Permeable Walkways with Decomposed Granite and Natural

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This Online Learning Seminar is available through a professional courtesy provided by: Permeable Walkways with Decomposed Granite and Natural Aggregate Pathway Materials Kafka Granite LLC 550 East Hwy 153 Mosinee, WI 54455 Tel: 715-687-2423 Fax: 715-687-2395 Toll-Free: 800-852-7415 Email: [email protected] Web: www.kafkagranite.com

START Private Residence, WI

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Presented by: Kafka Granite LLC 550 East Hwy 153 Mosinee, WI 54455

Description: Parks, recreational areas, and common rural and urban spaces can be essential relaxing oases. Pathways that navigate through these public spaces should be functional and durable, and complement the natural environment. This course explores pathway materials and focuses on decomposed granite (DG) and natural aggregates. It discusses the types of pathways, their applications, installation, and maintenance, as well as their contribution to green design.

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The American Institute of Architects · Course No. AEC1038 · This program qualifies for 1.5 LU/HSW Hours.

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Purpose and Learning Objectives

Purpose: Parks, recreational areas, and common rural and urban spaces can be essential relaxing oases. Pathways that navigate through these public spaces should be functional and durable, and complement the natural environment. This course explores pathway materials and focuses on decomposed granite (DG) and natural aggregates. It discusses the types of pathways, their applications, installation, and maintenance, as well as their contribution to green design.

Learning Objectives: At the end of this program, participants will be able to: • describe the benefits and drawbacks of a variety of pathway materials and the key elements to consider in the material selection process • explain how decomposed granite (DG) and natural aggregate pathway materials support the goals of low impact development and contribute to meeting green design objectives • compare three different types of DG and natural aggregate pathways in terms of materials, performance, and suitable applications, and • discuss the installation and maintenance procedures applicable to each type of pathway to ensure a safe, functional, and durable installation.

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Table of Contents

Overview of Pathway Materials 7

DG and Natural Aggregate Pathway Materials 17

Types of Aggregate Pathways 25

Installation and Maintenance 38

Case Studies 52

Summary and Resources 65

Grande Cheese Headquarters & Research Center, Fond du Lac, WI Click on title to view

Overview of Pathway Materials

Metropolitan Correctional Center, Chicago, IL

The Appeal of a Pathway

A pathway can welcome visitors, entice users to explore areas, or simply facilitate movement from one point to another. It keeps feet out of the mud when crossing over damp areas, and can help transport heavy loads without getting stuck. A pathway can create a formal or informal feeling, and have an urban or natural aesthetic. A well-designed and well-built pathway will enhance the functionality of a space.

Although functionality may be the main purpose of a pathway, aesthetics do not have to be compromised. There are a variety of material choices, color combinations, and designs available to complement any landscape and function.

Pedestrian thoroughfares, especially those on commercial properties, are subject to a lot of foot traffic, and possibly vehicular traffic as well; therefore, the hardscaping materials chosen need to stand up to whatever traffic or environmental elements they are exposed to, day in and day out, year after year. Max McGraw Wildlife Foundation, Dundee, IL

Pathway Materials: Urban Aesthetic

Concrete Concrete provides a smooth, consistent surface that is ideal for ADA applications: steel in concrete keeps it from deflecting, preventing tripping hazards. It is durable, and installations should last 20+ years. It can be used in flood areas and on steep slopes, and does not easily break apart. The surface does not get muddy, keeping pedestrians clean. When concrete does not require a gravel base (refer to local code), there is less impact on trees than with asphalt installations. The initial installation can be expensive. The surface is impervious and contributes to runoff. Concrete is subject to cracking as it undergoes freeze and thaw cycles in colder climates. The surface is hard on joints, and therefore not the best choice for a running path.

Pathway Materials: Urban Aesthetic

Asphalt Asphalt has a good starting surface that is very smooth. It is also slightly cheaper than concrete in terms of initial cost.

However, over time edges in contact with vegetation will crack and crumble, so a wider pathway should be installed to account for future narrowing. Depending on where it is installed, it may require moderate to constant maintenance, including crack filling and sealing. Asphalt pathways may dip and sag over time with repetitive wear and must be overlaid about every 8–10 years.

Asphalt does not have the same structural strength as concrete and requires greater initial excavation to provide the required rock base depth. And like concrete, it is an impervious surface that will contribute to stormwater runoff.

Pathway Materials: Natural Aesthetic

Mulch A mulch pathway can be composed of organic items such as bark, pine needles, or even sawdust. It is ideal for a smaller, informal pathway that will not see a large volume of traffic. The material can be chosen based on the environment the pathway is in, for example, pine needles along a pathway through evergreens. The downside of organic mulch is that it will get soft and muddy and decompose over time, and will require periodic refreshing. Grass A grass pathway can be used to blend in with or complement the surroundings. The installation cost is quite low but maintenance costs add up quickly as regular weeding, watering, feeding, and mowing are required. In addition, a grass pathway will have a difficult time surviving if exposed to high traffic. Grass does not grow well in deeply shaded areas or beneath trees that compete for water and nutrients.

