It is hard to tell when people are pulling your leg on a forum. Did you catch the part that said this was a cattle guard? Cattle are prevented from using a major highway. If this is a private gravel road, typically there is a lifetime gate next to it that the concrete trucks have to use.
Engineered drawings? 5000 psi concrete? Vibrators? Funny stuff. The stiff mix is solid advice. I suggest being careful the footing isn't washed out from flash floods or taken out of service by filling up with mud from heavy rains. No one even looks at a cattle guard once it has been in for a few years.
The stiffer mixes are a good idea. Those crimped synthetic macrofibers are cheap if you want to add a few ounces. Also, try not to pour in 100ーF heat. Usually, a fence post is banged on the form and a rod is poked down in several places instead of vibrating. They do make cordless vibrators if you need to fill your tool box. My concrete supplier
encourages a 3 yard minimum. Where are you putting the rest of the load?
I hate concrete work.
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