Performance of Cardboard Carton Forms
By David K. Isbell, P.E.
Abstract: Cardboard carton forms (void boxes) are commonly used to form the void space between the bottom of grade beams and slabs over expansive soils. However, other than laboratory compression tests and 100% humidity tests, there is little documentation for the actual performance of these boxes in place. This paper summarizes field tests done in an attempt to simulate actual conditions to answer the following questions:
• Do the boxes deteriorate at an acceptable rate?
• Does the wax coating or impregnation and a polyethylene vapor barrier affect deterioration?
• Will the boxes fail under heave conditions?
• Are trapezoidal boxes appropriate and do they perform in an acceptable manner?
• Which type of boxes are appropriate in each situation?
• What are some of the construction considerations necessary to insure proper function of the boxes?