What factors influence polycarboxylate superplasticizers?
Release Time:
2016-08-05
Source:
What factors influence polycarboxylate superplasticizers?
Polycarboxylate superplasticizer The incoming inspection data show a significant discrepancy with actual production conditions: under the same admixture dosage, the water requirement for producing concrete is approximately 20 kg higher than that indicated by the incoming inspection. Moreover, the slump loss of the concrete mix accelerates markedly. The primary reasons are the large batch sizes in production and the elevated temperature of the cementitious materials in the powder silos—often exceeding 80°C in summer. Higher material temperatures lead to increased adsorption of the polycarboxylate superplasticizer, thereby reducing its water-reducing effectiveness. In addition, the high discharge temperature of the concrete further accelerates slump loss. Therefore, during incoming inspection of polycarboxylate-based pumping admixtures, the water content can be controlled at 150–155 kg/m³, with the fresh concrete slump reaching 210 mm or more.
If the pumping admixture is not from the same batch, differences in the water-reducing effectiveness of the raw materials can cause the water-reduction rate to increase or decrease at the same dosage. In actual production, if there are no significant changes in other raw materials and the water content remains constant, but the resulting concrete mix becomes too dry, this indicates that the water-reducing rate of the pumping admixture has decreased; the dosage of the admixture should be increased immediately. Conversely, if the concrete mix becomes too fluid, this indicates that the water-reducing rate has increased, and the dosage of the admixture should be reduced immediately. The specific amount of increase or decrease should be determined based on the difference between the slump of the concrete mix and the required discharge slump: for every 20 mm difference in slump, the admixture dosage should be adjusted by ±0.1%.
The setting time of concrete pumping admixtures varies with ambient temperature. The admixture dosage is formulated based on the recent average ambient temperature. When there is a sudden change in ambient temperature, failure to promptly adjust the pumping admixture dosage can lead to delayed setting of the concrete. This is particularly common in late autumn and early spring, when windy and cooling weather frequently occurs. Upon receiving a forecast of such conditions, the concrete mix design should be adjusted 12 hours in advance by upgrading the mix grade, reducing the pumping admixture dosage by 25% (relative to the original dosage), and increasing the water content by 15–20 kg. These measures help prevent delayed setting of the concrete.
