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Billy NY
01-01-2005 19:59:51
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Re: Cement mixer in reply to Woodrow, 12-28-2004 18:27:13
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Spending most of a career in building construction, and having a decent knowlege of concrete, from design mixes to forming, placing, and finishing, depending on the size of the slab or increments of which you plan to pour, using a small mixer will be a fair if not, quite a bit of work for any sizeable pour. You have to handle, the portland in bags, the aggregate and sand or ready mix in the bags, which would be more consistent and should be a certain strength design mix, also measure your water, so as not to exceed the water-cement ratio. By the time you get to the latter batches of your pour, the concrete my begin to hydrate (set-up) before you have placed it all in the form, as it takes time to do the mixing in small batches. Small jobs and making mortar would seem a more fitting job for these mixers, but any pour of size, the quality may suffer, due to varying water to cementitious material ratios ( H2O to portland cement ), fluxuation in aggregate amounts if mixing your own, air entrainment from over mixing etc., I find it better to call for a ready mix truck to deliver the design mix I specify, or is called for on any sizeable pour. 3000-4000 p.s.i. should be good for a building slab. You can still form, place reinforcing rod or 6"x6" woven wire mesh ( W.W.M.)and place the material, if you are not a proficient finisher, depending on the size, hire a finisher or 2 to follow up behind you after you place the material, power trowel it off after it sets up a bit, if you want a polished finish or whatever. You can estimate the cubic yardage easily by taking the square footage of your slab, multiply that by the thickness ( convert thickness in inches to decimal, always keep your units the same ) which will give you the total cubic feet, then divide by 27 ( 27 cubic feet in 1 cubic yard ), that will give you the cubic yards to order, add 1/2 yard to the order and you will be on the money. If you want to test compressive strength, you can pour 4 test cylinders, fill them in thirds, using a rod to pack each level 25x, then screed the top off clean, a testing lab can do 7 day, 14 day, 21 day and 28 day breaks to confirm the strength, ( this is kind of overkill, but you will know that it came up to strength if you need to) Using a small mixer, you could also pour smaller sections, certainly realize the cost of concrete by the yard is not cheap, neither are contractors to do the work, but buying ready mix and having it delivered takes some of the work out of the job, and you can still do a majority of the work yourself and realize a cost savings.
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