Understanding Different Types of Lightweight Aggregate Concrete

Lightweight concrete has been used in construction for centuries, and its use has grown with advances in building technology.

Its benefits, including reduced dead load, better insulation, and sound reduction, have made it a popular choice in building and design.

However, not all lightweight concretes are created equal. The key difference lies in the aggregates used in the mix, which can significantly affect the installation process and the performance of the finished slab.

In this article, we’ll look at the main types of lightweight concrete: low-density natural aggregate concrete, processed or synthetic aggregate concrete, cellular or aerated concrete, and high-performance concrete.

• Where Lightweight Concretes Differ
• Where Lightweight Concretes Are the Same

Understanding the characteristics of each type will help you make informed decisions when choosing and working with lightweight concrete.

Lightweight concrete dates back to ancient Rome, where builders used pumice as a lightweight aggregate. It became much more common in the 20th century, after a rotary kiln process for making expanded shale aggregate was developed around 1918. Today, different types of lightweight concrete continue to be developed, offering advantages in weight, insulation value, sound reduction, and workability.

The basic description of lightweight concrete is simple: it weighs less than standard concrete because it uses lower-density aggregates. Structural lightweight concrete typically weighs about 90 to 115 pounds per cubic foot, compared with roughly 140 to 150 pounds per cubic foot for normal-weight concrete, and nonstructural types such as cellular concrete can be much lighter. But with advances in technology and new materials being tested, it quickly becomes clear that lightweight concrete is not all created equal.

Where Lightweight Concretes Differ

The real difference, and it can be a significant one, is in the aggregates used in the concrete mix. They affect not only the finished weight but also, often, the process or products needed for a successful installation.

Low-Density Natural Aggregate Concrete

Most natural low-density aggregates are volcanic in origin and include pumice, tuff, scoria, and cinders. Diatomite is also sometimes used. The advantage of these aggregates is that they often need no processing beyond crushing and screening.

Pumice is the most commonly used. It’s a volcanic glass that forms when frothy lava cools quickly into a porous rock.

Other natural materials, like perlite and vermiculite, are also used. These are expanded by rapid heating before they go into the mix. Cinders from coal or coke combustion are sometimes used too, but their use is limited because sulfur compounds in the cinders can affect the performance of the concrete.

Processed or Synthetic Aggregate Concrete

Some lightweight concrete formulations use processed by-products or synthetic materials as the aggregate.

• Expanded shale or clay: Prepared shale or clay is heated until gases inside the material expand it. Coatings with higher fusion points are sometimes added to keep the particles from sticking together during processing or storage.
• Expanded slag: Blast-furnace slag treated with steam or water can also produce an acceptable aggregate for lightweight concrete.
• Synthetic aggregates: The synthetic aggregates being tested and produced range from recovered fly ash or oil sands to recycled plastics, paper, or glass to expanded polystyrene beads. Weights vary widely from product to product, and the potential to put by-products and recycled materials to use has made this type of aggregate a focus of development.

Cellular or Aerated Concrete

This type of lightweight concrete is the result not just of the materials but also of the process. It’s produced by introducing tiny air pockets into the concrete mix. One method uses a chemical reaction, adding aluminum powder or hydrogen peroxide to the batch so it generates gas within the concrete and expands it.

In autoclaved aerated concrete (AAC), which is usually made as precast blocks and panels, the expanded material is then cured with high-pressure steam. The other method uses a preformed foam that is mixed into the slurry to create tiny air voids in the finished concrete.

High-Performance Concrete

High-performance lightweight concrete is “enhanced” to allow longer placement times or to achieve specific density, volume, or performance properties for severe or specialized environments.

These mixes generally use not only low-density aggregates but also additional admixtures to get the desired qualities in the finished concrete.

Because of the many possible combinations of aggregates, admixtures, processes, and end products, “lightweight concrete” is a broad umbrella term. Each mix must be specified job by job and fully understood for its final density, compressive strength, and production and installation requirements.

Where Lightweight Concretes Are the Same

Whatever their composition, all lightweight concretes need accurate moisture testing during drying, and again later if moisture intrusion is suspected.

With so many variables affecting the drying schedule of a lightweight concrete slab, accurate moisture testing is what tells you when it’s ready for finishes or flooring.

ASTM F1869, the calcium chloride (CaCl) test, has specifically excluded lightweight aggregate concrete since 2010. That leaves in-situ relative humidity (RH) testing following ASTM F2170 as the ASTM test method for these slabs.

Other surface-based tests, such as plastic sheet or hood tests, have also proven problematic for measuring moisture in lightweight concrete.

Free Download – 4 Reasons Why Your Concrete Is Taking Forever to Dry

RH testing, such as with Wagner Meters’ Rapid RH^®, gives an accurate picture of the internal moisture conditions that will affect the concrete’s long-term performance. The sensor is placed at 40% of the slab’s depth,¹ the depth research has shown best indicates the moisture level the slab will reach once it’s covered.

Moisture isn’t evenly distributed through a slab while it dries, but once the slab is sealed by flooring or a coating, the remaining moisture redistributes through the slab. That is the moisture level the installed flooring or finish will be in contact with over time.

RH testing gives an accurate picture of the internal moisture conditions in a lightweight concrete slab, so building schedules and product decisions can be made with good information.

Advances in lightweight concrete technology continue to expand the possibilities for resource-efficient building, and accurate RH testing helps those slabs perform as intended over time.

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¹ 40% of the slab’s depth is the correct test hole depth if the slab is drying from one side; for slabs drying from two sides, it’s 20%.

Jason Spangler

Jason has 20+ years’ experience in sales and sales management in a spectrum of industries and has successfully launched a variety of products to the market, including the original Rapid RH® concrete moisture tests. He currently works with Wagner Meters as our Rapid RH® product sales manager.

Last updated on October 19th, 2026