Nitrite diffusivity in calcium nitrite-admixed hardened concrete

Abstract

The apparent diffusivities (Dapp) of nitrite in concrete were estimated by monitoring time-dependent concentrations of nitrite leached into water from calcium nitrite-admixed hardened concrete specimens. Experiments were conducted with five different concrete mixes and with deionized water (DI), limewater, or synthetic seawater as the leaching agents. The Dapp in Type II Portland cement concrete for long curing times and a w/c ratio of 0.40 was ∼1.7×10−8 cm2/s when leached at 22 °C with limewater. The Dapp was relatively insensitive to nitrite dosage and to DI or limewater as the leaching agent, but an increase in the w/c ratio to 0.49, or an increase in temperature by ∼14 °C, increased Dapp by ∼50%. A 20% Type F fly ash cement replacement reduced the apparent diffusivity by ∼60%. The Dapp decreased with concrete curing time. The magnitude of the Dapp and its dependence on concrete and exposure parameters were comparable to those observed in the transport of chloride ions in concrete.