Does adding Portland cement to quikrete make it stronger?

To answer your question, yes adding some portland cement will add a bit of strength, up to a point, then other additives are needed to get super concrete.

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View Full Version : A question about Quickcrete

Dave Zellers I do a lot of projects myself, start to finish. Like decks. Now I'm doing a porch 8 feet off the ground. One thing I've always done is use Quickcrete 80 lb bags to fill the Sonotubes as the footers. Years ago, I started buying a bag of Portland cement and adding a shovel to each bag as I mixed it thinking that would make it stronger. Am I right that this improves the strength of the concrete or not? Thought I would post this here in case someone might know. Ron Kurzius Pretty much a waste of time and money There is no need for the concrete to be so strong in that application. If it makes you happy keep doing it but it certainly isn't necessary. My dad told me about building houses in the fifties and they would throw a couple more shovels of portland in the mixer when they saw the inspector coming down the street to do a slump test. He said most of those foundations you could drive a 20d nail in them months after they were poured and they never cracked. These were small single family homes with ten inch walls. There wasn't any transit mix when this was going on and labor was cheap but the cement was expensive so I'm told. :) Jerome Stanek Concrete is very strong when it come to compression it is like a stack of pennys you can put a lot of weight on them stack up but there is very little strength is the are on their side Steve Peterson Quickrete is a company name with products ranging from 750 psi mortar mix to 10000 psi bridge repair mix. Check the bag to make sure you get the one designed for footings or deck supports. Some of the products are only good for fence posts.

Steve

Ole Anderson To answer your question, yes adding some portland cement will add a bit of strength, up to a point, then other additives are needed to get super concrete. Do you need to? Probably not for foundations as long as you use the proper mix as Steve noted. Often you see the dry mix used to fill the holes, counting on ground moisture to actually complete the concrete mix. Personally, I would never count on that. To some degree, the drier the mix, (as long as there is enough water to hydrate the portland cement) the stronger, a sloppy mix will loose strength. Mark Bolton With bagged material adding a bit of portland is really a technique to improve workability. Straight quickcrete/sakrete is about a 3500# mix which is fine for footer and porch posts but can be nearly impossibe to finish for flatwork (sidewalks, steps, and so on) because there is so little cement and fines you almost cant smooth it at times and it does vary wildly from bag to bag. For concrete piers for a porch I wouldnt worry about it OR I would skip the cost and labor of buying a bag of portland and just use the 5000# material. Its probably cheaper in the long run to buy one material, dump it in the mixer, and forget it, as opposed to buying two products, guessing at what "a shovel full" is.... The thing to remember is on top of the mix your strength comes from the size an shape of the aggregate. All bagged mixes use 3/8" at the very most and its likely not very sharp so its not going to be super strong. The strenght of the paste bond is going to be minimal on such small aggregate so your splitting hairs.

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Tom M King If you feel the need for extra strong, just buy the 5,000 lb. mix. John K Jordan I do a lot of projects myself, start to finish. Like decks. Now I'm doing a porch 8 feet off the ground. One thing I've always done is use Quickcrete 80 lb bags to fill the Sonotubes as the footers. Years ago, I started buying a bag of Portland cement and adding a shovel to each bag as I mixed it thinking that would make it stronger. Am I right that this improves the strength of the concrete or not? Thought I would post this here in case someone might know. Dave, I do the exactly the same thing, even for footers. The extra cost and effort is almost nothing. I started adding a shovel of cement when I noticed the quality of the bagged concrete going down. Some was worse than others. Extra cement also makes a better finish on exposed concrete. With a porch as high as yours it doesn't pay to skimp. I built a 1000 sq foot 7 level deck with some of the levels about 12' off the ground and used 4x6 posts. I didn't fill sonotubes for footers but did fill 12" holes augered 4' into the ground with rebar and bagged concrete mix, enhanced as mentioned. (Frost depth is 18" here) I formed an above-ground square of 2x4s for the exposed surface and it was still perfect 30 years later. I've seen other installations start to crumble. As you know, the water and mixing and rodding has to be right too... I admit I may be a little more sensitive to the concrete consistency and quality since I worked as a concrete inspector in the 70s. I have plenty of stories of concrete failures. BTW, one way to guarantee a good concrete mix on the truck is to tell them you are a concrete inspector and will do a slump test on site. :) My concrete finishers laughed when they saw the rebar I put into my shop slabs, 12" centers and every intersection welded, but 3 years so far and not one crack, inside or out. Then they asked if I could do their forming and rebar when they built their own shop.

339340

BTW2, I do everything myself too (except finish concrete) This shop is 24x62 and every detail from the soil compaction to the light switch wiring is exactly the way I want it!

JKJ

Dave Zellers Dave, I do the exactly the same thing, even for footers. The extra cost and effort is almost nothing. I started adding a shovel of cement when I noticed the quality of the bagged concrete going down. Some was worse than others. My concrete finishers laughed when they saw the rebar I put into my shop slabs, 12" centers and every intersection welded, but 3 years so far and not one crack, inside or out. Then they asked if I could do their forming and rebar when they built their own shop.JKJ It's like we're brothers from a different mother. I've taken grief from workers about my anal attention to detail and then later heard yeah I do it that way now too, thanks.

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BTW2, I do everything myself too (except finish concrete) This shop is 24x62 and every detail from the soil compaction to the light switch wiring is exactly the way I want it!

JKJ

Don't you just love that?! At 64 it's getting harder to do so much myself and I'm finding myself making more compromises than I used to but I also run into a lot of subs who would love to do higher quality work but feel like they can't if they wan't to be competitive. I want to thank everyone for all the responses to my question. Excellent information. If adding a bit of portland cement makes it stronger then I will continue to do that but I also will check out this 5000 lb mix mentioned. Interestingly, after I posted this here, my neighbor told me that the sonotube footings under his deck built 27 years ago are starting to crumble and he is going to have to look at replacing them. Concrete done right the first time shouldn't do that. John K Jordan ...At 64 it's getting harder to do so much myself and... Hey, I had a whole lot more energy WAY back when I was 64! Just kidding - I just turned 66 and for now doing ok! Maybe running around the farm here keeping up with the horses and llamas and beehives and things keeps me in shape. Life is good!

JKJ

Stan Calow more cement or (less water) makes it effectively a drier mix, which means less slump. Low slump generally means greater strength. Optimal is what the manufacturer recommends. John K Jordan more cement or (less water) makes it effectively a drier mix, which means less slump. Low slump generally means greater strength. Optimal is what the manufacturer recommends. The slump can be varied but that alone doesn't absolutely define concrete strength. We did slump tests on site then poured cylinders which we compression tested in the lab at various curing stages. Some great slump tests failed the compression tests miserably. The problem I increasingly found (especially with bagged premix) was the manufacturers were apparently cutting back on the cement (maybe to save money). This results in a grainy, more porous, and weaker concrete which is more likely to deteriorate. When "stabbed" with the shovel the mix should stand up and and where the back of the shovel smoothed the mix it should look smoothly "plastic" with no aggregate visible. When the bags I bought quit mixing properly I started adding a little cement until it looked and felt right.

A quick search found this which explains about too little cement:

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0ahUKEwiDr7bDn7LNAhVDVFIKHefgBAkQFggrMAI&url=http%3A%2F%2Fwww.ce.memphis.edu%2F3137%2FDocum ents%2FBasic%2520Tenets%2520of%2520Mix%2520Design. pdf&usg=AFQjCNHedRHurS8Jh3O0T-lh5sQn1CvnQw&sig2=I4-FYIa1Hb2tgLQW5OqTgg&cad=rja

JKJ

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