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Tag: Jack Moore

FAQs: Lightweight Geotechnical Fills

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Ask Our Expert: Jack Moore, Geotechnical Applications

Since the raw material is clay, what happens to the lightweight aggregate when it’s exposed to water?

ANSWER: We get that question quite a bit because in the geotechnical world, clayey soils can be problematic and not easily built upon. So when we talk about our raw material being clay, it does cause some questions.

But in this particular case, we’re taking the raw clay that we mine and placing it into a rotary kiln where it’s fired up to around 2000°F. At this temperature, it expands, creating air voids, and the particles change state and become vitrified. Due to this process, they don’t revert back to their original clay state, meaning your embankment or retaining wall structure will not degrade if exposed to water.

What is the in-place density of the lightweight aggregate?

ANSWER: The density can vary based on the source and grading, but generally, we look at loose bulk densities between 35 and 45 pounds per cubic foot. In-place densities are around 45 to 55 pounds per cubic foot.

The density varies with the grading: coarser material is lighter, while finer grading makes it slightly heavier.

Is lightweight aggregate significantly lighter than other fill materials?

ANSWER: Right, and that’s a good point. When comparing it to select fill commonly used in mechanically stabilized earth structures or embankments, select fill is typically around 120 pounds per cubic foot, while our lightweight aggregate is about 50 pounds per cubic foot or less.

It’s generally at least half the weight of conventional fill material, which is significant when addressing settlement concerns and similar issues.

Can conventional compaction equipment be used to achieve desired densities?

ANSWER: Yes, since lightweight aggregate is a granular material, standard earthwork equipment used by a typical grading contractor can be used for compaction.

Our material can be handled, placed, and compacted like ordinary materials. Unlike other lightweight materials, no specialized contractors, crews, or equipment are needed for fill placement.

What is the internal friction angle of Arcosa’s lightweight aggregate?

ANSWER: The internal friction angle is an important geotechnical feature for any fill material, especially for structures needing to resist lateral earth pressure.

Our material generally has a friction angle of around 40 degrees or higher, which is beneficial for stability. This value is used in geotechnical analysis and adds another benefit to the material’s low bulk density.

Lightweight Aggregate Plays a Key Role in Pier Expansion

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This Arcosa Lightweight aggregate provided a unique solution by reducing vertical stresses and minimizing the lateral forces acting on the steel bulkhead wall system. These advantages allowed the design team to downsize the gauge and diameter of the supporting pipe piles, delivering critical cost savings without compromising structural integrity.

A Big Project!

Since the 1950s, Port Canaveral has been a vital hub for Florida’s trade and tourism. As part of the port’s 30-year master plan, engineers demolished the outdated CT-3 and designed a modern terminal complex to accommodate some of the world’s largest cruise ships, including Carnival Cruise Line’s Mardi Gras. The project scope included a new 188,000-square-foot terminal, a parking garage, and an expanded 1,309-foot berth. Lightweight aggregate played a crucial role in achieving these goals, helping the project stay within its $155 million budget by reducing costs in shipping, placement, and structural systems.

Efficiency Delivers Value

The sheer volume of lightweight aggregate required—approximately 60,000 cubic yards—posed logistical and budgetary challenges. Lightweight aggregate’s low density (35-55 pcf, compared to 95-135 pcf for traditional fill) allowed for reduced shipping and handling costs. The material was transported by rail to Florida, unloaded onto trucks, and then delivered 15 miles to the project site. Because each truckload could carry nearly twice the volume of traditional fill, the number of shipments was reduced by over 50%. This reduction in truckloads streamlined delivery and minimized delays, ensuring construction could proceed efficiently.

Lightweight Aggregate’s Slight Edge

Once the material arrived, lightweight aggregate continued to show its advantages. Contractors used standard earthwork equipment—loaders, rollers, and compactors—to place and compact the fill, with no need for specialized machinery. Due to the angularity and gradation of Arcosa’s lightweight aggregates, compaction required fewer passes, optimizing the stability and density of the fill. These efficiencies reduced potential maintenance costs, as the lower applied vertical pressure from the lightweight fill reduced settlement, increasing the durability of the new wharf.

Reducing Adjacent System Costs

Beyond shipping and compaction, lightweight aggregate helped the project team reduce the gauge and diameter of the steel pipe piles in the bulkhead wall system. The material’s low density and high internal friction angle (over 45 degrees) significantly lowered lateral earth pressures compared to natural fill materials. This allowed the design team to specify smaller and lighter steel components in the wharf’s structural systems, delivering considerable cost savings.

Benefits Beyond Pier Construction

Completed in mid-2020, CT-3 now accommodates the largest cruise vessels, solidifying Port Canaveral’s status as one of the world’s busiest cruise ports. Thanks to Arcosa’s lightweight aggregate, the terminal expansion demonstrates the effectiveness of value engineering and serves as a model for future projects requiring secure land creation over water. Lightweight aggregate’s low density, high durability, and cost-saving advantages make it an ideal choice for similar projects, whether creating stable land from open water or reducing lateral support costs for other geotechnical applications.