Browse Forums Paving & Concreting 1 Mar 13, 2011 3:12 pm Hi guys, I am after some advice about curing an exposed aggregate driveway. I sought advice about concreting last year and finally had an onsite meeting with my builder’s concreter this week (viewtopic.php?f=22&t=40301). The guy in question is a second generation concreter so I would imagine he knows his trade but I can’t help feeling a little uneasy after reading the thread about concrete problems and also considering some of the things he told me... First of all, I actually sourced some hessian on the advice I received in the earlier thread. I told my concreter I would like to cover the driveway with it after the pour but he said not to. He said that covering the driveway and wetting it would dilute the acid they pour on top to stop it from setting and that they would not be able to wash it off with high pressure the following day to expose to aggregate. I am pretty sure as well that he said they seal it later the same day they expose it- isn’t that too soon?! Can someone please advise of the best method of curing exposed aggregate as this one part of the build I want completed absolutely spot on? The concreter also told me that cracks in the concrete are inevitable (which is not acceptable to me). Can anyone advise if this is true? I would have thought that a driveway constructed to optimum specifications would not crack, or rather the cracks would run along the saw cut joins thus being invisible. I didn’t think to ask him of the exact strength he would order but he did agree it would need to be strengthened on account of the oxide colour I’m getting put in the concrete. I’m thinking of nominating a strength so that we are absolutely clear on this- is 32mpa at 80 slump ok?? The concrete plant doing the mix is located only about a 10-15 minute drive away so it shouldn’t set that much and the area I’m getting poured is about 25m², so only a small job. The mix is 90% 7mm bluestone and 10% 7mm pebble with 8.3% charcoal oxide. I managed to talk him into providing F72 mesh instead of F62 so I am happy about that. He will also provide bar chairs even though he said he never uses them- would you believe that he was trying to tell me that “lifting” the mesh manually into the concrete was acceptable and industry practice?! His reason for this was to avert the risk of damaging the mesh during saw cutting, which I then advised is impossible if the driveway is 100mm thick and the mesh is at 50mm and the saw cut is 35mm deep according to him. He also said that because they don’t use a pump, the truck breaks the chairs when it backs up over the mesh. Now this reason seems more credible but that really should not be my problem now, should it? FYI he will also be providing Dowell bars to the garage slab and crossover as well as an expansion join to the garage slab. One last question I have is roughly how many square meters should there be between saw cuts and within what temperature range should the concrete be poured?? Thank you for reading this essay. I realise that I have asked a lot of questions so please feel free to answer any part- perhaps you can quote a particular question and respond in red font. I appreciate all responses and am sure this will be a useful resource for other members too! Cheers guys! Re: Best method of curing an exposed aggregate driveway? 2Mar 13, 2011 4:06 pm There are sealer's that can be applied applied the day of the pour, they will help with curing. warning you that cracks in concrete can be inevitable is a way of covering his arse...sometimes its true.. a contractor can so all that they can do, and the concrete can crack. much can depend on the ground your laying the driveway on. There are a few streets near me where every single driveway has lifted at least 20-30mm at the curb, even the ones that were dowelled due to highly reactive soils, some have cracked through the centre of saw cut sections. That may well be avoidable, but your driveway will cost you 5 times as much. Ive seen engineered designed driveways... the average contractor and client alike would fall over at the cost and work involved. And he shouldnt be backing the truck over the mesh... the sections of mesh can be cut and put aside. and layed back in and chaired as the truck moves out... Re: Best method of curing an exposed aggregate driveway? 3Mar 13, 2011 6:30 pm Hi I would recommend having a read of this: http://www.concrete.net.au/publications ... veways.pdf Unfortunately I am not impressed with a second generation contractor as there is no good industry training from contractors, all most of them know is how to lay and finish concrete with the minimum effort and no understanding of the long term behaviour of the slab. (My son is a concretor and I know what goes on, which is a lot different to how I was taught when I was involved in constructing concrete pavements for airports.) One common fault is that the reinforcement is put in with no plan for the joints. This mean that the you sometimes see that mesh is overlapped at the joint position which will stop the joint cracking and will cause the slab to crack across the middle instead. You can apply a spray on curing compound for concrete once it has been laid and then reapply it the following day after the aggregate is exposed. At this stage you could also put the wet hessian on for a few days. 