Can I build a temporary driveway ramp over a new concrete curb?
If the boards flex and bend under the load and crush the green concrete curb, you will be responsible for the full cost of the road crew returning to the site, removing the mess, and pouring new curbs. 

Right now only the bossman thinks you're stupid. You don't want to hear the same thing from a judge. 

If you can find some cement blocks or other firm braces, you can support the boards right next to the curb. Make sure it can't wobble. You're still taking a chance, though. 

Don't do this job alone. You should have at least two helpers, one to watch the ramp as you drive onto it and stop you if it shifts or bends, and the other to hold your beer.