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Cooler than the Conventional

An estimated 3 to 4 million square feet of concrete grid paving units pave intermittently used parking lots, fire lanes, ditches, slopes, and boat ramps each year in the U.S. and Canada.

ICPI publishes a Tech Spec technical bulletin (No. 8, see www.icpi.org) on this product typically used to help reduce stormwater runoff while accommodating vehicles by reinforcing grass with concrete. Unlike plastic grids, concrete grids have an ASTM product standard, C1319-17 Standard Specification for Concrete Grid Paving Units. This standard defines a concrete grid and provides requirements for compressive strength, absorption and freeze-thaw durability.

Grids have maximum dimensions of 24 x 24 in. and a minimum thickness of 3 1/8 in. The percent solid recently has been updated in C1319 to range from 45% to 75%. This enables grids to conform to the minimum 50% unbound (non-solid) requirement in LEED version 4, Sustainable Sites. An Urban Heat Island Reduction credit is earned when an open-grid pavement system is used. This credit is included in LEED because grids can reduce microclimate temperatures by as much as 4° C compared to conventional pavements.

Grid pavements allow a cooler surface by combining the durability of concrete with grass.

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HNA 2017 Highlights

Contractor briefing session

Last October, contractors and dealers from across the U.S. and Canada attended HNA. This year, HNA will take place on Oct. 18–20, at the Kentucky Exposition Center in Louisville. Registration for HNA 2017 is already surging ahead of last year’s record crowd.

CONTRACTOR BRIEFING SESSIONS

Seven FREE Contractor Briefing Sessions will take place in the Trade Show Floor Classroom, including:

  • Five Ways to Future-Proof Your Hardscape Business
  • The Biz-Builder Blueprint for Contractors
  • OSHA’s New Crystalline Silica Regulation
  • ICPI Installer Certification, Advanced Designations, and Their Value
  • Opportunities for Permeable Pavers in Residential and Commercial Marketing

HARDSCAPE DEMONSTRATIONS IN THE HNA OUTDOOR ARENA

Nationally renowned instructor Bill Gardocki, owner of Interstate Landscape Co., Inc., will lead a live continuous two-day build that will highlight interlocking concrete pavement, SRW and permeable interlocking concrete installation best practices. The build will also include one-hour sessions on tools of the trade, hardscape lighting and outdoor kitchens.

EXHIBIT FLOOR

850 companies will exhibit indoors and out, including more than 170 hardscape exhibitors. The trade show floor will feature top paver manufacturers and leading suppliers of materials, equipment and services to the concrete paver industry. You will also gain access to the largest hands-on outdoor exhibit area through both HNA and the GIE+EXPO (Green Industry Equipment EXPO), included in your trade show admission.

HNA CONFERENCE SESSIONS

Conference sessions will provide attendees with a broad range of important education for their businesses, including:

  • Estimate Accurate Job Costs to Always Make a Profit
  • Emerging Online Lead Generation Trends for Residential Hardscape Businesses
  • Strategies to Win More Profitable Contracts and Overcome The Low Bid Process
  • Setting Up Your Hardscape Crews with the Right Technology to Increase Profits and Efficiency

DEALER ACTIVITIES

HNA Awards

The HNA Dealer Program, in its seventh year, is designed to help dealers accomplish two objectives: overcome the challenges in their market in order to grow their companies and identify what works and what doesn’t in a company’s unique market area—urban and rural. The program will feature Alan Beaulieu, one of the nation’s most informed economists examining the prevailing challenges confronting business. In addition, Dealer Day activities give dealers a one-of-a-kind networking opportunity and a first look at the trade show floor before it opens to everyone.

INSTALLER COURSES FOR CERTIFICATION AND DESIGNATION

Pre-show courses at the downtown Hyatt Regency Hotel in Louisville give HNA participants an opportunity to earn credentials to help differentiate themselves from their competitors. ICPI courses include the Concrete Paver Installer, Advanced Residential Paver Technician, Commercial Paver Technician and Permeable Interlocking Concrete Pavement Specialist. Three additional NCMA segmental retaining wall system installer courses are also offered.

HNA INSTALLER CHAMPIONSHIP

Installer championship

Twenty-four of the most talented installer teams will compete for the coveted championship. The competition will test and recognize the skill, dedication and passion of hardscape contractors from Canada, the U.S. and Mexico. The Grand Prize package is valued at over $10,000!

HNA AWARDS

Award-winning projects from throughout the U.S. and Canada will be on display and honored. The HNA Awards recognize outstanding hardscape projects by contractors building residential and commercial walkways, patios, driveways, commercial plazas, parking lots, streets and more. Project categories include concrete paver, clay paver, segmental retaining walls, combination of hardscape products and, brand new for 2017, the porcelain paver category.

