The occurrence of thaumasite in newly built concrete constructions under the semi-arid climate of Northeastern Algeria

Abstract

The formation of thaumasite, a distinct form of sulfate attack that occurs usually in cold wet climate conditions, is by far the most damaging deterioration mechanism in the concrete used for modern constructions. Premature severe deterioration of concrete was reported at the infrastructure and superstructure levels for a large number of newly constructed housing projects commissioned for northeastern Algeria region, which is characterized by a semi-arid hot climate. The cementitious material showed significant yet characteristic symptoms of deterioration such as map cracking, whitish deposits at the vicinity of the cracking surface, and expansion of the concrete, only two to five years after their construction. Extensive tests were carried out on the altered concrete core samples and examined using a combination of tools including petrographic observation, X-ray diffraction analysis (XRD), and a scanning electron microscopy (SEM–EDX) examination. The analysis revealed that the aggregates used in the concrete were mostly micritic and bio-clastic limestone containing microcrystalline, dolomitized silicified sections. The aggregates further contain clay and ferruginous minerals, which are found providing a source of sulfur, suggesting on one hand the occurrence of an internal sulfate attack. On the other hand, the sulfate-rich groundwater and the dolomitic nature of the soil were found to be the triggers for the chemical reactions in the buried concrete, confirming the occurrence of an external sulfate attack. These two internal/external processes led to a thaumasite sulfate attack within the concrete at unexpectedly higher temperatures and kinetic.