Pathway Materials: Natural Aesthetic

Stone Stone (pavers and stepping stone) provides an elegant aesthetic but is expensive and challenging to install. It can be set loose in sand, or professionally installed in concrete with mortar joints. It is more suited to smaller pathways or patio areas. For the most natural look, native stone will typically blend well with the surroundings.

Brick and Concrete Pavers Brick and concrete pavers are available in a variety of colors and shapes and can be laid in countless patterns. Pathways are relatively affordable and require little maintenance, and pavers are easy to work with, especially if the pattern chosen minimizes cutting. Brick and concrete pathways are firm and durable—especially in cold or wet climates. It is best to use pavers with a rough surface for grip, and to install edging to prevent them from spreading and shifting underfoot.

Pathway Materials: Natural Aesthetic

Gravel Gravel is a loose aggregation of rock fragments that is permeable, cheaper to install, and more natural-looking than concrete or asphalt, and is suitable for flat areas out of flood plains.

Loose gravel does have high ongoing maintenance costs; it is difficult to maintain consistent surface quality, and gravel migrates on steep trail slopes. Environmental damage can be caused by gravel erosion, and silt deposits can be hard to remove after heavy rains. It is difficult to use in winter due to soft, wet, and muddy conditions. Although the surface is softer on joints, loose gravel is less stable for running and walking on, and for riding bikes on. It is difficult to meet ADA-compliant surface standards by using loose gravel.

Pathway Materials: Natural Aesthetic

Decomposed Granite and Natural Aggregate Decomposed granite (DG) and natural aggregate (crushed stone) offer a natural-looking gravel path but with the durability of a hardscape path. This type of pathway provides a permeable, fast- draining surface. The materials are non-slip and come in a range of colors and sizes to complement virtually any environment, and are easy to install and maintain.

The remainder of this course will focus on DG and natural aggregate pathways.

Private Residence, Lake Geneva, WI

Material Selection: Things to Consider

Environment The type of environment a path is getting placed in will determine how you build the path as well as what type of pathway will work best. • What is the environment you’ll be constructing a pathway in? • Is there a preexisting pathway that will have to be removed? • Are there steep hills? Is it a highly erosive environment? • Is permeability important for the surrounding ecology? • Will the pathway pass through a damp and natural environment?

Traffic Load The pathway material used, as well as the depth the material is installed, will differ depending on if it will only carry foot traffic or a combination of foot and vehicular traffic during its lifetime. • How much traffic will this pathway need to be able to endure? • Will there be foot traffic only? • Will there be bicycle, golf cart, small or large vehicle traffic? • Will this be an ADA-compliant surface?

Material Selection: Things to Consider

Cost Regardless of the project taken on, there is a budget in place. The budget must take into account material and installation costs, and must also plan for future maintenance and repair costs. So know the benefits and limitations of the options available and keep the cost effectiveness over time in mind.

Design Goals Lastly, consider the project’s design goals. The aesthetic desired might not be achievable with cold-looking concrete or obtrusive asphalt. Pathway materials such as DG and natural aggregate have an organic aesthetic, and as pictured here, are available in a wide variety of colors. They can complement residential, commercial, and natural settings. From blacks and browns to whites and greens— pathway aggregate blends can be vibrant or neutral in color, making them suitable for practically any application.

DG and Natural Aggregate Pathway Materials

Grande Cheese Headquarters & Research Center, Fond du Lac, WI

Why Use Them?

Naturally occurring decomposed granite, commonly known as DG, is created as granite is compressed over millions of years and broken down into a combination of sand and gravel. True decomposed granite is available in a limited range of colors. However, other materials can be used to produce pathway products that perform in the same manner as true DG, but in a broader range of colors.

Some manufacturers will also crush different colors of solid quarry rock such as granite, marble, quartzes, and quartzite, and may also use recycled materials such as firebrick, porcelain, and slag to make good pathway materials. The crushed stone and recycled materials mimic the qualities of DG. It just takes more consideration by the manufacturer to make any crushed aggregate work in these applications. A certain percentage of “fines” or “dust” needs to be added to aid in proper compaction. These products require little maintenance and are self- healing. They do not crack and crumble like hardscape materials and can easily be “freshened up.”

Max McGraw Wildlife Foundation, Dundee, IL

Why Use Them?

Both naturally occurring decomposed granite and natural aggregate pathway materials are completely organic and environmentally safe.

DG and natural aggregate pathway materials have a natural look and feel and are available in a variety of colors, making them aesthetically versatile. Pathways composed of these materials can be made firm enough to withstand heavy traffic and can be designed to be ADA compliant. They can be a cost-effective alternative to other types of materials. DG and natural aggregate pathways can be designed to be permeable, which helps meet green design goals. Downtown East Commons, U.S. Bank Stadium, Minneapolis, MN

Green Design Drivers

There are many factors that drive green design, including: • increasingly stringent land development codes and stormwater management regulations • the sustainable design movement: developers, owners, and building professionals are striving to meet green building codes and standards, such as LEED®, and • costs over the lifetime of the project.

