applications. There is a desulfurized gypsum manufacturer with an annual output of 100,000 tons of gypsum powder. In order to produce qualified plastering gypsum powder, last year it invited experts in the industry for guidance and invested funds to transform the calcining system. After nearly a year of commissioning, the product The quality result is still not up to the requirements. First, the initial setting time is short, and the second is that the second water phase is too high and the characteristics are unstable. It is difficult to adjust to the required indicators for plastering gypsum, and the production line can only be shelved. Of course, some are the defects of the desulfurization gypsum itself, some are the problems of the calcination process, and some are the reasons for the improper adjustment of the process parameters. In the application, problems such as short setting time, unstable setting time, low strength, etc., have caused the construction. This is one of the reasons why the application of desulphurization plastering gypsum is difficult in reality. Based on our practical experience, try to discuss the above-mentioned problems in the process of desulfurization gypsum, in order to communicate with colleagues in the gypsum industry.

 

(1) The initial setting time is short and it is difficult to prepare plaster plaster

The desulfurized hemihydrate gypsum has a high content of dihydrate phase. The desulfurized dihydrate gypsum contains two water molecules. After calcination, 3/4 of the water molecules are removed, leaving 1/4 of the water molecules, so it is called hemihydrate gypsum. The finished hemihydrate gypsum often contains three phases, namely an anhydrous phase, a semi-aqueous phase, and a two-aqueous phase. According to industry standards, the composition ratio of each phase in the calcined hemihydrate gypsum is that the semi-aqueous phase is more than 80%. Anhydrous phase <15%, two water phase <5%. According to the current calcination system, the proportions of the phase components of different process systems are different. The same process system is the same, and the phase components produced by each manufacturer are also different. That is, the phase composition of the semi-hydrated gypsum produced by one manufacturer is also different. Differences will occur. According to what I know, the current problems encountered by various manufacturers are mainly the high dihydrate phase and high dihydrate phase in the desulfurized hemihydrate gypsum. The problem is that the initial setting time is short, and the increase in slow The setting time of plastering gypsum can not be achieved by the setting time of plastering gypsum. At the same time, it is impossible to prepare qualified plastering gypsum by increasing the retarder, increasing the cost and reducing the strength. difficulty.

 

(2) The content of the two water phase is unstable

The content of the di-aqueous phase in desulfurized hemihydrate gypsum is unstable. The importance of the di-aqueous phase was mentioned above. At present, there is still a problem of the instability of the di-aqueous phase, which is also a key issue. There is a processing company that has 2 For a sample, the initial setting time is about 16 minutes before the retarder is added, and the strength is about 3.0. It should be suitable for plastering plaster. The problem is that after the retarder is added, the initial setting time of a sample reaches 160 minutes. The other sample only took 26 minutes, and the difference between the two samples was as much as 5 times. One construction unit used this gypsum product as gypsum mortar. After arriving at the site, workers could not operate it and could only exchange other high-quality gypsum. It can be seen that the importance of the two-aqueous phase in hemihydrate gypsum, so this problem has to arouse the attention of various desulfurized hemihydrate gypsum manufacturers.

 

(3) Use high-strength building gypsum raw materials

The strength of desulfurized semi-hydrated gypsum. Semi-hydrated gypsum in plastering gypsum is used as a cementing material. In addition to gypsum, a large amount of sand is also mixed. Generally, sand or other fillers are mixed in a ratio of 1:3. The strength of gypsum The key function is that the strength of gypsum is low. First, it is easy to pulverize the surface. Second, the proportion of sand mixed is low. If the strength of semi-hydrated gypsum reaches 3.5 or more, the processed plaster gypsum can exceed the strength of the nationally regulated plaster plaster. And it can also increase the ratio of sand. We have a user who has tested the formula and formulated it at a ratio of 1:3, and the strength standard of the plaster made reaches 2.6. Therefore, as a semi-hydrated gypsum manufacturer, it should produce high-strength products to meet the product standards of plastering gypsum. Manufacturers of plastering gypsum should purchase high-strength gypsum as raw materials as much as possible, so that they can provide qualified products and seize the market with quality.

 

3. Experience in producing construction gypsum suitable for plastering gypsum requirements

 

Plastering gypsum requires two main parameters for construction gypsum raw materials. One is that the initial setting time is preferably greater than 10 minutes, and the other is that the two water phase in hemihydrate gypsum is less than 4%. Generally speaking, building gypsum calcined at high temperature has a fast initial setting time, and building gypsum calcined at low temperature and slow speed has a slow initial setting time. The key is the level of the two water phase in the construction gypsum after low-temperature calcination, which becomes the key to the quality of plastering gypsum. The following discusses some experiences on the production of hemihydrate gypsum:

 

(1) The use of appropriate process technology and equipment is the basis for reducing the two-aqueous phase

The use of appropriate process technology and equipment is the basis for reducing the two-water phase. There are many desulfurized gypsum processing processes, mainly in energy consumption, setting time, strength, etc., and manufacturers and customers have their own needs and requirements. , All have its rationality, it is difficult to say which kind of technology is good or bad. For gypsum processing enterprises, the most important task is to first understand the market surrounding the enterprise, and then choose gypsum products and process equipment that suit the market requirements. This is often ignored by current gypsum processing enterprises. Some enterprises The surrounding ceiling gypsum board market is large, but the semi-hydrated gypsum produced is not suitable for the time requirements of manual operation of the ceiling due to the slow initial setting, and the product is not suitable for the market. Some gypsum processing companies produce products with fast initial setting, which do not meet the requirements of slow initial setting of plastering gypsum, and they have no choice but to face the surrounding plastering plaster market. In fact, the raw material requirements for plastering gypsum can be said to be higher than other gypsum raw materials. Nowadays, many gypsum processing enterprises, the most difficult thing to achieve, its two-aqueous phase standard cannot meet the requirements of plastering gypsum products. According to the practical experience of senior experts in the gypsum industry, the proportion of dihydrate in hemihydrate gypsum is controlled below 4% to meet the requirements of plastering gypsum. At present, the dihydrate phase in hemihydrate gypsum produced by gypsum processing enterprises is generally above 5%. If you want to meet the requirements of plastering gypsum, you can only rely on the adjustment of admixtures, which increases the cost and reduces the strength of the gypsum. Moreover, for some gypsum with high dihydrate phase, adding retarder adjustments will not help. So choosing the right process equipment is the key.

