LANDSCAPING SERVICES
CONCRETE BLOCK PERMEABLE PAVING FOR TREES
Recent trials of various , older concrete block permeable paving projects following long-term use back-up previous research , endorse current minimal maintenance recommendations and debunk misconceptions about clogging up of joints . This research has important implications for the whole life costs of permeable paving generally . But it also reveals major benefits of permeable paving opening up new opportunities to satisfy growing demand for trees in our towns and cities .
Concrete Block Permeable Paving ( CBPP ) technology has proven itself over successful use around the world since the mid-1980s . It is suitable for all types of paving , ranging from driveways , car parks and adopted residential roads to industrial areas and distribution centres . Two decades of experience in the UK has demonstrated its longterm performance with minimal , if any , maintenance . But one of the most persistent misconceptions about CBPP technology , impeding its uptake and adoption , is that – without maintenance – the joints quickly become clogged with debris and , within a short time , become impermeable preventing water from draining into the paving .
Permeable Paving in Practice In fact , over time detritus and silt collects in the upper part of CBPP joint material between blocks , where a surface ‘ crust ’ ( around 5-10mm deep ) is formed , protecting the laying course and sub-base material but still allowing infiltration . Also , the performance of CBPP is not significantly affected by moss or weeds in the joints , or by leaves collecting on the surface . Even where localised blockages do occur , in a storm event excess water simply flows to more permeable , adjacent areas .
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 .
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