Any walkway or surface with a slope greater than 1 inch for every 20 inches of run, is a ramp. When you are making a concrete ramp, you must use a slope less than 1 inch for every 12 inches in order to meet the safety standards as set by the American Disability Act (ADA). There may be additional regulations in your community, so check with your local building authority. Although all ramps are slightly different in size, there are some basic techniques to observe when making a concrete ramp. You should have some knowledge of concrete production before you begin.
Pour a direct ramp if the landing height is 12 inches or less. This includes curb ramps and ramps that provide access to buildings and stores that are no more than one or two steps above grade. Frame the ramp with plywood, cutting the top edge to form the slope of the ramp and secure the plywood in the ground with stakes.
Remove any sod from beneath the pour and add a layer of sand but do not allow the sand to reach the edge of the forms. It should be at least 2 inches from all edges in order to allow the new concrete to settle. Dig out the ground in the lowest portion of the ramp in order to increase the concrete thickness. All portions of the ramp must be at least 4 inches thick.
Pour and screed the ramp. This is a fairly small and easy pour, due to the low height. Use a rubber mallet to "tamp" the sides of the form when filled with wet concrete. This tamping action encourages bubbles to rise to the top, preventing air voids. You can use a simple 2-inch by 4-inch board, cut a couple of feet longer than the ramp width as a screed with one person on each side, pulling it back and forth quickly.
Pour sidewalls if your ramp must ascend a landing height greater than 12 inches. This is more common in residential homes that rest on an elevated foundation. In this situation, you may not do a direct concrete pour, since the pressure of the concrete is too great to contain within the plywood forms.
Form your sidewalls a minimum of 6 inches thick and use concrete ties to support and reinforce the integrity of the forms. Secure the concrete ties in place on either side of the plywood forms with rebar.
Remove the forms when the sidewalls are set and allow the concrete to cure for a day or two. Then you may pour the bulk concrete in the ramp portion. Follow the same method as for the smaller ramp. Trowel the top of the ramp carefully. Trowel and screed from side to side to keep from shifting wet concrete downwards in the forms.
Brush barely damp concrete before it dries. This is essential to the safety of the slope. Concrete, when wet, becomes slippery and hazardous. Use a large commercial broom and make sweeping horizontal strokes across the surface. This will create pleasant looking streaks that will provide traction for wheelchairs and persons with canes or walkers.