Metropolitan Correctional Center, Chicago, IL

Low Impact Development

In the article “Urban Runoff: Low Impact Development,” the EPA defines low impact development (LID) as “systems and practices that use or mimic natural processes that result in the infiltration, evapotranspiration or use of stormwater in order to protect water quality and associated aquatic habitat.” LID attempts to reproduce the predevelopment hydrologic system through site design engineering techniques aimed at infiltrating, filtering, evaporating, harvesting, and detaining runoff, as well as preventing pollution.

The fundamental principles of LID include using, preserving, or recreating natural landscape systems and creating multifunctional landscapes; preventing runoff by minimizing effective imperviousness; and treating stormwater as close to the source area as possible by creating functional and appealing site drainage. By implementing LID principles and practices, water can be managed in a way that reduces the impact of built areas and promotes the natural movement of water within an ecosystem or watershed. BJC Hospital, St. Louis, MO

Low Impact Development

The use of permeable or porous pavements is just one of the many practices that have been used to adhere to these principles. They allow stormwater to drain through where it is infiltrated into the underlying soil or temporarily detained. They provide filtration, storage, or infiltration of runoff, and can reduce or eliminate surface stormwater flows compared to traditional impervious paving surfaces.

The EPA’s best management practices (BMPs) treat rain where it falls. They address criteria critical to the management of urban stormwater runoff and combined sewer overflows: • Volume: Reduce/delay the volume of stormwater that enters the sewer system. • Peak Discharge: Reduce the maximum flow rate into the combined system by decreasing the stormwater volume and lengthening the duration of discharge, lowering the frequency of sewer overflows. • Water Quality: Improve water quality through volume reduction, filtering, and biological and chemical processes.

Permeable or porous pavement is an example of an “area BMP,” which is a land-based management practice that affects impervious area, land cover, and pollutant input.

Potential LEED v4 Contributions

Sustainable Sites (SS) Intent Permeable Pathway Materials Construction Activity Pollution To reduce pollution from construction activities by All permeable pathway projects must implement an erosion Prevention (prerequisite) controlling soil erosion, waterway sedimentation, and and sedimentation control plan for all construction airborne dust. activities.

Rainwater Management To reduce runoff volume and improve water quality by Permeable pathway materials allow rain to infiltrate, replicating the natural hydrology and water balance of thereby reducing runoff and promoting groundwater the site, based on historical conditions and undeveloped recharge. ecosystems in the region.

Heat Island Reduction To minimize effects on microclimates and human and Wet, permeable surfaces allow evaporation of the wildlife habitats by reducing heat islands. moisture, resulting in lower surface temperatures. The reflectance of light colored decomposed granite and natural aggregate is high, resulting in less heat buildup.

Materials and Resources (MR) Intent Permeable Pathway Materials Building Product Disclosure and To encourage the use of products and materials for Aggregate can be made from recycled products that would Optimization – Sourcing of Raw which life cycle information is available and that have otherwise end up in a landfill. For example, some Materials environmentally, economically, and socially preferable life manufacturers use firebrick, porcelain (from sinks and cycle impacts. To reward project teams for selecting toilets), gypsum, and slag for their pathway materials. products verified to have been extracted or sourced in a responsible manner.

Cost

Green construction methods and materials often cost more than traditional methods and materials; however, costs over the lifetime of the project are typically lower.

DG and natural aggregate pathways are an excellent alternative to asphalt or concrete in terms of cost. While initial costs may not always be lower, pathways made from DG won’t endure the same type of damage asphalt or concrete will. Asphalt pathways can dip and sag over time with repetitive wear, and concrete has the tendency to crack as it thaws and freezes in colder climates. Both types of damage require repair and maintenance time and time again. DG pathways can flex with freeze/thaw cycles and can be easily repaired or freshened up by adding more granite until level, then watering and compacting in place.

Noguchi Fountain Sculpture Courtyard, Macalester College, St. Paul, MN

Types of Aggregate Pathways

Oakbrook Center, Oak Brook, IL

Standard Pathway

Standard DG and natural aggregate pathways perform better than many other pathway materials as they create a firm surface while retaining a natural feel and aesthetic.

Standard pathway mixes are screened to a ¼-inch minus aggregate. This specific size allows the product to compact well, while retaining permeability.

Whether to use edging or curbing on any type of DG or natural aggregate pathway is based purely on aesthetics, and options vary depending on the look desired and the structural requirements. Edging and curbing choices include pavers, concrete, sod, natural grasses, and wood chips. Metropolitan Correctional Center, Chicago, IL

Standard Pathway

Standard DG and natural aggregate pathways are very permeable, and therefore provide great drainage. They provide a firmer surface than loose gravel, and are easy to maintain. They are also the most affordable of the DG pathway types.

They are also the most erosive of the DG pathway types, and installations should not be exposed to concentrated running water. Drainage routes should be established and standard pathways should be installed on flat areas. Standard pathway surfaces work great for low-traffic walkways, residential driveways, nature paths, dog runs, bike trails, and garden trails.

Illinois Institute of Technology, Chicago, IL

Stabilized Pathway

A stabilized pathway is one that is made from decomposed granite aggregate or crushed stone screenings mixed with a stabilizing binder. Aggregates are crushed and/or screened to very precise size specifications to ensure optimum compaction and drainage.