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Success from Failures

Most progress in pavement design comes from failure. For accurate and predictable pavement design, pavements must be damaged and eventually rendered useless by repeated truck wheel loads to understand where that point lies. In fact, modern highway pavement design was originally based on load testing from trucks conducted by the American Association of State Highway Officials in the 1950s. The notion of an 18,000 lb (80 kN) equivalent single axle load as the basis for loading in pavement design emerged from these tests. Among many things, this testing discovered Miner’s Law, i.e., doubling wheel loads increases pavement damage to the fourth power. This exponential relationship between wheel loads and pavement damage is why truck owners pay high road use taxes—trucks do the most damage.

Since the 1950s, machines were invented that quickly apply truck wheel loads (or greater) without drivers. These large machines go by different names—accelerated load facility, heavy vehicle simulator, etc.—but all render 20 years of wheel loads in a matter of months. Often housed at universities or state departments of transportation, these machines have tested thousands of asphalt and concrete pavements. This research via load testing is the norm for conventional pavements. Testing, most of it funded by tax dollars, led to longer-lasting designs. Such research superbly uses tax resources because of the huge ROI: accelerated load testing costs millions; road networks cost billions.

For permeable interlocking concrete pavements (PICP), accelerated load testing validated ICPI design tables for subbase thicknesses published in 2011. Load testing was conducted in 2014 by the University of California Pavement Research Center in Davis (see picture). The design tables developed by the Center, with help from mechanistic modeling, provide for slightly thinner bases in some situations than those in the ICPI design tables. Accelerated load testing doesn’t come cheap: the testing at Davis cost about $400,000, co-funded by the ICPI Foundation, California paver manufacturers and the Cement Association of California and Nevada.

Institutionalization from this industry investment include Caltrans PICP design tables in their pervious pavement literature, and in the ASCE national PICP standard to be released later this year. While the testing certainly confirmed that heavy trucks can repeatedly traverse PICP, additional accelerated load testing is needed using stronger subbases, thereby expanding PICP use to busy urban streets (while storing and infiltrating stormwater).

While there has been accelerated load testing (mostly in the 1980s) of interlocking concrete pavements (ICP) here and overseas, they have taken mostly an experiential, empirical path toward validation of their structural capacity. Validation has come from millions of square feet used in airfield and port applications withstanding wheel loads as much as 10 times greater than trucks. For road applications, some of the busiest downtowns have seen repeated bus and truck traffic. Downtown North Bay, Ontario, and San Antonio, Texas, are examples. Built in 1983, North Bay is likely approaching 4 million standard axle loads and San Antonio around 3 million, built in 1986.

While experience is informative, the interlocking concrete pavement industry might consider systematic full-scale load testing to undergird current structural design methods. A multimillion dollar investment will put ICP in the same testing league that refined conventional asphalt and concrete pavements over the past several decades. ICP accelerated load testing will instill immeasurable confidence in designers, boost the industry’s technical credibility, and help lead to institutionalization by government road agencies and civil engineers. Like the PICP load testing, funds for ICP load testing will likely come from industry and not tax dollars, since there aren’t yet hundreds of miles of ICP roadways owned by municipal or state transportation agencies.

Success in expanding ICP road applications will come from taking ICP to the point of failure via accelerated load testing. Testing to failure is the sine qua non of pavement research and design. This can add further fuel to justifying lower life-cycle costs from investing in ICP.

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Enforcement Postponed

The U.S. Department of Labor’s Occupation Safety and Health Administration (OSHA) recently postponed enforcement of new, stricter rules regarding worker exposure to silica dust on job sites. Originally scheduled to begin June 23, 2017, enforcement of the new rules will now begin Sept. 23, 2017. Current rules will be changed this fall to reflect substantial reductions in exposure to airborne dust on job sites. A key rule change is a reduction in the 8-hour exposure limit from 100 to 50 micrograms per cubic meter of air averaged over an eight-hour day. Determining exposure to these small concentrations is typically done by workers wearing lightweight, portable air monitoring equipment that captures dust while on the job site.

Current rules require a written exposure control plan with specific tasks to protect workers. This is implemented by a designated, competent person who articulates housekeeping practices that reduce exposure with feasible alternatives. Employers must offer medical exams including chest x-rays and lung function tests to employees. These must be done every three years for workers who wear a respirator for 30 or more days annually. There must be ongoing worker training in saw cutting and other operations that result in silica exposure with instruction in ways to limit exposure. Finally, employers must keep records of workers’ silica exposure and medical exams.

