Time of Wetness and HR-T Complex as Tools for Corrosion Risk Evaluation in a Concrete Block Exposed to a Humid Tropical Environment

Abstract

Tiempo de Humectación y el Complejo HR-T como herramientas para evaluar el riesgo por corrosión en un bloque de concreto expuesto a un ambiente tropical húmedoPedro Castro-Borges ( Abstract Material surface time of wetness (TOW) and temperature (T) are critical variables that influence the corrosion behavior of reinforced steel bars in concrete, and concrete durability. In concrete structures, both variables are indirectly dependent on the atmospheric relative humidity/ temperature complex, and specific structural characteristics: concrete composition, water/cement ratio, curing time, geometry and orientation in the environment. Concrete internal TOW and T distribution data were collected using Cu/Au electronic sensors arranged at 15, 40, 65 and 75 mm depths in a concrete block (300 x 300 x 150 mm; w/c 0.5) exposed for one year in a rural-urban humid tropical climate in southeast Mexico. Concrete internal TOW allows structure designers to define concrete cover thickness over steel reinforcement bars. The results indicate that under the tested exposure conditions, the side of the block with the highest TOW values (west) would require a thicker concrete cover than that with lower values (east). Longer TOW can increase the possible permeation of gases such as CO2, and consequent concrete carbonation, as well as lead to loss of the passive state in steel reinforcement and initiation of the corrosion process. ResumenEl tiempo de humectación (TOW) y la temperatura (T) de la superficie de un material son variables críticas que influencian el comportamiento corrosivo del acero de refuerzo en el concreto y su durabilidad. Estos factores tienen una dependencia indirecta del complejo atmosférico humedad relativa/temperatura, debido a las características específicas del concreto: composición, relación agua/cemento (w/c), tiempo de curado, geometría y orientación en el ambiente. Con el objetivo de adquirir datos para la distribución interna del TOW y T, se colocaron sensores electrónicos de Au/Cu a diferentes profundidades de 15, 49, 65 y 75 mm en un bloque de concreto (300x300x150 mm; w/c 0.5), expuesto durante un año en clima rural-urbano tropical húmedo, del sureste de México. El TOW registrado en el bloque de concreto es importante para diseñadores de estructuras, para definir el espesor del concreto sobre el refuerzo. Los resultados obtenidos mostraron que en las condiciones de esta exposición, la cara oeste del concreto debería ser más gruesa que la orientada al este. La existencia de un largo TOW causará una mayor posibilidad de entrada de gases como CO2, lo cual conllevaría a carbonatación del concreto, pérdida de la capa pasiva del acero e inicio de su corrosión.

Atmospheric Corrosion Behavior of Carbon Steel and Galvanized Steel after Exposure in Eretan and Ciwaringin, West Java Province, Indonesia

“…The other factors that may be considered are wind direction and precipitation. The electrochemical process initiates on the surface of a metal to corrode gradually at a critical level humidity (RHcrit) of 60% [5], then the corrosion rate increases [15]. The existence of a thin electrolyte layer spreads on the metallic surface takes place when reached to RHcrit [8].…”

“…The highest of RH tends to initiate the electrochemical process on the surface of a metal, which allows a longer time of wetness (TOW). TOW is defined as the time during wetness (condensation process) that took place on the exposed surface to the environment when RH is greater than 80% at a temperature greater than 0 °C [5]. In addition, both Ciwaringin and Eretan Districts are located in tropical regions, which have warm temperatures, ranges from 23 to 33 °C during field tests [16].…”

“…However, it is very difficult to simulate the real condition with many factors into a laboratory scale. The vulnerability of atmospheric corrosion to steel structures in the coastal environment has been reported by many researchers, where metal degradation is major concern [5][6][7]. In addition, the severity of atmospheric corrosion depends on the location of the environment, including inland (rural), urban, industry and marine regions, where marine region is one of the most severe locations.…”

Study on the Correlation between Humidity and Material Strains in Separable Micro Humidity Sensor Design

“…Therefore, a study embedded and placed temperature-humidity sensors into concrete blocks in a moist tropical environment. Through a one-year experiment, it became apparent that the west side of a concrete block was most likely to experience carbonation in a high humidity environment [ 17 ]. Humidity is very important in the maintenance of concrete structures.…”