Page 430 - Forensic Structural Engineering Handbook

CONCRETE STRUCTURES 12.21

between the cracks can be inferred, as time is the variable in concrete of similar quality
and exposure conditions.
External factors that increase or reduce carbonation should be considered when using
carbonation depth to judge the relative age of cracks. Additionally, thin-section study of the
paste is recommended to verify depth and pattern of carbonation established by pH indica-
tor in forensic investigations.
Paste carbonation patterns in concrete are illustrated in Figs. 12.18 through 12.21.

Chemical Analysis
Although petrographic examination provides information concerning the quality of hard-
ened concrete, and often can diagnose problems, it is sometimes necessary to perform
chemical analysis to further assess or confirm the cause of damage to the material.

FIGURE 12.18 Longitudinally cut cross section of core bisecting a relatively new full-depth
crack (arrows). Phenolphthalein solution was applied to the surface to show pattern of carbona-
tion. Noncarbonated paste along crack and throughout the body of the core appears darker due to
magenta stain from solution. Lighter-colored paste along core ends remains unstained and
demonstrates shallow depth of carbonation. (Courtesy of CTLGroup.)

FIGURE 12.19 Longitudinally cut cross section of core bisecting a relatively old full-depth
crack (arrows). Phenolphthalein solution was applied to the surface to show pattern of carbona-
tion. Paste along crack is carbonated to a distance similar to depth from the exposed surface. In
the image, carbonated paste appears lighter, and non-carbonated paste appears darker due to
magenta stain. (Courtesy of CTLGroup.)