durability of fly ash based geopolymer concrete. Geopolymer concrete samples were prepared
from high calcium fly ash, sodium silicate solution, sodium hydroxide solution, fine aggregate from
river sand, and two types of coarse aggregate viz., recycled concrete aggregate and crushed limestone
coarse aggregate. Test results indicated that recycled concrete aggregate can be used as a coarse
aggregate in high calcium fly ash geopolymer concretes with the 7-day compressive strengths of 30.6
e38.4 MPa which were slightly lower than those of high calcium fly ash geopolymer concretes containing
crushed limestone. The use of high sodium hydroxide concentrations of 12 and 16 M resulted in
better performances both in strength and durability than that of 8 M.