some problems in the application of polycarboxylate superplasticizerii
Dosage and water consumption of polycarboxylate superplasticizer:
Polycarboxylic acid high-efficiency water reducing agent is characterized by low dosage and high water reducing rate. When the dosage is 0.15-0.3%, the water reduction rate can reach 18-40%. However, when the water-cement ratio is small (lower than 0.4), the dosage is more sensitive than when the water-cement ratio is high. The water reduction rate of polycarboxylic acid water reducing agent varies with the dosage of cementitious material. Under the same conditions, the water reduction rate of cementitious material dosage less than 3 is less than 400kg/m3, and this difference is easily ignored. However, in the process of use, it will be found that this traditional empirical method is not suitable for polycarboxylic acid water reducing agent, mainly because polycarboxylic acid water reducing agent is more sensitive to water consumption than traditional water reducing agent.When the water consumption is reduced, the concrete will not be able to achieve the expected compatibility; when the water consumption is high, although the slump becomes larger, there will be a lot of water seepage, or even a little segregation, which will have a negative impact on the overall performance of the concrete. This will bring a lot of inconvenience to the actual site construction. Temperature has a great influence on the dosage of polycarboxylic acid water reducing agent. In practice, it is found that the dosage of admixture is low during the daytime in normal production, and at night (the temperature is lower than 15℃), the slump is often “back to large”, and even water seepage and segregation.
Concrete is very picky about the saturation point and water consumption of water reducing agents. Once the amount is exceeded, the concrete will have the undesirable phenomena such as segregation, water seepage, running slurry, hardening and excessive air content.
(1) The replaced raw materials should be re-tested for trial mixing test and adjust the dosage to achieve the best effect;
(2) The dosage of polycarboxylic acid high-efficiency water reducing agent and the water consumption of concrete must be strictly controlled during the use;
(3) In the specific test of raw material water reducing agent, try to adjust the water reducing agent to “slow” type, in order to achieve the purpose of insensitive to raw materials and water consumption.