ICPI Releases Technical Bulletin on PICP Maintenance

Available at, this 12-page bulletin with 33 figures walks the reader through a range of maintenance practices mostly to prevent sediment from collecting on the surface, or remove it should it remain.

The bulletin covers practices supporting surface infiltration, such as not using sand in the surface or within the pavement assembly, conducting effective erosion control during and after construction, and maintaining joints filled with aggregate so sediment can be more easily removed from the surface.

The text then moves on to surface infiltration inspection and testing, which includes inspection points before and after a rainstorm, as well as surface infiltration testing per ASTM C1781 Standard Test Method for Surface Infiltration Rate of Permeable Unit Pavement Systems. A tool at for calculating surface infiltration using this ASTM standard is referenced to facilitate better surface infiltration monitoring.

Tech Spec 23.

Tech Spec 23 published Feb. 2017.

The document explains routine and restorative surface cleaning. Routine means periodic preventive cleaning, i.e., keeping the surface water infiltrating. Restorative cleaning is often required when cleaning is neglected. This often results in water ponding on the surface. Sediment must be drawn out of the joints with the help of equipment to increase surface infiltration.

Advice then moves into preventive maintenance equipment options for maintaining various sized PICP applications. This section provides a range of technologies for cleaning, from a simple broom to sophisticated vacuum truck equipment. For clogged PICP with low overall surface infiltration, restorative infiltration maintenance techniques for small and large clogged surfaces are also covered.

An inspection list is provided for maintaining surface infiltration as well as a checklist for addressing distresses such as settlement or rutting. Guidance on winter maintenance is included as well as directions on how to reinstate PICP over underground utilities. This information supports cities that use PICP in highly urbanized areas.


2017 HNA Awards Entry Open

The HNA Awards recognize outstanding hardscape projects by contractors building residential and commercial walkways, patios, driveways, commercial plazas, parking lots, streets and more.

Award winners and honorable mentions will be recognized during the 2017 Hardscape North America trade show at the HNA Awards Recognition Ceremony in Louisville on October 19.

They also will be announced in a national press release, featured in Interlock Design magazine, and highlighted on the HNA website and in several major industry publications.

A distinguished panel of industry experts will select award winners and honorable mentions.
Entry Rates

Complete your online entry, submit photos and project description by August 14, 2017 for early bird rates ($100 for Members of ICPI, NCMA or BIA/$140 for Non-Members).

Entries will be accepted up to September 11, 2017 at a higher rate ($200 for Members of ICPI, NCMA or BIA/$240 for Non-Members).
2017 HNA Award Categories

Projects for consideration must have been completed between November 1, 2013 and June 30, 2017.
[insert award chart]
*Awards 12-15 can include natural stone, masonry veneer and mortared walls.


Don’t Be Fooled

Having worked with segmental and monolithic pavements for a few decades, one growing notion popularized in marketing/technical information for competing pavement systems is H-20 loading. Product literature for plastic pipes, chambers, stormwater storage crates, grids, etc., state confidently that their products can receive an H-20 load.

While that may be true, here’s a more complete picture. The H-20 load notion comes from bridge design and not from pavement design. The concept is found in the American Association of State Highway and Transportation Officials (AASHTO) Standard Specifications for Highway Bridges. Most bridges that receive trucks label such loads as H-20 or HS-20 in the bridge design process. The ‘20’ stands for a 20-ton vehicle, i.e., 4 tons on the steering axle and 16 tons on the drive (rear) axle. Adding an ‘S’ means the truck is a tractor-trailer combination. This adds 16 tons to a third (rear) axle, making a 36-ton vehicle.

The H-20 load is used in bridge structure design, a process that examines how the structure deflects under the weight of the bridge itself (dead load) and the applied truckloads (Iive). Computerized structural design models find the right size beams that limit their movement (deflection) under truckloads. The deflection in the structure is analyzed under H-20 and HS-20 loads, and likely other loading options depending on the anticipated traffic.

H-20 or HS-20 is a single truckload used in the analysis of bridge designs. These designations don’t apply to pavement design. Pavements are not designed to receive a single truck on them. In fact, my grassed front yard could easily receive an H-20 load. Obviously, that lawn is not a suitable pavement structure for repetitive loads from trucks.

Whether grass or something else, pavements do not typically fail from one H-20 or HS-20 load. Their limitations are defined by their ability to receive thousands or even millions of axle loads from trucks. Since axle loads vary with every vehicle, the AASHTO 1993 Guide for Design of Pavement Structures provides a process to equalize them to 18,000 lbs using a pavement concept developed in the 1950s called equivalent single axle loads or ESALs. Applying the ESAL concept, one H-20 load equals about 10 ESALs and one HS-20 load equals 26 ESALs.

Pavement failure (an unserviceable pavement) is typically seen as rutting in asphalt and cracking in rigid concrete pavements. In either case, the pavement surface slowly fatigues from repetitive loads over time due to tension and resulting horizontal strain at the bottom of the pavement surface. This eventually causes the pavement surface to bend or break.

Interlocking concrete pavements have a much higher compressive strength than conventional concrete (8,000 psi versus 4,000 psi). This makes the paving units especially resistant to fatigue from repeated loads compared to conventional asphalt or concrete surfaces. Most interlocking concrete pavements wear out deeper in the pavement, i.e., from repeated compressive strain within the bedding sand, base or at the top of the soil subgrade layer. This suggests that the base thickness needs to be sized and then constructed correctly, as well as testing conducted on soil subgrade compaction.

ICPI provides guidance documents to help with design on ICPI Tech Spec 4 Structural Design of Interlocking Concrete Pavements is one such document. Another is ASCE 58-16 Structural Design of Interlocking Concrete Pavement for Municipal Streets and Roadways. Both documents provide structural designs up to 10 million ESALs, a very busy major urban thoroughfare.

In the meantime, don’t be fooled. When the term H-20 appears in product literature, ask what happens when that load is repetitively applied? How long does the pavement last? When does it become unserviceable and fail from rutting or cracking? These are the core pavement design questions that require an answer for designers to create reliable pavements.