Forum Message



Name: Milan   Lipensky
Heading: 1.2RE:Designing Pervious Concrete Mixes
Message:
One of our cement customers is very interested in selling pervious concrete mixes. He wants me to design a pervious concrete mix with about 17% voids. We ran a mix with 100% 1/4" crushed material and our voids ended up aroud 32 - 34%. I want to lower the voids content down to 17% by adding a coarse sand, but I'm not sure how much sand to add to get down to the 17%. I have done material gradations, dry rodded unit weights and specific gravities on all the materials, but I'm not sure how to make it all work. I guess where I am getting confused is that I am using dry rodded unit weights and absolute volumes to design the mix and I am not sure how to do the calculations to make it work. When I run the mixes my Unit weights on the pervious are really low and my yield is way over 27 cu. ft. If anyone can direct me to a good book on this matter or if you have personal experience on designing pervious mixes I would greatly appreciate any assistance you can provide.
Best Regards,

John


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John Cherne


Absolute volume method is not the answer. A simple way to start is to use your SSD unit weight of the coarse agg. and figure how many pounds will yield 27cu ft. this is your agg weight for the design.
Particle shape of coarse agg. and amount of cement/pozzolan will dictate your void structure. It is what it is, you can decrease voids by adding more cement/pozzolan,sand or finer particles. I suggest Document ACI 522 Pervious Concrete as a guide for design and placement.

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Milan Lipensky
 
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