ICPI Interlock Design Issue 3 2019

Issue 3 • 2019 ® esign interloc 12  CONTRACTOR’S corner Contractors Beware: Permeable Bases Under Interlocking Concrete Pavements In some regions of the US and Canada, there are trends towards using open-graded bedding and base aggregates on concrete pavers and paving slab projects, especially for residential patios and walkways. Open-graded bedding aggregate is typically ASTM No. 8 or 89 gradations. Base aggregate gradations replicate that for ASTM No. 57 stone or similar. This material is often called open-graded base or OGB. These assemblies aren’t constructed as permeable pavements. They would be considered permeable if the joints contained permeable aggregates such as ASTM No. 8, 89, or 9 gradations. In these systems, the subbase, base, bedding, and jointing aggregates are compatible and meet choke criteria provided by ICPI. Indeed, there are many resources available on www.icpi.org for permeable interlocking concrete pavement (PICP) design, construction, and maintenance. There are a few variations on the systems proposed, but they all use concrete sand or stabilized sand to fill the joints while the pavers rest on an open-graded bedding and base. The systems may or may not include geotextile placed under the pavers or under the bedding layer. If the bedding layer under the pavers is ASTM No. 8 or 89 stone, the jointing sand—stabilized or not—will work its way downward, out of the joints and into this layer.  Continues on page 14 Stabilized or not, joint sand does not choke into ASTM No. 8 stone Sand ASTM No. 8 stone ASTM No. 57 stone