Page 431 - Forensic Structural Engineering Handbook

12.22 MATERIAL-SPECIFIC FORENSIC ANALYSES

FIGURE 12.20 Longitudinally cut cross section of core bisecting a full-depth crack.
Phenolphthalein solution was applied to the surface to show pattern of carbonation. Paste along
the crack near the exposed surface at left is carbonated in a V-shaped pattern (outlined) ending
near the arrows. Beyond the arrows, paste along the crack is not carbonated. This change in depth
and extent of carbonation suggests that the deeper portion of the crack developed later and is
younger than the near-surface portion of the crack. (Courtesy of CTLGroup.)

FIGURE 12.21 Transmitted-light photomicrograph of concrete viewed in thin section shows
carbonated paste near a crack (light speckled area) and non-carbonated paste farther away. Paste
appearance, texture and mineralogy differ between carbonated and uncarbonated paste. Width of
field is approximately 1.2 mm. Cross-polarized light. (Courtesy of CTLGroup.)

Chemical analysis can be used to identify such properties as excessive alkalies in cement,
cement content, types and amounts of admixtures, presence of fly ash, presence of slag, and
chlorides in concrete.
The durability of concrete is often more important than its strength, but ways to mea-
sure or predict durability are still being debated. As more and more chlorides have been
used as deicers, corrosion of reinforcing has become a serious problem.
One important measure of potential durability is the ability of concrete to protect the
reinforcing steel from the penetration of chloride ions from deicing salts or seawater.