Strengthening of concrete bridges using reinforced sprayed concrete under state and fatigue loading
The Department of Transport's bridge assessment programme has revealed that a significant number of bridges are not strong enough to carry the much heavier commercial axle loads that will soon be applied to UK bridges. To address this problem, this research investigates a technique of strengthening concrete bridges by bonding and encapsulating an extra layer of reinforcement using sprayed concrete to the soffit of the bridge to increase the flexural capacity. An experimental investigation on approximately one eighth scale reinforced concrete slabs strengthened by different amounts of reinforcement placed at varying depths below the soffit and encapsulated by professionally applied dry-mix sprayed concrete, have shown that increased flexural capacity of up to eight times the original capacity is possible with no sign of breakdown of the bond at the soffit interface. Separate interface shear tests both direct and indirect were carried out and showed high shear capacities were obtained in all specimens. The susceptibility to weathering causing a breakdown of the interface bond was investigated by freeze-thaw tests. Fatigue load tests have also shown that the strengthened slabs have a similar life span to that of normal reinforced concrete. An analytical study was carried out, complemented by the fatigue load test results, to assess the life span of two highway bridges when subjected to fluctuating traffic loading, taking into account the proposed increasing use of heavier axle loads. All the slabs tested to failure under both static and fatigue loading failed in flexure and extremely good bond between the sprayed concrete layer and its substrate concrete was maintained right up to failure, even without shear connectors. The potential use of this technique in practice was therefore well demonstrated.