(1) excessive use of Polycarboxylate superplasticizer
Polycarboxylic acid water reducing agent has the characteristics of high water reducing rate and low content (folding solid 0.20% or so), and can obviously improve the concrete slump. But the mixing amount is too large, the water reduction rate is high (close to the limit mixing amount, the water reduction rate is more than 40%), the dispersion ability is too strong, will significantly reduce the concrete cohesion, so that more free water is released, increase the possibility of concrete bleeding water. Especially the use of slow release slump protection type polycarboxylic acid water reducer, the dosage is too large easy to cause concrete lag bleed serious, resulting in segregation. Therefore, the use of polycarboxylic acid superplasticizer, should be advanced when the test, observation of concrete state changes.
(2) Polycarboxylate superplasticizer is sensitive to ambient temperature and has a slow release
Compared with other water - reducing agents, the water - reducing and slump - preserving properties of polycarboxylic acid water - reducing agent are greatly affected by temperature. When the temperature is high in summer, the slump of polycarboxylic acid superplasticizer with good slump protection performance may occur when the temperature suddenly drops. Therefore, when the temperature suddenly decreased when the use of polycarboxylic acid superplasticizer, should be the first of the original polycarboxylic acid superplasticizer test, production of appropriate extension of mixing time, the polycarboxylic acid superplasticizer fully dispersed release, so as to avoid later due to slow release and play a role, resulting in poor concrete water retention, water precipitation.
