This research compares the mechanical-microstructural properties and thermal conductivity of the solid, green construction bricks that contain different percentages of sodium-hydroxide-activated residual rice husk ash and class-F fly ash. The brick specimens were prepared following the guidelines of Vietnamese national standard in term of mixing, forming, and curing. Various percentages of rice husk ash (0%, 10%, 20%, 30%, 40%, and 50%) were added to a standard brick mixture in order to evaluate the influence of rice husk ash content on the strength development, void volume, water absorption capacity, bulk density, and thermal conductivity of the hardened bricks. Moreover, scanning electron microscopy was used to characterize surface morphologies of the brick samples. Further, the suitability of using a binder of rice husk ash and fly ash to produce alkali-activated construction bricks was investigated. The bricks that were produced demonstrated generally good engineering performance and conformed to the relevant Vietnamese codes. Of particular note, the addition of rice husk ash influenced the properties of the bricks significantly, with brick strength peaking at a rice husk ash content of 10% and decreasing progressively at higher percentages. The findings from the present study support the efficacy of using a binder that contains rice husk ash and fly ash to produce green alkali-activated construction bricks.