LANDSCAPING SERVICES
Previous research has demonstrated that the infiltration rate of CBPP will decrease due to this build-up in the jointing material , but then stabilise with age . Even after allowing for clogging , the long-term infiltration capability of permeable pavements ( shown red in the graph ) will normally substantially exceed UK hydrological requirements ( shown blue ).
Latest Research In order to better understand the effect trafficking , weathering and time have on CBPP systems , field tests have recently been undertaken by an Interpave member on three projects installed 6- , 17- and 19-years ago , respectively . To measure the permeability of these existing CBPP pavements , the trials used the American Standard ASTMC1781 / C1781M method .
The research demonstrates that all the CBPP sites tested , despite receiving no specific maintenance to improve permeability , still provide infiltration rates that would cope with any likely UK rainfall event .
Case Study and Video One of the projects considered – Martlesham Park and Ride , Suffolk – is the subject of a video showing the trials . In this test 10 litres of water in a sealed tube created a head of about 140 millimetres – equivalent to more than a month of heavy rainfall . Here , the surface absorbed the 10 litres of water in 8 minutes and 1 second , equivalent to a rainfall intensity of 1,055mm per hour .
For context , the heaviest UK rainfall event in history was 92mm per hour . The video also includes an illuminating interview with the original project designer about longterm performance and maintenance , and also the benefits of CBPP for trees . Constructed in 2003 , this large out-of-town car park receives regular daily trafficking from commuters and shoppers . With around 500 car spaces , the 13,000 m2 of concrete block permeable paving has delivered problem-free performance over 17 years .
The grit-filled joints do have moss in them but , as a porous substance itself , water passes through without problems . The site is surrounded by vegetation , with some tall trees and well-established shrubs . Maintenance has effectively been cosmetic – occasionally sweeping tree debris and vegetation from the surface after storms and leaf fall in the autumn .
Permeable Paving and Green Infrastructure Extensive mature trees around and within the site were simply retained as part of the scheme . The CBPP removes pollutants from water passing through , providing treated water sustenance for trees . The roots have continued to grow within the permeable pavement sub-base but – importantly – there have been no visible signs of block rutting or lifting , or roots coming through the surface .
As CBPP allows the same pattern of run-off transfer to the ground as natural vegetation , it allows water to reach tree and shrub roots , despite providing a hard surface above . This is endorsed by the current Code of Practice for accessibility in the external environment , BS 8300- 1:2018 , which states that : ‘ Tree grilles should be avoided . Smooth or paved permeable surfaces should be used wherever practicable ’.
Concrete block permeable paving technology will , in future , play a key role in introducing and retaining trees , and other green infrastructure , within our towns and cities . In addition to new permeable pavements for developments , CBPP overlays to existing , conventional road bases can be used in conjunction with raingardens or bioretention areas to store water for irrigation while improving the public realm .
Interpave Information Resource A full report on this research and project video – as well as more information , detailed guidance and case studies on concrete block permeable paving – are available from the Interpave website . www . paving . org . uk
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