Concrete strength

[downsizingnow48]

I would not use it for a beam without a lot more info. See picture of a concrete beam.

 

[RedNeckRacin]

I have a chance to get some concrete that is 1 foot square, with 4 pieces of 5/8 rebar in it. It would span 7 feet over a drive way to let water under. Any idea what those concrete pieces would carry in weight. There would be 9 of them but the tires would ride on just two of them.

NOPE, 4 pieces of longitudinal rebar do not a beam make. There needs to be stirrups to prevent shear cracks from causing a beam failure.

 

[Egon]

Is there any rebar installed transverse in the beam
Unless the concrete Is homemade the strength should be 3000 PSI minimum
Aggregate size does not factor in beam strength

It does in rebar placement.

 

[Streetcar]

It does in rebar placement.

Aggregate is usually sized for rebar clearance, not the other way.
What are the beams from .
4 #5 bars sound like a small column

 

[Egon]

Aggregate is usually sized for rebar clearance, not the other way.
What are the beams from .
4 #5 bars sound like a small column

So the aggregate size is a factor.

 

[Industrial Toys]

Concrete has very poor tensile strength and it's only the rebar that allow such tensile loads, so don't even think of the rebar just strengthening the concrete in this application. It IS the strength. If that was designed as a column, the loading was engineered very differently.

 

[Billrog]

Actually if it is actually only a 7' span put them down with some planks on top and you could drive anything over it.

 

[downsizingnow48]

Does op know if they have stirrups or just the longitudinal rebar? Who made the columns? What was intended purpose?

 

[Streetcar]

So the aggregate size is a factor.

Aggregate size is not factor in design strength. It is factor in workability of wet concrete

 

[Streetcar]

Concrete has very poor tensile strength and it's only the rebar that allow such tensile loads, so don't even think of the rebar just strengthening the concrete in this application. It IS the strength. If that was designed as a column, the loading was engineered very differently.

Concrete will fail in tension when loaded.
Columns are designed as beam/ columns usually. A combination of compression and bending loads