What is CLC

House made of Lightweight Concrete Blocks

Cellular Lightweight Concrete (CLC) is conventional concrete, where natural aggregate (gravel) is exchanged for the best insulation medium available, namely air, embedded in an organic and bio-degradable foam that offers no chemical reaction but solely serves as wrapping material for the air. Consequently CLC behaves, like conventional concrete, in particular concerning curing, hardening and most important “ageing “. CLC infinitely increases its strength by hydration (forming of crystals in cement) as long as exposed to humidity in the atmosphere.

For structural (steel-reinforced) application, CLC is used in densities of 1,200 to 1,400 kg/m³, which, due to the billion of micro-sized and uniform air bubbles offer 500 % more thermal insulation and a substantially higher fire-rating than conventional concrete. If a wall of conventional concrete should offer the same thermal insulation as CLC, the wall produced would have to measure 5 times thicker and therefore also use 10 times more material (sand, gravel, cement) to produce. CLC structures in hot climatic zones require only 1/5th energy for air-conditioning when compared to traditional clay-brick structures.

Since the early twentieth century, two ideas were developed to produce lightweight concrete – Aerated Autoclave Concrete (AAC) and Cellular Lightweight Concrete (CLC). Each is based on the idea that adding air bubbles to mortar would lower its weight while at the same time improving the product.

The difference between AAC and CLC lies in how the air bubbles are generated.

AAC uses aluminum powder to catalyze a reaction that generates hydrogen gas – bubbles formed from the reaction and are trapped in a lime, flyash, gypsum and very small percentage of cement slurry. The slurry is allowed to set and then the product is cut into panels or blocks and placed in an autoclave to cure (an autoclave is required because the slurry has low cement contents).

CLC is a process based on making air bubbles in the form of a foam and then mixing the foam into a cement / flyash slurry. The slurry is then poured into moulds. Since CLC slurries have higher cement contents, no autoclave curing is required – instead, the finished product is cured like normal concrete or Steamed Cured with low pressure to achieve early strength.

As compared to AAC lightweight products, CLC air bubbles are significantly smaller, stronger, and each bubble is part of a closed cell system – which means Brickwell CLC block products have lower water absorption – about half of the water absorption as AAC And Brick. Like Cement, CLC blocks increase in strength when exposed to moisture. Hence CLC bricks become tougher over time.