Report Topic:Deterioration of concrete foundations: the role of pyrrhotite bearing aggregate
Reporter:Researcher Rui Zhong, National University of Singapore
Location:Academic Hall of State Key Laboratory
Dr. Rui Zhong obtained his doctoral degree from the University of Connecticut in 2015. He continued as a postdoctoral fellow at the University of Connecticut after graduation. To further diversify research experience, he joined Hong Kong Polytechnic University as a postdoctoral fellow in 2017. In the summer of 2018, he joined National University of Singapore as a research fellow. Dr. Zhong’s research interests include the static response and impact resistance of ultra-high performance fiber reinforced concrete (UHP-FRC), deterioration mechanisms of concrete and high performance pervious concrete (HPPC). He has published more than 10 peer reviewed journal papers on top journals in the field of cement based composite materials such as Cement and Concrete Composites, ASCE Journal of Materials in Civil Engineering, Construction and Building Materials etc. He also served as reviewers for journals such as Journal of Cleaner Production and Construction and Building Materials.
Premature deterioration of concrete foundations has been reported for a large number of homes in Eastern Connecticut of the United States. The characteristic symptoms are map cracking, whitish deposits at the vicinity of the cracking surface and wide crack opening. It is hypothesized that the volume expansion associated with the oxidation of pyrrhotite-bearing aggregate and the following internal sulfate attack (ISA) due to the delayed secondary mineral formation are the primary causes of premature deterioration. Extensive tests were carried out to validate the hypothesis using a combination of tools such as scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF) and energy dispersive X-ray (EDX).
The results showed that pyrrhotite and its oxidation products, such as ferrihydrite, goethite and sulfur, were present in or at the surface of the aggregates of the deteriorated concrete, suggesting the occurrence of pyrrhotite oxidation. Expansive secondary mineral formations (SMF) such as ettringite and thaumasite were also identified. The abundance of these SMFs, their spatial distribution in the open spaces together with their close association with matrix cracking suggest the cause of premature deterioration.