A stabilized pathway provides a durable, permeable, and natural aggregate surface. Compared with traditional aggregate materials, a stabilized pathway better resists the erosive effects of weather and foot or vehicle traffic, while retaining environmentally-friendly qualities and a natural aesthetic. Brooklyn Bridge Park, New York, NY

Stabilized Pathway

Stabilizing binder formulations and performance will vary by manufacturer, but typically organic stabilizing binders are made from psyllium that is intricately blended with DG or manufactured stone dust. The binder swells into a gel each time it is in contact with water. This gel grips onto all the fines around it, creating an invisible buffer zone. This buffer zone allows water to stream over the surface without eroding the material. The stone dust that is used as fines in pathway materials increases the sustainability of the pathway, both economically and environmentally.

Midwest Palliative & Hospice CareCenter, Glenview, IL

Stabilized Pathway

A stabilized pathway surface can withstand traffic and weather extremes; however, some erosion can occur on the top layer with prolonged exposure to concentrated running water. Because of the binder, a stabilized pathway has a firmer surface than conventional gravel or a standard pathway, reducing mud and dust, but it is still permeable, and drainage routes need to be established.

The surface retains a natural look and feel over time, inherently “crunching” under foot. The pathway self-heals, which reduces maintenance requirements. The surface can be made ADA compliant, but that is dependent on the type of stabilizing binder used.

Stabilized pathways blend in well in natural settings, making them popular for use in botanical gardens, green roofs, nature paths, greenways, golf course cart paths, trails, parks and recreational spaces, corporate settings, or any environment where a more organic feel is desired. Max McGraw Wildlife Foundation, Dundee, IL

Stabilized Pathway: Testing

The performance of the stabilized pathway is greatly influenced by the type of stabilizer used in the pathway mix. The manufacturer should have test results available for review.

One type of test performed on stabilized pathway mixes is an erosion resistance test. In this type of test the performance of each material is tested using a rainfall simulator designed to replicate a very heavy rainstorm.

In this test example, samples of DG were combined Sample A Sample B Sample C with each of three different binders at a rate of 1.71% Time = 0 Minutes of the total mass. Each sample was thoroughly mixed and combined with 12% water by weight and pressed firmly into the sample container (aluminum channel stock cut into 12-inch sections).

Stabilized Pathway: Testing

The samples were then placed in a rainfall simulator— calibrated to ensure that all samples received the same amount of simulated rain—and tested for 120 minutes. The rainfall simulator was halted at various intervals so that the material losses could be documented. Some of the interval results are pictured here.

Stabilized Pathway: Testing

Once the simulation was complete, the samples were dried and weighed, and the amount of material lost during the simulation was calculated. The results clearly demonstrate significant performance variations among stabilizers.

Rainfall Simulator Results

92.4% 100.0% 88.8% 90.0% 80.0% 70.0% 60.0% 50.0% 40.0% Material Lost Material 30.0% 20.0% 0.9% 10.0% Sample A Sample B Sample C Time = 120 Minutes 0.0% Sample A Sample B Sample C

Wax Polymer Pathway

A wax polymer pathway mix intricately blends DG, natural crushed stone, or recycled materials crushed to meet a sieve specification with a polymeric wax to create a unique paving alternative. The engineered polymers coat each stone particle to make this mix impermeable, and render a sealed, highly durable, natural-looking surface for pathways, patios, driveways, and plazas. This unique process allows for greater creativity in design applications, and provides solutions for demanding traffic projects.

Wax polymer pathways can lend a highly desired natural aesthetic to virtually any space. While standard and stabilized pathway mixes are not suitable for very steep areas, wax polymer pathways can withstand intense erosion and be laid on the steepest of hills.

Photo: Paul Hundley, Erin Hills Golf Course, Hartford, WI

Wax Polymer Pathway

A wax polymer pathway is the most expensive type of DG or natural aggregate pathway. This type of pathway also enjoys reduced maintenance requirements, as it too is self-healing and won’t crack or crumble. It is a sealed, dustless, and mud- free solution that can be designed to be ADA compliant.

Because water cannot penetrate this type of pathway, it is not susceptible to freezing, flooding, or erosion.

Deer Grove Forest Preserve, Palatine, IL

ADA Compliance

As stated, a wax polymer pathway can be made ADA compliant, as can a stabilized pathway if it is made with a stabilizing binder that has been tested for ADA accessibility and has met the maneuverability performance requirements of ASTM F1951, “Standard Specification for Determination of Accessibility of Surface Systems Under and Around Playground Equipment.”

Under the 2010 ADA regulations, accessible outdoor flooring and ground surfaces must be stable, firm, and slip-resistant. The ADA regulations define a stable surface as something that resists movement, while a firm surface is something that resists deformation by applied force, and an accessible surface is something that remains unchanged by external forces, objects, or materials.

