So What Can Lightweight Aggregates Do For You?
by Eric Nelson, ASLA

Park maintenance professionals and designers know of the challenges facing parks, golf courses, and sports fields. The demand for quality conditions exists but often runs counter to the reality of budget cuts, aging facilities, and increased use of the facilities. Yet, a common thread in quality park conditions start with the soil and that’s where lightweight aggregates can help. If used properly, they can help save water and reduce maintenance, add environmental benefits, and provide a stream of new revenue.

Lightweight aggregates are produced by firing raw shale, clay, or slate in a rotary kiln at extremely high temperatures, cooling the material and then crushing and screening it for various applications. What makes this material unique is that it is very lightweight, durable, porous, and free of pathogens and weeds.

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Photo shows the size variation of expanded shale for horticulture as manufactured by Texas Industries. These materials are most used for amending clay soils, planting bed preparation, bioretention mediums, turf overflow parking, fire lanes and structural soils. Image courtesy Texas Industries.

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Photo shows the size variation of expanded shale for horticulture as manufactured by Texas Industries. These materials are most used for amending clay soils, planting bed preparation, bioretention mediums, turf overflow parking, fire lanes and structural soils. Image courtesy Texas Industries.

So what can lightweight aggregates do for you? For one, they can help keep things green and natural looking while improving soil infiltration and environmental filtering. Take, for example, parking lots. Often parking lots are designed for peak flows for a few times each year. They are typically impervious with no infiltration or environmental benefit, and are costly to install. When mixed with a suitable sandy clay loam, expanded shale can be used to create temporary overflow parking areas, fire lanes, maintenance access routes in parks and golf courses, and special event areas that drain well, help filter runoff, and provide stable footing for cars, emergency vehicles, tables, chairs, and foot traffic. Best of all, they provide a good structure for turf development that blends into the natural park setting.

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Overflow turf parking areas at the Dallas Cowboys Stadium in Arlington, Texas use a special blend of expanded shale and clay loam that supports vehicle parking and pre-game tailgate festivities. This soil structure also works for growing turf, capturing runoff from adjacent parking areas, and maintaining green space. In this project, use of the expanded shale and clay loam proved to be less expensive than using impervious pavements. Image courtesy Texas Industries.

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Park districts have opportunities to create special event areas to accommodate outdoor weddings, festivals and corporate events to generate revenue. At the roofless Nasher Sculpture Center in Dallas, Texas, a special soil uses expanded shale for improved drainage and to withstand heavy foot traffic, reduce compaction around trees, and provide a firm base for large sculptures on loan to the museum. Image courtesy Texas Industries.

Expanded shale is a natural amendment for clay soils. It adds air and pore space to the tight nature of the clay particles, helps retain moisture, and does not break down. In turf, it can improve infiltration of poorly draining soils and help relieve compaction of high traffic areas. Many established trees in high use park areas have compacted soils that threaten their health. Arborists have used expanded shale in “drill and fill” operations beneath canopies and in soil mediums after the removing compacted soils with an air spade. In landscape beds, the blending of expanded shale and organic material into clay soils combined with subsurface irrigation and a top layer of mulch provides the highest savings on irrigation.

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The University of North Texas’s new Leadership Building in Denton, Texas used native and locally-adapted plants, amended clay soils with organic matter and expanded shale, installed a subsurface drip irrigation system, and added mulch to reduce weeds and retain moisture. Image courtesy Texas Industries.

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Seasonal plantings are a big part of the Dallas Arboretum. Expanded shale and compost added to the heavy clay soils improve drainage, add porosity, and help retain moisture. The increased air and pore space makes it very easy to cultivate beds and to change out seasonal plantings. Image courtesy Texas Industries.

Bioretention is one of many best management practices to control runoff for small watersheds. Many parks and golf courses are designed in floodplains due to the reduced land cost and natural settings. A good formula for creating bioretention mediums is to develop a 2-foot deep detention/filtration zone using 50 percent plant-based compost, 25 percent expanded shale and 25 percent native soil, resting atop a 1-foot deep retention/recharge zone with expanded shale or pea gravel and a 4-inch perforated drainage pipe as an overflow. This practice does a great job of filtering the first flush of contaminants such as fertilizers and silt, and hydrocarbons/oils from parking lots before they reach nearby waterbodies.

Quality baseball infields hold moisture, reduce dust, and are safe and consistent for play. There are several kinds of infield conditioners made from expanded shale and clay along with drying agents, marking dust, and mound clays to service any field from the recreational to professional level. Park managers have come to love the consistency of the materials, ease of application and great service. The payback for great playing surfaces is satisfied players, more league play, and increased field rentals.

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The Texas Rangers in Arlington, Texas, as well as other professional teams, universities, and park districts use expanded shale and clay products to maintain consistent, safe, and quality playing surfaces. Image courtesy Texas Industries.

There are several companies across the United States that manufacture lightweight aggregates; the Expanded Shale Clay and Slate Institute ( is a great source to locate producers in your region.

Eric Nelson, ASLA, is a senior sales representative with Texas Industries of Dallas, Texas. He can be reached at      

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