Common problems in the application of polycarboxylic acid admixtures
In the process of using polycarboxylic plasticity, there are sometimes encountered such issues, and some problems have not been met when using traditional water-reducing agents. For example, sometimes the factory slump, fluidity, and water retention are good, but two extreme phenomena occur after some time.
Either the concrete mixture becomes very dry, and the discharge is painful, or the bleeding is severe, the segregation, and the delamination is serious.
There are many reasons for the problems in the use of a polycarboxylic acid concrete plasticizer. On the one hand, the quality of the polycarboxylic acid water reducing agent is unstable, and the variety of synthetic raw materials causes large fluctuations in the product. The technical level, production process, and quality control methods of polycarboxylic acid water-reducing admixture manufacturing enterprises have not ensured the quality.
On the other hand, the fluctuation of concrete raw materials caused the adaptability change with polycarboxylic acid,
Please specify the following:
(1) cement. The chemical components of cement, the type of gypsum, grinding aids, the amount of active and inactive mixed materials, alkali content, fineness, and temperature during use will all affect the adaptability of polycarboxylic acid water reducers. Sometimes small changes can cause large changes in real properties. Therefore, it is not appropriate to replace cement frequently in actual production. Selecting cement with reliable quality and stable quality is a necessary prerequisite for concrete quality assurance.
(2) The mud content of coarse and fine aggregates has an important influence on the adaptability of polycarboxylic acid water reducer. As the mud content of aggregates continues to increase, the rheological properties of concrete will be doubled, resulting in concrete mixing. Material quality control is challenging.
(3) Loss of ignition and fineness of the admixture (mineral powder, fly ash) also affect the adaptability of the polycarboxylic acid water reducing agent. When the amount of burning loss is large, the polycarboxylic acid polycarboxylate superplasticizers will be adsorbed, causing The slump loss of the concrete mixture is fast.
Precautions when using polycarboxylic acid superplasticizer admixture
(1) Reasonable control of water consumption
Polycarboxylic acid superplasticizers are very sensitive to water consumption, especially when using superplasticizers with high solid content. During the trial and production process, it was found that sometimes the water consumption increased slightly by 1kg ~ 3kg, and the concrete mixture would have severe bleeding, piled up exposed stones, and seized the bottom. Therefore, in the production process, on the one hand, the water consumption of a single party is strictly controlled, and the moisture content of the sand and gravel is accurately calculated. The newly washed sand should be left for some time and used when the moisture content is relatively stable. On the other hand, low solid content polycarboxylic acid water reducing agent is used to reduce sensitivity.
(2) Use a reasonable amount of polycarboxylic acid
The appropriate dosage is determined through tests during use. When the dosage is low, the concrete's slump retention is poor, the slump loss is fast, and the fluidity becomes poor. When the dosage is too large, the concrete mixture is likely to cause serious bleeding, segregation, Take the bottom. Before production, you should test the optimal cut-in point of the water consumption of concrete and the amount of polycarboxylic acid plasticizer and superplasticizer agent, that is, the optimal amount of water and admixture. At the same time, pay attention to mastering the fluctuation of raw materials and mixing of a polycarboxylic acid agent. The impact of the amount. The raw materials used in the project should be used in the test to facilitate production control. If necessary, the site construction conditions should e simulated according to the construction requirements.
(3) Dare to break the traditional thinking mode
When formulating high-strength grades, we strive to overcome the problem of using more cement and fewer mineral admixtures. We believe that this is safe, and the strength will be higher. Otherwise, the amount of cement tends to be thick, and the strength of the concrete develops quickly in the early stage, and the growth in the later period is slow or even not. Sometimes adding 30kg of cement is about the same strength as concrete without adding cement, and sometimes it is better not to add it. Properly increasing the amount of mineral admixture will increase the strength of concrete by 5% to 10%, and the strong increase in the later period is also satisfactory. It will help reduce hydration heat, prevent cracks, and improve durability.
(4) Naphthalene-based admixtures are strictly prohibited
Companies using both naphthalene-based superplasticizers and polycarboxylic acid-based superplasticizers, if conditions permit, are best used in separate stations. If the same unit has both polycarboxylic acid and naphthalene-based, when used alternately, The admixture weighing container, pipeline and mixer are thoroughly cleaned, and the concrete tanker should also be cleaned and refilled. It is strictly forbidden to mix naphthalene-based superplasticizer and polycarboxylic acid superplasticizer, especially at the construction site, when the method of "adding admixtures" is needed to adjust the workability of the concrete mixture, the concrete inside the vehicle must be clarified. The types of admixtures used can avoid the "rapid setting" of concrete caused by a mixing, which will cause the vehicle concrete to be scrapped.
(5) Strengthen inspection
When the polycarboxylic acid water reducing agent is received, first check the various technical indicators of the water reducing agent to ensure the stability of quality. Secondly, the raw materials used should be selected, and the production mix ratio should be used for testing. If problems are found, the technical staff of the admixture production enterprise should be adjusted in time.
(6) Timely communication with the construction unit
Before concrete production, the construction party should be informed of the technical requirements of the concrete.
The transportation distance, the construction process, and the temperature of the day, and if necessary, go to the work site for a site inspection to understand the concrete pumping method, whether the pipeline routing is reasonable, and the distribution of the steel bars.
The staffing and construction team quality of the construction unit shall be reasonably allocated, and the vehicles shall be dispatched according to the actual situation.
(7) Familiar with the characteristics of the polycarboxylic acid plasticizer and superplasticizer used
Through experiments, the change rules of polycarboxylic acid water-reducing agents in concrete trial production-production-construction are summarized, which is convenient for dealing with emergencies. Explore these laws in test and production practice, accumulate experience, and promptly propose reasonable solutions in case of sudden changes in the solid-state, to avoid causing higher losses, and achieve "timely, scientific, and reasonable."
Polycarboxylic acid water reducing will be used in both foamed cement and ordinary cement concrete. If the superplasticizer is used correctly, it will play a role in enhancing plasticity in cement. Be sure to control the method and amount of polycarboxylate superplasticizer strictly.So that the effect of small amounts and significant impact.
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