ADA Compliance

Wheelchair Accessible Pathway Specifications To be classified as an accessible route, pathways must meet or contain one or more of the following requirements and attributes: • A running slope no steeper than 1:20. • The cross slope of walking surfaces cannot be steeper than 1:48. • Changes in level with a maximum of ¼ inch are permitted to be vertical. • Changes in level between ¼ inch and ½ inch need to be beveled with a slope not steeper than 1:20. • Changes in level greater than ½ inch must be ramped.

Image Courtesy of United States Access Board The width of the pathway must be at least 36 inches, which can be narrowed to 32 inches wide for a length of 24 inches every 48 inches. An accessible route with a width less than 60 inches must provide passing spaces at intervals of 200 feet. Additionally, if the pathway contains any 180º turns, the turning space must be either 48 inches, or 60 inches, depending on the width of the pathway.

Installation and Maintenance

Photo: Paul Hundley, Erin Hills Golf Course, Hartford, WI

Standard Pathway Installation

Proper pathway installation will reduce maintenance, rutting, and degradation, and increase longevity.

1. Prepare the Base The base, or material beneath the standard pathway mix, should be an aggregate base, such as a local DOT-approved road base. The compacted base depth should be a minimum of 4 inches for pedestrian traffic and a minimum of 8 inches for vehicular traffic.

Standard Pathway Installation

The aggregate base should be installed in multiple 2–3-inch lifts and compacted to a minimum of 90%. The finished base should be uniform and free of deleterious debris such as organic materials, nails, stones, and loose soil. Prior to placement of the standard pathway mix, presoak all areas of application.

Please remember the exam password ORGANIC. You will be required to enter it in order to proceed with the online examination.

Standard Pathway Installation

2. Drainage With standard pathways, areas where there are steep slopes, or anywhere there would be concentrated running water should be avoided, or at minimum, drainage routes should be established.

3. Weed Barrier Depending on preferences, a weed barrier or filter fabric may be installed after the base. A weed barrier is optional; it is not a requirement.

4. Curbing and Edging The use of curbing or edging is also optional, not required. If utilized, the compacted standard pathway mix should not exceed the top of the curbing or edging.

5. Spread Material Spread the standard pathway mix as desired to achieve a uniform smooth finish. The final compacted depth should be a minimum of 3 inches for pedestrian traffic and a minimum of 4 inches for vehicular traffic. If installing more than 3 inches, install in 2–3-inch lifts.

Standard Pathway Installation

6. Water Wet the standard pathway mix to ensure the water has penetrated the full depth of the material. The material should be damp but not muddy.

7. Compact Compact the pathway with a one- to three-ton roller or vibratory plate compactor. In small areas that are difficult to access, hand tamping can be done, with multiple passes required. Check for low areas and add additional material as needed, water, compact, and ensure the pathway is level.

Standard Pathway Maintenance

The pathway should be firm, but loose aggregate will appear on the surface as time passes, providing a natural look and feel. If the loose material on the surface is excessive, water the surface and recompact as needed. If ever low or uneven areas should occur, additional material can be spread, watered, and compacted as required.

Private Residence, WI

Stabilized Pathway Installation

1. Prepare the Base The base, or material beneath the stabilized pathway mix, should be an aggregate base, such as a local DOT-approved road base. The compacted base depth should be a minimum of 4 inches for pedestrian traffic and a minimum of 8 inches for vehicular traffic. The aggregate base should be installed in 2–3-inch lifts and compacted to a minimum of 90%. The finished base should be uniform and free of deleterious debris such as organic materials, nails, stones, and loose soil. This product should not be installed in the winter (during freezing temperatures) or in very rainy conditions. Although porous, it is recommended to have proper drainage (e.g., ditches to reroute water or drains to funnel water underneath the path) available to ensure no standing water on the surface or adjacent to the stabilized aggregate. Areas with slopes over 10% are susceptible to erosion due to running water and should be avoided.

Stabilized Pathway Installation

2. Presoak the Base To assist with the bonding of materials and to prevent a layering effect, presoak the base prior to placement of the stabilized pathway mix.

3. Curbing and Edging The use of curbing or edging is optional, not required. If utilized, the compacted standard pathway mix should not exceed the top of the curbing or edging.

4. Activate Prewet the stabilized pathway mix at the job site—this activates the organic stabilizing binder. Turn the aggregate pile until a moisture level of 10–12% has been reached. The product should be moist, not saturated. If you can easily make a ball out of the aggregate with your hands, there is too much moisture.

Stabilized Pathway Installation

5. Place The stabilized pathway mix must be spread and compacted. Place material to sufficient depth to allow 3 inches for light traffic or 4 inches in depth for high traffic, after compaction. Using a paving machine for this step is highly recommended to ensure the material is evenly spread at the specified depth. Occasionally, in extremely dry conditions, the top layer will dry out in between prehydrating and compacting. If this occurs, lightly mist the surface before compacting. For smaller projects, screed when possible.

6. Compact Compact the stabilized pathway mix using a one-ton to three-ton double drum or single static drum roller. Do not use a vibratory plate compactor or vibratory setting for this step. When no further visible roller marks can be seen on the surface, compaction of the pathway is complete.