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: Best method of curing an exposed aggregate driveway? 4Mar 13, 2011 9:54 pm That sounds funny. I know nothing about exposed agg driveways. But I would always do a driveway with SL72 mesh; it should be all tied together. No inspector would pass a slab to be poured without bar chairs. I have never seen a truck back over the mesh, very strange. It would be funny to watch with bar chairs smashing and mesh bending everywhere. Maybe suggest you supply bar chairs you can get strong steel ones. Still bend but the truck may think twice about driving over them. Hessian good idea, sounds logically to me, acid in a curing compound sounds illogical but never used curing compound and would prefer hessian. No cracks should be the norm but never truely guaranteed. Saw, cuts through the steel no problems. Just get another concreter he sounds he too should pass on to the third generation concreter. I would not be using him, he may do a great job. Good luck Pulpo Re: Best method of curing an exposed aggregate driveway? 6Mar 16, 2011 5:28 pm Hi guys, Thanks for your replies and thank you bashworth for the link- a very handy little resource. It actually answered a lot of my questions. I will pay due consideration to control and expansion joins too. Pulpo, I have to use this concreter because he is engaged by my builder, not me. The only reason I am dealing with him is because my builder is so sick of my micromanagement that they have some of the trades deal with me directly. I made a mistake in my original post where I said the concreter applies acid to the surface after the pour. The correct procedure for exposed aggregate as I understand is soaking the fresh concrete with a chemical retardant to stop it from setting. The following day this chemical is washed away with a high pressure acid wash to reveal or ‘expose’ the aggregate mix. A coat of sealant is then applied. So... given that a chemical retardant is applied to the concrete, does this mean that I should not cover the driveway with wet hessian until the following day after it has been exposed and sealed (and assuming that the sealant is the special curing type)? Would love to hear if there are alternatives to curing exposed aggregate driveways, or am I just over thinking all of this like I tend to?! Oh and just quickly, is 32mpa reasonable for concrete with the specifications in my original post, or will 25mpa suffice? Is it the stronger the concreter the more expensive? I would think so logically, as otherwise everyone would be getting the strongest possible! Cheers Re: Best method of curing an exposed aggregate driveway? 8Mar 16, 2011 7:35 pm Hey BW - bashworth Unfortunately I am not impressed with a second generation contractor as there is no good industry training from contractors, all most of them know is how to lay and finish concrete with the minimum effort and no understanding of the long term behaviour of the slab. (My son is a concretor and I know what goes on, which is a lot different to how I was taught when I was involved in constructing concrete pavements for airports.) I might have missed something?? Reveal as it is known is a sugar based product the 'breaks' the hydration process of cement for the few mm that it ingresses. Acid is to remove residue cement( a thin layer ) that covers the stones, the sealant 'enhances' the colour of the stones. Driving over a compacted sand base with a truck?? over mesh and chairs WTF?? Second generation Knob by the sounds of it... sorry to be course but really WTF? Onsite training is for 'best practice' no one whom attends a concrete pour for the first time would be allowed to do anything of a serious nature. Lots of BAD info is out there, lots of BAD contractors are out there.... Same as ANY trade.. Yes trade!!!!!!!!! Where you are coming from is where you are going to... Re: Best method of curing an exposed aggregate driveway? 9Mar 17, 2011 9:14 am inverell Oh and just quickly, is 32mpa reasonable for concrete with the specifications in my original post, or will 25mpa suffice? Is it the stronger the concreter the more expensive? I would think so logically, as otherwise everyone would be getting the strongest possible! Also heard that it's not a bad idea to use F82 for dwys, as well as a sand base and, of course, the chairs. And that's all I heard about that ... My signature is distracting people from my wise posts ... Re: Best method of curing an exposed aggregate driveway? 10Mar 17, 2011 9:19 am OK, I'm reading this thread back to front (almost) ... jsut noticed that he wants to dowel your dwy into the garage slab??? Is it really warranted?? I would definitely just ask him for the expansion "sponge" to be placed against the old concrete (ie. your house slab) and not let him touch the slab. BTW, from all that you've mentioned, I would also not give him the job. My signature is distracting people from my wise posts ... Re: Best method of curing an exposed aggregate driveway? 