what we learned from christchurch taking the risk out ... - PlaceMakers

FEATURESCCANZPaving the way – Design (Part 1)Driveways, paths and patios are among the key finishing touches that complete a home.This second article in CCANZ’s series on residential concrete focuses on designThe basic function of residentialpavements such as driveways,paths and patios is to providesafe, easy access onto or arounda property. Concrete is typicallyused to not only provide a durablepaving surface sloped to providesurface water run-off, but one whichcan also incorporate a wide rangeof decorative finishes to complementthe design and landscaping of theresidence.While providing a concrete pavement onthe ground is relatively straightforward,there are many aspects of design andconstruction that need to be consideredin order to produce a finished productthat will satisfy both the functional andaesthetic requirements demanded byhomeowners.CONCRETE STRENGTHConcrete with a specified compressivestrength of 20 MPa compliant withNZS 3104 is recommended forresidential pavements. A higherstrength may be required in certainsituations, such as:• Heavier loads. If the pavement isbeing used by vehicles between 3 and10 tonne gross mass, and infrequentlyby heavier vehicles that do not exceedthe statutory limits for tyre, wheeland axle loads, a specified strength of25 MPa or 30 MPa is recommended.Such pavements also need to bethicker (see Table 1).• Abrasion resistance. This is the abilityof the concrete surface toresist wear; it is directly related tothe strength of concrete and thequality of the surface finish. A 20 MPaconcrete is satisfactory for mostresidential paving applications, includingtypical driveways. The higher strengthrecommended for heavier loadswill also produce a higher abrasionresistance provided the surface finishand curing are carried out correctly.• Freezing and thawing.A 25 MPa concrete should be usedif the pavement is subjected tooccasional freezing. Where morethan 50 freezing cycles occur eachyear, a 30 MPa concrete should beused. Also, an air-entraining agentshould be used in the concrete mixtargeting a 5% air content.The constructionof driveway pavementswithout reinforcing meshis not recommendedTHICKNESSTable 1 shows recommended thicknessalong with concrete compressivestrength. The load the slab can carry isalso dependent on the adequacy of thesubgrade to support the loaded slab.OTHER PROPERTIESIf properties in addition to strength arerequired, ‘Special Concrete’ shouldbe specified and the means by whichcompliance is established. For colouredand decorative pavement finishes,some of the properties (apart from thestrength) that may be required include:• Colour pigments. Supplier, colourand percentage by weight of cementto be used.Pavement UsePaths & Patios(Foot traffic only)Typical DrivewayVehicle use < 3 t grossPavement with vehicles3 t to 10 tTable 1: Pavement thickness and specified concrete compressive strength• Aggregates. For exposedaggregates, any information necessaryto identify the stone required – size,type, texture, colour (eg nominal10 mm aggregate consisting of 90%brown rounded river gravel and10% crushed white quartz).• Cement colour. Normal grey,off-white or white. Note that theavailability of these should be checkedprior to specifying. An alternative toachieve a lighter colour is the use ofa titanium white colour pigment.PERMEABLE PAVEMENTSPermeable (or pervious) pavementsare being specified in areas whererun-off from existing hard surfacesdue to extreme rainfall events causesoverloading of the stormwater systems.Permeable concrete is similar tono-fines concrete and has continuousvoids, which allow water to infiltratethrough the pavement. Alternatively,permeable pavers can be used.The water is held in storage under thepavement, which effectively reducesthe peak run-off entering the sub-gradeor the stormwater system. Informationon permeable pavements is found atwww.concretenetwork.com/pervious.SEGMENTAL PAVEMENTSConcrete segmental pavers rangingfrom small brick-sized units to thelarger flag pavers are availablein a variety of colours, finishes andPavementThicknessPavement ConcreteSpecified Strength75 mm 20 MPa100 mm 20 MPa150 mm 25 or 30 MPa18www.ccanz.org.nz