A method of cementing a geothermal wellbore includes pumping a first volume of cement slurry down a wellbore. The first volume of cement slurry has a first water to cement ratio. A second volume of cement slurry is pumped down the wellbore. The second volume of cement slurry has a second water to cement ratio that is less than the first water to cement ratio. The first volume of cement slurry hardens at a vertical portion of the wellbore, and the second volume of cement slurry hardens at a horizontal portion of the wellbore.

A strengthening concrete admixture for the production of high-strength concrete products is provided. The strengthening concrete admixture comprises water; a set retarder comprising a salt of gluconic acid; one or more set accelerators; one or more hardening accelerators; and at least one stabilizing agent. Incorporation of the strengthening admixture in a cement mixture enhances both early and late age strength development and allows for sustainable and more energy efficient construction practices.