We know that 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 45 minutes. If the foam stability is poor, cement and other cementitious materials have not initially set, and the foam produced by the cellular lightweight concrete foaming agent has burst, then the foam cannot form pores in the concrete. In general, the minimum requirement for foam stability of cellular lightweight concrete foaming agent is to make the foam stabilization time longer than the initial setting time of the gelling material by 10-20 minutes. Since the initial setting time of various gelling materials is inconsistent, the requirements for foam stabilization time are also different. In general, for foams with fast gelling materials, the stabilization time can be shorter, and for foams with slow gelling materials, the stabilization time should be as long as possible. Even if the same kind of cementing material has different temperatures, its initial setting time is different, and the changes are quite large. For example, ordinary Portland cement may initially set in less than 40 minutes in summer, while it will not set in 80 minutes in cold winter below 5°C. Therefore, the stabilization time of cellular lightweight concrete foaming agent foam cannot have a constant specific standard, which should be determined according to the situation. In order to make the cellular lightweight concrete foaming agent foam suitable for various use conditions, it should be stabilized for as long as possible.
The stability time of cellular lightweight concrete foaming agent should meet the following requirements:
(1) When used in Portland cement and no accelerator is added, the stabilization time should be greater than 60min; ideally, the maximum is 3h;
(2) When used for fast-setting cement such as sulfoaluminate cement, high-alumina cement, ferro-aluminate cement, fast-setting Portland cement, etc., the stabilization time should be greater than 30 minutes, preferably greater than 60 minutes;
(3) When used in magnesium cement, the foam stabilization time should be greater than 40 minutes, preferably greater than 80 minutes;
(4) When used for cementitious materials mixed with a large amount of fillers or active waste residues such as fly ash, the stabilization time should be extended. The greater the amount of filler or active waste slag, the longer the stabilization time should be.
The specific cellular lightweight concrete foaming agent stabilization time should be determined by small tests, based on the principle that the mold does not collapse after pouring, the pores are not connected after they are formed, and they are not excessively deformed.
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