Cement gives Ken the ability to manipulate cement-based material simply by being in contact with the surface. It does not give him the ability to create new cement, he can only reshape existing cement.
Concrete can be molded into any shape Ken desires, no matter in what state or form it is found, and he is free to weaponize said material as long as he keeps touching it. In the right conditions, even those with enough power to destroy concrete may easily get overwhelmed by Cement.
Because of the nature of this Quirk, Ken has a large combat advantage on urban areas, where concrete is abundant. Inversely, he holds little fighting ability on settings where concrete is rare or nonexistent, such as in the countryside.
In the anime, Ken' hands appear to glow in a faint green light whenever he's using Cement.
During combat, Ken uses Cement both for offense and defense, materializing huge walls of concrete to surround and trap enemies within.
With Cement, Ken can create all sorts of structures for others to work with, such as Gym Gamma and the arena used for the fighting portion of the U.A. Sports Festival. Ken is seemingly able to build complex constructs in a matter of minutes, showcasing expert skills over his Quirk.
- Earth Flow is a Quirk that works similarly to Cement, the only difference being the element that can be manipulated, as Earth Flow deals with the soil itself.
- Cement - Wikipedia article about the substance found in objects Ken can manipulate.