It was mix for teaching new construction inspectors generic concepts. As you know each construction project of any size may have several custom mix designs from a sidewalk mix to high strength concrete for column or bridge decks.
Generic is right. It’s textbook stuff like this that new superintendents on job sites retain the most. Thanks for the clarification. The variables of mix designs can make ones brain explode. It doesn’t help that engineers and architects keep coming up with new crap all the time. Too bad concrete isn’t as simple as it used to be. Some of the hardest slabs I have ever demoed were 50-100 years old.
Thanks for sharing Randy.
I agree, we now add water-reducing agents, superplasticizers, air entrainment, fly ash, set retarder or switch to Type III cement, add ice during hot weather, and the list goes on. Builders 100 years ago would not recognize today’s concrete mix. Before I retired I had a project with a drainable concrete base. It was an open-graded mix and just to satisfy my curiosity I had a water truck hose down the cured mix and it would allow water to pass through as fast as the truck could pump it out.
Unfortunately, this parts my hair right down the middle, but I do think the last image maybe should have the word “strain” instead of stain" and might include the term “reentrant corners”, unless I’m wrong. I don’t usually try to correct anyone with PE after their name about structural issues. I thought maybe it was a typo.
I know all these charts and formulas may be too deep in the weeds, but the basic information I want inspectors to take from these is shrinkage cracks typically occur in the first 6 to 12 months. Too much water in the mix or exposing new concrete to hot dry weather while curing in the first few months will both increase the shrinkage crack size. Finally you can estimate the maximum amount of expected concrete shrinkage by multiplying the wall or slab length in inches by 0.000780. For example a basement floor slab 50 foot long should shrink 50 x 12 x 0.000780 = 0.468 inches or approximately 1/2 inch. This mean you could expect one 1/2 inch crack or multiple cracks that add up to 1/2 inch, including the gap between the slab and the basement walls.
Thanks for the clarification. The variables of mix designs can make ones brain explode. It doesn’t help that engineers and architects keep coming up with new crap all the time. Too bad concrete isn’t as simple as it used to be. Some of the hardest slabs I have ever demoed were 50-100 years old.