 

(2) Choosing reasonable calcination parameters is the key to stabilizing the two-aqueous phase

After selecting the appropriate equipment, the optimal calcination parameters must be adjusted according to the process equipment and raw materials. The current desulfurization gypsum discharge is roughly controlled between 140 degrees and 190 degrees, which is selected according to product requirements and process equipment. As for the selection of the appropriate discharge temperature, it must be determined according to the experience of the processing enterprise, and cannot be generalized. In addition to the high dihydrate phase of the currently produced hemihydrate gypsum, there is another reason for the instability of the dihydrate phase. The hemihydrate gypsum produced by some gypsum processing enterprises sometimes has a dihydrate lower than 4%, even reaching 2%. % Or less, if it can be stably controlled on this basis, it is a product of very good quality. The problem is that the time is high and the time is low. Especially after adding a retarder, the setting time fluctuates too much, and the construction site cannot be operated. It is also the bottleneck in the application of desulfurized hemihydrate gypsum in plastering gypsum. There is a desulfurization gypsum processing enterprise. After equipment transformation and process adjustment, the hemihydrate gypsum produced has improved in the initial setting time and two-water phase, but the quality is not Stability, not up to the original intention at the time, left a regret. I have observed several processing techniques, different process equipment, the product parameters must be different, that is, the same process equipment using a fluidized furnace, the final product is also very different, including the difference in the dust removal system and the difference in the drying system. , The difference in calcination parameters is the same process and equipment. After the technical transformation of gypsum processing enterprises, the final product quality is also different. It is not surprising that the desulfurized semi-hydrated gypsum products have their own characteristics. Due to its inherent characteristics, desulfurized gypsum is very different from natural gypsum processing. This is also the problem of current desulfurized gypsum processing. According to my observation and experience, the reasons are roughly as follows. One is the process and equipment. At present, some investors are not familiar with gypsum processing technology and requirements, especially ignorant of desulfurization gypsum, and blindly choose process equipment. If the choice is improper, There is no shortage of weather, and no matter how to adjust it after it is put into production, it will not help. The second is the control of the parameters of the calcination process. Desulfurized gypsum has many particularities. The adjustment of parameters is a difficult point. How to maintain uniform heat exchange between heat and materials in the calcination equipment is a difficult point, especially desulfurized gypsum, which has fine particles and moisture content. High, how to ensure uniform heat exchange in the heating process is an urgent problem to be solved. The current practitioners in the gypsum processing industry have low professional levels and can only do simple operations. I don’t know the principle and process of heat exchange in the equipment. , This is also an important reason.

 

(3) Choosing high-quality raw materials is the key to stabilizing the two-aqueous phase

Since the fineness of desulfurized gypsum reaches 250 meshes or more, which is far greater than that of natural gypsum, the biggest difficulty in the processing of desulfurized gypsum is that the internal crystal water is maintained at a stable level, and the quality of gypsum is stable. Some crystal water>10, some crystal water<2, although the phase composition can be changed after aging, it is difficult to adapt to the requirements of plastering gypsum due to the high stability requirements of the semi-aqueous phase of plastering gypsum. From the requirements of plastering gypsum for raw materials, one is to require a stable supply of raw materials. It is best to choose raw materials from a power plant. Relatively speaking, a power plant has a fixed supply of desulfurizer. Once the control parameters are adjusted, the various indicators of gypsum are compared. It is stable, and the quality will not fluctuate greatly, and the quality of desulfurized gypsum can be guaranteed. Second, for power plants, it is best to choose good quality limestone raw materials and maintain the stability of limestone quality, and do not change the limestone supply unit casually. Secondly, adjust the desulfurization operating parameters, especially the PH value and the density of slurry discharge during gypsum must be well controlled to ensure that the content of calcium sulfate dihydrate in gypsum is above 90%. The third power plant must use flushing water equipment to reduce the chloride ion content and strive to meet national standards. As long as there is a stable supply of raw materials, with appropriate process equipment and adjustment of parameters, the quality of semi-hydrated gypsum products will be guaranteed.

 

In fact, in reality, the above requirements are more difficult to achieve, that is, the gypsum production line invested by the power plant itself. Because the focus of power plant management is power generation, the focus of production and multi-department evaluation indicators is different, and coordination difficulties often occur, which affects Plaster quality. At present, gypsum processing enterprises in various places often use desulfurized gypsum from multiple power plants. The quality of gypsum in each power plant is different, and the quality varies greatly. The semi-hydrated gypsum produced on the same production line will also adapt to different types of gypsum. The calcination temperature causes the difference in the quality of hemihydrate gypsum, which is also an important factor for the unstable quality of desulfurized hemihydrate gypsum. Therefore, the calcination of desulfurized gypsum in the same power plant requires certain technical personnel in the processing company to determine the appropriate calcination temperature of various gypsum through practical experience and testing methods to calcinate qualified hemihydrate gypsum.