Basement slab reinforcement
Not really a “green building” question per se, but too much knowledge and too good a response time for me to not ask here.
My basement slab will be poured in the near future. It is currently planned as a 4000 psi slab with expansion joints. No reinforcement is specified. I have read articles recommending fiber and no wire and articles recommending wire and no fiber…and obviously both would be strongest. The basement is not drive in. It will contain a weight-room, and I’d like to be able to drop 500lbs from ~3′ up onto rubber tiles and not have the floor crack under them. Should I have the floor reinforced? If yes, how?
平板的周长和周围会有回收的泡沫……如果将其绿色足够适用……
谢谢！
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吉姆，
通常，在地下室板中包括6x6焊接网格，但是代码不需要加固。钢筋会过度杀伤。
和混凝土裂缝在任何case. I also looked in to fiber reinforcement. If you are planning to finish your concrete floor, it might not be the best choice. The fibers apparently can create a layer of fuzz on top of the slab that might be a problem when staining and polishing.
Our polished concrete floors were placed about 18 months ago. We incorporated control joints into the design, rather than space them equally. We also placed them closer together than is typically recommended. We specified 4000 psi and peastone aggregate, 4" reclaimed XPS over well compacted 3/4 stone and 6x6 wire mesh. No cracks yet.
谢谢你。我是否正确地理解6x6焊接网状网格不一定防止破裂，而是要防止板块的破裂部分垂直不一致？这是对平板倒在固体基材上的压实石头床上的问题吗？
Edit: I should also ask, how effective is it? If I include 6x6 wire reinforcement, can it be counted on to hold a cracked slab on one plane to a degree that would allow installation of a finished floor, for example?
过度简化一些：如果您需要在平板上进行任何明显的拉伸强度，则需要钢筋。电线网将有助于保持对齐状态。切碎的纤维会减少滋扰破裂。什么都不会totally防止破裂，但是扩展/控制接头将使您能够place您想要的大裂缝。
切碎的纤维将要make a mess of the slab top surface as poured/screeded. This is not a problem if you will be grinding or blasting the slab surface for a concrete finish, or covering the slab with underlayment for flooring.
Some types of polymer floor coatings (e.g., BASF methyl methacrylate) are flexible enough to prevent cracks (even cut control joints) from telegraphing through to the finished surface. However, having used such a coating in a machine shop, I will tell you that any impact which can spall the surface of naked concrete will damage the coating and also spall the concrete underneath.
You have a requirement which is a bit unusual for residential service: repeated impact resistance. I think I'd use a minimum 4" thick slab with chopped fiber, with a healthy underlayment under those rubber tiles. As a conservative, I'd also use the wire mesh, although if your concrete contractor tells you he/she would prefer to use rebar, you'd be advised to listen. Wire mesh is very, very often pushed to the bottom of the slab, where it's nearly useless, during the process of pouring a slab because it gets walked on.
The single biggest thing you can do to prevent cracking is to keep the concrete very damp for at least a week. More is better. It typically reaches 90% of its potential strength after 28 days. If it dries out, the chemical reaction stops and the concrete is left weak and prone to cracking.
Thank you guys for the input. My contractor did recommend rebar and I will follow his recommendation. I will keep the slab damp. They stripped my wall forms today; would it be beneficial to keep them damp as well? Would it be at all benneficial to hose the walls down a couple times a day, or would they need to be covered in plastic for it to be worth the effort?
Spray some water on there a bit. That should help, especially if the forecast ahead is for dry weather. As to rebar, I would put it just where you expect to have the weight room. The amount of weight you are planning to place on a basement slab is so minute that it is a little absurd to use steel of the basement is not the kind with a garage. After all, the Christmas bulbs, Halloween decorations, spare pantry goods, tool chest and couch (assuming you are going to build a finished portion) won't be exuding any force on the slab. If you compact the gravel well on virgin soil, your settleage will be very minimal. Fibermesh is similar. Wet your concrete after the pour. That is the best way to have good concrete in such a place. If you are using rebar under the weight room, raise it on stools, tie it off in a 12" grid. Make sure it is in the very center of the slab as if it is too close to the top or bottom it is also useless. Don't waste your money in steel where you don't need steel. Place it carefully. Spend your money on things you need. Unless you are Bill Gates using an alias. Then who cares?
Joe thanks for the advice. There is definitely not unlimited money; in fact, the opposite is what motivated me to add reinforcement. The foundation is by far my biggest single expense and the only thing I plan to use a contractor for, so I want a great product. The contractor did agree to let me install the rebar. Actually, he offered to sell it to me at cost, deliver it, throw in the ties, and let me use his tools for install - so for under $1,000, I get a grid on 2' centers under the whole 28 x 50 slab - which I feel is generous of my contractor and a good investment if only in peace-of-mind. Now I just need to hope my sons end up big enough to need the reinforced weight room floor and college scholarships make it a fantastic investment.
吉姆，the more water the better. Contractors almost always underestimate the importance of keeping the concrete fully hydrated for as long as possible, then they say that cracking is inevitable, which is not true.
板的传统方法是用粗麻布和雾气覆盖，每天几次，或者如果是干燥/干燥的话。塑料也可以工作；您会失去轻松添加更多水但捕获蒸发水分的能力，因此它可能相等。
For the walls, the forms should have been left on for a week, but everyone likes to strip the forms after a day or two at most, because it's easier to strip when the concrete is still green and they are in a hurry to get building. Burlap would help but I might go with plastic, after a very heavy wetting.
As others have said, rebar is probably overkill for a basement slab, but it won't hurt anything so go for it.
(我第一次了解了具体的从我爸爸,was a highway engineer and built long stretches of interstate with very large slabs of cast-in-place concrete. They have lasted 40+ years without cracking.)
提供了很多好的建议，以最大程度地减少裂纹：压实的底座，缓慢的固化，控制接头等。没有提及的重要考虑因素是混凝土混合物本身。尽管混凝土混合设计中的许多因素会影响收缩，但水/水泥比是最重要的，最容易控制的。混凝土通过需要水（水解）的化学过程来硬化，但在水解中仅使用了一小部分混合水。混凝土混合物中的大多数水都是用于可加工性的。在固化的混凝土中未化学结合的大部分水会从固化混凝土中蒸发。流离失所的水量将减少平板的体积并导致收缩开裂，就像粘土土壤在雨后干燥时的开裂一样。因此，减少收缩裂缝的关键是将水的量最小化，仅适用于适当放置所必需的量。浇水的混凝土会增加收缩并降低强度。可以将混合物（增塑剂）添加到混合物中，以减少水泥/水泥，同时保持可工程性。
A few rules of thumb for control joints: Space them 2 to 3 times in feet the thickness of the slab in inches (4" slab = 8' to 12' max); Joints should create nearly square sections; joints should be struck or sawn to a depth of 1/4 the slab thickness; Sawn joints need to be cut before shrinkage cracks occur, no more than 12 hours.