The United States military protects China's freedom to trade worldwide. It does not protect the economic interests of the people of the United States.
U.S. Foreign debt is not like a bank loan. Regarding China, nearly all is held in the form of U.S. governments bonds specified in U.S. currency. The United States will always be able to pay off its dollar obligations and the only factors keeping it from doing so today are anti-inflation policy and trade policies, both of which at this point favor China more than the United States.
The Romans regarded roadways as military structures. China is currently financing a bigger canal from the Pacific to the Atlantic and it would make sense that they would want reliable transoceanic roads to service their outlying colonies in North America.
It's been a long time since the United States military was dedicated to the interests and the security of the U.S. It protects the gobal economy. Any government dominating the global economy gets to set the military agenda of the United States -- among the many ways it gets to influence the federal government.
China does not have to worry about going broke in the process of establishing a worldwide empire. The colonies are there to finance their own colonialization.