Energy Efficient Paving Stones  

TransMaterial has a post on a material made from recycled glass that takes less half the energy to make compared to clay or portland cement pavers - Bottlestone.

Bottlestone is a solid surface material designed as an alternative to stone. Made from 80% post-consumer recycled glass, Bottlestone is suitable for a variety of commercial and residential horizontal surface applications, such as countertops, tabletops, and fireplace hearths.

Bottlestone is manufactured from post-consumer glass using a flexible process that allows the inclusion of a wide variety of sources, such as fluorescent light bulbs or waste door and window glass. Because no special cleaning is required, water use is minimized during fabrication - unlike the recycled glass found in some concrete countertops.

Bottlestone also compares favorably to stone and brick in terms of embodied energy and strength. A one-inch thick Bottlestone paver, for example, requires 9,800 BTU/SF, as opposed to 26,750 BTU/SF for a Portland cement paver or 20,000 BTU/SF for a clay paver of equivalent strength.