Discussion on Drying and Shrinkage Regularity of Autoclaved Aerated Concrete
The research and production application of this material for aerated concrete, although it has a history of more than 0 years in foreign countries, has only a long history in China. In recent years, it has developed rapidly.
However, many people, including design and construction professionals, lack the necessary understanding of the wood properties of aerated concrete, especially in the application of traditional methods of construction to treat aerated concrete, without paying attention to the application of its characteristics Technology and supporting materials will inevitably have one or more problems such as cracks in the construction process.
Although the causes of cracks in buildings are complex, this involves the main factors such as drying shrinkage, improper construction, and improper design of blocks, but the drying shrinkage of blocks is often considered to be the main reason causing cracks in buildings.
Like other materials, aerated mantles dry shrink and absorb moisture to expand.
In the application of construction, if the drying shrinkage is too large, the stress formed by the shrinkage exceeds the tensile strength or bond strength of the product when there is restraint to prevent deformation, and cracks may occur at the product or the joint.
Therefore, the use of high-pressure steam curing of aerated concrete greatly reduces the shrinkage value of the products. Generally, there is no coarse aggregate in the aerated concrete. It cannot rely on aggregates to reduce shrinkage, as in ordinary concrete. Therefore, it must be adopted in the structure and construction. The measures, while carefully studying the drying shrinkage of aerated concrete and its impact on the application, to help the majority of design and construction personnel have a correct understanding of aerated concrete.
The experimental analysis was based on two types of aerated concrete commonly used in Guangdong Province (pulverized coal ash aerated concrete and lime sand aerated concrete, based on the special drying shrinkage rule studied and analyzed.
The shrinkage curves of fly ash aerated concrete and agglomerated aerated concrete obtained by the same test method are shown in Figure 1.
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Tushan eleven two = Qu ~ Gong Shi is called moisture content name research and discussion experiments show that dry sand shrinkage aerated concrete and fly ash aerated concrete drying shrinkage curve, has a completely different form curve The moisture content of fly ash aerated concrete is the curve of the shrinkage. The curve is the moisture content of aerated concrete. A rate of shrinkage. The abscissa is the change of water content. The vertical axis is the shrinkage value. Test value Standard test piece The shrinkage value from saturated moisture content to equilibrium moisture content The so-called equilibrium moisture content refers to the relative humidity of air relative humidity under the conditions. It refers to the balance measured by Hong Kong Datong Company in the past two years using Guangdong related aerated concrete block. Moisture content is a saturated water content curve of the curve. The saturated water content of the curve is the water content of the kettle on the curve day. The total dry shrinkage value of the curve of the dry shrinkage of the curve is approximately 1. Times.
o The moisture content of the sample in the water-saturated state is about the beginning. When the water content in the kettle state is about, the curve is steep, indicating that the contraction deformation is very significant. At this time, the contraction value of the sample is relatively flat, and the contraction deformation is relatively Smaller, at this time, the shrinkage value is the slope of the curve when the water content of the sample falls from the kettle. When the contraction deformation decreases, the moisture content of the sample decreases from 3, the curve hardly shrinks, and it shows a negative growth trend. That is, the slope of the curve does not shrink, but the slope of the curve remains basically unchanged, indicating that with the change in water content, the shrinkage deformation gradually decreases. When the moisture content of the test piece is increased from that of the sample to the equilibrium water content of the service, the curve A shows a negative growth, ie, the shrinkage deformation. When moisture decreases, Specimen A does not shrink but instead expands below the moisture content, the curve contraction begins to increase sharply until it is absolutely dry, and the contraction is completed and the curve decreases from the water content to the absolute value of 5 and then to the absolute state, the slope of the curve. Keep basically unchanged, shrink gently, until the completion of contraction can also be seen from the curve from the saturated state of water containing about 70 to the kettle state of the water content curve of the contraction value to the equilibrium moisture content, the total shrinkage value As for the shade, the line has completed its own drying shrinkage deformation from the state of full water to the state of the kettle. At this time, the shrinkage deformation of the curve is a self-discharging state in which only the completion of its own total drying shrinkage is reached to an equilibrium moisture content. The maximum shrinkage deformation value of the curve is a negative one-two growth, that is, the drying shrinkage of the raw material composition, or the change of the same raw material composition, is not only not shrinking but also has a slightly expansion curve to complete the total deformation of the test specimens with the reduced water content. Although the deformation is not consistent, the laws of contraction deformation of fly ash aerated concrete and aerated concrete with agglomerated sand, as shown in Fig. 1, are quite different. This is basically the same.
Conclusion It is easy to conclude from the above that the fly ash aerated pulverized coal has completed its own shrinkage and deformation before discharging the pot until it is in a balanced state of moisture. There is no need to worry about its shrinkage problem, because it not only does not shrink, but instead After the slightly expanded fly ash aerated concrete block is discharged from the kettle, even if it is put into use under high moisture content, there is no need to worry about the large shrinkage stress of the masonry due to drying shrinkage and the lime sand aerated concrete exits. Since the kettle is self-balanced in the watery state, it must also be completed in the dry shrinkage deformation, so be careful in construction applications that the change in the slope is too large and brings about an inherent hidden danger of construction. It must be reminded that we are paying attention to the application range. At the same time as the internal research, we must also pay attention to the sharp shrinkage characteristics of fly ash aerated concrete in high moisture state and the negative growth of drying shrinkage when the water content is lower than the following, even though its internal mechanism and its properties The impact is not yet clear, but the serious impact it may have on the application of the product is obvious.
Because the fly ash aerated concrete has a higher moisture content (dry shrinkage deformation before the product is out of the kettle is very sensitive, and is nearly four times higher than the lime sand aeration.
This means that if the fly ash aerated block is subjected to dry-wet cycling in an unexpectedly high water-absorbing condition, there is a high probability of destructive deformation, and an unexpected condi- tion with a high moisture content in Guangdong Province. Under the current operating conditions of the unit, it can be said that there are no rain-proof measures such as construction site blocks without rain, unconstructed construction water at the construction site, local water accumulation in the building due to a certain reason, so that the local moisture content of the masonry is too high, etc. It often causes fatal damage to the application of fly ash aerated concrete blocks.
In addition, in the case of unavoidable high moisture content outside the enthalpy, fly ash aerated water to shrink shrinkage up to about 1.
After attachment, the masonry does not shrink, but the agglomerate does not shrink, but the lime sand and aerated scum are only noisy. This means that the shrinkage deformation of the lime sand in the case of accidental high water content is much smaller than that of the fly ash. In the case of unexpectedly high moisture content, fly ash aerated masonry is more prone to cracks, which is the basic problem of fly ash refueling in the application site, and the total shrinkage deformation value of the lime sand refueling is far less than In addition, the slope of the curve is basically the same, and the shrinkage deformation speed is gentle so that no sharp shrinkage deformation occurs, so it is relatively easy to cause problems.
Therefore, the fly ash aerated block should be specially noted to avoid increasing the accidental water content in the construction process, and the lime sand aerated block can be slightly more relaxed. .
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