Effect of admixed chloride and molarity of NaOH solution on early-age strength and reinforcement corrosion in FA/GGBS geopolymer concrete

Abstract

Chloride persuaded steel reinforcement corrosion is an important durability issue in concrete structures. In this present study, the corrosion of reinforcing steel was evaluated in 0% and 3% sodium chloride admixed fly ash (FA)/ground granulated blast furnace slag (GGBS) GPC mixes. Two different molarities of NaOH solution i.e. 8 M and 10 M were used for preparing the GPC mixes with FA/GGBS proportions of 100/0 (wt.%), and 70/30 (wt.%). Reinforced geopolymer concrete prismatic specimens were prepared for half-cell potential and linear polarization resistance (i.e. LPR) measurements after 28 days and 180 days of its manufacturing. The obtained results showed that the early age 7 days compressive strength of GPC mixtures reduced with the existence of NaCl. The higher value of compressive strength was detected in GPC prepared with FA/GGBS proportion of 70/30 as compared to that made with FA/GGBS proportion of 100/0. Further, GPC made with higher molarity (10 M) of NaOH solution showed greater strength than that made with lower molarity (8 M) of NaOH solution. The less negative half-cell potential value and lower corrosion current density (Icorr) value of steel reinforcement in GPC was observed at the later age i.e., at 180 days in all GPC mixes as compared to 28 days. The higher chance of rate of corrosion, and the higher Icorr of steel reinforcement was detected in 3.0% NaCl added geopolymer concrete. Further, more negative half-cell potential and higher Icorr of steel reinforcement were detected with a rise in molarity of NaOH solution in GPC made with FA/GGBS proportion of 70/30 at both ages (i.e. at 28 days and 180 days). However, mostly less negative half-cell potential and lower Icorr of reinforcing steel were detected with a rise in molarity of NaOH solution in GPC made with FA/GGBS proportion of 100/0 at both ages.