Lightweight concrete block or AAC? Differences and choice

Where does lightweight concrete get its lightness?

Lightweight concrete gets its low weight in one of two ways. One is a lightweight aggregate such as pumice. The other is to create a great many small air pores inside the material. This second group is called cellular concrete.

Autoclaved aerated concrete and the Redblok lightweight concrete block both belong to the second group. They look alike from the outside. But the way the pores form and the way the material hardens are completely different, and that difference directly affects the block's dimensional accuracy, drying shrinkage and strength.

How is autoclaved aerated concrete made?

AAC is calcium silicate based. Lime and/or cement, silica sand or fly ash are mixed with aluminium powder or paste. The reaction releases hydrogen gas, which makes the mass rise and forms the pores. The risen mass is cut and hardened in an autoclave with high-pressure saturated steam.

This step needs pressurised steam, so AAC is made only in factories, as blocks or panels, and reaches site as a cut product. AAC masonry units are covered by EN 771-4 (TS EN 771-4 in Türkiye), and reinforced AAC precast elements by EN 12602. TÜRKBETON does not produce AAC; it appears in this article for comparison only.

How is the Redblok block made?

Redblok is a non-autoclaved lightweight concrete with closed air pores, made by the foam concrete (CLC) method. There is no gas-forming reaction. Air bubbles are prepared separately and mixed into a cement-based paste, and that is how the pores form. The mix is cast into block moulds and sets through normal cement hardening, with no autoclave. The blocks are then cured, cut to size, palletised and stretch-wrapped.

The amount of air in the paste sets the block's density. We measure fresh density on every mix and record every batch. We use a separate mix design for each density class; the admixtures and their proportions are specific to our company. The design band for wall blocks is 500–800 kg/m³.

Lightweight concrete made this way needs no autoclave, so in general it can also be poured fresh on site; AAC cannot. TÜRKBETON does not do poured work. We produce only standard-size Redblok lightweight concrete blocks.

What are the real strengths of AAC?

AAC's strengths in wall blocks should be stated plainly. AAC blocks are generally made with high dimensional accuracy and laid with thin-joint adhesive, which makes a true wall surface easier to achieve. Steam curing in the autoclave forms the mineral tobermorite, so AAC has low drying shrinkage and its dimensions stay stable.

The known weak point of non-autoclaved concrete is lower strength and higher drying shrinkage at the same density. We developed the Redblok mix design specifically around that point. We follow a strict curing routine and measure shrinkage, dimensions and strength in every batch. Even so, compare the two blocks at the same density, for tolerance, shrinkage and strength, using test reports.

Which block suits your wall?

For non-loadbearing interior partitions and infill walls within a frame, both blocks are candidates. If tight dimensions, thin joints and low shrinkage are your priority, AAC is a strong option. With the Redblok lightweight concrete block, you choose the density class to suit the wall's job. The site's distance from the factory and the project specification also shape the decision. Our Şanlıurfa Birecik factory is in production, and our factory in the Erzurum organised industrial zone (OSB) is under installation in 2026.

Keep one difference in mind. AAC products are defined by their own product standards. Cellular lightweight concrete falls outside the scope of TS EN 206, the Turkish adoption of the European concrete standard, so its performance is defined by the project specification and laboratory testing. The values for Redblok's density classes are design targets, verified by trial mixes and laboratory tests. On request, we add the batch records to your project file.