New Concrete Driveway....Is It Strong Enough?
Just had a new concrete driveway poured. The driveway will average 4" thick, will cure in 30 days (it's been 32 as of today) to 3,000lbs per square inch. Buckeye Fibers were also added and mixed int...
Forum Discussion
With Concrete, you can decide where the cracks will occur (cut or form them, cutting is more reliable but must be done fairly quickly after it sets) but not if they will occur. Reinforcement can allow you to increase the spacing of cracks but not eliminate them entirely.
Big issue with thin slabs (4" is thin) is how good is the sub-base. If it's not been solidly compacted, it may crack now or it may crack in a few years when the sub-base settles and the concrete tries to bridge. If others reading this can take anything away from this discussion, put in good sub-base and compact the heck out of it before the pour.
3000PSI does not mean each tire can support hundreds of thousands of pounds. The PSI rating is how much pressure before test cylinder of concrete literally crushes (it's fun running the machine). Your drive will crack long before that loading is reached. Cracking occurs when the forces try to bend the slab over a weak spot in the sub-base. In that situation, the bottom edge of the slab is in tension and concrete is horrible in tension. Design strength is officially tested at 28 days but you almost always beat the rated strength as the supplier doesn't want to risk failure by putting out a 2950psi batch and getting caught (residential of course tends to be a lot more sloppy as road agencies do regular testing and residential owners rarely do)
I would have bumped up to 5-6" if I knew I was putting that truck on there. Cheap insurance. Upping to 4k or 5k psi concrete doesn't hurt but thickness will have a bigger impact as tensile strength is still lousy and thickens reduces the tensile force applied.
PS: Concrete is the glue that holds the aggregate (sand and gravel) together. Portland Cement is used in what laypeople refer to as "concrete" the other common alternative is asphalt cement to produce asphalt concrete. One thing a lot of people don't realize is on a well built dirt road, clay is used as the cement. No problem calling PC-Concrete as cement though, everyone knows what you are talking about.
Big issue with thin slabs (4" is thin) is how good is the sub-base. If it's not been solidly compacted, it may crack now or it may crack in a few years when the sub-base settles and the concrete tries to bridge. If others reading this can take anything away from this discussion, put in good sub-base and compact the heck out of it before the pour.
3000PSI does not mean each tire can support hundreds of thousands of pounds. The PSI rating is how much pressure before test cylinder of concrete literally crushes (it's fun running the machine). Your drive will crack long before that loading is reached. Cracking occurs when the forces try to bend the slab over a weak spot in the sub-base. In that situation, the bottom edge of the slab is in tension and concrete is horrible in tension. Design strength is officially tested at 28 days but you almost always beat the rated strength as the supplier doesn't want to risk failure by putting out a 2950psi batch and getting caught (residential of course tends to be a lot more sloppy as road agencies do regular testing and residential owners rarely do)
I would have bumped up to 5-6" if I knew I was putting that truck on there. Cheap insurance. Upping to 4k or 5k psi concrete doesn't hurt but thickness will have a bigger impact as tensile strength is still lousy and thickens reduces the tensile force applied.
PS: Concrete is the glue that holds the aggregate (sand and gravel) together. Portland Cement is used in what laypeople refer to as "concrete" the other common alternative is asphalt cement to produce asphalt concrete. One thing a lot of people don't realize is on a well built dirt road, clay is used as the cement. No problem calling PC-Concrete as cement though, everyone knows what you are talking about.