OSHA’s new silica exposure rules are delayed to give more time for construction companies to comply. Silica dust on job sites requires control measures via wet (or dry) saw cutting with a vacuum system and worker protection equipment. The pavers shown here are among 5 million square feet in container yards at the Port of Oakland, CA.

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ICPI Releases Technical Bulletin on PICP Maintenance

Available at icpi.org, 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 icpi.org 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.

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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.

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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 www.icpi.org. 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.

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Resetting the Bar

The Transportation & Development Institute (T&DI) of the American Society of Civil Engineers (ASCE) recently updated and released ASCE 58-16 Structural Design of Interlocking Concrete Pavement for Municipal Streets and Roadways. According to the ASCE, “The standard provides preparatory information for design, key design elements, design tables for pavement equivalent (to asphalt) structural design, construction considerations, applicable standards, definitions, and best practices.” This new version, which replaces Standard ASCE/T&DI/ICPI 58-10, includes updated references to quoted ASTM standards, clarification of subgrade type and drainage characteristics, and the addition of new green infrastructure rating systems.

The 42-page design guide provides tables for base thickness using aggregate, asphalt-treated, cement-treated and asphalt bases under interlocking concrete paving units that conform to ASTM C936. The book provides thicknesses for various soil subgrade conditions under traffic up to 45 mph and exerting no more than 10 million lifetime 18,000 lb (80 kN) equivalent single axle loads or ESALs. Transportation engineers, road designers, planners, pavement manufacturers and municipal officials can rely on this comprehensive guide to interlocking concrete pavements.

ASCE Standards_August 2016_new green.inddDave Hein, P. Eng., Vice President of T&DI and chairman of the technical committee that created and updated the standard, notes that, “ASCE 58-16 continues to provide municipal and consulting engineers with this tool to design and implement interlocking concrete pavements in streets, alleys and parking lots. When properly designed and constructed, these pavements can be more cost-effective over their life than conventional asphalt and concrete. And besides, pavers upgrade the appearance of any street.”

Purchase the updated standard at www.asce.org/booksandjournals. The price is $60 for ASCE members and $80 for non-members.

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Clarify and Confirm

Last summer, ASTM approved C1782 Standard Specification for Utility Segmental Concrete Paving Slabs. Needed for decades, the industry now provides a baseline product standard for segmental concrete paving units from 12 x 12 up to 48 x 48 in. (300 x 300 up to 1,200 x 1,200 mm). ASTM C1782, however, was written for paving units that do not require close dimensional tolerances. Such tolerances noted in Table 1 at right are from that standard.

Utility paving slabs often have architectural finishes and are used in residential and some commercial applications for at-grade and roof ballast applications. Architectural finishes include (but are not limited to) blasted, hammered, tumbled, textured and polished surfaces. The Interlocking Concrete Pavement Institute is proposing a second ASTM standard for slabs with closer (tighter) dimensional tolerances. Like products conforming to C1782, products conforming to the proposed standard typically have architectural finishes. However, the main difference between C1782 and the proposed new standard is that the latter has closer dimensional tolerances required for pedestal-set roof applications, as well as for at-grade bitumen-set and some sand-set applications. The new proposed standard formalizes these dimensional tolerances used with architectural paving units for these applications for over 20 years. This proposed new standard below is very similar to ASTM C1782 except for the closer dimensional tolerances shown in Table 2.

Rather than provide optional closer dimensional tolerances within C1782, a new standard is being proposed that differentiates itself from C1782 with higher dimensional tolerances for architectural paving slabs. Also, two distinct paving slab standards (standard and architectural grade) can help reduce confusion between these two groups of paving products among specifiers, contractors, and other users. Freeze-thaw durability and flexural strength requirements are proposed to remain the same as those in C1782. Acceptance of this new standard is anticipated in 2018, but this depends on the outcome of voting by ASTM members.

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Doing the Math

Thanks to a grant from the ICPI Foundation for Education and Research, design tables were developed earlier this year that provide technically conservative base solutions for paving slabs subject to vehicles. The tables were developed using finite element modeling that simulated pressures from truck tires on paving slabs of various sizes and flexural strengths. The modeling included a 1-inch (25 mm) thick sand bed under the slabs, three base materials, and three soil subgrade conditions. This article previews the design approach for pedestrian and vehicular applications derived from that modeling.

For pedestrian applications, 12 x 12 in. (300 x 300 mm) units can be placed on a minimum 6 in. (150 mm) thickness of compacted aggregate base. Thicker bases (generally 8 to 12 in. or 200 to 300 mm thick) should be used in freezing climates and/or on weak clay soils (CBR < 3%). Designers should consider using a lean concrete or concrete base for larger paving units because achieving a very smooth base surface can be difficult with compacted aggregate base.