Stabilized Pathway Installation

7. Level Ensure the pathway is level. The aggregate should rest true to elevation and shouldn’t vary more than ¼ inch at any spot when tested with a straightedge. The surfaces should be crowned at a minimum of 2% and be flush with adjacent materials or edges. The pathway should also be sloped at least 1% to drain away from structures.

8. Clean Poor Installation After the pathway has been compacted and leveled, apply a light spray to the surface to give it a clean appearance. Once the water begins to run off the surface, stop spraying the pathway.

9. Cure Once the surface of the stabilized pathway has visually dried, light pedestrian traffic can take place on the new surface. However, the stabilized pathway should fully cure before vehicle traffic is allowed. Depending on the path’s moisture content, time of installation, climate, and depth of installation, curing times vary. Good Installation

Stabilized Pathway Maintenance

Remove debris by mechanically blowing or hand-raking the surface as needed. Winter plowing should involve the use of a rubber baffle on the plow blade or wheels on the plow that lift the blade ¼ inch off the aggregate surface. For minor repairs, pathways can be rewet and rolled anytime. During the first year, a minor amount of loose aggregate will appear on the surface. If this material exceeds ¼ inch, redistribute the material over the entire surface. Water material thoroughly to the depth of 1 inch and compact with a minimum one-ton power roller. After the repaired area has cured and settled, it should look and feel like its surrounding pathway counterparts. Illinois Institute of Technology, Chicago, IL

Wax Polymer Pathway Installation

It is remarkably easy to install wax polymer pathways. This is a waterless pathway solution, which means that there is no need to mix the aggregate with water before installation.

1. Prepare the Base Prepare the base material prior to laying the wax polymer pathway. Again, the compacted base depth should be a minimum of 4 inches for pedestrian traffic and a minimum of 8 inches for vehicular traffic. The aggregate base should be installed in 2–3-inch lifts and compacted to a minimum of 90%. The base should have a minimum 1.5% cross slope. Make sure to clear the base of debris, nails, etc.

2. Curbing and Edging The use of curbing or edging for the wax polymer pathway is completely optional. However, if it is used, ensure that the compacted polymer mix sits no further than ¼ inch below the top of the edging or curbing.

Wax Polymer Pathway Installation

3. Spread For a final depth of 3 inches, loosely lay the pathway mix 4 inches deep. Spread the pathway mix where desired, ensuring it lies evenly and smoothly before compacting. The use of a paving machine is highly recommended for large projects to evenly spread the material at the specified depth. For smaller projects, screed when possible.

4. Compact Once the wax polymer pathway material is laid where desired, it needs to be compacted. The entire area should be compacted using a one-ton to three-ton roller. Misting the area lightly with water before compacting may help prevent material from sticking to the roller. Do not use the vibration mode on the roller drums as this may cause the binder to separate from the aggregate and discolor the material. In tough-to-reach areas, making multiple passes with a vibratory plate compactor is acceptable. The wax polymer pathway should be firm immediately after compaction, but note that the most frequently used areas will become even firmer with time.

Wax Polymer Pathway Maintenance

Wax polymer pathways are durable and practically maintenance-free. The material retains flexibility and will not crack and crumble. In areas of vehicular use and/or with continued exposure to dirt and debris, surface darkening may occur. Scarifying the surface ⅛-inch deep with a nail drag will quickly clean the surface and expose the fresh underlying material. This procedure will become less frequently needed over time. In areas in need of repair, remove the damaged material. Square the corners and edges with a shovel. Lightly mist the exposed base and edges and fill the area with fresh wax polymer pathway mix and compact as previously described. Deer Grove Forest Preserve, Palatine, IL

Case Studies

Middle Path, Kenyon College, Gambier, OH

Perkins Woods

Project: Perkins Woods Location: Evanston, Illinois Date: October 2013 Contractor: Century Contractors

Perkins Woods, a suburban forest preserve in Cook County, is seven acres of heavily wooded land where wildlife, migratory birds, and citizens of Evanston, Illinois come together. Serving as the romping ground for people of Cook County who want to enjoy the serenity of nature without traveling too far, Perkins Woods is enjoyed by many.

The Problem With so much use, the existing asphalt trail had become dilapidated over time. Worn, cracked, and crumbly, the path had grown to be a hazard to those trying to walk through the woods. Perkins Woods is an especially damp and wet area as well, and the culverts beneath had been silted in, causing further deterioration to the path due to standing water and lack of drainage.

Perkins Woods

The Solution Residents argued over whether to replace the asphalt trail with a larger 10-foot- wide concrete path or a more natural crushed granite trail. After heavy pushing from a small group of residents, it was decided that a smaller granite path, which could allow water to seep through while retaining a natural look and feel, would only enhance the beauty of Perkins Woods.

The Cook County Forest Preserve chose to use a stabilized pathway installed at a three-inch depth—an all-natural pathway solution. The color of the crushed granite complements the natural tones and hues found within the woods, while the improved permeability of the crushed granite, when compared with the old asphalt path, helps the surrounding soil and plants.

