Browse Forums Paving & Concreting 1 Mar 24, 2017 4:24 pm Hi, I am trying to find out more info on concrete driveways and paths and I have researched with the use of steel mesh on bar chairs it is suppose to prevent cracks and keep the concrete as one. However, some people say even with all the right reinforcement using bar chairs and mesh the concrete still cracks and others say they don't use reinforcement and their concrete has no cracks. Can anyone tell me the importance and purpose of steel mesh reinforcement in a concrete driveway? Is it an absolute must (like a building code)? Also, are bar chairs required as well? Many thanks Re: Concrete Reinforcement 2Mar 24, 2017 5:47 pm Yes it's an absolute must. Concrete is strong in compression but week in tension, so that's where the steel comes in as its strong in tension. Combine the two and you have a match made in heaven. It also comes down to things like correct expansion joints, the way it is placed (I.e. vibrated well to remove air pockets), the slump of the concrete or how wet it is and also them temperature when it is poured. Kind Regards James Mason - Our Build. www.renovationjunkies.com.au www.ourbuildhandyman.com.au Re: Concrete Reinforcement 3Mar 24, 2017 6:11 pm Reinforcement isn't necessary as long as all the other elements of good design and quality control are followed. I've designed unreinforced concrete paving that has been used for Jumbo Jets for 25+ years without cracking. To get that result:
If you have reinforcement you are wasting your money if you don't have bar chairs (See Bar Chairs) The Harder You Try - the Luckier You Get ! Web site http://www.anewhouse.com.au Informative, Amusing, and Opinionated Blog - Over 600 posts on all aspects of building a new house. Re: Concrete Reinforcement 5Mar 24, 2017 7:02 pm If it's for a driveway you would be crazy not to install it. Kind Regards James Mason - Our Build. www.renovationjunkies.com.au www.ourbuildhandyman.com.au Re: Concrete Reinforcement 6Mar 24, 2017 8:50 pm Concrete is going to crack, you can't stop that. How you design and construct it will control where and how much. Depending on its intended use, you'll have to determine the type of concrete used and its thickness. A standard residential driveway for instance will require a minimum of 25MPA concrete (strength rating), 150mm thick, and reo. I personally wouldn't lay concrete without reo unless it was a very basic garden path with very good site prep prior. A well compacted base, regular control joints, and decent thickness. Concrete when going off (drying) is going to shrink as the water content drops. That's just logic. Remove the water from anything and it'll reduce in size. It won't be much, but it'll be enough for it to crack FOR SURE. This is where design comes in. You place the reo where you don't want it to crack, and make control joints in areas where you allow for it to crack (the control joint is simple a cut/line made into concrete about a third of the way down, forcing the concrete to crack along this straight line nice and neat instead of zigzagging all over the place). Reo should NOT be placed where you want the concrete to crack. An expansion joint is something completely different... where a buffer is made between an existing hard surface (ie house brickwork) and your intended concreting. You can buy this bitumen foam stuff from bunnings, but this has to be placed between the two. If you aren't sure where to place control and expansion joints, go look at nearby houses. It's not hard to see when you look hard enough at the detail most people ignore. But long story short, concrete WILL crack. It continues to 'go off' years after its laid. Gets harder and harder as time goes on and moisture leaves it. If the surface area is too big without joints, it'll crack and make its own joint. Believe me. Re: Concrete Reinforcement 7Mar 24, 2017 8:58 pm Thanks for the info. I have had alook around other homes for a while. Most have the steel mesh reo for the driveway only and not the path. But i dont see anyone using the bar chairs or spacers. There are so many contractors out there that all use different methods and say different things which is what i am confused about thats why i was wondering if there was a building requirement that was needed to be followed which would make it easier. Will steel mesh reo with expansion joints suffice without using bar chairs? Re: Concrete Reinforcement 8Mar 24, 2017 9:05 pm Nope. Bar chairs to hold the reo halfway through slab is only way to do it, or otherwise dont use reo at all. You can buy 20 bar chairs in a pack for like $20 at Bunnings. Definitely need to keep that reo level and halfway all the way through. I've never seen a concreter just put reo down on the ground and lay a driveway. Have you actually seen it laid? ie On the day of pour they'll go along and put the chairs in just prior to pour, because typically the truck needs to drive over a section of reo to get to the other end of the driveway (concrete truck chutes only extend about 2-2.5m). Use bar chairs! Re: Concrete Reinforcement 11Mar 25, 2017 7:22 am I think the Australian Standard is AS3600 for concrete structures. If you google the BCA and Australian Standards you should be able to find a copy on line. Kind Regards James Mason - Our Build. www.renovationjunkies.com.au www.ourbuildhandyman.com.au Re: Concrete Reinforcement 12Mar 25, 2017 8:10 am Hi Kitty1 To reinforce or not to reinforce is a conundrum in corrosive environments These days engineers use BIM & Multiphysics simulations to design infrastructure projects Here is an interesting stair example video its on G+ Community An brief overview of bim, modelling and data use & presentation output BTW the rebar would be cheaper than the simulations...so I would put it in Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Concrete Reinforcement 13Mar 25, 2017 8:14 am Thanks. I guess with so many different contractors doing it their way i wondered if there was a requirement enforced by the NCC that must be followed in using reinforcement or not for driveways and concrete paths. Re: Concrete Reinforcement 14Mar 25, 2017 8:30 am True, But it mostly boils down to price 100mm Concrete driveway materials cost Concrete $15m2 + SL62 mesh costs $7m2 = $22/m2 material+ labour + Plant + Profits $45-$50 m2 is a fair price IMO Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Concrete Reinforcement 15Mar 26, 2017 8:24 pm There is a standard AS3727 - 1993 Guide to residential pavements although it is not an NCC referenced standard. Effectively it is a best practice guide. If you can't get your hands on the standard, a great guide is the Cement Concrete & Aggregates Australia (CCAA) Data Sheet Residential Concrete Driveways and Paths. Hope this helps. Re: Concrete Reinforcement 16May 21, 2017 2:02 pm kitty1 Thanks. I guess with so many different contractors doing it their way i wondered if there was a requirement enforced by the NCC that must be followed in using reinforcement or not for driveways and concrete paths. I think you'll find they mostly do it all the same way. Some use bar chair, other just pull up the mesh as the concrete get poured to a hopefully suitable level. Bar chairs are more accurate. A residential driveway construction is not subject to NCC. Use reo or not, but you would be a fool not to use it, the concrete will crack more if you dont use it, but as Bashworth said, the substrate is important. If your substrate is clay based soil, it will heave when wet, so you must use reo. As far as walk paths are concerned, you do not use reo for foot traffic, just cut regular stress joints every metre. Bedding sand laid first before pouring concrete works great to reduce cracking. To my understanding early saw cuts are to control shrinkage cracks, so doing them now would be pointless. Control joints may reduce ugly cracking during periods of soil… 3 9863 Hi all I need a guidance on how far I need to space expansion joints in the concrete driveway and its type (keyway/foam.) Contraction joints are at 3m max for a 125 slab. Thanks 0 10947 |