Design options become a bit more complex for vehicular applications. The first step is determining the maximum number of lifetime 18,000 lb equivalent single axle load or ESAL repetitions. (Caltrans Traffic Indexes are provided in parentheses.) Determining ESALs or TIs can be done using Table 1. It divides them into five categories. Higher ESAL categories generally require thicker units and concrete bases. Applications exceeding 75,000 lifetime ESALs should use interlocking concrete pavers.


Math-Table1


The next step is determining the soil strength. The minimum values for designs is a resilient modulus of 5,100 psi (35 MPa), 3% California Bearing Ratio, or an R-value = 7. The maximum values are 11,600 psi (80 MPa), 10% and 18, respectively. Soils with higher values use the latter set for determining the unit size and thickness. after laboratory tests determine the soil strength, that points to specific slab sizes and bases that will work given the anticipated design ESALs in Table 2. Square paving units are recommended over rectangular ones for vehicular traffic with placement in a running bond pattern.

The ICPI design method offers three base options described below in ascending order of supporting stiffness. Construction should include compacting the soil subgrade and bases/subbases to at least 95% of standard Proctor density per ASTM D698 Standard Test Methods for Laboratory Compaction of Soil Standard Effort.

(a) A 12 in. (300 mm) thick compacted aggregate base with gradation conforming to provincial, state or municipal specifications for road base used under asphalt pavement. If there are no guidelines, use the gradations in ASTM D2940 Standard Specification for Graded Aggregate Material for Bases or Subbases for Highways or Airports and as described in ICPI Tech Spec 2 Construction of Interlocking Concrete Pavements.

Slabs can take a modest amount of trucks but using thicker units. The ICPI guide tells designers and contractors how thick.

Slabs can take a modest amount of trucks but using thicker units. The ICPI guide tells designers and contractors how thick.

(b) A 4 in. (100 mm) thick lean concrete base over a 6 in. (150 mm) thick compacted aggregate base. The lean concrete should have a minimum 725 psi (5 MPa) compressive strength after 7 days per ASTM D1633 Standard Test Methods for Compressive Strength of Molded Soil-Cement Cylinders. Lean concrete is typically a lower strength concrete or a cement-treated base of similar stiffness and strength where an aggregate base is charged with cement (typically 3% to 6% by weight) to bind the aggregates when the cement cures.

(c) A 4 in. (100 mm) thick concrete base over a 6 in. (150 mm) compacted aggregate base. The concrete should have a minimum compressive strength is 3,000 psi (20 MPa) per ASTM C39 Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens.

Table 2 presents a sample of the design tables using a concrete base. The designer finds the paving slab length and width and thickness that corresponds to the soil subgrade strength and slab flexural strength. Paving slab length and widths start at 12 x 12 in. and go up to 48 x 48 in. As an illustrative example, Table 2 only goes to 24 in. slabs and not up to 48 in. due to space limitations. Slab thicknesses are 2, 3, 4 and 5 in. If the exact paving slab length and width are not on the table, the designer finds the closest size paving slab, using a smaller and/or thicker unit as a conservative design measure. The design tables cover square and rectangular slabs only.


Math-Table2


An example follows on how a design table works. The highlighted 24 x 24 x 3 in. thick slab is selected by the designer. This will be a concrete base and aggregate subbase over a 5% CBR subgrade with a minimum 750 psi flexural strength for the slabs. The intersection of the highlighted horizontal and vertical columns is marked OHV which means the maximum lifetime load is 75,000 ESALs per Table 1. If the designer wants to use a 24 x 24 x 3 in. slab on a weaker soil subgrade, then the maximum allowed ESALs would be 30,000. 

Designs using a concrete base include a 1 in. (25 mm) thick sand setting bed under the slabs. This design solution also applies to paving slabs in a bitumen-sand bed (typically 1 in. or 25 mm thick) since bitumen-set applications require a concrete base. This introduces an additional measure of conservative design since bitumen-sand materials provide a modest increase in stiffness and increased stability resisting repeated turning, accelerating, and braking tire lateral loads.

This article was intended to sample how structural design is done with paving slabs. Similar, additional design tables have been developed for planks and an ICPI Tech Spec is expected later in 2017. As partial validation, the ICPI Foundation for Education and Research is funding the construction of a full-scale load testing area at a paver manufacturing facility in Maryland. The area will receive trucks loaded with paving products where each truck pass will exert several ESALs. The condition of the slabs and planks set on aggregate and concrete bases will be monitored to see how quickly or slowly the slabs will crack, as that defines failure. The testing will likely begin in spring 2017 and run for a few years.