CPD 7: Sustainable block paving

Introduction to block paving

Block paving is specified to create attractive external environments for many types of development, including housing, education, retail, commercial, leisure, industrial and civic schemes. Key benefits of block paving include the variety of aesthetic effects that can be achieved, its heavy load-bearing capacity, lower lifetime costs, speed of installation, easy access to underlying systems, and ease of repair. When manufactured to certain standards, block paving can also offer high standards of sustainability.

Specifying block paving

When specifying block paving, it is important to choose products that are manufactured to the relevant British standard. The British standard that relates to the manufacture of concrete block paving is BS EN 1338:2003, “Concrete paving blocks - requirements and test methods”, which replaced BS 6717:2001. This states that systems should achieve a minimum average compressive strength of 3.6MPa, and also that concrete block paving should be subject to a number of performance tests to meet minimum standards on resistance to splitting, weathering, abrasion and slipping/skidding.

A number of British standards relate to the structural design of block paving systems, such as:

• BS 7533-1:2001 Pavements constructed with clay, natural stone or concrete pavers. Guide for the structural design of heavy duty pavements constructed of clay or concrete pavers
• BS 7533-2:2001 Pavements constructed with clay, natural stone or concrete pavers. Guide for the structural design of lightly trafficked pavements
• BS 7533-3:2005 Pavements constructed with clay, natural stone or concrete pavers. Code of practice for laying precast concrete paving blocks and clay pavers for flexible pavements
• BS 7533-11:2003 Code of practice for the opening, maintenance and reinstatement of pavements of concrete, clay and natural stone
• BS 7533-13:2009 Pavements constructed with clay, natural stone or concrete pavers. Guide for the structural design of permeable pavements.

To ensure that the specified products are used on the scheme design, designers are recommended to use the manufacturer’s NBS product sheets.

Surface wear and colour

Surface wear should be a key consideration when specifying block paving. Products with a soft surface can wear very quickly, exposing large white stones and giving the blocks a tired and unsightly appearance. To ensure products retain their appearance over many years, almost all European manufacturers now produce blocks with a hardwearing surface layer, a practice that has become common over the last 20 years.

This is done by using two different concretes within the blocks. The lower section of each block is made using traditional materials, while the top layer uses much higher levels of cement and pigment, thus creating a much harder, more durable surface with stronger, deeper colours. These blocks can withstand wear and tear much better and retain their colour for many years, even in heavy duty applications. According to BS EN 1338:2003, the surface layer should have a minimum thickness of 4mm.

Efflorescence

Specifiers should also be aware of the risk of efflorescence, a natural phenomenon that can affect concrete products, spoiling their appearance. Efflorescence is caused by the loss of water within the concrete to the air, which leaves a white salt residue on the surface of the product. Vapour-curing during the manufacturing process can significantly reduce the effectsof efflorescence. For example, Tobermore products are subject to a minimum of 12 hours of vapour-curing.

Environmental standards

The carbon footprint of block paving products is dependent on a number of factors, and manufacturers can improve the environmental credentials of their products in a number of ways:

• Using energy from renewable sources
• Using water harvested from a rainwater harvesting system
• Using a high proportion of recycled content
• Ensuring the product can be recycled at the end of its life
• Minimising the journeys undertaken during manufacture, for example by sourcing materials locally and locating factories close to where products will be used
• Using an ISO 9001 quality management system
• Using an ISO 14001 environmental management system.

For example, Tobermore’s Eco product range is manufactured in the UK from locally sourced materials using 100% renewable energy and 100% harvested rainwater. The Tobermore Eco Mayfair Flag contains at least 82% recycled content and is 100% recyclable. The manufacturer also uses an accredited ISO 9001 quality management system, and its manufacturing facilities are accredited to ISO 14001. This has enabled its Eco block paving products to achieve an A rating in the BRE Green Guide to Specification, and an A+ rating can be achieved with a recycled sub-base (see below).

Installing block paving

All block paving should be installed to the British standard BS 7533-3:2005. There are several layers to a block paving system. The base is a compacted subgrade layer, over which a sub-base is laid. This should be well compacted and any uneven layers graded out, leaving a fine finish which allows for even gradients and falls - a minimum longitudinal fall of 1.25% and crossfall of 2.5% are recommended to ensure adequate surface drainage. The material used for the sub-base will depend on the condition of the subgrade layer. Over this, there is a bedding or laying course, which consists of a 20-40mm layer of sharp sand or grit that is screeded and levelled. It is then compacted using a plate vibrator.

Paving is laid on top of the compacted sand or grit, and dried sand or grit is brushed over the surface to fill the joints. A plate vibrator is passed over the area to ensure joints are filled with jointing sand. Jointing with sand rather than mortar allows the paving to support substantial loads, because the sand generates significant friction between adjacent blocks, therefore distributing loads horizontally from block to block. If grit is used as the bedding or laying course, fine sand must not be used for jointing because it can percolate into the bedding layer and cause pavement failure. Very fine jointing sand is not suitable for heavily trafficked areas. It is also important that edging is used to restrain the paved area to prevent movement of the blocks.