Structural lightweight Concrete

Light Weight Concrete in General

Light Weigh Concrete can be defined as a type of concrete which includes an expanding agent in that it increases the volume of the mixture while giving additional qualities such as nailbility and lessened the Dead Load, It is lighter than the normal weight concrete. The used of light weight concrete has been widely spread across countries such as USA, United Kingdom and Sweden.

Structural Lightweight Concrete

Has an in-place density (unit weight) on the order of 90 to 115 lb/cu.ft (1440 to 1840 kg/cu.m) compared to normal weight concrete with the density in the range of 140 to 150 lb/cu.ft (2240 to 2400 kg/cu.m), For Structural applications the concrete strength should be greater than 2500 psi (17.0 Mpa).

The Concrete mixture are made with lightweight coarse aggregate such as

·         Rotary kiln Expanded Shale
·         Clay or Slate materials
·         Air-cooled blast furnace slag
·         Pelletized or extruded fly ash

The Primary use of structural light weight concrete is to reduce dead load of the concrete structure which then allows the structural designer to reduce the sizes of the columns, beams, footings and other structural concrete element of the structure.

Based on ACI-318R-08

Lightweight concrete has lower tensile strength which can reduce shear strength, friction, and properties, splitting resistance, bond between concrete and reinforcement and increase development length compared with normal weight concrete with the same compressive strength.

Mixing Criteria of Light weight Concrete

In General, procedures for mixing lightweight structure concrete are similar to those weight concretes, but some of the more absorption aggregates may require prewetting prior to addition of other mix ingredients. Water added at the batching plant should be sufficient to provide the specific slump at the building site; slump at the batching plant will probably be appreciably higher.

Adequate Workability as indicated by the concrete slump, is necessary in order to realize all the desired properties of the hardened concrete.

Advantage of Structural Lightweight Concrete

·         Provides more strength-to-Weight ratio in Structural element

·         Provides a high fire-rated Concrete Structure

·         Provides higher R-values of wall elements for improved insulation properties that help energy conservation

·         The Porosity of lightweight aggregate provides source of water for internal curing of the concrete that provides continued enhancement of concrete strength and durability

·         Rapid and relatively simple construction

·         Economical in terms of transportation as well as reduction of Manpower

Disadvantage of Structural Light Weight Concrete 

   

·         Very sensitive with very water content in the mixtures

·         Mixing time is longer than conventional concrete to assure proper mixing

Compressive Strength of Lightweight Concrete

Lightweight Aggregate particle strength varies with the type and source of aggregate and there is no reliable correlation between aggregates and have strength ceilings, that is the maximum strength attainable with a reasonable quantity of cement. The compressive strength of light weight aggregate concrete is usually related to the cement content at a given slump, rather than the to the water-cement ratio,

Some approximate relationships between average strength and cement content

approximate relationships between average strength and cement content and Average strength  for concretes with  3 to 4-inch slump and 50 to 7 percent air
Compressive strength, psi	Cement content, pounds per cubic yard
	All lightweight	Sanded lightweight
2500	400-510	400-510
3000	440-560	420-560
4000	530-660	490-660
5000	630-750	600-750
6000	740-840	700-840
Based on data from ACI 213R-79

Structural lightweight Concrete has been used for Bridge decks, piers and beams, slab and wall elements in steel and concrete frame buildings, Parking structures, tilt-up walls, topping slabs and composite slab on metal deck

List of Sample Projects that made of light weight concrete

·         Chateau on the Lake, Branson, MO.

·         First National Bank, Omaha, NE

·         Tabor Center, Denver CO.

·         Alameda Towers, Kansas City, MO

·         Kansas City International Airport City, MO

·         Heart of America Bridge Kansas City MO.

·         Metropolitan Square St. Louis, MO.