CPD Specifier May 2015 issue September 2014 | Page 43

Outdoor Engineering Fit for Purpose - the key issues for grass reinforcement With increased demand for grass paving to driveways, access roads and commercial and domestic parking, there are important considerations that building specifiers and installers should make Today’s wide choice of grass paving systems means that specifiers need to be more informed when selecting a product. Without an industry standard - making that choice is difficult. Grass Concrete, experts in permeable paving, highlight a few considerations. WEIGHT LOAD IMPACT In most instances ground reinforcement failure, stems from either an inability to accept weight load or an issue of water logging Both cause loss of grass and weakened support; with, in some cases, both of these problems being evident. With a long established history of installations, Grasscrete is uniquely placed to work closely with engineers and architects to recommend appropriate systems, where areas can be effectively maintained with plastic, or the more vulnerable areas with concrete alternatives. How do you choose something that will stand the test of time and achieve sustainability? For example, a car park in daily use: will the grass cover and the structure stand up to that sort of regime? If the application is to slopes: will it function as an armouring layer and will it offer grip? These are challenging questions that should be asked to ensure a correct specification. FIT FOR PURPOSE With more than 40 years industry experience, Grass Concrete guides clients to choose the most appropriate system to meet their need. Whether that is insitu concrete, pre-cast concrete or plastic systems, they will advise where there is an appropriate use of a particular system. Grass Concrete is being increasingly approached by clients looking to replace failed areas of cellular plastic pavers, re-emphasising the need of specifiers to consider fit for purpose systems - which is key to maintaining the reputation of the grass paving industry. When considering a design there are a few golden rules to consider: l Think about the potential for unplanned heavy use such as refuse and skip vehicles. l For fire applications think about the need to support the modern CARP 18 tonne emergency fire vehicles on the fire access roads as part of building regulations. GRASS CONCRETE LTD GROUND CONDITIONS Subterranean conditions are critical to performance. Most circumstances will see a sub-base depth of 150mm as being sufficient This should, however, be proportionally increased where CBR values of 4 per cent or less are encountered. Care should be taken in specifying the type of sub-base, DOT Type 3 materials may suggest high rates of percolation while Type 1 material less so. However they provide a greater consistency both in grading and in availability. For watercourses Grasscrete recommend the installation of a geo-textile of appropriate flow rating below the paving layer. Given the demands for Sustainable Urban Drainage, grass reinforced systems can permeate at up to 90 per cent the rate of natural grass, a safe lag time can be achieved. Lag time is beneficial in the prevention of flooding and can be extended by introducing an underlying drainage blanket across the full extent of the paved area. Grasscrete can and does combine with proprietary forms of sub-ground attenuation. For permeable paving solutions talk to the 40 year experts. TEL: 01924 379443 WWW.GRASSCRETE.COM 43 READER ENQUIRY NO: 55