HydroLite Lightweight Aggregate Plays Key Role in Record-Breaking Structure

• Teaser: Wilshire Grand Center, which stands at an impressive 1,100 feet, is recognized as one of the tallest buildings in the western United States. The project’s engineers needed to significantly reduce the building’s overall weight to achieve this height, which is why they opted for structural lightweight concrete.
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  With over 15,000 cubic yards of lightweight aggregate used in the concrete mix—10,000 cubic yards of which incorporated Arcosa’s HydroLite® vacuum saturated lightweight aggregate—the project achieved not only the necessary height but also critical fire resistance and improved pumpability, allowing for more efficient construction.

The structural design of the building incorporates multiple lightweight concrete slabs, with lightweight concrete poured on metal decking to form the floors and core, spanning over 1.2 million square feet across the entire tower.

The ability to pump lightweight concrete all the way up to project’s soaring height was key to the successful completion of the building, which now features 900 hotel rooms, a 70th-floor sky lobby, and 445,000 square feet of office and retail space.

According to Clint Chapman, Western Region Marketing & Technical Manager for Arcosa Lightweight, the lightweight concrete used for the project was pumped at heights of 1,300 feet, with 1,100 feet of that being vertical pumping.

“The fact that our HydroLite is presoaked made pumping it up to the building’s very high floors more efficient compared to traditional materials,” explains Chapman.

HydroLite® is a vacuum saturated lightweight aggregate produced by Arcosa Lightweight. This process allows the aggregate to absorb water, providing improved pumpability, reduced slump loss, and better consistency during placement. The vacuum saturation also enables the aggregate to maintain internal moisture, contributing to better curing and minimized cracking in the concrete.

Chapman also notes that the LWC used for the project also helped achieve the project’s strict fire rating requirements without needing additional fireproofing layers.

Wilshire Grand Under Construction

Turner Construction, the general contractor, led the build, with Conco Cement Company handling the concrete pumping, and Catalina Pacific Concrete, a division of CalPortland, providing the ready-mix. Arcosa Lightweight supplied the lightweight aggregate for the concrete that was used on the metal decking surrounding the building’s core and elevator towers.

Arcosa’s structural lightweight aggregate was manufactured at its Frazier Park, California plant, with the ready-mix supplier replacing standard weight granite with the lighter HydroLite aggregate.

“The HydroLite reduces the concrete’s unit weight from 147 pounds per cubic foot to just 115 pounds per cubic foot,” Chaman notes.

The Wilshire Grand Center project is a prime example of exceptional collaboration among the general contractor, the ready-mix concrete supplier, the concrete placement subcontractor, the pumping subcontractor, and the lightweight aggregate supplier.

“This project showcases the value of a cohesive team,” says Chapman. “Everyone worked together seamlessly to ensure the success of this monumental build.”

Shasta Arch Bridge Project: Using Arcosa Lightweight Aggregate for High-Performance Concrete Solutions

• Teaser:The newly completed Shasta Arch Bridge, with its striking design and sweeping arches, serves as a crucial route for travelers in Northern California. Built with Super High Performance Concrete containing Arcosa’s lightweight aggregate, the bridge’s reduced structural load enhances both its durability and aesthetic appeal, ensuring long-term reliability for all who traverse this remote and scenic area.
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  Ric Maggenti, who was a Senior Materials & Research Engineer for the California Department of Transportation (Caltrans) before his retirement, explained, “Lowering demand consisted of changing the structure concrete (stem, bent caps, and deck) from a normal weight, normal strength concrete to a high strength, lightweight concrete.” Maggenti emphasized that lightweight concrete has been successfully used in numerous bridges worldwide, citing the Bay Bridge, which has shown no observable deck distress after more than 80 years of service, and the Napa River Bridge, which continues to perform well even after the 2014 Napa earthquake.

Originally, the bridge was designed using normal weight concrete with a specified compressive strength of 4,000 psi. Maggenti explained, “The increased design strength [for the lightweight concrete] eliminated any need to significantly adjust for rebar developmental lengths, or accounting for lower shear, creep, modulus of elasticity, and modulus of rupture values used in the original design.” By increasing the compressive strength to 6,000 psi, Maggenti noted, “these other property values converge to those of a lower strength normal weight concrete,” addressing concerns such as Alkali Silica Reaction (ASR), Delayed Ettringite Formation (DEF), deck permeability, and cracking.

“The increased design strength eliminated any need to significantly adjust for rebar developmental lengths, or accounting for lower shear, creep, modulus of elasticity, and modulus of rupture values used in the original design.”

Arcosa’s Hydrolite® expanded clay aggregate, produced in Frazier Park, California, was selected for the project due to its ability to meet the strict performance requirements. Pre-conditioned at the Frazier Park plant, the aggregate arrived at the ready-mix concrete plant in a near-saturated condition, simplifying the production of pumpable lightweight concrete.

Maggenti directly addressed concerns about the pumpability of lightweight concrete, stating, “[Caltrans] was not at all subjectively distracted by a belief that lightweight concrete is inherently difficult to pump.” He explained that the difficulty in pumping lightweight concrete arises when the aggregate is not saturated, but that Arcosa’s pre-saturated aggregate eliminated this issue. Maggenti continued, “A 125 pcf concrete imparts by its mass a pressure of 0.87 psi resisting its vertical motion inside the pipe while a 150 pcf concrete imparts by its mass a pressure of 1.04 psi per cubic foot of concrete. That is a 20% increase in force to move normal weight concrete. So why would a lightweight concrete be more difficult to pump than a normal weight concrete?”

Ultimately, the lightweight concrete mix exceeded expectations, with pumping rates occasionally reaching over 100 cubic yards per hour (cy/hr), far surpassing the original target of 60 cy/hr. “The mix pumped better than anybody expected, and no additional pumping agent chemical admixture was used,” Maggenti added.

There were concerns about exceeding the maximum allowable temperature in the mass concrete within the diaphragms and bent caps due to the high cementitious content of 900 pounds per cubic yard. Two cooling pipes were installed longitudinally through the bent caps to control the concrete temperature, which had a target of 160°F. While temperatures exceeded this at times due to extreme ambient air temperatures and the difficulty of controlling water temperature in the cooling pipes, the concrete did not overheat.

“Initially it was believed the lightweight aggregate would exacerbate mass concrete issues. However, this was not the case for the Arcosa aggregate. The difference was the amount of water in the lightweight aggregate.” — Ric Maggenti

Maggenti explained that Arcosa’s aggregate, with an absorption rate of over 24%, requires more energy to increase its temperature than traditional mineral aggregates, which helped prevent thermal issues caused by the high cementitious content.

For this project, all of the requirements for a lightweight, air-entrained concrete mix that was pumpable, durable, and high-performing were met. All concrete strengths exceeded the specified requirements for high-strength concrete, and the 120 pcf equilibrium density target was achieved. The results of air content field tests on the plastic concrete were confirmed by petrographic examination of the hardened concrete.

“The requirement for a lighter structure was met by using Arcosa Lightweight Aggregate, producing concrete with a maximum equilibrium density of 120 pcf,” Maggenti stated. The pre-conditioned lightweight aggregate helped lower pump line pressures, allowing the concrete to be pumped efficiently, sometimes at rates exceeding 100 cy/hr. The consistency of the concrete remained stable throughout transport, even with extended durations of up to 1½ hours.

With these unique attributes, it’s no surprise Caltrans labeled the resulting material “Super High Performance Concrete” and anticipates it to be a model for future challenging situations.