Lightweight Concrete vs Normalweight Concrete: Comparing Cost and Load Reduction

Lightweight concrete (LWC) has been in the building industry for centuries. Its performance capabilities and benefits when used in various concrete construction applications including concrete flooring, precast, prestressed concrete members as well as bridge deck components have made it particularly relevant for large-scale projects. According to Michael Corrin, PE, at Stanley D. Lindsey and Associates Ltd., “Recent trends for long floor spans have once again pushed lightweight concrete to the forefront as it allows the minimal depth of structure, yet still provides damping resistance to minimize vibration.”

Despite the proven performance, confusion about its ability to reduce structural loads still exists, as do misconceptions about its cost implications. To set the record straight, this blog compares LWC’s ability to reduce design loads and aggregate cost compared to normalweight concrete (NWC).

Evaluating Design Loads in Lightweight Concrete Structures

LWC weighs about 90-115 pounds per cubic foot (pcf) compared to NWC, which is about 145 pcf for LWC (using equilibrium density with adequate drying with time). This means LWC is at least 20 percent lighter than NWC. Specifying expanded shales, clay or slate lightweight aggregate in the concrete mixture can help LWC achieve comparable strength and drying times as NWC. When concrete components are lighter, engineers can plan smaller structural systems, including foundations. The material’s reduced weight is also advantageous for seismic design considerations.

A report on the structural portion of a five-story commercial building in downtown Salt Lake City, Utah compared a design using a 5.25-in. thick LWC floor with a density of 110 pcf to a design using a 6.5-in. thick NWC floor with a density of 145 pcf. Both floors achieved a two-hour fire rating. The study found that using LWC on a metal deck resulted in a total floor weight that was 18.3 percent lighter than would have been possible with NWC. This weight reduction led to a 23 percent decrease in seismic mass and a 21 percent decrease in base shear. This comparison demonstrates the significant benefits of using lightweight concrete in reducing structural loads and improving seismic performance.

Is Lightweight Concrete Cost-Efficient?

While LWC made with ESCS aggregate may incur additional production and shipping costs, assuming that it is not economical could be inaccurate. Given the numerous advantages of LWC, such as reduced design load, thinner sections meeting fire ratings, and increased tensile strength for longer spans, project teams can often offset the higher per cubic feet cost. When building professionals consider a concrete structure as a whole, LWC proves to be a cost-effective choice for many projects.

According to the aforementioned comparison report of a five-story building in Utah, the pcf cost of LWC was 7.5 percent greater than NWC. But LWC provided cost savings in other areas and proved to be 9.2 percent less expensive than NWC concrete design. Hence, LWC made with ESCS lightweight aggregate helped the project team save over $435,000.

The greatest cost savings were found in the footings, where LWC presented a 27 percent reduction in the material costs due to lower structural load. Lightweight concrete’s low density and thinner slab requirements also minimize dead load. Consequently, steel framing costs in the project were decreased by 10.5 percent. Furthermore, lighter components are easier to install and enable additional labor savings to offset the additional material cost.

Realizing Design and Cost Efficiency With Lightweight Concrete

When the complete design of a building is considered, LWC made with ESCS aggregate can result in reduced design load and help drive economies that not only offset its higher initial cost but can lead to net savings in a building’s bottom line. Reach out to your nearest ESCS manufacturer to discuss LWC for your project needs.