They do make products to use for this exact situation. They are called threshold ramps or sometimes called curb or kerb ramps. There are lots of people who need such a product, factories where they have to move various types of rolling carts around the facility, places where people are in wheelchairs and mobility carts.
Here is a listing for one made of solid rubber that comes in a variety of heights. If you do more searching online you might be able to find one that is wider from other sources or you can just cut one in half and place sections where the wheels will be rolling in. I will let you do the further searching, I need to get on with other things.
You could secure it in place using a suitable product that is rated for exterior use on concrete. But most likely some type of urethane construction adhesive will work. Hopefully they also sell the adhesive..