watertown

Tennessee High School Boasts 450,000 Lightweight Block

Ten years after its completion, Watertown High School continues to serve the fast-growing community of Watertown, Tennessee, as a 208,000 square-foot educational facility. Constructed using approximately 450,000 lightweight concrete masonry units (CMUs) produced by Southland Brick and Block of Murfreesboro, the school was designed by KBJM Architects of Mount Juliet and built by RGAnderson Company of Nashville.

Southland’s Steve Honey described the project as a milestone for the region. “It’s a very large school,” Honey says. “All of the block above grade are lightweight, and the exterior walls consist of a 4-hour fire-rated block assembly.”

Why Lightweight CMUs Were Chosen


The decision to use lightweight CMUs for the project provided a combination of strength, fire resistance, and ease of construction. Block producers, like Southland, can easily provide 4-hour fire-rated units by following a specific mix design developed in 1992.

“We call those Q-LITE or SmartWall units,” says Bill Wolfe, Marketing & Technical Manager for Arcosa Lightweight. “The fire rating of a concrete masonry unit is based on the equivalent thickness of the unit and the materials used. The reason lightweight block has a superior fire rating is that it contains lightweight aggregate that’s been fired in the manufacturing process. Aggregates that have already been fired won’t expand, so they remain thermally stable under fire conditions.”

Achieving the Fire Rating


Lightweight concrete masonry units can achieve two-hour, three-hour, and four-hour fire ratings. Due to the extensive Underwriters Laboratories (UL) testing conducted when Q-LITE was introduced, concrete block producers can now easily provide UL-certified blocks to architects and building engineers.

“They don’t need to go through the fire test or build a wall for testing because we’ve already done that,” Wolfe explains. “The producer just needs to follow our mix design using lightweight aggregate, and UL will issue a certified fire rating for those units.”

Wolfe also explains that producers can obtain a UL certification by engaging the lab’s follow-up service, where UL inspectors sample the aggregates and ensure the blocks meet the specified standards. “This extra step provides valuable third-party certification, which is often sought by architects for assurance that the materials will perform as specified,” says Wolfe.

Independent Certification for Architects


The benefit of going the extra step for third-party certification through UL is highly valuable for architects, according to Wolfe. “A third-party certification assures architects that they’re getting exactly what they need,” he says.

Additionally, the block producer can offer a UL Certified concrete masonry unit without needing to conduct an individual fire test for each project. This method allows producers to manufacture CMUs with the same fire resistance and thermal stability without requiring 100% lightweight concrete in every unit.

Final Result


The $37 million Watertown High School was completed on time in 2014. The project was so large that it required two masonry contractors—RG Masonry and CG Masonry—to collaborate on the installation of the lightweight blocks.

In addition to classrooms, the facility features an updated football field and gymnasium, with a capacity to accommodate up to 1,000 students from across Wilson County. The school was designed with geothermal technology for heating and cooling, providing energy-efficient climate control throughout the building.

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