Precautions for the Use of Polycarboxylate Superplasticizer
Release Time:
2016-08-03
Source:
Precautions for the Use of Polycarboxylate Superplasticizer
Polycarboxylate superplasticizer The performance of polycarboxylate-based pumping admixtures is highly sensitive to the silt content of aggregates; excessive silt can significantly degrade the admixture’s effectiveness, as silt particles adsorb a portion of the admixture, leading to a marked reduction in its water-reducing efficiency. Therefore, when using polycarboxylate pumping admixtures, it is essential to rigorously control aggregate quality. If the silt content of the aggregates increases, the dosage of the polycarboxylate pumping admixture should be increased accordingly. During visual inspection of incoming sand and gravel, careful attention should be paid to any obvious differences in silt content; if such differences are detected, samples must be promptly taken for testing. If the silt content exceeds the previous batch by more than 1%, the newly delivered material must be stored separately and the mix proportions adjusted before use. Otherwise, the slump of the concrete at the plant may fluctuate unpredictably—sometimes too high, sometimes too low—and upon arrival at the job site, the concrete mix may lose slump excessively fast or exhibit severe segregation, potentially even causing blockages in the pumping lines, thereby creating significant operational difficulties for the client.
Polycarboxylate-based pumping admixtures must not be mixed with naphthalene-based water-reducing agents. When using polycarboxylate pumping admixtures, mixing equipment and concrete mixer trucks that have previously been used with naphthalene-based water-reducing agents must be thoroughly cleaned; otherwise, the polycarboxylate pumping admixture may experience reduced water-reducing efficiency and a significant decrease in concrete strength. The compatibility of polycarboxylate pumping admixtures with other types of pumping admixtures shall be determined through testing.
Polycarboxylate-based pumping admixtures should be kept away from prolonged contact with ferrous materials. Because these admixtures are typically acidic, long-term contact with iron can lead to a slow chemical reaction, potentially causing discoloration—darkening or blackening—and resulting in a decline in product performance. It is recommended to store the admixture in polyethylene plastic drums or stainless steel drums to ensure its performance stability.
For concrete with a strength grade of C45 and above, a high-performance, specialized polycarboxylate-based pumping admixture shall be used. If a conventional polycarboxylate pumping admixture is employed instead, the concrete mix will become excessively viscous, making it difficult to pump. When conducting mix-design trials for concrete of C50 grade and higher, the test for the backflow time of the fresh concrete in the slump cone may be extended (i.e., place the slump cone with its wider opening facing upward on a steel plate, fill it completely with concrete, compact and level the surface, then start the stopwatch as soon as the slump cone is lifted); the backflow time should not exceed 20 seconds. Otherwise, pumping difficulties are likely to occur.
