(4) Improper use of retarder when compounding Polycarboxylate Superplasticizer

In order to obtain good slump retention performance of concrete, a certain amount of retarding component is often added when compounding Polycarboxylate Superplasticizer. If the amount of retarding component is too large, or when the compounded Polycarboxylate Superplasticizer encounters a sudden drop in temperature when the temperature is good, the excessive retarding component will slow down the cement hydration and cause concrete water seepage. When using retarders for slump reduction, attention should be paid to the effect of the retarding component on the water seepage of concrete. For retarders or slow-release Polycarboxylate Superplasticizer mother liquors that are prone to water seepage, an appropriate amount of water-retaining and thickening components can be compounded to reduce the probability of concrete water seepage. When compounding Polycarboxylate Superplasticizer, attention should be paid to the compatibility of cement and water-reducing agent. It should be avoided that when the dosage is low, the water reduction rate and slump reduction performance are not obvious. Once the water-reducing agent dosage is added and the slump meets the requirements, the mixture begins to bleed again. At this time, it is necessary to add a certain amount of water-retaining and thickening components.

(5) Compatibility of cement and Polycarboxylate Superplasticizer

Concrete components are complex and there are uncoordinated chemical changes between the components. In particular, the compatibility problem between cement and Polycarboxylate Superplasticizer is particularly prominent. If the compatibility of cement and Polycarboxylate Superplasticizer is poor, the saturated dosage of water-reducing agent will be increased. The excess water-reducing agent will prolong the initial setting time of concrete and cause the free water in the concrete to precipitate. In addition, when the soluble alkali in cement is low, the cement hydration rate slows down and bleeding often occurs. When the CA content or activity in cement decreases, the cement hydration rate tends to decrease, thereby increasing the occurrence of bleeding in concrete mixtures.

(6) Fluctuation in the quality of coarse and fine aggregates

In the concrete production process, the quality of sand and gravel aggregates often fluctuates, such as the mud content increases or decreases, the water content fluctuates, and the aggregate grading changes, the sand fineness modulus changes, etc., which may increase the possibility of concrete bleeding. For example, if the fineness modulus of fine aggregate increases, the water consumption decreases, the aggregate particle size increases, and the mud content decreases, resulting in a decrease in the number of adsorbent admixtures, all of which can cause bleeding in concrete mixtures. Therefore, process control should be strengthened during concrete production to reduce the probability of concrete bleeding. In addition, it should be avoided that the machine-made sand contains flocculants. Sudden changes in the flocculants often cause bleeding or excessive slump loss, and attention should be paid to observation during production.