Paving Slab Progress
Approximately 25 years ago, a request was made by the U.S. Army Corps of Engineers to ASTM to create a product standard for segmental concrete paving slabs. When this request was made, no industry association existed to develop a draft standard for consideration by ASTM. Moreover, there was little industry consensus on the requirements of such a standard. The closest example was one first published in 1972 by the Canadian Standards Association called CSA A231.1 Precast Concrete Paving Slabs.
Since the advent of the Interlocking Concrete Pavement Institute (ICPI) and the expansion of paving slab sales in residential, commercial, municipal at-grade and roof applications, ASTM is now considering a draft product standard called Standard Specification for Segmental Concrete Paving Slabs. While yet to be approved and published, the draft has passed through two rounds of voting by ASTM Committee C15. A final, published standard is expected during 2016 after at least one more round of voting.
The current ASTM draft includes requirements for slabs made with any manufacturing process, e.g., hydraulically pressed, as well as for dry- and wet-cast (low and high water/cement ratio) concrete. Paving unit properties are defined for dimensional tolerances, warpage, flexural strength (modulus of rupture) and freeze-thaw durability.
Since some paving slab applications are subject to vehicular traffic, flexural strength is a key contributor to slab longevity. Flexural strength is being researched through a grant from the ICPI Foundation to Applied Research Associates, Inc. They are conducting finite element modeling that assesses vehicular loads and resulting slab stresses in a range of paving slab sizes, thicknesses and flexural strengths.
While not included in the product standard, this research will inform development of pavement thickness recommendations by ICPI for various traffic loads using various bedding, base and soil types. Prior to the modeling, the project initially reviewed overseas research and paving slab structural design literature. Upon approval by ICPI, charts will be included in a new ICPI Tech Spec bulletin on paving slab structural design and referenced in another bulletin on construction.