As water is redistributed to the surrounding land, water pooling during heavy rain is minimized and the pathway remains non-slip, ensuring the safety of nature- seekers who might get caught in the rain. And when installed correctly, a stabilized pathway is compliant with the Americans with Disabilities Act; so although the pathway is natural, it’s completely wheelchair accessible.

Perkins Woods

Site Obstacles There were a few issues that came up during and after the installation of the Perkins Woods walking path.

The first issue to be addressed was how to dampen the material. The organic stabilizing binder chosen had to be activated—activation of the stabilizing binder is achieved by mixing it with water. This process has to occur in a location where the pathway mix won’t become contaminated with dirt, leaves, or other debris, making activation in the middle of the woods impossible.

Mixing the stabilized pathway mix outside of the woods on a nearby side street, with the help of a skid steer and a water truck, proved to be the ideal solution.

Perkins Woods

The second issue arose soon after the installation of the path. Perkins Woods has above-average moisture levels, extending the cure time of the stabilized pathway. While not yet cured, a tree-trimming group had driven a vehicle onto the path, disrupting it and causing minor damage.

The Cook County Forest Preserve was served well by being encouraged to invest in an extra sack of the stabilized pathway mix at the outset of the project. After scarifying the surface of the damaged area, the extra pathway mix was blended with water to activate, leveled, and compacted over prepped areas of the pathway. After a proper cure time suitable for the environmental conditions of Perkins Woods, the new pathway can withstand the weight and abuse of nature-goers and vehicles, and the Cook County Forest Preserve is happy with the completed pathway.

Instead of opting for a large and obtrusive concrete pathway, Perkins Woods found a pathway that complements the natural essence of the land through both its aesthetic value and its permeability, which allows water to drain instead of pool. With proper maintenance, the Cook County Forest Preserve and the residents of Evanston can enjoy this natural pathway for many years to come.

Middle Path at Kenyon College

Project: Middle Path, Kenyon College Location: Gambier, Ohio Date: Three phases, 2014–2016 Landscape Architects: Michael Van Valkenburgh Associates

Kenyon College is Ohio’s oldest private college. It is situated on a 1,000-acre campus that includes a 480-acre nature preserve, providing a pastoral setting. Middle Path runs the length of the college’s campus, serving as a footpath, gathering place, and village green. A few years ago, Middle Path was a 3,600-foot-long walk made from a local river stone, which provided color, texture, looseness, and sound.

By cdorobek, Washington, DC. Middle Path at Kenyon College, CC BY 2.0, via Wikimedia Commons

Middle Path at Kenyon College

The Problem Although the path performed well in fair weather, in foul weather it became impassable. The major issue was that the river stone washed away and left potholes and soft, muddy spots that would lead to puddling or ice formation, depending on the season. The college set out to restore Middle Path with the goal of making the surface universally accessible in all types of weather, while retaining the look, feel, and sound of the iconic walkway. The restored path was to be more easily maintained than the previous path and was to feature improved drainage.

The Solution The architects recommended installing a stabilized DG pathway to address accessibility and drainage, while maintaining a natural feel and look. Their approach included a program of design-phase mock-ups and manufacturer’s product development, and innovations in installation methods.

After a few test panels, and subsequent failures, the architects worked with the DG manufacturer to develop a solution. The manufacturer conducted its own trials, making several test panels that varied the stabilizer type, quantity, and DG aggregate size. There were some successful panels that were formed using an alternate organic stabilizing binder. As a result, two new test panels were installed at Kenyon College using the new product formulation. The panels successfully survived the Ohio winter, and based on their performance, the project proceeded.

Middle Path at Kenyon College

Michael Van Valkenburgh Associates states the following as lessons learned during the Middle Path restoration: • The right stabilizer is critical. • Prehydration needs to be done correctly. • Get the compaction right. • The use of formwork aids installation. • Well-designed drainage is a must. • When possible, have the manufacturer’s representative on site. • Work directly with the manufacturer on the mix ratio. • Grain size affects bonding. • Minimize vehicles when saturated.

As per the architects, “Like all materials, DG has its challenges. It should never be represented as carefree in either installation or maintenance. Winter maintenance in temperate climates, for example, will always be a consideration. But its advantages are many, including the absence of distracting joints or color shifts and the rich experiential dimension in the sound of it underfoot. It is a unique material with a beguiling mix of casualness and sophistication that encourages a slightly slower pace, and it provides a special vantage from which people can appreciate their surroundings.”

Erin Hills Golf Course

Project: Erin Hills Golf Course Location: Hartford, Wisconsin Date: Fall of 2012 to Spring of 2017 Installers: Erin Hills Grounds Crew

Carved from glacier movement thousands of years ago, Erin Hills is a golf venue that cannot be rivaled by many. The 652-acre course still maintains some of the streams that were carved by the last glacier to cover Wisconsin, and offers visitors exquisite vistas composed of rolling hills and swaying grasses. It was chosen to host the 2017 U.S. Open, with 156 players from all over the world attending. With so many players coming, Erin Hills decided to replace their existing walking paths with new, highly durable paths that could withstand the harsh Wisconsin winters and the course’s hilly terrain. Photo: Paul Hundley

Erin Hills Golf Course

The Problem Erin Hills desired natural-looking cart and walking paths that blended in with the course, but there were issues with erosion due to the hilly terrain. Their grounds crew was spending far too much time maintaining their walking paths when their valuable time could have been spent maintaining the course. Refusing to settle for obtrusive hardscapes such as asphalt or concrete, they opted for an aggregate path with a natural look and feel. The pressure was on to update all of the walking paths before the June 2017 U.S. Open event.

