Abstract
Concrete core samples extracted from different areas of the Mequinenza Dam (Spain) have been studied and expansive reactions affecting the structure were not found. However, expansive reactions in the concrete of certain parts located near the abutments of two galleries have been observed as a consequence of an external sulfate attack due to the sulfur compounds contained in the lignites that are present on the surrounding terrain. Secondary gypsum, ettringite, and thaumasite, as well as several sulfate efflorescence have been detected. The thaumasite formed in the degraded concrete is related to a Thaumasite Sulfate Attack (TSA). Scanning Electron Microscopy (SEM) and Rietveld analyses of the TSA samples would show that thaumasite could have been formed thanks to ettringite acting as nuclei or by a direct precipitation from solutions within the pores of the cement matrix.
Highlights
Sulfate attack on concrete is a widely-studied and well-documented type of degradation [1,2,3]
The present paper shows the study of expansive reactions that occur in certain parts of Mequinenza dam (Spain), in some cases with massive presence of thaumasite, this does not pose a structural problem
The Mequinenza dam concretes are made with rolling aggregates which mostly have a carbonatic nature
Summary
Sulfate attack on concrete is a widely-studied and well-documented type of degradation [1,2,3]. In addition to newly-formed gypsum and ettringite, another product is formed under certain circumstances as a result of sulfate attack: thaumasite (CaSiO3·CaCO3·CaSO4·15H2O) This product does not arise from a reaction involving the aluminates in the cements that make up the concrete and could appear in a concrete where sulfur resistant cement has already been used. The appearance of thaumasite in structures affected by sulfate attack has been documented by numerous researchers in recent years [14,15,16,17,18,19] These authors provide cases of thaumasite formation in structures, buildings and various cement materials in many places. The present paper shows the study of expansive reactions that occur in certain parts of Mequinenza dam (Spain), in some cases with massive presence of thaumasite, this does not pose a structural problem. The application of Rietveld and SEM analyses allowed us to perform a crystallographic study of the thaumasite in order to formulate a hypothesis about its origin and relationship with ettringite
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