Summary of application pain points of gypsum mortar retarder
1. Retarder gypsum has poor adaptability: It has a good retarding effect on some gypsum, but a poor retarding effect on some gypsum. If the dosage is increased several times, the retarding effect on different batches of gypsum will vary greatly.
2. Dosage of retarder is too sensitive: When the dosage is low, the retarding effect is very poor, but when the dosage is increased appropriately, the retarding effect is too good. As a result, the setting time is too long and the dosage range that meets the ideal setting time is too narrow.
3. Alkali resistance of the retarder is relatively poor: After adding cement or gray calcium, the setting time is too short and the dosage is increased. The setting time does not change much.
4. Ineffective setting time of the retarder is too long: Interval from loss of operability to setting is too long, bringing more risks of plastic cracking. Even if the coagulation time tested is very long, the operable time is too short, and the coagulation time is not of great significance.
The setting time problem of gypsum-based self-leveling
The phosphogypsum setting time is sensitive to alkali content. Under alkaline conditions, the residual phosphate in phosphogypsum has a strong retarding effect. It will cause long-term non-condensation and slow strength development. Whether it is washed with water and the final residual phosphate content are very important.
Particularity of self-leveling requires the addition of cement or gray calcium in most formulas. For phosphogypsum, more attention is paid to whether the setting time is too long. Setting time of gypsum provided by the phosphogypsum manufacturer is of little significance for self-leveling of gypsum.
Mixing partially desulfurized gypsum into the raw material before calcining phosphogypsum is very effective in solving the self-leveling setting time of phosphogypsum.
For the selection of retarder in phosphogypsum self-leveling:
1) Active substance content does not need to be too high: avoid too low dosage.
2) A type that can condense even if it is over-mixed: Try not to choose a retarder that does not condense for 24 hours after being over-mixed. And it needs to have good alkali resistance.
3) Setting time changes linearly with the dosage of gypsum retarder: avoid the setting time being too long or too short.
4) Good adaptability: A retarder with good overall applicability to different types of gypsum.
Summary of setting time issues of gypsum-based mortar
Operable time is a more important indicator than setting time.
For different cementitious material systems, an appropriate compound retardant system is effective in adjusting the operable time.
Desulfurization gypsum is more concerned about the problem of too short setting time.
Phosphogypsum is more concerned about whether the setting time is too long.
Gypsum-mixed systems pay more attention to system stability.
Pay attention to the differences in coagulation time and thickening loss of systems with different alkali contents.
Focus on the influence of the thickness and bulk density of gypsum on setting time and stirring and dispersion.
Pay attention to the effect of water reducing agent on setting time.
HPMC produced by Landcel is used for gypsum addition. It can effectively alleviate various problems in gypsum construction. Improve construction results and reduce later problems.