Influence of Cement Foaming Agent on Foam Concrete(1)
Commodity prices are on track for their biggest rally in more than a century, while fixed-income assets have seen their longest run of outflows as the war in Ukraine adds to inflationary pressures in the global economy emerging from the coronavirus lockdown, according to Bank of America.
"Commodity prices this year are on track to record their biggest gains since 1915." the bank said in its weekly briefing. They cite many factors, such as pandemics, lockdown, civil strife, wars, excessive monetary and fiscal stimulus, and supply chain disruptions, that have led to "historically" high inflation.
By the same token, it said government bonds were heading for their worst year since 1949, and "negative-yielding bonds will quietly disappear" from the market as central banks embark on a monetary tightening cycle and raise interest rates to tame soaring inflation.
The prices of many commodities like the concrete foaming agent are expected to increase in the future.
The cement foaming agent is the key to the quality of foamed concrete. A good cement foaming agent can be made into high-quality foamed concrete. The following is a talk about how each performance index of cement foaming agent affects the quality of foamed concrete.
1. The more uniform the better, the bubble diameter should be the same size
The more narrow the ideal pore size distribution the better, that is, the pore size of the pore is as consistent as possible, the difference is not too big. The corresponding requirements of the foam should be uniform, not different sizes. The bubble diameter of the foam cannot be the same but should be similar, the bubble diameter range as small as possible, and the difference between the maximum and minimum bubble diameter is not too big. It is required that the pores formed by the foam be uniform, which can avoid the concentration of compressive stress in the bullae and reduce the compressive strength. If the size of the foam is not uniform, the stress is concentrated in the bullae, which is very easy to cause it to become a weak link and crack first when under pressure.
2. The higher the foam stability, the better; the longer the stable bubble time, the better
Foam with good stability has tough liquid film and good mechanical strength, which is not easy to burst or excessive deformation under slurry extrusion. In addition, it has self-retaining water, the water on the liquid film is not easy to be lost under the action of gravity and surface tension, and can keep the thickness and integrity of the foam liquid film for a long time so that the foam can stay for a long time without bursting.
The stability of foam has three influences on the porosity: it can make most of the foam not disappear, and it is fixed in the foam concrete after the initial setting of the slurry to form the porosity. If the foam stability is not good, most or a small part of the foam will burst after pouring, forming few pores, and even make the slurry collapse soon after pouring, which is commonly known as collapse mold, resulting in complete failure of pouring.
Foam with good stability, the slurry is not easy to be deformed too much under extrusion, and has certain pressure resistance to keep itself approximately spherical, which can eventually form spherical pores with good shape;
Foam with good stability, the liquid film is not easy to burst in the slurry body, and it is not easy to form connected holes formed by gas collusion after bursting. Therefore, it eventually forms an ideal closed hole. The less stable the foam, the fewer closed holes, and the more connected holes. Therefore, the stability of foam should not only not collapse after pouring as the standard, but should not collapse after pouring, the final formation of pores approximately spherical, disconnected three indicators as the standard. Most people take no collapse after pouring as the standard to measure foam stability, which is a misunderstanding in understanding and the lowest standard of foam stability.
When there is no standard measuring instrument to measure the foam stability, the foam stability time can be used to measure the foam stability. The foam stabilization time should meet the initial setting needs of the cementitious materials used. After the initial coagulation of the slurry, it can fix the foam, retain the shape of the foam, and make it into an st.
As we know, any cementing material, including cement and magnesite, has an initial setting time, especially the most widely used ordinary Portland cement, the initial setting is mostly later than 45min. If the foam stability is poor, cement and other cementing materials have not set, the foam has burst, then the foam cannot form pores in concrete. In general, the minimum requirement for foam stability is to make the foam stability time longer than the initial setting time of the gelled material of 10 ~ 20min. As the initial setting time of various cementitious materials is not consistent, the foam stability time is also different. In general, the foam stability time for fast gel setting materials can be shorter, while the foam stability time for slow gel setting materials should be as long as possible. Even if the same cementitious material, temperature ma is different, its initial setting time is different, the change is quite big. For example, put Si cement needs 40min to set in summer, and in the winter of 5℃ below, 80min will not set in the beginning. Therefore, the stabilization time of bubbles cannot have a constant specific standard, should be determined according to the situation. To make the foam adapt to the needs of various use conditions, it should be stabilized for as long as possible.
Generally speaking, the stabilization time of bubbles should meet the following requirements:
1. When used in Portland cement and without coagulant, the stability time should be greater than 60min; The ideal maximum is greater than 3h;
2. When used in sulphoaluminate cement, high alumina cement, ferric aluminate cement, fast setting Portland cement, and other fast setting cement, the stability time should be greater than 30min, preferably greater than 60min;
3. When used in magnesium cement, the foam stability time should be greater than 40min and preferably greater than 80min;
4. When used for cementitious materials mixed with a large amount of filler or active waste slag such as fly ash, the foam stability time should be extended. The larger the amount of filler or active waste residue is, the longer the foam stabilization time should be.
The specific bubble stability time should be determined by a small test, so as to not collapse after pouring, not connected after the formation of pores, and not excessive deformation as the principle. The big rule is that the longer the bubble, the better.
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