Hey everyone! Planning on laying a concrete foundation for a generator near the house. A Nissan SR20 engine will power two 5500 watt generator heads, and a 300A alternator will power a couple inverters. Tired of power outages all the time here in the Japanese sticks Anyways.. looking to lay a slab around 6' x 4' and 3" deep. The rebar will be a metal framework with all the mounts for the engine poking through the top of the foundation. Since I know there are some self reliant folks on this site, just wondering what mixtures are recommended for portland cement. I have laid down some concrete in my dog run using only 1:1 cement and sand, but wondered if gravel is a necessary additive, or what. I see so many conflicting things online, it is hard to tell who is doing what correctly. My dog run technique isn't going to handle a 160hp engine chugging away.
I don't have much concrete mixing experience but I think you would need high psi concrete 10-15,000psi and mix according to instructions. If your mixing your own concoction using portland cement make sure to add some silica fume to make it really strong. Another option i had in mind was... They make pre-formed pads for package ac units that size. Its a combinatioin of concrete and fiberglass. I don't know what kind of weight they support though.
The basic mixture for concrete is 3 parts aggregate, 2 parts sand, 1 part portland cement and only enough water to make it workable(around 1/2 part). http://www.source4me.co.uk/calculate_concrete_mix.php
Can you post Some Pics of your setup after? i am also going to need to make one soon. But i am going to use a 1980's VW Diesel motor
The basic mix is 3 gravel: 2 sand: 1 cement. I would go 4" and buy or fashion some standoffs to hold the rebar at the 2" height. Pieces of stone or bent rebar will do - max strength is with the rebar in the middle of the slab not the bottom! You might want to consider a 6" deep by 6" wide "thickened edge" which on a small project like this would not be too hard. 2 or 3 lengths of rebar bent into a rectangle placed in the trench and tie or weld the cross pieces and it will be super solid.
I really don't know very much about the mix of concrete but the prep is key. As far as the rebar do it as a grid on 12'' centres and tying will be more than fine . Make sure that the rebar is propped up by pins or bricks. Is this pad fully floating or will it be up against the house? If floating depending on the soil I might pour a couple of piles. If it is up against the house drill into the foundation and pin it to the house. 3" is to thin of a pad. I would pour 4" for this application. As far as the concrete do they not rent mini batches there? That would be optimal...
Because of the odd dimentions in back of the house, the pad will be "fully floating". I will have to get prices for a truck to come out. Pretty expensive with the yen rate, but no doubt a back saver in the long run. Maybe I can finish the dog run, and pour the generator base in one swoop. Really don't think renting a mixer will do the job.. am I wrong? I thought there might be a way to do it piece by piece.. but it doesn't look that way.
The mini batch company here rents the concrete in a trailer mounted mixer. Really convenient for fence post and other small jobs
Doubt I could get a mixer like that even near my area. I think saving up and having a place pour it for me is probably the best answer.
I broke out the chainsaw, and started clearing the small trees in the way today, and had an idea. Instead of laying a foundation, why don't I concrete in a large engine test stand of sorts? Heavy steel framework, with a platform about waist high... the fuel tank can be bolted underneath, and the engine mounted on top. Much easier to dig 4 holes, and concrete 4 legs into the ground, than to level, rebar, and pay a truck to come out. Thoughts?
considering the vibration, you might want to increase the slab thickness to 4". CSA exposure class: C-1 Maximum water to concrete ratio (W/CM): 0.40 Minimum specified strength: 35MPa Air entrainment: 5-8% Max aggregate size: 20mm slump range: 80mm +/- 20mm reinforcing: 150x150 welded wire mesh rst277 idea of making a slab thickening around the edges is a good idea. Another suggestion is to provide 2" of rigid insulation beneath the entire slab. This will help prevent heaving, erosion and eventual failure of the slab. Another thing not mentioned is good soil compaction of all disturbed soil beneath the pad. Anything you leave loose will settle and create a void beneath the slab, leading to failure. I'd lay at least 150mm of crushed limestone beneath the insulation for drainage. cover the whole area with 2" then compact it with either a vibrating compactor or a hand tamper, then lay another 2" and do the same etc. Compaction needs to happen in stages, if you lay it all at once then start compacting only the top is compacted and the bottom loose. Given the size of your pad, the things I’ve suggested won't add considerable cost but will give you a considerably better finished product.
