Abstract: A slip form or screed for forming elongated concrete formations, such as a highway barrier wall wherein a concrete receiving hopper is located forwardly of the slip form, and the front wall of the hopper is provided with a hinged gate pivotal between open and closed positions. The gate structure permits stationary objects to enter the hopper and slip form as to become a part of the formed concrete formation, and the gate structure includes concrete retaining means to confine the concrete when the gate is opened, and control the flow of concrete forwardly through the opening when stationary objects are received within the form.