Slab Rebar vs Macro Fiber
Which is better for strength and durability?
4″ slab with #4 rebar @ 12″ o.c.
4英寸平板，带＃3钢筋 @ 24英寸O.C.
4英寸平板，没有钢筋，只有宏纤维 @ 5磅/cy
4,000 psi mix
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
For strength, resteel.
To reduce shrinkage cracks, fiber mesh.
Peter, I'm guessing you might have a typo--did you mean to ask about #4s at 24" oc and #3s at 12" oc? That would be a closer comparison. #3s have about half the cross-sectional area of #4s and about half the tensile strength, so using twice as many as you would with #4s will result in about the same tensile strength.
There is more to the strength, though--the deformed surface of the rebar mechanically bonds to the concrete (along with a weaker chemical bond) to prevent the rebar from slipping inside the concrete. The surface area of #3s is 75% that of #4s, so using twice as many #3s will grip the concrete better.
If this is a slab exposed to weathering agents (water or salt) such as a garage or driveway there is another concern; in case the rebar corrodes, larger dimension steel will last longer.
最后，有一个问题是什么样的力量很重要。在大多数住宅板或地下室板中，田间的钢筋主要是为了减少因收缩而减少裂纹，而在周长或基础上的钢筋则在那里支撑载荷。本质上，该领域没有钢筋的风险。焊接线网与直径较小的电线具有相似的作用。它的主要缺点是，在放置混凝土时很难保持适当的位置。
There are other things you can do to reduce cracking, such as using only as much water as necessary for hydration and placement, letting it damp-cure slowly, and various additives.
I don't have experience with macro-fiber but often spec micro-fibers to limit fine cracking. If the slab is to be a finished floor, be very careful with what fibers they use, or use a different method, or you'll have a hairy floor. There are also structural fiber additives that can replace some rebar .
Good summary!
The only thing I would add is when you specify too tight a pattern (e.g. 12") on residential projects it's hard for the workers to step between the rebar while doing the pour. As a result, especially with a careless contractor, there's more chance they'll put the rebar on the ground in certain places, and it becomes worthless. This is why I NEVER use wire mesh. It NEVER ends up at the right height in the concrete floor.
从结构设计的角度来看，在许多司法管辖区，不承担轴承层（即未设计的平板）很少需要任何钢筋。但是，我个人总是坚持要钢筋减少裂纹分离，动荡等。当您确实需要钢筋时，这主要是关于混凝土横截面的钢筋总横截面间。
另一个选择是在带有1或2（交错）屏幕层的椅子上＃3钢筋，并连接到钢筋。
Fiber is not added for strength
On my current house they used #3 rebar at 24" oc and a 4,000 psi hydro-mix and I have ZERO cracks in my garage (house floor is covered with tile but I assume it's like the garage floor).
Of course the sub base was 4" of compacted AB (fines/sand and 3/4" or smaller rock).
#4 or #3 rebar is completely overkill and unnecessary for a garage slab. 6x6x10 Welded wire mesh is all that is needed with 3000 psi concrete. If you have a heavy truck bump it 4000 psi or a 5" or 6" slab. Leave the steel for walls and reinforced point load areas.