1999 Volume 10 Issue 3 Pages 61-68
The effects of cement characters on the performance of superplasticizers for concrete was investigated by the fluidity tests using cement pastes with combinations of six kinds of cements and six kinds of superplasticizers. Based on the results, two parameters, i. e. critical dosage and dispersing ability, were proposed. There was a minimum value of superplasticizer dosage to show the dispersing effect, which named as the critical dosage. Less than the critical dosage, superplasticizer did not work. Over the critical dosage, the fluidity of cement paste increased proportionally to the dosage. The increment of fluidity per unit dosage of superplasticizer was named as the dispersing ability. In the relationship with cement characters, the critical dosage was closely related to hydraulic reactivity of cement at early age. The dispersing ability was related to alkaline sulfate amount in cement in the case of polycarboxylate-type superplasticizer.