EddieWalker
Epic Contributor
Cracks in concrete are caused by excessive water in the mix while pouring the concrete. Rebar, wire and fiberglass are all used to hold the concrete together when it cracks. Most cracks are so fine that they are almost impossible to see.
Fiberglass is a low cost insurance that does not replace rebar or wire. Since you do not have cracks, you got away with it, but it should not be used to replace rebar.
Wire is also a low cost material to replace rebar, but on big pads, it's almost worthless because it is impossible to spread concrete over it and not walk on it. When you walk on it, you push it to the bottom of the pad. One of the biggest lies told by concrete people is that they pull it up into the middle of the pad while spreading the concrete. They even do this for pictures early in the pour, but quit pretending once things get busy. Then they walk all over it getting the concrete spread out and leveled.
Rebar on chairs, 16" to 24" apart is the proven standard. Anything else is cutting corners and gambling on the results. Ensuring that no extra water is added to the mix is more important then anything else at reducing cracking.
Poorly compacted soil is usually blamed for cracks, but it's actually very rare and it takes years, if not decades to happen. If it cracks in the first couple of days to a month, it's from too much water that is evaporating from the slab.