(1) The mix with 100% replacement of N-sand by QD showed higher compressive strength compared to replacing N-sand by different proportion of M-sand and QD.
(2) Though the compressive strength slightly reduces due to the replacement of N-sand or QD by M-sand, the M-sand is considered as a viable alternative to conventional sand due to depletion of natural resources. The slight variation in the compressive strength might be attributed to the aggregate shape and texture.
(3) The usage of 100% M-Sand in POFA-FA-based geopolymer mortar produced comparable strength as that of 100% N-sand.
(4) The use of QD as fine aggregate also reinforces the use of waste material as replacement for conventional N-sand; the high strength of specimens with 100% QD is attributed to the rough surfaces of QD that enhances the bond between the paste and the aggregates.
(5) The replacement of conventional N-sand with M-sand and QD shows comparable strength as that of N-sand based specimens and the use of M-sand and QD is recommended in geopolymer concrete.
(6) The high concentration of sodium hydroxide solution increases the compressive strength.
(7) The mixes with more fine particles require more paste to cover the surface areas, but for the mixes with constant binder content, the influence of the finer particles cannot be ignored.
(8) The failure mode of geopolymer mortar was found similar to that of Portland cement mortar.
(9) The density and compressive strength relationship of N-sand/M-sand/QD based geopolymer mortar was also found similar to that of the Portland cement mortar.