A two-stage mixing process for concrete involves mixing a slurry of the binder and water separate from the aggregates, and then adding the slurry to the aggregates and continuing mixing. This process could improve cement hydration, concrete homogeneity, and the interfacial transition zone (ITZ) between aggregate and paste. This study deals the first stage of the two-stage mixing process, slurry mixing. The objectives are to determine the optimum mixing time and intensity based on the paste binder properties tested and to make recommendations for further investigation of the second stage of the process. Two mixers were used for slurry mixing. A high shear and low shear mixer with varying mixing time and speed. Different binder combinations were tested utilizing cement, fly ash, and slag. Heat of hydration, maturity, and rheology tests were performed on fresh paste samples. Compressive strength, degree of hydration, and scanning electron microscope (SEM) imaging tests were completed on cured specimens. The results show that increasing the mixing energy (mixing speed and time) produces a more workable and uniform slurry. This conclusion is supported best by the degree of hydration and rheology tests of paste. After mixing energy reaches a certain level, rheological properties of a given paste may show little or no change with increasing mixing time. For a given mixing time, a high shear mixer generally provides paste with higher early-age strengths than a normal mixer. Based on the tests, an optimal mixer and mixing time are recommended for further research on the two-stage mixing process.