Title: Environmental Conditions in Concrete Housing Foundations Walls Incorporating Reactive Sulfide-Bearing Aggregates: Results from On-Site Monitoring Over a Year Period
Presented By: Rodolfo Castillo-Araiza, Université Laval (crib-Ulaval)
Description: Over the past 10 to 15 years, two significant incidents occurred in Trois-Rivie res, Canada, and Connecticut, USA, where the presence of pyrrhotite, an iron sulfide found in aggregate particles, caused severe damage to concrete structures. Pyrrhotite is unstable in the presence of oxygen and water, resulting in a redox reaction of iron and leaching of sulfur in the interfacial transition zone, which then transforms to sulfuric acid, leading to the attack of the cement paste. The objective of the study highlighted in this presentation is to better understand harmful reactions in concrete foundations containing reactive sulfide-bearing aggregates. Vaisala temperature, humidity and oxygen sensors were used to monitor the foundations of four houses over a period of one year. A datalogger recorded hourly measurements and the sensors were placed at 2.5 and 4-inch depths in three different positions (heights) on the concrete foundations (approximately 20 inches from the ends of the wall). The foundations were selected based on several criteria, including wall orientation and type of heating system. The results showed that as the internal temperature of the concrete decreased, the internal relative humidity tend to become drier. In interior concrete surfaces exposed to ambient conditions, there was a tendency for the concrete to equilibrate with the room. All sensors located at 2.5 inches showed a greater impact of the drying effect mentioned above. In addition, the exterior concrete walls exhibited 90-100 % internal humidity during the warm seasons and decreased to 65%-75% during the cold seasons monitored due to the heating systems. These findings suggest that cycling in relative humidity levels plays a significant role in the oxidation reaction of sulfide-bearing aggregates.