Foam concrete is the foaming agent fully foamed by mechanical means through the foaming system of the foaming machine, and the foam is evenly mixed with cement slurry.Then through the foaming machine pumping system for cast-in-place construction or mold forming, through the natural conservation formed by a large number of closed pores of a new type of lightweight insulation materials.As a new type of energy-saving and environment-friendly building material, domestic and foreign scholars have done a lot of research and development on it, making it widely used in wall materials.Advantages: small density, light weight, thermal insulation, sound insulation, seismic performance.
1 Foam Foam production commonly known as "foaming", the specification is "foam", the main equipment is the foaming machine.
1.1 Foam making process.Foaming process is to add water to dilute the high solubility of foaming agent 20 to 30 times, become foaming agent diluent, and then pump into the foaming machine, through the action of high pressure air, forming foam.
1.2 Foam quality control.After the variety and quality of foaming agent have been determined by testing, the quality control of foam does not need to be determined by the testing of foamed concrete, only through the determination of the foam meter in the field can control its quality.Foam quality control items are mainly its stability and moisture content.Both of them can be measured by controlling the bleeding water and settling distance respectively.
(1) Settlement distance: it mainly represents the stability of the foam. After the bubble bursts, it will cause the reduction of foam volume and cause the settlement.By measuring its settling distance, its stability can be known.The foam settlement distance of the wall shall not exceed 90mm within 1h.
(2) Bleeding rate: it mainly represents the moisture content of foam.The greater the water content of the foam, the greater the bleeding.The greater the water content, the worse the quality of the foam, which means that the number of bubbles in the foam decreases while the water content increases.Foam water more, will lead to the porosity of foam concrete reduced, and increase the capillary, foam concrete water absorption and thermal conductivity increased, affecting its usability, the wall reflects pouring, requiring its 1h bleeding rate less than 90%.
(3) Bubble diameter: the bubble diameter in the wall embodiment foam is mostly 1~2mm, a small number of 2~3mm and 0.5~1mm, too large bubble diameter (greater than 3mm) is not qualified, if 60% of the bubble diameter is less than 0.5mm, also considered unqualified.
1.3 Control factors of quality foam
Making high quality foam, not just foaming agent to decide, foaming machine, dilution water, environmental temperature and so on have an impact.Therefore, to obtain high-quality foam should be from the following aspects of comprehensive, comprehensive quality control.
(1) Control of foaming agent.Foaming agent has influence on settlement distance, bleeding rate and bubble diameter, but it has the biggest influence on settlement distance.High quality foaming agent made of foam, in the case of ensuring high foaming multiple, bleeding rate is also small.In addition, different foaming agent although using the same foaming machine its bubble diameter is also different.Generally speaking, the high viscosity of the foam agent produced by the finer.Foaming agent due to the variety of surfactant, foam diameter is also different, some surfactant produced foam is very dense, and some is not fine.
Therefore, the selection of suitable foaming agent is very important.Current, the foaming agent breed on the market is numerous, should judge its actor bad through all sorts of detect, and not be by feeling by instruction book.
(2) Control of foaming machine.The foaming machine has the biggest influence on bleeding rate, bubble diameter and foaming multiple, and has a small influence on settlement distance.Foaming times do not belong to the quality of foam, but the quality of foaming agent, which is not discussed here.Foaming machine air compressor pressure has an optimal interval value, the pressure is too large, the bubble wall is too thin, the settlement distance is larger.And the pressure is too small, can not produce foam, or foam machine production decline.Different foaming machines have different optimum pressure ranges.
(3) Water control.Different hardness of water has different influence on the stability of foam.Of course some foaming agents are resistant to hard water with little or no effect.But the impact of water can't be ignored.
The foam quality varies with the pretreatment of water.Some pretreatment, will improve the stability of foam, reduce bleeding rate.Some pretreatments will increase the amount of foam and foam multiple, but it is not conducive to the stability of foam.
(4) Temperature control.Different temperature will have different effect on foam quality.In general, high temperature will increase the output of foam, but the foam wall becomes thinner and the foam stability is not good.Low temperature, not easy foaming, foam moisture content increased, but better stability.In the summer foam machine should not be in the hot sun operation, so as to avoid excessive temperature and affect the quality of foam.In winter, should be in the heating conditions of foaming, or the use of hot water to dilute foaming agent, in order to improve the foaming effect.
2. Make foam concrete slurry
This process mixes the foam with the cement slurry to form a foamed concrete slurry that can finally be poured into the wall cavity.
(1) Mixing process.There are two kinds of mixing process: batch mixing and continuous mixing.At present, each enterprise generally USES is the continuous mixing bubble, although the intermittent mixing bubble has the application, but few.In the early stage of the development of foamed concrete, batch mixing is a widely used process. The process is to produce foam and cement slurry first, and then add both into the vane type foam mixing machine and mix them into foamed concrete slurry.This method is more suitable for the production of products, for cast-in-situ due to low efficiency, not suitable for on-site operation.
(2) Continuous mixing is to send the foam and cement slurry into a static mixer at the same time, and make the foam cement slurry quickly through static mixing without power.The static mixer is commonly known as the foam mixing cylinder. It is a high-pressure steel cylinder with a diameter of 1000mm ~2000mm. A static mixing piece is installed in the middle.
(3) Quality control of mixed foam.The quality of foam is mainly reflected in two aspects: uniformity of foam cement slurry, namely uniformity, and density control of foam cement slurry.The slurry should have a high degree of uniformity, and its appearance is bright and smooth, with elastic hand pressure, no foam floating, and no visual phenomenon of uneven mixing.
The slurry density shall meet the design requirements, and the difference in wet density shall not be more than 5%, without fluctuation and instability.At present, a prominent problem of cast-in-place is the density fluctuation, which causes the quality instability.And the reason for that is that when you mix it up, the amount of foam goes up and down, and how you control the density is a key issue.
(4) Main factors controlling the optimization of foamed cement slurry:
a. Uniformity control factor.The controlling factors of foam cement slurry uniformity are mainly whether the design parameters of the static mixer are reasonable, especially its length, the number, Angle and arrangement method of the internal mixing pieces.These parameters have an optimal match. If the match is not reasonable, the slurry will be uneven.Different manufacturers have different designs, the core is to be able to achieve the rationality, whether the design before the test optimization.
b. Density control factors.The controlling factor of foam cement slurry density is the ratio of foam to cement slurry entering the static mixer, that is, whether the ratio of foam to cement slurry is reasonable and accurate.The bigger the ratio, the lighter the slurry.If the ratio of the two is not precisely controlled, the density will fluctuate.The key factor is whether the equipment is involved in the installation of foam and slurry control mechanism, and the degree of automation of this mechanism.At present, some equipment is not installed on the control mechanism, density is not easy to control.
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