Used to allow light to basement areas, pavement lights first appeared in London in the late 1880s in the form of cast iron frames glazed with cut squares of glass. Plain glass fenestration was quickly superseded by pressed glass lenses, which in turn were succeeded by pressed glass prism lenses designed to transmit as much light as possible.
Reinforced concrete, patented in France by Joseph Monier in 1867 (for the production of garden ornaments), and the introduction of machine-made glass in 1903, allowed French architect Joachim to build the first glass and concrete dome a year later. In 1907 Friedrich Keppler, founder of Deutsche Luxfer Prismen-Gesellschaft, applied for a patent for solid glass blocks to be fitted into support structures of reinforced concrete. Shortly after Keppler’s patent the first reinforced concrete and glass block pavement lights were used in London.
Pavement lights can be constructed in situ, but precast units dominate UK usage.
There are no British or European standards covering pavement lights or other precast concrete panels with glass block or paver inserts. BS EN 1051-1:2003 gives definitions and descriptions of glass blocks for use in nonloadbearing walls, and of glass paver blocks for incorporation into precast concrete panels used as pavement lights and in other horizontal applications, which may be capable of taking vehicular traffic.
It is unfortunate that the diagrams in the standard are missing dimensions and have misleading titles. Interpretation is possible only by comparing them with the nomenclature and details given in the two tables within Annex C, which are themselves given different names but the same number. It is essential to use manufacturers’ technical literature and advice to achieve a successful specification. In particular, the range of block and paver sizes available from manufacturers is much more limited than the extensive listing in the standard.
Types of unit
Reinforced concrete and glass blocks or pavers are combined not only to produce pavement lights, but also roof lights and floor lights. Manufacturers test their products to determine loading, thermal, acoustic and fire performance, and compliance with local authority requirements. Slip resistance is less well covered, but experience has proven that the face size limitation for glass pavers (100 mm x 100 mm), imposed by the London authorities in the 1930s, produces acceptable results. Some anufacturers use sandblasted pavers and add chromite or carborundum grains in the concrete wearing surface to improve slip resistance. The concrete soffit of cast units is usually left as cast, but manufacturers may be able to offer post-casting alternatives.
UK manufacturers use imported blocks and pavers with factory-mixed concrete cast in moulds and hand floated to a finish. The default is for the concrete to be left uncoloured, but bespoke colours and textures can be provided. Unglazed units with special surface finishes are available, to allow for the addition of in situ surface coverings to match the surrounding area.
Access to plant in basements is often provided by using lift-out pavement lights or non-glazed concrete units. Units can also act as break-out smoke outlets and can be fire rated. All such uses must be determined with the manufacturer and clearly identified by cast in plates and demarcation strips.
The spanning ability of precast units depends on the required loading but spans up to 4.4 m can be achieved with distributed loadings up to 20 kN/m2.
Vertical precast reinforced concrete panels, doubled glazed with paver lenses, are made as windows and rooflights for use in cells and detention rooms. Such units have to comply with Home Office requirements to withstand a static loading of 165 kN/m2. To ensure compliance always consult the manufacturer before specifying and detailing.
Precast concrete stair treads incorporating glass pavers or blocks are increasingly being specified, particularly in combination with glazed floor panels. Manufacturers offer treads requiring support at each end and capable of spanning up to 1490 mm. Bespoke cantilever treads are also available.
The imaginative use of glass blocks and pavers in reinforced concrete flooring and roofing construction, combined with the size imitations imposed by transportation, is getting beyond the scope of precast units. In situ construction may be about to see a revival and will be considered for inclusion in future updates of H14.