EVALUATING RISK TO PYRRHOTITE AFFLICTED CONCRETE FOUNDATIONS IN NORTHERN CONNECTICUT AND SOUTHERN MASSACHUSETTS
Assessing risk for concrete deterioration for any individual test result is possible if a relationship exists between pyrrhotite concentration and the degree of deterioration due to the pyrrhotite reaction. We use map (spider) cracking as the diagnostic visual symptom of the pyrrhotite reaction and have recorded the existence of map cracking, and where it occurs, in basement homes at the time of concrete core extraction. We present two methods to assess the likelihood that map cracking may occur: 1) We calculate the percentage of map cracked afflicted homes (regardless of age) for homes within a similar range for both MSL and total sulfur; 2) We calculate a logistic regression for the data set (R software, GLM function) where the binary dependent variable is the presence of (or lack thereof) map cracking at the time of analysis and the independent variables are the concentration of pyrrhotite (using either MSL or total sulfur) and the age of the concrete. Results indicate that map cracking is not observed in concrete with MSL values below 5 × 10-8m3/kg. Based on the linear relationship between MSL and total sulfur, this translates to approximately 0.15% pyrrhotite by mass in concrete. Both the descriptive statistics and the logistic regression indicate that the probability of map cracking increases incrementally above this value.