Study On Molecular Structure And Slump Retention Mechanism Of Polycarboxylate Superplasticizer

The dispersion of polycarboxylate superplasticizer for cement was based on their molecular structure, study on the relationship between the molecular structure of polycarboxylate superplasticizer and the water-reducing effect. Use HPA to modified the polycarboxylate superplasticizer and evaluate the dispersion capacity, the dispersion retention capacity and rheological properties of the slurry system of the modified polycarboxylate superplasticizer. then study on the slump retention mechanism of the ester modified polycarboxylate superplasticizer on based of the above study. The main contents and results, including the following aspects:1.The carboxyl density is the most important factor that affect the the superplasticizer’s initial dispersion capacity, the higher the concentration of carboxyl groups, the higher the initial dispersion properties, when the carboxyl density value is greater than7:1the initial dispersion properties will have no significant change. Carboxyl density increases cause the volume of superplasticizer molecules increase, then the molecular weight of the water reducer that manifested become larger.2.Chain transfer agent dosage is the most important factor that affect the polycarboxylate superplasticizer molecular weight and molecular weight distribution, the chain transfer agent dosage is inversely proportional to the molecular weight of polycarboxylate superplasticizer, and the reciprocal of the dosage of chain transfer existence of a third relationship between the molecular weight of the carboxylic acid water reducing agent. Superplasticizer molecular weight affect the water reducing agent dispersion capacity and its dispersion rentention performance, As the gradual increase of the molecular weight of the superplasticizer, the initial dispersion properties first increase and then decrease.3.Temperature and the dosage of the initiator mainly affect the monomer conversion rate of the polycarboxylate superplasticizer, when the temperature is low than65℃or the amount of initiator is less than1%the monomer conversion rate will be very low, the dispersion and the dispersion retention will be very low. High temperature conditions will lead the polycarboxylate superplasticizer molecular weight slightly decrease, caused by excessive dosage of SO42-introduced by the initiator the dispersion properties of polycarboxylate superplasticizer will decrease.4.HPA modified polycarboxylate superplasticizer can achieve the purpose to maintain the concrete slump, the hydrolysis of water-reducing agent in the slurry model system is a typical first order reaction. Compared to the retarding agent, the release function of the HPA modified polycarboxylate superplasticizer does not lead the hydration of the cement paste exothermic peak significantly delayed, so the water reducer application to the ready-mixed concrete can shorten the construction period and accelerate the turn over rate of mold.5.the polycarboxylate superplasticizer water which was not modified have high dispersion properties, the higher the concentration of carboxyl groups, the stronger dispersion properties of the water reducer. Reduce the dosage of the superplasticizer in order to ensure the testing of cement paste and concrete does not segregation in which case we will have to lower the water-cement ratio which will lead to a loss of fluidity (workability). So in the area which have high demanding of slump loss, we must modified the polycarboxylate superplasticizer.