The aim of this project was to assist the Highways Agency in re-assessing current designs and specifications for continuously reinforced concrete pavement (CRCP) in the light of performance data from the UK and other countries. The findings of this work have been used to develop more economic designs for sustainable long-life roads, which would give increased value for money and support the Government aims for sustainable construction. The performance and design parameters investigated were crack patterns, concrete strength, steel reinforcement, foundations, hard shoulders and edge strips, traffic loading and terminations. The effects of these parameters on the structural integrity and durability of CRCP were assessed and the results were used to develop new design curves. The performance of CRCP is mainly determined by the condition of the surface cracking and defects, with the greatest influence arising from medium, wide and bifurcated cracks, and localised punchouts. It was found that the aggregate type in CRCP has more influence on the cracking pattern than the subbase type. Locating the reinforcement at the third-depth of the slab significantly improves the crack pattern of CRCP made with siliceous gravel. A review of international standards and practices has shown the widespread use of flexural strength rather than compressive strength for design purposes, which is more related to the structural performance of pavements. Reliable relationships between flexural and compressive strength were established and used to develop new CRCP designs with thinner slabs for higher strength concrete. Cracks in CRCP provide the route for chlorides, from de-icing salts, to penetrate the slab and initiate reinforcement corrosion. Corrosion mainly occurs in the transverse reinforcement, which tends to be coincident with the transverse cracks, with no evidence of significant corrosion in the longitudinal reinforcement. No significant consequences of corrosion damage on the performance of CRCP have been found in the UK. The currently specified cemented subbase under CRCP in the UK has significantly higher strength than that used in other countries. This high strength can increase the risk of discontinuity of the foundation support. The new designs consider lowering the subgrade strength requirement for a subbase only, without capping, to 5 per cent CBR. Also, the use of bound materials in Foundation Classes 2, 3 and 4, could result in significant economic benefits, as they may incorporate alternative materials. Recommendations are given against the use of asphalt shoulders alongside CRCP and to retain the maximum cumulative traffic loading given in the current designs to allow for the possibility of an increase in the maximum permitted axle load. Thermal movements at CRCP terminations indicated that the ground beam anchorage system restrains only 40 per cent of the CRCP end movement but requires little maintenance. For the wide-flange beam system, the CRCP end movement is mainly accommodated by the joint between the CRCP and the steel beam, and therefore there is a potential to reduce the number of transition bays. Recommendations are given to reduce the amount of thermal movement at terminations by locally increasing the subbase friction and reducing the coefficient of thermal expansion of the concrete. A proposal is made to develop a more economic termination system based on bridge-type joints. (Author/publisher)
Abstract