The Economy of Concrete Compressive Strength
The Economy of Concrete Compressive Strength
(OP)
I've never really thought about concrete strength and have always used the standard 4000 psi concrete. Recently, I have been reading up on some of the factors to take into consideration when specifying a concrete strength, such as the inherent safety in designing for a lower concrete strength - such as 3000 psi and then specifying a 4000 psi concrete for peace of mind during construction ( In case the concrete does not pass the compressive test) .
How economical is high strength concrete ? The cost of concrete that I have found is as follows (I live in the Southeast Asia so prices are a lot lower):
3000 psi - $67 / M3
4000 psi - $77 / M3
5000 psi - $85 / M3
What would your justification be for selecting 4000 psi concrete as opposed to 3000 psi one ? or even 5000 psi as opposed to 4000 psi concrete
How economical is high strength concrete ? The cost of concrete that I have found is as follows (I live in the Southeast Asia so prices are a lot lower):
3000 psi - $67 / M3
4000 psi - $77 / M3
5000 psi - $85 / M3
What would your justification be for selecting 4000 psi concrete as opposed to 3000 psi one ? or even 5000 psi as opposed to 4000 psi concrete






RE: The Economy of Concrete Compressive Strength
I just recently spec'd 5,000 psi for foundation walls where I would normally use 4,000. I typically use 4,000 as a minimum and increase from there if I need to.
RE: The Economy of Concrete Compressive Strength
RE: The Economy of Concrete Compressive Strength
RE: The Economy of Concrete Compressive Strength
RE: The Economy of Concrete Compressive Strength
I can't see many reason to spec footings above 25mPa, and if it was a mass pier than I would probably spec 20mPa.
for slabs that are on ground with low loadings I prefer lower cement content concrete, for a house slab I would prefer 20mPa over 40 mPa any day of the week.
As for spec'ng a higher strength concrete for the fun of it, it can be interesting if your pushing Mcr. I prefer to get the concrete I specified delivered and require.
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RE: The Economy of Concrete Compressive Strength
I worked on a project where we needed some additional strength in the walls from the standard 3,000 psi concrete so we specified 4,000 psi concrete. The project was phase 2 with phase 1 complete under the same circumstances. The contract was design-build with the contractor as the lead (who I was hired by). I received a call from the contractor complaining about the increase to go from 3,000 to 4,000 psi concrete which they didn't "budget" for. I explained that the specifications for phase 2 were exactly the same as phase 1 and that he never complained on phase 1 and should have known about the switch in phase 2 after constructing phase 1 (which we had compressive test on that met the needs of the specifications). I never knew increasing the compressive strength would cause that much of a problem.
We usually use a compressive strength of 3,000 psi. Most of the concrete work we do is for foundations and suspended slabs on metal decking. We have had complaints about SOG cracks and cracks on suspended slabs when we have specified higher strength concrete and complaints from clients about the cost. In the end I always explain to my client that the only way to keep concrete from cracking is to keep it in the bag.... or reinforce the s**t out of it (within limits of the code of course).
RE: The Economy of Concrete Compressive Strength
It looks like your concrete cost is directly related to strength. But if you consider total costs, with formwork, reinforcing and finishing, the concrete cost is at most one third of the total placed costs. And for elevated work or walls it's about 10%. So your $10 a cubic meter is maybe 1% to 3% of the placed concrete costs.
RE: The Economy of Concrete Compressive Strength
RE: The Economy of Concrete Compressive Strength
RE: The Economy of Concrete Compressive Strength
And I don't agree that higher strength concrete always means more shrinkage and cracking. There is more cement but the W/C ratio for higher strength concrete is usually lower. If mixed and placed correctly, the higher strength concrete is stronger, more durable, and provides greater corrosion protection for your rebar.
RE: The Economy of Concrete Compressive Strength