Cleaning and Stain Removal

                           Routine Cleaning

Concrete segmental pavements can be routinely cleaned just like any other pavement. However, precautions must be taken during the very early life of the pavement to avoid removing the jointing sand during cleansing operations. In particular, unless the pavement has been sealed (see Chapter 7), the use of vacuum sweepers and water jets should be avoided until the joints have become naturally-clogged with detritus. This normally occurs once the pavements have been open to traffic for two to three months. Until this occurs it is prudent to operate street sweepers without vacuum using their brushes only. Once the joints have become naturally-clogged vacuum sweepers and water jets can normally be used without problem.

Irrespective of whether the pavement has been sealed or allowed to clog naturally the condition of the joints should be periodically monitored once routine cleaning operations commence. Any procedure that leads to loss of jointing sand should be modified or suspended until the problem is rectified because experience has shown that inappropriate cleansing can lead to the failure of pavements carrying traffic if the joints lose too much sand.

                      Stain Removal

Many materials such as leaves will stain pavers only if they are left in prolonged contact with the pavement. Accordingl,y the best strategy to keep a pavement in pristine condition is to ensure that all rubbish and leaves are regularly removed using sweepers and thereafter, the pavement is flushed with water. The use of water alone to flush debris from the pavement is not recommended because this will often concentrate organic materials likely to cause staining in low lying areas and adjacent to drains.

Staining can be minimised by sealing the pavements (see Chapter 7) or its impact can be reduced by using multi-coloured pavers. Light, non-penetrating stains can often be removed by brushing with a stiff broom in conjunction with a light application of sharp sand. Where persistent stains do occur they can be removed using a variety of chemicals and proprietary cleansing agents. These must be chosen with regard to occupational health and safety and the environmental impacts of runoff etc. As a general guide, information on stain removal is provided in Table 1 . Broadly these methods fall into the following categories

• Spotting. Isolated spots of materials such as soil, bitumen, chewing gum or mortar should be scraped to remove excess material. This should be done before using chemicals or attempting widespread cleaning.
• Dry brushing with hand or mechanical brooms. This can be aided by a light application of clean sharp sand that can be swept up and removed after the stain is gone. The brooms should be fitted with fibre, plastic or brass bristles. The use of steel bristles should be avoided.
• Wet scrubbing using abrasive or scouring compounds followed by washing with water
• The use of high-pressure water jets operating at pressures up to about 14 MPa with flow rates up to 40 litres/min. Use low water pressures (< 1 MPa) to remove efflorescence with proprietary cleaning chemicals. Use higher water pressures to remove stains. The use of detergents and scrubbing with stiff brushes may be needed to supplement jetting for stubborn stains. Water jets are best handled by experienced professional cleaners.
• The use of chemical pastes or poultices that can be applied to the paver surface to remove spots of material such as tar or creosote.
• Acid washes. These are sometimes selected to permanently remove cement or mortar residues or to temporarily remove efflorescence. Acids should not be allowed to drain onto landscaped areas. Barriers of lime spread around the areas being cleaned can neutralise the acid but care must be taken to sweep up and remove this material once cleaning is complete. Acids are sometimes usefully combined with detergents in proprietary compounds for general purpose cleaning.

The methods set out in Table 1 are for general guidance only. Stain removal is seldom accomplished without visible and often permanent changes to the colour and texture of the pavers. For this reason any stain removal compound should be treated with caution. Indeed, in many cases, where staining is localised, it may be preferable to replace the discoloured units with pavers drawn from the maintenance stockpile rather than to attempt to clean them. This is of particular relevance in the case of pavers stained with asphalt or oil because such stains are difficult to remove completely irrespective of the type of chemical used. However, paver replacement can be more expensive than insitu cleaning.

                        Efflorescence