Before determining the amount of gypsum retarder, it is necessary to test the raw gypsum powder purchased. For example, test the initial and final setting time of gypsum powder, standard water consumption (that is, standard consistency), and flexural compressive strength. If possible, it is best to test the content of II water, semi-water and anhydrous gypsum in gypsum powder. First measure the indicators of gypsum powder accurately, and then determine the amount of gypsum retarder according to the length of initial setting time of gypsum powder, the proportion of gypsum powder in the required gypsum mortar and the operation time required for gypsum mortar .
The amount of gypsum retarder has a lot to do with gypsum powder: if the initial setting time of gypsum powder is short, the amount of retarder should be larger; if the initial setting time of gypsum powder is long, the amount of retarder should be less. If the proportion of gypsum powder in the gypsum mortar is large, more retarder should be added, and if the proportion of gypsum powder is small, the proportion of gypsum powder should be less. If the operation time required for gypsum mortar is long, more retarder should be added, otherwise, if the operation time required for gypsum mortar is short, less retarder should be added. If the operation time is too long after the gypsum mortar is added with retarder, it is necessary to reduce the amount of gypsum retarder. If the operation time is short, the amount of retarder should be increased. It is not to say that the addition of gypsum retarder is static.
After the gypsum enters the factory, multiple samples must be taken to test its various indicators. It is best to sample and test every few days, because with the storage time of gypsum powder, its various indicators are also changing. The most obvious thing is that after the gypsum powder is aged for an appropriate time, its initial and final setting time will also be prolonged. At this time, the amount of gypsum retarder will also be reduced, otherwise the operating time of gypsum mortar will be greatly extended and increase. It reduces production costs while affecting its workability and ultimate strength.
For example, if you buy a batch of phosphogypsum, the initial setting time is 5-6 minutes, and the production of heavy gypsum mortar is as follows:
Gypsum powder – 300 kg
Washed sand — 650 kg
Talc powder – 50 kg
Gypsum retarder — 0.8 kg
HPMC — 1.5 kg
At the beginning of production, 0.8 kg of gypsum retarder was added, and the operation time of gypsum mortar was 60-70 minutes. Later, due to reasons on the construction site, the construction site was shut down and production stopped, and this batch of gypsum powder has been stored for no use. When the construction site restarted in September, the addition of 0.8 kg of retarder was still added when the gypsum mortar was produced again. The mortar was not tested at the factory, and it still did not solidify 24 hours after it was sent to the construction site. The construction site reacted strongly. Since the manufacturer entered this industry not long ago, he couldn’t find the reason, and was very anxious. At this time, I was invited to go to the gypsum mortar manufacturer to find out the reason. After going to the first step, the initial setting time of the gypsum powder was tested, and it was found that the initial setting time of the gypsum powder was extended from the original initial setting time of 5-6 minutes to more than 20 minutes, and the amount of gypsum retarder was not reduced. , so the above phenomenon occurs. After adjustment, the dosage of gypsum retarder was reduced to 0.2 kg, and the operation time of gypsum mortar was shortened to 60-70 minutes, which satisfied the construction site.
In addition, the ratio of various additives in gypsum mortar must be reasonable. For example, the operation time of gypsum mortar is 70 minutes, and a proper amount of gypsum retarder is added. Accurately, if less gypsum mortar is added, the water retention rate is low, and the water retention time is less than 70 minutes, which causes the surface of the gypsum mortar to lose water too quickly, the surface is dry, and the shrinkage of the gypsum mortar is inconsistent. At this time, the gypsum mortar will lose water. cracking.
Two gypsum plaster formulation are recommended below:
1. heavy gypsum plaster mortar formula
Gypsum powder (initial setting time 5-6 minutes) – 300 kg
Washed sand – 650 kg
Talc powder – 50 kg
Gypsum retarder – 0.8 kg
Cellulose ether HPMC (80,000-100,000 cps)—1.5kg
Thixotropic lubricant – 0.5 kg
The operating time is 60-70 minutes, the water retention rate is 96%, and the national standard water retention rate is 75%
2 .lightweight gypsum plaster mortar formula
Gypsum powder (initial setting time 5-6 minutes) — 850 kg
Washed sand – 100 kg
Talc powder – 50 kg
Gypsum retarder – 1.5 kg
Cellulose ether HPMC (40,000-60,000)—2.5 kg
Thixotropic lubricant – 1 kg
Vitrified beads – 1 cubic
Post time: Dec-08-2022