Evolution of pyrrhotite oxidation in aggregates for concrete

Abstract

Rocks containing pyrrhotite bands are sometimes used to produce concrete. These rocks oxidize and produce long-term expansive reactions that damage concrete structures, leading to important economic and risk related repercussions. The present study analyses several aspects that affect the oxidation process of the aggregate such as the existence of preferential paths for the entrance of the oxidizing agent and the conversion process of the chemical elements involved in the reaction. For that, host rock samples containing pyrrhotite were investigated by scanning electron microscopy and energy dispersive spectroscopy. The results shows that the pyrrhotite appears in bands that create planes of weakness and present cracks that serve as preferential paths for the entrance of oxygen. Furthermore, a new representation is proposed for the oxidation process. RESUMEN:Evolución de la oxidación de la pirrotina presente en áridos para hormigón. Rocas con bandas de pirrotina han sido usadas para producir áridos destinados a la fabricación de hormigones. Las mismas son susceptible a un fenómeno de oxidación que a largo plazo produce la degradación del material, llevando a importantes repercusiones económica y en cuanto a la seguridad. El presente estudio evalúa la influencia de diferentes aspectos que pueden afectar dicho proceso de oxidación del agregado, tales como la existencia de caminos preferentes para la entrada del agente oxidante y los elementos químicos involucrados en la reacción. Para ello, muestras de roca con pirrotina han sido analizadas mediante microscopía electrónica de barrido. Los resultados indican que la pirrotina aparece en bandas que dan lugar a planos de debilidad y fisuración. Esas fisuras actúan como caminos preferentes a la entrada del oxígeno. Asimismo, con base en los análisis realizados se ha propuesto una nueva representación para el proceso de oxidación.

Sulphide oxidation mortar tests for evaluation of the oxidation potential of sulphide-bearing aggregate

“…Deteriorations and expansions were reported for concrete elements containing aggregates with small amounts of iron sulphide minerals [1][2][3][4][5][6][7]. The deteriorations appeared in the form of whitish deposits, yellowish coloring, stains, pop-outs and map cracking [4,6,7].…”

Deterioration and Protection of Concrete Elements Embedded in Contaminated Soil: A Review

“…Zhong et al [61] analyzed the premature corrosion of concrete foundations in residential buildings located in Eastern Connecticut in the United States; this deterioration is related to the expansion of the aggregate, caused by the alkali-silicate reaction (ASR) and internal sulfates attacks, resulting in map cracking and wide crack openings in foundation elements [62]. To determine the original causes of the aggregate expansion, 70 core samples were taken from different residential house foundations affected by premature corrosion.…”

“…Francke et al [62] proposed a new coating material modified with cementitious mortar to perform waterproof and chemical protection. Based on polymer-cement products, this coating material effectively performed the functions of concrete carbonation protection by reducing the carbonation depth by 24% and increasing in 7% the adhesion strength in frost and storm environments.…”

Lessons learned about the diagnosis of pathologies in concrete dams: 30 years of research and practice

“…The internal sulphate attack (ISA) is another reaction identified in a smaller number of cases. Abundant studies from the literature addressed the chemical, the mechanical and structural aspects of these reactions [2][3][4][5][6]. However, limited information is available on the diagnostic procedure adopted to confirm the causes of the problem observed in the dams from a practical standpoint.…”