Structural Efficiency with LW Concrete

A major reason lightweight concrete is used is for weight reduction, which often enhances the functionality, architectural expression and/or constructability of a structure. ESCS lightweight aggregate optimizes structural efficiency by improving the strength to weight ratio as shown in the following applications:

Buildings – In building this is achieved by thinner fire resistant slabs, longer spans, expressive roof design, taller buildings, additional floors added to existing structures and when building are on locations with poor soil conditions. Weight reduction optimizes land use by affording a smaller footprint, which allows surrounding space to be more people friendly.

Less building materials are also used:

  • The reduction in foundation loads may result in smaller footings, fewer piles, smaller pile caps, and less reinforcing
  • Reduced dead loads may result in smaller supporting members (decks, beams, girder, and piers)
  • Reduced dead load will result in reduced inertial seismic forces

Bridges – With bridges, this may allow a wider bridge deck (additional lanes) being placed on existing structural supports with minor or no modifications. Improved constructability may result in balanced cantilever bridge construction where lightweight concrete is used on one side of a pier and normalweight concrete used on the other to provide equal weight while accommodating a longer span on the lightweight side of the pier. This has permitted locating piers closer to land with significant reductions in cost. On bridge deck replacements or overlays the deck may be thicker to allow more cover over reinforcing or to provide better drainage without adding additional dead load to the structure. Lightweight concrete has been used to create longer bridge spans, thereby reducing the need for costly and aesthetically unacceptable piers.

Precast / Pre-stressed – Longer or larger precast members can be manufactured without increasing overall weight. This results in fewer columns or pier elements in a system that is easier to lift or erect with fewer joints or more elements per load when transporting. There are several documented cases where the savings in shipping cost far exceeded the increased cost of using lightweight concrete. At some precast plants each elements shipping cost is evaluated by computer to determine the optimum concrete density;

Marine – In marine applications such as offshore oil platforms or floating bridge pontoons, lightweight concrete allows for increased topside loads and the reduced draft often permits easier movement out of dry docks and through shallow shipping channels.

Specified Density Concrete – Specified density concrete is becoming increasingly used to enhance design flexibility and project economics. Specified density concrete is defined as concrete that has been specified to a specific equilibrium density for a specific reason. The reasons to do this are numerous but often include the following:

  • To lower shipping cost by maximizing the number of precast concrete elements per truck
  • To increase the size of concrete elements that can be transported
  • To lower the draft or increase the load caring capacity of floating concrete structures
  • To obtain very low density concrete in the range of 70 lbs/CF
  • To lower construction cost by optimizing design efficiency and flexibility
  • To allow for the maximum architectural expression
  • To improve the durability and performance of concrete by using small amounts of lightweight aggregate to enhance the hydration of cementitious materials. This enhanced hydration is commonly called internal curing.

In general, the amounts of lightweight aggregate used per cubic yard of concrete can range from small amounts for internal curing to 100% lightweight aggregate for very light mixtures. In the precast/prestressed concrete industry specified densitiy concrete ranging from 115 lb/ft3 (1920 kg/m3) to less than concrete composed entirely of normalweight aggregates are very common. The increasing usage of specified density concrete is driven by engineers’ decisions to optimize the concrete density to improve structural efficiency (strength to density ratio), to reduce concrete product transportation and construction costs, and to enhance the hydration of high cementitious concrete with very low w/cm (ACI 213R-03).

Insulation – The use of LWA lowers the thermal conductivity of concrete and provides significantly better insulating qualities for thermally sensitive applications such as cryogenic applications or high temperature petroleum storage structures.

ESCS Aggregate/Cement Interface


Construction Efficiency – Lowering Environmental Impact