Hi , I have to mix a strong mix for foundations for a steel beam post. The initial foundation is going to be about 60x60 and at least 100 cm with some vertical bars. I have been advised to achieve C35 strength I have been online trying to find the correct mix for the cement, sharp sand and gravel, but it seems they all differ for C35. The water ratio seems to be 1 kg cement to 0.5 liter of water to get a good hydration but for the mix I have now got a few options, 1 - 2 - 2 or 1 - 2 - 4. or even 1 - 1.5 - 2.5 . I don't have a vibrating poker and was wondering what manual alternatives there are to get rid of the trapped air. Can anyone give me some direction on this, Thanks in advance
Who has told you C35? All the concrete really needs to be in this situation is stronger than the soil it's sat on unless your post is doing more than just sitting on it. If you go with 1:2:2 you'll have plenty of strength but keep the water down: excess water is where strength is lost. Tamp it thoroughly in layers with a bit of 2x2
Thanks for the reply, the steel post is transferring the weight of the beam holding up the upper floor and a wall above, parallel to the beam, so there suppose to be a lot of weight which needs to be taken by this foundation. I have a span of almost 7 tmr, one post in the middle, then two either side
Known as 'water to cement' ratio. Aggregates also play a part, large aggregates leave voids, as does too much water, it evaporates again leaving voids. And ratio of cement to aggregates, too much or too little, can also affect the mix. Peeps think wrongly adding more cement makes better mixes,etc.
All this is way over the top for the OP's requirement. All in ballast would be fine for this job. i would personally use 1:6 for this. Aggregate size is one of many factors in designing concrete. Surface texture, shape and uniformity are also factors. Large aggregate won't leave voids if the aggregate grading is right. Design is always finalized by trial mixes in industry as there so many variables.
Thanks, but I have the materials on site, it's sharp and 20 mm , no use of a vibrating poker, so just need a strong mix to be sure of the strenght
We used to slump test every batch on big pours. Good indicator of correct water content Regards PhilSo
If you have the stuff then use it for sure. If you're worried about strength then go 1: 2 : 3 but keep the mix stiff and tamp well.