Abstract:
Utilization of the fly ashes is a major problem in many developing countries and in South Africa only
about 7% of the fly ash produced annually by coal-fired power stations, is being utilized. Although, fly
ashes can be used as an alternative binder in alkali-activated concretes, strength development of these
concretes at room temperature is slow limiting application of the material. Direct electric curing is
proposed for heat curing of alkali-activated fly ash concrete which will open new opportunities for insitu
applications of these concretes in the construction industry thus increasing the amount of benefi-
cially utilized fly ash. Alkali-activated fly ash concretes containing unclassified low calcium fly ash, sodium
hydroxide and sodium silicate solutions were cured at 60 C by means of direct electric curing. The
electric resistivity and compressive strength development of the concretes were investigated. The resistivity
strongly depends on the type of activator used. Compressive strength up to 33.8 MPa and
48.5 MPa at 2 and 28 days respectively, can be achieved after a short period of direct electric curing. This
opens new opportunities for wider application of alkali-activated fly ash concretes and for more
extensive utilization of fly ash.
