EVALUATION OF REACTION PROGRESS IN PYRRHOTITE-IMPACTED CONCRETE FOUNDATIONS USING A WD-XRF METHOD

The use of aggregate containing sulfide-bearing minerals in concrete has led to the widespread deterioration of concrete structures worldwide. This study presents a quantitative method to determine individual sulfur species (sulfide and sulfate) in cementitious materials. Two complementary analyses are used: the ratio of sulfide to total sulfur and the ratio of sulfate to total sulfur is determined using wavelength dispersive X-ray fluorescence (WD-XRF), and specifically the ratio of the SKβ′/SKβ and SKβ/SKα fluorescent line intensities of sulfur. The total sulfur is determined either by a standard addition method using WD-XRF, or by an elemental analyzer, and the concentration is used to quantify the total sulfide and total sulfate in concrete. The sulfur concentration of the aggregate is then estimated by subtracting the sulfate introduced by Portland cement. The results are used to estimate the sulfur speciation, amount of pyrrhotite, and reaction progress in concrete samples. Results from field samples obtained from replaced foundations with advanced structural deterioration in Northeastern Connecticut are presented and discussed.