DURABILITY CHARACTERISTICS OF SELF-COMPACTING CONCRETE CONTAINING LOW CALCIUM FLY ASH

Abstract

Self-compacting concrete (SCC) would be an ideal choice for thin structural members with congested
reinforcement as they pass freely and fill the formwork completely without segregation. Four SCC mixes with strengths
of 30 MPa, 40MPa, 50MPa and 60MPa were cast using a rational mix design procedure evolved for SCC mixes using
low calcium fly ash. The cement content in the mixes varied from 250 Kg/m3
to 500kg/m3 while the percentage of fly ash
in the mixes varied from 52% to 18% of the binder content. A carboxyl Ted ether based superplasticiser in dosages of
0.4% to 0.7% of the binder content was helpful in enhancing the deformability of the mixes. A commercially available
Viscosity Enhancing Agent (VEA) with a dosage of 0.1% of binder content was useful in enhancing the thixotropy of the
mixes. The durability related properties of these mixes such as water permeability, percentage saturated water
absorption, rapid chloride permeability test (RCPT), sorptivity and shrinkage were evaluated after 28 days of water
curing and presented in the paper. It was observed that high strength SCC showed lower percentage of water absorption
and coefficient of water permeability as compared to low strength SCC. However, based on the RCPT values, SCC
having strengths up to 40 MPa could be categorized as ‘very low’ permeability and above as ‘low’ permeability concrete
indicating the high degree of chloride impermeability of low strength mixes. Hence, low strength SCC could also be
proportioned to be highly resistant to chloride diffusion. The investigations clearly demonstrated that SCC mixes could
be considered as highly durable concrete.