The U.S./Mexico border is 1,954 miles long which is about half this size of the actual wall of the Great Wall of China. If Donald Trump were able to build the wall that he wants to build to divide the nations he would need a lot of concrete. On top of that, the highest ladder in Mexico is 40 feet so the wall would be 50 feet high to be safe and 30 feet deep into the ground to prevent tunnels.
How much cement would that require? Take a look:
We've got dimensions: 80 feet high from the bottom of the foundation and 10 feet wide. That's 800 square feet of cross-section, but concrete is sold in cubic yards, so let's see how much we need:
800 square feet / 9 feet per yard = 89 square yards cross-section
1760 yards per mile * 1954 miles = 3439040 yards
3,439,040 yards * 89 square yards = 306,074,560 cubic yards of concrete needed
For reference, the Hoover Dam contains 3,250,000 cubic yards of concrete.