Lightweight Aggregate Provides Practical, Cost Effective Geotechnical Solutions

With about half the density of ordinary fill materials, lightweight aggregate is both easier to handle and more versatile, and offers practical solutions for projects including underground pipelines and conduits, bulkheads, highway embankments and situations where adequate drainage is of paramount importance.benefits that range from structural, to thermal, to aesthetic.

What it Is and Why It Makes Excellent Fill Material

Lightweight aggregate is produced from select shale, slate, or clay. After mining, the raw material is crushed and is screened for size, then fed into a rotary kiln, where it is heated to temperatures of up to 2200°F. As the material is heated, it becomes molten and gas bubbles form, causing expansion to about twice its original size. After cooling, the lightweight aggregate is screened, stockpiled, and shipped. The expanded material is a ceramic aggregate that has structural properties similar to natural aggregate, but is less dense.

“Aside from its light weight, another advantage of lightweight aggregate, particularly in backfill applications, is that it develops an angular, multifaceted surface during the manufacturing process. This produces a very high angle of internal friction once the product is placed, and that adds both strength and lateral stability,” according to Jeff Speck, Technical Director at Trinity Lightweight, a leading manufacturer and supplier of lightweight aggregate. “The predictable high angle of internal friction, or phi angle, of the material can reduce the effect of lateral forces by 50 percent or more, compared to conventional backfill,” Speck said, adding that “the material has excellent insulating properties as well.”

By: Scott Ramminger

Kiln in operation at Erwinville, LA

Technical Article Geotechnical Backfill

Lightweight aggregate makes great sense as fill material in a wide range of applications. The material is ceramic, so it is water insoluble, chemically inert, has high strength and durability, and is easier to handle and place than competitive products. And it is readily available throughout the U.S.

Using lightweight aggregate as fill is a particularly good idea in areas with soft soil or unstable soil conditions. It is great for bedding and backfill for pipes and conduits, waterfront applications, backfill for bulkheads and retaining walls, shallow foundations, highway embankments, and many other projects.

Backfill Protects Concrete Culvert

In this October 2012 photo, lightweight aggregate is used as a backfill in an interstate project near Birmingham, Alabama. The LWA was used to ensure an existing concrete drainage system would not be crushed

by the weight of new traffic lanes.

Excellent in a Wide Range of Geotechnical Applications

Lightweight Stacks Up Well Against All Competition -- Not Just Conventional Fill

In today’s competitive construction products market, lightweight aggregate stands up well against the competition -- not just other types of granular aggregate -- but newer products as well, such as EPS geofoam.

Lightweight aggegrate used as a backfill in New Orleans, known for its soft compressible soils.

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In Texas, the Department of Transportation is comparing the performance of lightweight aggregate used as fill on one side of a highway embankment project with with geofoam blocks, used on the other side.

“We don’t see any settlement or cracking of the pavement at that end of the bridge,” according to Richard Willammee Jr., P.E., Materials Engineer with the Ft. Worth District of the Texas Department of Transportation (TxDOT). “We’re still very satisfied with it (the lightweight aggregate).”

The installation used 1,000 cubic yards of Trinity Lightweight expanded shale aggregate.

The Fort Worth District had struggled for many years with settlement problems on both ends of the bridge, which is heavily traveled by large trucks going from rock and sand quarries in Southwest Johnson County into the Dallas-Fort Worth area. It is also a major truck route from the Dallas-Fort Worth area to south and west areas of Texas, Willammee said.

According to Ed Bell Construction Company, the general contractor, the installation of the expanded shale was simple and fast. The geofoam block system was more expensive and more labor

intensive because of the need to cut and stack each block to fit the embankment area. Marshy areas, or areas where the soil is highly expansive -- where it is necessary to keep the weight on the base soil to a minimum -- are good candidates for using the lightweight aggregate fill. There are numerous examples of lightweight aggregate fill in marshy areas from Louisiana to Minnesota, and from Florida to Texas.

Contact Trinity Lightweight, or visit TrinityLightweight.com today to find out more about how lightweight aggregate can help solve your specific geotechnical or other construction challenges.

Scott Ramminger has written extensively about construction and construction products, for a wide range of publications. He is the former CEO of a construction products trade association and a former Director of Marketing for the National Concrete Masonry Association.

Resources: Expanded Shale, Clay, and Slate Institute (ESCSI) www.escsi.org

Put Lightweight Aggregate To Work in Your Application

TxDOT utilizes expanded shale aggregate on the west end embankment of the US 67 bridge over State Highway 174 near Ft. Worth.

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