بخشی از مقاله (انگلیسی)
Corrosivity category of the atmosphere in coastal regions is usually very high. Reinforced structures frequently show short service life if adequate measures are not applied. Determination of time-to-corrosion-initiation (ti) and time to corrosion with induced cracking (tcc) to calculate the service life in buildings located in coastal cities is not usually performed. Changes in ti and tcc, depending on the w/c ratio, and concrete covering thickness, were determined in extremely aggressive coastal outdoor exposure site located within 10 m of the shoreline in Havana, one of the most aggressive coastal sites in the world. The electrochemical corrosion rate was determined in the reinforced concrete specimens. It is a very important parameter to follow environmental degradation of concrete. Environmental parameters were determined at the site. Calculated Chloride deposition rate is over the maximum level established in ISO 9223 standard (S3). Effective capillary porosity, compressive strength and ultrasonic pulse velocity were determined for all specimens. An acceptable service life was obtained for w/c ratio 0.4. However, effective capillary porosity is an important parameter to determine the concrete quality assessment before building reinforced structures exposed to extreme corrosivity. It is recommended to consider this parameter to predict a service life in very aggressive coastal sites.
Many reinforced concrete (RC) structures located in coastal cities and exposed to the direct influence of marine aerosols present generally a severe deterioration, indicative of short service life (Sl), caused mainly by atmospheric corrosion of the reinforcement steel [1–4]. The RC structures are often built using very permeable concretes with low quality.
Different softwares (Life-365, Eucon, and Duracon/fib MC SLD) have already been developed to calculate the Sl of RC structures in coastal cities . Some input basic parameters as cement type, concrete constituents, water/cement (w/c) ratio, additions, air content, concrete covering thicknesses, and protective systems, play a fundamental role in the determination of Sl. However, some input basic parameters depending on concrete quality as effective capillarity porosity, compressive strength, ultrasonic pulse velocity, and behavior of electrochemical corrosion rate in the reinforcement steel are not included in the software. Atmospheric transitory processes such as chloride deposition rate, relative humidity, and wind speed influencing in the corrosivity category of the atmosphere, and in the electrochemical corrosion rate in the reinforcement steel, neither are included in the software as input basic parameters [6, 7].
The Sl of RC structures in extremely coastal site of a city like Havana, considered one of the most aggressive environments of the Ibero-American region, depends on concrete quality, and atmospheric corrosion of reinforcement steel. Changes in the w/c ratio and concrete cover thickness, determined significant changes in the atmospheric corrosion rate of reinforcement steel in RC specimens exposed to extreme (CX) corrosivity categories of the atmosphere. The role of concrete cover thickness with respect to the Sl in RC structures become important for 0.4 w/c ratio.
Prediction and determination of the Ic, as indicator of atmospheric corrosion of reinforcement steel bars in RC specimens exposed in a coastal outdoor exposure site, can be used to obtain ti plus tcc. The importance of obtaining ti from the prediction and determination of Ic in the reinforcement steel is confirmed in the research work.