Photo: Paul Hundley

Erin Hills Golf Course

The Solution Erin Hills was looking for a natural solution that would blend in perfectly with their gorgeous scenery and decided to use both stabilized and wax polymer pathways in a color to match their famous fescue grass. They opted for a natural aggregate path blended with wax polymer for the hilly terrain. On flatter terrain, they chose to combine their aggregate with a stabilizing binder to better withstand forces that would otherwise lead to erosion, which was the issue with the previous crushed stone mix that Erin Hills had been using.

Photo: Paul Hundley

Erin Hills Golf Course

Challenge One hurdle that had to be overcome was finding the correct binders for the pathway mixes. The binders are chosen based on local climate, pathway slope, and individual aggregate type. With a property as large as Erin Hills, the manufacturer worked hard to derive the proper binders needed, devising and implementing a brand new wax polymer binder that was cleaner and performed better than the planned original binder.

The wax polymer pathway is preblended for easy installation, and maintenance crews chose not to compact the new pathways with a one- to two-ton roller. For a more natural-looking pathway system, it was decided to let foot traffic compact the new pathways naturally. Photo: Paul Hundley

Erin Hills Golf Course

Wax polymer pathways were a great alternative for the Erin Hills project because these pathways do not get muddy or dusty like more traditional walkway options, keeping all golfers and observers dry and clean during the U.S. Open and making the pathways ideal for local golfers all season long. Additionally, the Erin Hills grounds crew will no longer be spending large amounts of time maintaining the pathways and will now be able to focus on the course itself. The wax polymer pathways are easy to maintain and can be easily manipulated if subtle changes are needed, and the new pathways won’t have a problem standing up to the harsh freeze/thaw cycles that the course is subjected to in Wisconsin, due to their impermeable composition.

The stabilized pathways used at Erin Hills were chosen for their affordability, permeability, and design. The manufacturer was able to duplicate the custom aggregate blend already used for the wax polymer pathways, allowing for a seamless transition into the stabilized pathways. The stabilized pathways will withstand heavy foot traffic and reduce mud, dust, and erosion, while still remaining permeable. Erin Hills installed three inches of prehydrated stabilized pathway mixture over a DOT-approved base course for proper stability and drainage. Because of its affordability and versatility, Erin Hills utilized a stabilized pathway mix whenever the more durable wax polymer mix was unnecessary.

Zachary Reineking, Director of Course Maintenance for Erin Hills states, “Over the years Erin Hills has tried an array of products for our undulating walk paths. The wax polymer and stabilized crushed granite...provides a superior combination of ease of installation, durability, limited maintenance, and great aesthetics.”

Summary and Resources

Luther Ely Smith Square, Gateway Arch, St. Louis, MO

Summary

Decomposed granite and natural aggregate pathway materials are used where a firm pathway is required for pedestrian or vehicular traffic, but a natural look, unlike hardscape surfaces, is preferred.

Decomposed granite pathways come in three variations: • standard pathway • a firm surface that compacts well, while retaining permeability • stabilized pathway • stabilizing binders create an even more durable natural pathway, while retaining permeability • the stabilized mix better resists the erosive effects of weather and traffic, while retaining a natural look and feel • wax polymer pathway • a completely sealed, impermeable pathway solution that eliminates erosion and dust • the wax polymer mix maintains a natural look, while being most suitable for extremely high-traffic areas or steep slopes

Decomposed granite and natural aggregate pathway materials are an affordable and aesthetically pleasing alternative to concrete, asphalt, pavers, and other hardscape surface materials.

Resources

“Best Management Practices (BMPs) Siting Tool.” EPA.gov. U.S. Environmental Protection Agency (EPA), October 7, 2015, www.epa.gov/water-research/best-management-practices-bmps-siting-tool. Accessed May 2017.

Budzinski, Neil, and Matthew Girard. “The Right Path.” Landscape Architecture Magazine, November 2016, pp. 46, https://landscapearchitecturemagazine.org/2016/11/08/the-right-path. Accessed May 2017.

Envirobond, n.d., www.envirobond.com/organiclock. Accessed May 2017.

Kafka Granite, n.d., www.kafkagranite.com. Accessed May 2017.

“2010 ADA Standards for Accessible Design: Chapter 4: Accessible Routes.” Access-Board.gov. United States Access Board, 2010, https://www.access-board.gov/guidelines-and-standards/buildings-and-sites/about-the-ada-standards/ada- standards/chapter-4-accessible-routes. Accessed August 2017.

“Urban Runoff: Low Impact Development.” EPA.gov. U.S. Environmental Protection Agency, n.d., www.epa.gov/nps/urban-runoff-low-impact-development. Accessed May 2017.

Conclusion

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