As engineering professionals, we continually seek innovative ways to improve our industry, enhance efficiency, and ensure the safety of the public.
One way that public safety is enhanced is through periodic inspection of structures susceptible to deterioration by the elements.
Periodic inspection often uncovers issues, the remediation of which may require significant funding.
When reviewing the results of periodic inspection, asset owners often ask how these costs can be reduced in the future. The answer: service life optimization.
What Is de Sitter’s ‘Law of Fives’?
About 40 years ago, Wolter Reinold de Sitter published an often-cited theory, commonly referred to as the “Law of Fives.”
The theory proposes four distinct phases of the lifecycle of any concrete structure:
A: Good Practice (initial design and construction, quality control)
B: Maintenance (general maintenance practices; periodic inspection)
C: Repair and Maintenance (isolated concrete removal and replacement)
D: Renovation (widespread concrete removal and replacement)
The name of the theory originates from the statement that:
“One dollar spent in (phase) A equals $5 in (phase) B equals $25 in (phase) C equals $125 in (phase) D.”
…which implies an increase by a factor of five in spending from phase to phase.
Although the specific financials on any given structure will vary, the point de Sitter makes — funds invested wisely during original design/construction and general maintenance will provide a significant return on investment — is what is important:
“Of course the figures in dollars must not be taken too exactly. However, they serve to indicate where the focus of attention should be; the (phases) A and B.”
de Sitter begins the article by explaining the deterioration mechanism, which is the primary cause for deterioration of concrete structures:
“One of the main reasons for the increase in interest in the subject of durability of concrete is the regrettably frequent occurrence of damage due to corrosion of reinforced steel.”
Figure 1 from de Sitter’s article
Shown are two curves plotted (cost and corrosion) against time.
Although not explicitly stated, cost is correlated to corrosion, particularly as corrosion, over time, can be attributed to a significant portion of the deterioration of concrete structures.
Stay tuned for the next iteration in this series, where we will discuss practical applications of de Sitter’s Law of Fives.
About the Author Nick Heim, P.E.
Nick Heim, P.E., is a civil engineer with six years of experience in the repair and restoration of existing structures. Nick is also the host of the AEC Engineering and Technology Podcast (“AECTECH”) and brings valuable insights and expertise to listeners worldwide.
Nick’s interests lie at the intersection between the built world and technology, and he can be found looking for the ever-changing answer to the question, “How can we do this better?” He can be found on LinkedIn, producing content about use of technologies in his civil engineering career and small business.
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