Characterization of Mortar with Mineral Additives
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Characterization of Mortar with Mineral Additives M. R. Mejía Durán1, A. A. Torres Acosta2,3, M.G. Arroyo Contreras1 and M. Rendón Belmonte2. 1 Universidad Autónoma de Querétaro, Querétaro, México. 2 Instituto Mexicano del Transporte, Sanfandila, Querétaro, México. 3 Universidad Marista de Querétaro, Querétaro, México. ABSTRACT It has been an increase on the number of concrete structures with corrosion induced damage in Mexico in recent years. It is also well known that cathodic protection (CP) is the only method that stops corrosion in an efficient way. Since the 1990’s Florida and other USA states have been installing in concrete pile substructures, in bridges and piers, a three part hybrid galvanic CP system. This hybrid galvanic CP system includes a thermal sprayed part (located at the aerial zone of the pile), a zinc mesh encapsulated in mortar and inside a glass fiber jacket (located at the change in ties zone), and a submerged zinc bulk anode (in the submerged zone). From a previous investigation performed by the present authors, it has been found that the mortar inside the fiberglass form may decrease the mesh anode activation and thus decrease the CP system efficiency. Therefore, this investigation includes an evaluation of different additions placed in mortar to increase its electrical and ionic conductivity to increase the efficiency of the entire hybrid system. Additions include carbon, zinc and alumina powders, and this investigation presents preliminary experimental results obtained from the tested mortars (i.e. mortar physical characterization: electrical resistivity, ultrasonic pulse velocity, and total void content). INTRODUCTION Reinforced concrete is the most used material in construction industry nowadays. Nonetheless, it presents the disadvantage of being susceptible to corrosion failure (del Valle et al. 2001). When reinforcing steel bars (rebars) corrode, a passive layer of the steel surface is consumed, and corrosion products (iron oxides or hydroxides) grow on the rebar perimeter. The volume occupy by the expansive oxides (hydroxides) is bigger than the original steel, creating pressures against the surrounding concrete. These tensile pressures cause cracks, concrete delaminations and finally the structural element resistance decreases (Andrade et al.1993, Torres-Acosta and Martinez-Madrid, 2003). Different repair and rehabilitation methods have been tested elsewhere in deteriorated structures in general. Cathodic Protection (CP) systems have proven to definitely stop corrosion in corroding reinforced concrete structures. The name CP is mainly due to how the protected metal is forced to behave like a cathode (metal where the reduction reaction takes place) (Genescá and Ávila, 1986). Corrosion, in practical terms, is the loss of electrons in the anode (metal which corrodes), causing the iron oxide (or hydroxide) formation on its surface. Therefore, the aim of a CP system is to provide additional electrons to stop corrosion and transform the metal into a cathode. One of these CP systems includ
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