Glass block flooring

Glass block flooring is used in many different situations, from bridge walkways and mezzanine floors to balconies, corridors and public highways. They are most commonly used as pavement lights - glass lenses set into precast concrete as part of pavement construction to allow natural light into the space below.

They were developed in the 1880s as cast iron frames glazed with cut squares of glass, intended to provide a natural light source for basements and cellars beneath the pavement. Gradually these were superseded by reinforced concrete panels with plain glass fenestration, but these were then superseded themselves by pressed glass prism lenses, designed to transmit the maximum amount of light.

They can be constructed in situ, although in the UK they are predominantly precast in factory-controlled conditions to individual project specifications.

There are currently no British or European standards that apply to pavement lights or other precast concrete panels with glass block or paver inserts. Manufacturers must test their pavement light products to determine loading, thermal, acoustic and fire performance, as well as compliance with any local authority or building regulations requirements.

Design considerations include:

Type and percentage of light transmittance required.
Type of likely traffic (i.e. pedestrian, vehicular, etc.).
Loading requirements of the panel.
Fire integrity and thermal isolation rating of the panel.
Thermal performance.
Slip resistance.
Expansion joints.

Glass lenses are typically 20-22 mm thick, have a flat, smooth finish, and are available in 100 x 100 mm and 200 x 200 mm squares.

Pavement lights for heavy duty applications (such as loading bays, roadways, and so on), must be capable of sustaining significant loads. The required loading determines the spanning ability, but spans of up to 4.4 m can be achieved with distributed loadings of up to 20 kN/m2.

Slip resistance is measured on the overall surface of the panel, not just the glass or concrete. Improved slip resistance can be provided by sandblasted pavers which add chromite or carborundum grains in the concrete wearing surface.

Glass paver lenses can also be used for vertical precast reinforced concrete panels. These are sometimes used for windows and rooflights in spaces such as prisons and detention rooms.

Another variation is the precast concrete stair tread, which incorporate glass pavers or blocks, sometimes in combination with glazed floor panels.