In situ leaching investigation of pH and nitrite concentration in concrete pore solution

Abstract

Holes 3- to 5-mm in diameter were drilled in concrete and mortar specimens with and without calcium nitrite corrosion inhibitor. The holes were partially filled with distilled water to leach out soluble ions from the surrounding pores. The pH in the solution inside the holes was periodically monitored with a micro-pH glass electrode and a silver-silver chloride reference electrode. A small fraction of the solution (∼10 μL) was also periodically extracted for spectrophotometric nitrite content determination. The terminal nitrite and pH values of the water in the holes matched the pore water compositions obtained in confirmatory tests using a conventional pore solution expression technique. The specimens without corrosion inhibitor yielded terminal pH ∼ 13.4. Specimens with nitrite inhibitor had pH ∼ 0.3 units lower than those without inhibitor. The terminal solution nitrite ion content was ∼8,000 ppm, which indicated that ∼10% of the total admixed nitrite was present in the pores. The pH drop was found to be quantitatively related to limited solubility of Ca(OH) 2 and its precipitation upon introduction of Ca(NO 2) 2.