Cellular Lightweight Concrete and Its Effect on Compressive Strength

Cellular lightweight concrete, which also known as CLC, is a pre-formed foam method utilizing fly ash to replace cement. The foam entraps air in the aggregate, making the material light and stiff but strong enough for high load bearing applications. This paper presents the effects of replacing the portland cement by various levels of fly ash in a typical cellular lightweight concrete mix and compares its compressive strength at curing age 3, 14, 28 and 60 days to conventional portland cement. The results of this study indicate that replacing the cement by 10 and 20 percent by weight of the binder significantly improves the compressive strength of cellular lightweight concrete without affecting its water absorption or porosity.

The stability of the foamed concrete is dependent on the ability to retain the air bubbles during production, construction and in service. This can be achieved by maintaining a low Water-cement ratio during the forming process. The foam can then be mixed and pumped with the help of specialised foam generating, mixing and pumping equipment.

The optimum proportion of foaming agent is 0.6 to 0.8% by weight of the cement. Foam agents containing more than this amount are unstable and collapse easily. This is due to the reactions of the foaming agent with other products in the mix which can cause segregation and increase drying shrinkage. Furthermore, mixing the foam for longer than required destroys the bubbles. This affects the quality of the finished product.