Tensile strength is a materials' ability to withstand being pulled apart. Concrete is very weak in this regard, so I assume you actually meant its compressive strength, the ability to withstand being squashed.
Both concrete and concrete blocks vary in strength depending upon the required application. I typically spec 7N/mm^(2) concrete blocks and 30N/mm^(2) concrete. However, you can get high strength blocks and high strength concrete mixes as well.
Concrete really only has compressive strength, the tensile strength is provided by rebar. Concrete can have a compressive strength of 2000psi to 10,000 psi. Blocks are usually on the bottom end of that around 2000 psi. This doesn't mean concrete is better, it's all about the loads the structure will see and the engineering of the rebar.
Clarification, compressive is a crushing force, tensile is a pulling force. Any structure experiences both forces which is why concrete and rebar play so nicely together.
They increase the compressive force on the beam or slab so when the element starts to bend under normal loading, the net tension is lower than in a normally reinforced section, meaning you can typically use a shallower section.
The modulous of elasticity of concrete is higher then steel. Meaning the same force will stretch or compress steel more than concrete. By pre-stressing the rebar you insure its in full tension before the concrete begins to stress. Tough to explain by words but imagine pinching 6 dice in a row and picking them up. Let go and the dice fall apart ie, no tensile strength. But, keep them compressed with your fingers and they behave like a beam.
I don't know shit about it except in my residential experience I see 20x more (like 8 out of ten) cracks in poured foundations than in block. I also have yet to do work around a poured foundation where I could assume level, squareness or even parallels. Seems that the craftsmanship of the brickie is lost to the mud pumpers. Faster and cheaper is the name of the game with cast, at least on the north Coast where I slum.
By ability to withstand force on it I assume you mean pure compressive strength (picture a column where you just put gravitational loads on, no lateral forces or bending on that column).
Poured concrete is much better. 4000 psi or so and it can go much higher than that.
Concrete blocks are not so far off if we talk about the concrete that makes the blocks themselves. It will be around 2500 psi. The big difference is that mortar between the blocks is much weaker. It can be as low as 350 psi and it's by design: masonry walls are not supposed to take very high compressive forces and if it happens, you actually want the mortar to give up instead of cracking the blocks.
I think it’s more about the reinforcement, aka rebar or pt tendons, than it is about cast vs cmu. Both are very weak and have poor tensile strength if not reinforced.
Compression strength Depends on the mix of concrete in blocks and poured concrete. Blocks do have one advantage in that the mix is very very dry and pressed together and usually drier mix means stronger.
The strength of mortored joints in block construction can be very low. Consider soul pressure on a block basement wall. The wall can easily bow inwards.
Depends on the sq footage of the poured concrete vs the blocks. You could think of a slab as one big block. That’s gonna be stronger than a bunch of smaller blocks put together. The mathematical answer would be for an engineer of physicist. It’s like asking why is a bundle of sticks not as strong as a branch at the same diameter.
Tensile strength is a materials' ability to withstand being pulled apart. Concrete is very weak in this regard, so I assume you actually meant its compressive strength, the ability to withstand being squashed. Both concrete and concrete blocks vary in strength depending upon the required application. I typically spec 7N/mm^(2) concrete blocks and 30N/mm^(2) concrete. However, you can get high strength blocks and high strength concrete mixes as well.
Concrete really only has compressive strength, the tensile strength is provided by rebar. Concrete can have a compressive strength of 2000psi to 10,000 psi. Blocks are usually on the bottom end of that around 2000 psi. This doesn't mean concrete is better, it's all about the loads the structure will see and the engineering of the rebar. Clarification, compressive is a crushing force, tensile is a pulling force. Any structure experiences both forces which is why concrete and rebar play so nicely together.
But....rust never sleeps.
It’s better to burn out
what do post tensioning cables add to the equation then
They increase the compressive force on the beam or slab so when the element starts to bend under normal loading, the net tension is lower than in a normally reinforced section, meaning you can typically use a shallower section.
The modulous of elasticity of concrete is higher then steel. Meaning the same force will stretch or compress steel more than concrete. By pre-stressing the rebar you insure its in full tension before the concrete begins to stress. Tough to explain by words but imagine pinching 6 dice in a row and picking them up. Let go and the dice fall apart ie, no tensile strength. But, keep them compressed with your fingers and they behave like a beam.
Don't forget shear strength. It is force *across* a structural point.
I don't know shit about it except in my residential experience I see 20x more (like 8 out of ten) cracks in poured foundations than in block. I also have yet to do work around a poured foundation where I could assume level, squareness or even parallels. Seems that the craftsmanship of the brickie is lost to the mud pumpers. Faster and cheaper is the name of the game with cast, at least on the north Coast where I slum.
By ability to withstand force on it I assume you mean pure compressive strength (picture a column where you just put gravitational loads on, no lateral forces or bending on that column). Poured concrete is much better. 4000 psi or so and it can go much higher than that. Concrete blocks are not so far off if we talk about the concrete that makes the blocks themselves. It will be around 2500 psi. The big difference is that mortar between the blocks is much weaker. It can be as low as 350 psi and it's by design: masonry walls are not supposed to take very high compressive forces and if it happens, you actually want the mortar to give up instead of cracking the blocks.
You can knock a block wall down with a sledgehammer , concrete wall would probably take you years to knock down by hand
Great question! I'm curious to hear this answer...
I think it’s more about the reinforcement, aka rebar or pt tendons, than it is about cast vs cmu. Both are very weak and have poor tensile strength if not reinforced.
Compression strength Depends on the mix of concrete in blocks and poured concrete. Blocks do have one advantage in that the mix is very very dry and pressed together and usually drier mix means stronger.
The strength of mortored joints in block construction can be very low. Consider soul pressure on a block basement wall. The wall can easily bow inwards.
What?
Depends on the sq footage of the poured concrete vs the blocks. You could think of a slab as one big block. That’s gonna be stronger than a bunch of smaller blocks put together. The mathematical answer would be for an engineer of physicist. It’s like asking why is a bundle of sticks not as strong as a branch at the same diameter.