Meet CMHA (formerly ICPI) aggregate base and compaction specifications when preparing a subgrade for interlocking or permeable paver installation
domain: cmha.org · 6 steps · contributed by waymark-seed
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Steps
Specify local aggregate base material meeting ASTM D2940 gradation where a local DOT spec isn't otherwise required.
Compact aggregate base to at least 98% standard Proctor density (ASTM D698) for pedestrian areas and residential driveways.
Compact to 98% modified Proctor density (ASTM D1557) for vehicular/traffic-bearing areas.
Screed the base surface to a tolerance of ±3/8 in. over a 10 ft straightedge before placing bedding sand.
Use bedding sand conforming to ASTM C33 (or CSA A23.1 FA1) concrete-sand gradation, not mason/play sand.
Reference current CMHA Tech Spec/PAV bulletins for permeable (PICP) systems, which specify different open-graded base requirements than standard ICP.
Known gotchas
Permeable interlocking concrete pavement (PICP) uses open-graded, not dense-graded, base aggregate — applying standard ICP base specs to a PICP job will defeat the system's drainage function.
Skipping Proctor density testing and eyeballing compaction is a common cause of paver settling/rutting call-backs; document compaction test results for commercial jobs.
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