ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.

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Page 42 of 47

ASPIRE Summer 2018 | 41 Hydrodemolition: A Preservation Strategy for Concrete Bridges in the United States by Edward Liberati, Hydro-Technologies Inc. and Patrick Martens, consultant Hydrodemolition uses a controlled, high-pressure water jet to safely and selectively remove portions of reinforced concrete from a bridge while leaving the reinforcing steel and surrounding concrete intact. It was developed in Europe in the 1970s as an alternative to jackhammers and has become an acceptable method of removing concrete throughout the world. In the United States, hydrodemolition is predominantly used to remove concrete from bridge decks in preparation for a new concrete overlay. It can also be used to remove concrete from bridge abutments, piers, walls, and rails and to do full- depth deck removals. Other uses of hydrodemolition to remove concrete from reinforced concrete structures include tunnels, factories, piers, dams, defense facilities, and even amusement park rides. Logistics, costs, and feasibility are important considerations for the use of hydrodemolition on these special projects. Department of transportation specifications—such as those in Pennsylvania, Indiana, Kentucky, Ohio, Arkansas, and many more—are valuable resources when considering the use of hydrodemolition. Equipment and Process Overview Equipment consists of a hydrodemolition robot, a pump unit, and cleanup equipment. The robot is computerized, self- propelled, and remote-controlled and has many safety features. To meet various project needs, there are hydrodemolition robots designed to cut horizontally, vertically, and overhead. The hydrodemolition process begins when potable water is delivered from a hydrant or a tanker to the pump unit, where it is pressurized and the flow rate can be controlled. The high-pressure water is then delivered through hoses to the hydrodemolition robot, where it exits a secured nozzle and impacts the concrete surface. The computerized robot controls the movements of the water jet so the stream exposure time on the concrete surface is consistent over the removal area. A steel shell and skirting around the robot's cutting head that houses the water jet allows this operation to be performed safely. While hydrodemolition work is underway, cleanup of all rubble created from the operation is required. Cleanup of the concrete debris and excess runoff water is performed with water pumps and vacuum-collection equipment. The vacuum- collection equipment can quickly cleanup all water and wet debris remaining on the deck. As a final method of deck preparation before the placement of the overlay, the contractor performs a final high-pressure water blast and soaks the deck surface with water until it is at a point at which it will not dry out. Once the deck surface is saturated, the contractor covers it with plastic. This covering locks in the moisture, eliminates the need for bonding grouts, and prevents deck contamination from construction equipment. Fast-Track Hydrodemolition Fast-track hydrodemolition (FTH) is a technique used to prepare a bridge deck for a new latex-modified concrete CBP CONCRETE BRIDGE PRESERVATION Hydrodemolition robot working on a bridge deck. All Photos: Edward Liberati.

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