11Mar 17, 2011 10:45 am Dowelled & expansion jointing foam.(to prevent 'sandjacking') ...and yes probably not the person for the job Where you are coming from is where you are going to... Re: Best method of curing an exposed aggregate driveway? 12Mar 17, 2011 12:31 pm I need to ask a silly concreting question and don't want to start a new thread just for that, so I will hijack this a little. OK, here it goes: How can we know if the truck driver is adding water to the mix? I mean, is that really easily visible from the outside, or does he have a 'secret' pipe passageway hidden or more protected from external view, where the water pipe plugs directly into the mix 'drum'? I found this doco http://www.concrete.net.au/concrete_structures/residential_documents.php?id=176&page=1 where it says: "3. If additional water is requested, the driver has been instructed [by who?? the concretor??] to obtain a legible name and signature from an authorised person on the delivery docket before adding any water." Onc, so dowelling is OK? What is 'sandjacking' - escape of sand in between the heavy concrete and the sponge? Or not ... My signature is distracting people from my wise posts ... Re: Best method of curing an exposed aggregate driveway? 13Mar 17, 2011 1:50 pm Sand jacking is where water enters the 'joint' and either washes away(compacts) sand from under the concrete 'without' a footing. Water added is upto the grano... ... if the grano is any good they will know exactly how much water to add to bring the mix upto 80 slump or more if needed(& within spec). Some will add more, some will struggle with less and the concrete will suffer as the surface could be difficult to 'close' & and compaction might be under done. The water adding pump and hose is at the back of the truck and the water goes through a meter, so that and exact idea of added water is known. The whole thing is too complex to discuss here.. but I have NEVER been asked to sign for adding water.. in 25+ years and we go to very highly specified jobs. Added water is not the responsibility of the driver, they are drivers NOT concretors(Granos) Where you are coming from is where you are going to... Re: Best method of curing an exposed aggregate driveway? 14Mar 17, 2011 1:58 pm Thanks, onc ... So, I can easily see if some water-adding action is happening?? Also, would you agree that it is easier for the grano to work with a higher strength concrete, 32 and above? My signature is distracting people from my wise posts ... Re: Best method of curing an exposed aggregate driveway? 15Mar 17, 2011 2:31 pm Some will complain, some will be happy. For me it is about the needs(engineering of the job) neither are easy, The grey lady is a strange beast, treat her well and you are in front, poorly treated the she will control you and that is where the problem arises. The more cement the faster hydration occurs and becomes 'plastic... bleed water then cure' in a hurry. Closing the surface becomes problematic and why chips, blowout, crazing and cracks happen. Where you are coming from is where you are going to... Re: Best method of curing an exposed aggregate driveway? 16Mar 17, 2011 6:16 pm So much fear and distrust associated with the placement of concrete, We need a thread with positive concrete stories complete with pics of the awesome and unusual applications it can be used for. Make it happen Onc. Re: Best method of curing an exposed aggregate driveway? 17Mar 17, 2011 11:01 pm Where you are coming from is where you are going to... Re: Best method of curing an exposed aggregate driveway? 18Mar 18, 2011 8:44 am Aiah So much fear and distrust associated with the placement of concrete, We need a thread with positive concrete stories complete with pics of the awesome and unusual applications it can be used for. ... I always wonder how come most of the threads I read go like "Our installer / concretor / trader took care of everything ... he took care that xxxxxx, so the finished job was beautiful ..." and so on. We had no such experiences (yet). Therefore all the fear and anxiousness. Another really bad thing for the owner - the more you know about the steps or materials, etc., it simply doesn't help in the end. Just gets you more frustrated when you see how and what they do. We're talking about things that are so simple and common sense, not worth discussing, as they are a given in specific trades. Still, opposite happens. My signature is distracting people from my wise posts ... Re: Best method of curing an exposed aggregate driveway? 19Mar 18, 2011 11:46 am Uhuh, and is why I don't question the mechanic, but sometimes he doesn't get it right. I have to suck it up and move on... Lots of pro's don't offer any kind of warrantee, except you will pay their bill or legal action will follow. Where you are coming from is where you are going to... 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