No abstract

Zinc and hot dip galvanized steel are frecuently used metals in building application. They have relatively good atmospheric resistance to corrosion, due to its oxidation in air and formation of protective rust on its surface, which acts as barrier between the metal and environment. However, some part of the rust can be dissolved by pluvial precipitations and water condensed on the metal surface. This process, called metal runoff, contributes for zinc dispersion in soils and waters. In order to make accurate estimation of zinc runoff induced by atmosphere in humid tropical climate, samples of pure Zn and hot dip galvanized steel have been exposed in the Gulf of Mexico. The data reveal that this process is strongly influenced by factors which determine the aggressivity of the environment (pluvial precipitations, cycles of dry and rainy periods, atmospheric pollutants, air humidity). High annual rates of zinc runoff (6.5 -8.5 AE 0.30 g Zn m À2 yr À1 ) were released, being the runoff 63 -87% of the zinc corrosion rust. The zinc mass loss has been related to several independent parameters, presenting linear equation, which indicates the air contaminant SO 2 as the major factor controlling the runoff of zinc. The reported results show higher runoff of zinc samples, compared to that of hot dip galvanized steel

Recycling is an important habit to avoid waste. This paper evaluates the performance of masonry mortar, elaborated by replacing natural sand with recycled fine aggregate (RFA) obtained from mortar. Five families of mixtures were prepared with different replacement proportions: 20%, 40%, 60%, and 100%. A 1:4 volumetric cement-to-aggregate ratio was used for all mixtures by experimentally adjusting the amount of water to achieve the same consistency of 175 ± 5 mm. The effects of the following procedures were analyzed: (1) the use of a deconstruction technique to collect the RFA, (2) pre-wetting of the aggregates, and (3) the use of a commercial plasticizer. Experimental results show that it is possible to use this type of recycled fine aggregate as a substitute for natural sand by up to 60% in the manufacture of masonry mortar without significantly affecting its properties.

Worldwide hot dip galvanising is the most important application of a zinc coating as an efficient method for steel corrosion protection. In southeastern Mexico, in humid tropical climate, the domestic statistics reports that 63% of roofs and walls are made from galvanised sheets, which suffer corrosion damage. When zinc corrosion products are dissolved by dew and rain, zinc ions are released from the corroded surface and dispersed to the environment. This phenomenon, known today as the metal runoff process, is being paid enormous attention. In order to make an accurate estimation of zinc runoff induced by atmospheric corrosion in humid tropical climate, samples of hot dip galvanised steel have been exposed for two years in the Gulf of Mexico environments. The annual zinc runoff rates in both test sites decreased by y50% in the second year (2?70-3?28 g m 22 /year), as compared to those measured in the first year of exposure (6?52-7?98 g m 22 /year). The zinc mass loss has been related to several independent parameters, which control the runoff process. Runoff solutions collected from the samples in exposure after the first flushes of rain, always showed pH values in the range 5?5-7?0, when the rainwater was more acidic (pH 4?7-6?10). The carbonate ion CO 22 3 concentration detected in zinc runoff solutions reached values 1?6-1?7 times higher than those measured in rainwater, due to dissolved zinc carbonate corrosion product. Several chloride containing corrosion products, not released by rain events, were detected as major and minor phases by XRD during the exposure of galvanised steel.

During two years atmospheric corrosion process (metal loss) and runoff progress of zinc and galvanized steel where monitored. Metal samples were exposed to tropical humid climate in two environments (rural and urban) in the Gulf of México (Tabasco, Mexico). The rain events, as promoters of runoff process were registered and analyzed for ionic composition, pH and conductivity. The zinc runoff progress was monitored after each pluvial event, collecting runoff solutions from the metal samples in exposure, in order to determine the zinc mass loss, as a part of soluble, released corrosion products. The atmospheric corrosion of zinc fits a linear equation that relates the zinc corrosion with several environmental parameters. A schematic representation of zinc atmospheric corrosion products detected in humid tropical climate is also presented.