The Paver Substitution
A contractor on a 1.4-acre civic plaza has submitted a substitution request for the specified 2.375-inch-thick concrete pavers. The specification requires a minimum compressive strength of 8,000 psi and 60% recycled content. The proposed paver is 6,500 psi with 40% recycled content and costs 18% less. The contractor says the substitution will save three weeks because the original manufacturer is backed up. The plaza receives snow-removal equipment and deicing salts, and the base course is already installed at 1.5% slope. A mockup of the proposed paver was installed last week; after two freeze-thaw cycles in a lab test, two of ten units showed surface scaling. The owner's representative wants a recommendation before the next pay application. The design team has 10 days to respond, and the project is already 12 days behind schedule. The city has a 5% construction contingency and a one-year maintenance bond.
1. Evaluate the substitution request and recommend approval, rejection, or conditioned approval.
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Reject the substitution as submitted. The specified paver is 8,000 psi; the proposed is 6,500 psi, about 19% lower and below the specification. Recycled content is also lower, so the sustainability basis is not met. The lab scaling in two of ten units after two freeze-thaw cycles is a warning sign, not a pass; the plaza gets deicing salts and snow-removal equipment, which are severe exposure conditions. A three-week schedule saving does not offset a higher risk of scaling, spalling, and replacement. The 1.5% base slope is not a reason to relax paver strength.
If the owner wants to consider an alternative, require independent test data for compressive strength, absorption, freeze-thaw durability, and salt scaling, plus a larger field mockup and a warranty. But the design recommendation should be to deny this product and hold the specified paver, or approve an equal product that meets 8,000 psi and 60% recycled content.
2. What review and documentation process should the design team follow in the next 10 days?
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Log the request in the substitution register and issue a written response within 10 days, copying the owner. State the denial basis with the specification section and the test results. Do not let the contractor install the proposed paver while review is pending. If a variance is considered, require a 100-square-foot mockup in the actual exposure, an independent lab report, and written owner acceptance of reduced service life.
Handle the contractor's schedule claim separately: ask for a recovery schedule and a cost proposal, but do not trade quality for time without owner direction. Record the decision in the RFI and submittal log, daily reports, and meeting minutes. If the specified paver cannot be delivered, evaluate an equal product, not a lower-strength one.
3. How should the next pay application be certified if the proposed paver is on site and the mockup is not accepted?
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Certify only work in place and accepted. The mockup is not accepted, so do not pay for the proposed paver as installed work. If the specified paver is stored on site, pay for materials only through stored-materials procedures with bills of sale, insurance, and verification. Document the denial in the daily reports and the submittal log.
A 12-day delay does not justify approval. The one-year maintenance bond should not be reduced. Recommend that the owner direct the contractor to order the specified paver immediately and submit a recovery schedule. If the original manufacturer cannot deliver, evaluate an equal product that meets the strength and recycled-content requirements.