This document summarizes research into the compressive strength of geopolymer mortar made with ground granulated blast furnace slag (GGBFS) and fly ash activated by a 14 molar sodium hydroxide and sodium silicate solution. Cubes of geopolymer mortar were produced with different percentages of GGBFS and tested for compressive strength at ages of 1, 3, and 7 days. The results showed that compressive strength increased with GGBFS percentage and age. The maximum 7-day strength of 32.67 MPa was achieved with 80% GGBFS and a fluid-to-binder ratio of 0.45. Below this ratio strength decreased, indicating 0.45 is the optimum