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’?
In Part I of this series, we discussed the Law of Fives in detail.
To recap: The theory proposes four distinct phases of the lifecycle of any concrete structure:
- Good Practice (initial design and construction, quality control)
- Maintenance (periodic inspection; general maintenance practices)
- Repair and Maintenance (isolated concrete removal and replacement)
- 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.”
Practical Examples of the Law of Fives
For the purposes of this example, consider parking structures of various types as the subject asset. We will focus on phases B, C, and D.
B: Maintenance
Periodic Inspection
The goal of periodic inspection is to catch issues that fall in category B and create a plan to remedy them before they become more significant and start to trend toward categories C and D. The period between inspections can vary (twice annually, annually, every three years), but is typically recommended to not exceed five years.
General Maintenance Practices
General maintenance practices tend to deal with repair and replacement of nonstructural elements that protect the underlying structure from deterioration.
For a parking structure, these can include:
- Cleaning (debris, trash, bird droppings)
- Waterproofing (joint sealants, traffic coatings, sealers)
- Best practices for removal of snow (such that waterproofing elements are not damaged)
- Chloride washdowns and flushing of drains
Failed joint sealant between precast double tees, exposing structural connection. Inaction will eventually change the condition from category B (replacement of the joint sealant) to categories C and D (deterioration of the precast concrete and underlying structural connections).
C: Repair and Maintenance
At this phase, isolated concrete removal and replacement is necessitated typically due to issues or inaction in phases A and B. In general, the structure itself is salvageable and repair costs are not approaching the replacement cost for the entire structure.
Concrete deterioration at slab edge (left), and the same condition approximately three years later (right). Inaction and the subsequent corrosion of steel has accelerated the deterioration of the concrete, which is reflected in the cost to remedy this isolated condition.
D: Renovation
At this phase, widespread concrete removal and replacement is necessitated, typically due to issues or inaction in phases A-C. In general, the cost to repair the structure is approaching the cost to replace the structure in its entirety.
Widespread concrete removal and replacement, which is significantly more costly than general maintenance (phase B) or isolated repairs (phase C).
The next part of this series will address strategies for proactive maintenance.
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.
We would love to hear any questions you might have or stories you might share about costs for service life optimization.
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