Life Cycle Cost

The current use of any building material is predicated on cost, functionality, durability, aesthetics, or a combination of these. The traditional first cost methodology of owners, designers and public officials around the world has contributed to a non-sustainable system. Decisions based on first cost most often ignore life-long maintenance, rehabilitation and operating cost. Life cycle costing is the only way to properly evaluate the sustainability of a project.

The initial cost of ESCS lightweight aggregate per unit volume is usually higher than a comparable unit of normalweight aggregate. The embodied energy unit cost to produce ESCS is also higher than a comparable unit of normalweight aggregate. However, when analyzed from a holistic or product use perspective, the higher initial cost and embodied energy are almost always offset and in most cases result in significant net savings. These savings come from weight reduction that results in a reduction of overall materials being used, and in construction and performance efficiencies.

In structures, any increased up-front cost of components manufactured with ESCS is more than offset by the cost savings in the following areas: labor, lower dead loads, better fire resistance resulting in reduced concrete thickness, and less reinforcing required in building frames, girders, piers, and footings. Long-term heating and cooling costs will also be reduced due to the higher insulating properties and overall superior thermalperformance of the building.

For example, when comparing lightweight and normalweight concrete on a bridge with an 8-inch thick deck where the LWC has a $20 per CY premium, the finished deck cost is generally less than 1% higher. This increase is more than offset by the initial cost savings in reduced concrete and reinforcing in girders, piers, and footings. If the increased durability and longer service of the bridge are considered, the economic and environmental advantages of using lightweight aggregate can be substantial and clearly identifiable.

Energy Performance

Reducing the concrete density increases its thermal resistance. For example, concrete at 90 lb/ft3 has an R value of 0.26/inch while the R value for 135 lb/ft3 concrete is approximately .10/inch. In other words, the 90 lb/ft3 concrete has a 260% better insulation factor than the 135 lb/ft3 concrete (ESCSI Information Sheet 3201, 1999).

For concrete masonry, the increase in the thermal performance translates into savings of 5.5 cents per block per year. This energy cost reduction is significant and extends over the life of the structure. The life cycle cost savings are many, many times greater than the potential higher first cost of the block. See the masonry section for more detail.

Embodied Energy

It is well documented that the total embodied energy to build a building is only 1 to 3% of the total occupant energy used by that building over its useful life (Construction Technology Laboratories report project number 180028 conducted for ESCSI 2001). In light of the facts that approximately 97 to 99% of the energy used throughout the building life cycle is primarily a function of climate and occupant behavior, it becomes obvious that our biggest energy resource is efficiency.

The embodied energy to manufacture rotary kiln structural lightweight aggregate includes mining, manufacturing, and transporting the material to the jobsite, soil blender, or building product manufacturer. The cost of this embodied energy is often paid back in a very short period of time, because of the improved thermal performance, lower transportation costs, and reduction of labor costs associated with the building elements. For example the following embodied energy payback using expanded shale, clay and slate in concrete masonry is less than one year.