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Low-Density Concrete Basics

John Poullain, PE

This three-hour online course provides basic guidance for the properties of low-density concrete (LDC) and specified density concrete (SDC) and how they compare with those for normal-density concrete (NDC). The physical and mechanical properties, construction considerations, advantages, disadvantages and economic considerations of LDC are discussed. Also discussed are the guidelines for mixing, placing, curing, pumping and field controls during construction. Comparisons between the properties of low-density and normal-density concrete and special construction concerns are presented. Included tables summarize the differences in properties and the criteria for mix proportions described in the text.

The principal benefit for using LDC is the large mass that can be saved in a structure while having the same strength as with normal-density concrete. Since aggregate may be 60-70% of the weight of concrete, concrete densities can be 15-25% lower primarily because of the low-density of the manufactured aggregate. The benefits of reduced dead loads include the lighter weight of structural spans, lighter supporting members and reduced foundation requirements. Lighter loads or more pieces of prestressed members can be transported and truck concrete mixers can haul larger volumes because of the lighter weight concrete (provided legal and safety requirements are met).

Disadvantages include the higher cost for the manufacturing process of heating shale, clay or slate for the low-density aggregate and the transportation costs from the supplier. LCD requires an additional 15-50 lb/cy of cement to be comparable to normal-density concrete. Certain precautions must be observed to insure the aggregate is adequately saturated. If the aggregate is not adequately saturated, the slump will be decreased as the concrete mixture looses water to the under saturated aggregate resulting in reduced workability and pumping performance.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

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