Abstract This paper showed the result of experimental study carried out to study the mechanical
properties of Geopolymer concrete in the presence of blast furnace slag (BFS). Three different
geopolymer mixes were designed. Two mix designs were prepared by replacing fly ash with
blast furnace slag in the ratios of 10% and 20%, and another mix was prepared with 100% fly
ash to compare with the blended fly ash. The specimens were cubes of 100mmx100mm x100mm
which were cured in oven at 100oC for 48 hours and left at room temperature until the day of
testing. Mechanical properties of geopolymer concrete were evaluated such as workability,
compressive strength, flexural and tensile strengths.. Portland cement concrete with the same
mix proportions was designed as control. Sodium hydroxide and sodium silicate were used as
alkali activators with molarity of 14M concentration. The result showed that the workability of
OPC concrete is higher than geopolymer concrete. As the percentage replacement of fly ash in
geopolymer concrete increased, workability decreased. The compressive strength of
geopolymer concrete with 100% fly ash was higher than the control. Moreover, blending fly
ash with blast furnace slag gave very high compressive strength more than the control. Tensile
and flexural strengths increased as the percentage replacement of fly ash increased. From the
results, it is seen that OPC is not required in the production of geopolymer concrete.
Consequently, the global problem of greenhouse gases are drastically reduced. It can be
concluded that geopolymer concrete is a veritable alternative to OPC concrete and essential
for sustainable future development.
Keywords: Geopolymer, Blast furnace
slag, fly ash, compressive strength, flexural
and tensile strengths.