Abstract
A reliability-based method for identifying appropriate safety factors for use in predicting the service life (i.e., corrosion-free life) of concrete structures subject to carbonation is described in this paper. Reinforced concrete (RC) columns located in CO2-rich urban environments were investigated to estimate their service life. Carbonation depths and cover depths were measured for sound, cracked, and jointed concrete cover conditions. The measurements were used to calculate safety factors for columns subject to carbonation. Goodness-of-fit tests were used to obtain optimal probability distributions for carbonation depths and cover depths. A reliability index of 1.28, corresponding to a 10% probability of corrosion initiation, was taken as a threshold for determining the safety factor. The safety factor proposed in this paper can be used to estimate the service life of RC structures subject to carbonation. The sensitivity of the safety factor to the casting method and coefficient of variation of the cover depth were also evaluated.
Highlights
E extent of carbonation in concrete depends considerably on a number of factors related to the composition and microstructure of concrete
Guidelines and standards issued to date have specified two types of analysis procedures for the prediction of reinforced concrete (RC) service life: a full probabilistic method [10, 11] and a partial safety factor method [12, 13]. e full probabilistic method utilizes Monte Carlo simulation approaches [10, 14] to consider the uncertainty of design variables while compensating for variations in both the durability resistance to carbonation and the environmental load of carbonation
E safety factor method seeks to ensure a prescribed level of reliability for a concrete structure in an urban area over its lifetime using an appropriate design safety factor. is method is simpler than the full probabilistic method, the latter yields more precise results [15]. e safety factor method for service life prediction is based on reliability theory for structural design
Summary
E reinforced concrete columns of a bridge for a commuter train were examined in terms of carbonation after 18 years of exposure to urban atmospheric conditions in a metropolitan city. 17 RC railway bridge columns were examined to determine the carbonation depth. E carbonation depth of each sample was determined using a pH indicator such as phenolphthalein in a solution of water and alcohol [18]. E depth of the concrete cover, XC, of the RC columns was estimated using an ultrasonic radar that measures the size and location of the rebar in the concrete using magnetic induction. The cover depths of the 17 RC columns were measured at 47 points on each column
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