Page 292 - Forensic Structural Engineering Handbook

DEFECTS, DETERIORATION, AND DURABILITY 9.3

Deterioration Continuum
Another group of conditions that can result in failure is deterioration, the gradual loss of
desired material properties. Eventual deterioration is normal for most construction materi-
als due to aging and degradation factors (discussed later), which must be addressed
through strategic maintenance or replacement to avoid failure. For example, eventual dete-
rioration would be expected for a concrete parking garage structure (without proactive
maintenance); however, applying deicing salt can introduce chloride ions into the concrete
(an incompatibility factor, which is a subgroup of degradation factors) that can accelerate
corrosion (a deterioration mechanism) of the embedded reinforcing steel and eventually
lead to a structural failure.
For comparison to the defect continuum, the deterioration continuum presented here is
similar:
Degradation Factor(s) → Deterioration → Failure
Defects may influence the rate of deterioration or may initiate premature failure of materi-
als; hence the degradation and deterioration continua are not independent, but often are
involved in a cause-and-effect relationship. For example, missing waterproofing in a wall
(a defect) can contribute to corrosion (deterioration) of embedded steel (see Fig. 9.2).

FIGURE 9.2 A defect (improper exterior waterproofing) caused deterioration (corrosion of
steel box beam supporting concrete masonry).

This chapter provides examples of common defects and deterioration mechanisms
observed in existing construction. Identifying and understanding defects and deterioration
are critical in forensic investigations, and in extending the service life of existing structures.
Without detection through condition assessments and subsequent remedy, defects and dete-
rioration may lead to failure of components, systems, or even entire structures.
Determining whether deterioration is natural or premature may help to identify whether
defects are present within a system. However, deterioration can only be identified as “pre-
mature” if the expectations for normal service life are understood. Therefore, this chapter
also discusses durability, the relationship between the design life (expected service life) of
building materials and their actual service life. Finally, a glossary is provided for terms
commonly used in failure investigations and structural condition assessments, as used in
this chapter.