The Effect on Concrete Resistivity of Sulfate Content in Water
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exican Institute of Water Technology, Jiutepec, Morelos, Mexico;
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Centre of Arts of the State of Morelos, Cuernavaca, Morelos, Mexico.
ABSTRACT Sulfate attack on concrete has been studied worldwide for more than 60 years. However, the mechanisms of attack are still not entirely understood, and deterioration of concrete from sulfates still occurs. The source of the sulfates may be either external or internal. External sources are the naturally occurring sulfates in the environment or those sulfates that are the product of industrial processes or various human activities (e.g. fertilizers often release sulfates into the soil and groundwater). Internal sources of sulfates may include the sulfates introduced in the cements from which concrete is made. The purpose of this study is to find out the amount of sulfates that concrete can withstand in the water. Standards tests have been developed to evaluate the resistance of concretes to sulfate attack. Some, but not all of these tests, take into account the mechanisms of sulfate attack so far discovered in research work. The tests range from those that monitor changes in the strength of concrete specimens after set periods of immersion in known compositions sulfate solutions, to those that use x- ray diffraction to examine concrete specimens for expansive products (e.g. ettringite and thaumasite) that have resulted from sulfate attack. Keywords: Concrete, Sulfate Attack, Concrete Resistivity.
INTRODUCTION Cultural heritage, archaeology and historical buildings are subject to the deterioration and degradation action of the environment and microorganisms. These processes are normally referred to as weathering. This propensity (influenced by the climate) results in significant losses of precious cultural heritage. There are two general types of weathering: mechanical, involving only physical forces, and chemical, in which the chemical structure of the material is changed. In cold and/or dry climates, mechanical degradation is usually more important, whereas in the humid tropics and semi tropics, chemical degradation is predominant. The products of mechanical weathering include fragments of rock and materials formed by expansion and contraction of the rock, freezing and thawing cycles, and earth movements. Products of chemical weathering include the soil in its many forms and the migration of ions within the rock structure and within the surrounding environment. Ions may be mobilized by solution in water, which is enhanced by the presence of inorganic acids such as carbonic acid, sulfurous acid, sulfuric acid, and nitrous acid, and HNO3, derived from the gases carbon dioxide, sulfuric dioxide, nitrogen monoxide, and nitrogen dioxide, respectively. In the cases of iron and manganese, the chemical elements in the structure can be oxidized by atmospheric oxygen or reduced by volcanic H2S. *
Correspondent author: Dr. Luis Emilio Rendon, Tel: +52-7773293600, e-mail: [email protected];
Silicate rocks are complex salts of silicic acids. Cations such as magnesium and po
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