LIGHTWEIGHT CONCRETE IN HIGHWAY BRIDGES

Abstract Lightweight concrete has been used in American highway bridges for over 50 years and there are now nearly 200 concrete and composite bridges containing lightweight aggregates in the United States and Canada. In the USSR about 100 bridges have been constructed with lightweight aggregates in the past 20 years and in Western Europe numbers are steadily growing since the first lightweight bridge was built in the late 1960s. Examples are given of bridges in which lightweight concrete has been used successfully, ranging from simple reinforced concrete footbridges to long-span post-tensioned segmental box girder bridges. Weight savings of 25 to 30 per cent on the superstructure can be achieved in some cases, with consequent savings of reinforcing and prestressing steel and on piers and foundations. Overall cost savings of 10 per cent or more are possible after allowance has been made for the higher initial cost of lightweight aggregates. Lightweight concrete bridges have generally performed satisfactorily in service and there is increasing evidence that the durability is at least as good as normal weight concrete. The few cases of unsatisfactory performance are likely to have been a result of inadequate detail design or poor quality control during construction. There are indications that in practice creep and shrinkage are much less than small scale laboratory tests would indicate. Lightweight concrete appears particularly advantageous for precast, prestressed components to reduce handling costs where access is limited or where ground conditions are difficult. This has potential application to the upgrading of existing bridges and to local road improvements and urban renewal schemes where disruption to traffic flow must be kept to a minimum.