Lightweight Concrete

Lightweight Concrete

Lightweight means concrete and mortar with a low density. Either aggregates with a lower density are used or artificial voids are created to reduce the weight. The method used depends mainly on the lightweight concrete application and its desired properties.

Lightweight concrete is used for

·    Thermal insulation

·    Lightweight construction (ceilings, walls, bridge decks, slabs)

·    Precast products

·    Levelling concrete

·    Infill concretes

Characteristics of lightweight concretes

·     Reduction in fresh concrete density

·     Reduction in hardened concrete density

·     If lightweight concrete is used as an infill concrete with low load bearing requirements i.e. for dimensional stability, highly porous concretes and mortars are generally produced (aerated lightweight concrete)

·     If lightweight concrete with good mechanical properties (i.e. compressive strength) is required, special aggregates are used (naturally very porous but also dimensionally stable)

Production of lightweight concrete

·     Porous lightweight materials such as expanded clays must be prewetted to prevent too much water being drawn out of the concrete during mixing

·     Do not use too fluid a consistence due to the risk of segregation

·     Lightweight concrete with a specific gravity < 1600 kg/m³ can be difficult to pump

·     Correct handling of vibrators is particularly important (quick immersion, slow lifting) to prevent air entrapment

·     Cure immediately and thoroughly. Suitable methods are misting treatment and covering with sheets or spraying with curing agents. Without  proper curing there is a high risk of cracking due to excessive drying differences.

·     Foamed concretes often shrink considerably and have low dimensional stability