Study on the Compatibility Between Steel Slag-Based Admixture and Polycarboxylate Superplasticizer Based on the Marsh Method

Poor compatibility between water reducing agent and cement can lead to rapid loss of concrete fluidity and slump, and mineral admixtures will affect the compatibility between water reducing agents and cement. In order to investigate the compatibility between steel slag-slag-fly ash composite admixture and polycarboxylate superplasticizer, experiments were conducted using Marsh time as the index. A simplex lattice design method was employed for mixture design, and a Scheffe mathematical model with upper and lower bounds constraints was established to derive a regression equation between the composite admixture content and compatibility index. The optimal solution was determined through optimization. Two methods, composite admixture particle size distribution and compatibility index, were used to analyze the impact of the composite admixture on the compatibility with the water reducer and cement. The results indicate that when the composite admixture replaces 50% of the cement, the regression equation between Marsh time (60 min) and the content of each admixture component, based on the Scheffe mathematical model, showed “significant” variance analysis. When the Marsh time reaches its minimum at 60 min, the optimal ratio of steel slag-slag-fly ash is 0.23:0.30:0.47. Under this proportion, the compatibility index is maximized, signifying improved compatibility. The D value is reduced, indicating that the addition of mineral admixtures decreases the void fraction between cement particles, releasing more free water and enhancing the flow consistency of the cement paste.