CORROSION-RESISTANCE PERFORMANCE OF FLY-ASH BLENDED CEMENT CONCRETE

Accelerated corrosion tests were carried out on reinforced concrete specimens made with plain and fly ash blended cements. The fly ash blended cements were formulated by replacing 30 percent by fly ash on weight basis. The C3A contents of the plain cements used were 2.43 and 14 percent. Corrosion initiation time and corrosion rate of steel reinforcement in the post-corrosion initiation period were measured for plain and fly ash blended cements. To explain the corrosion resistance performance of steel in fly ash blended cement concrete, the effect of fly ash blending on pore solution composition and physical characteristics of hardened concrete have been evaluated. Results show that incorporation of 30 percent fly ash in Type y and Type I cement concrete increased corrosion initiation time by 2.5 and 1. 9 times. respectively. Corrosion rate was reduced by 1.6 times due to fly ash blending with Type I cement. Results of pore solution tests show that blending of 30 percent fly ash to both the parent plain cements reduced OH- concentration and unbound chlorides and caused moderate change in Cl-/OH-ratio of the pore solution. Partial cement replacement by fly ash caused significant pore refinement, reduced permeability to water and chloride ions, and increased electrical resistivity. The observed superior corrosion resistance performance of fly ash blended cement concrete compared to plain cement concrete in terms of corrosion initiation time and corrosion rate is attributable to the improved physical structure of the cement matrix due to fly ash blending. This distinct improvement n the physical characteristics seems to overshadow the effect of moderate increase in the Cl-/OH- of the pore solution of fly ash blended cement.