Durability of Materials in Pearl-Chain Bridges

Mia Schou Møller Lund

Research output: Book/ReportPh.D. thesisResearch

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This PhD thesis contributes to documentation regarding durability of materials
used in so-called “Pearl-Chain Bridges”. The Pearl-Chain Bridge technology is a
new precast bridge solution developed at the Technical University of Denmark. The technology reintroduces the arch structure as an economical beneficial solution primarily for road and railway bridges, and allows for the faster, more environmentally friendly, and cheaper construction of such bridges. A Pearl-Chain Bridge consists of two main parts: the load-carrying Pearl-Chain arch, and the fill material on top of the arch. The construction of the Pearl-Chain arch is simple. The arch is assembled on its side, next to the road that the bridge will span, by placing a number of plane prefabricated Super-Light Decks that consist of lightweight aggregate concrete and conventional concrete, in the desired arch shape. Mortar joints are cast between the decks, and because all decks have a duct cast through them longitudinally, they can be collected on a wire – like pearls on a string. The assembly of the arch is completed by post-tensioning the wire. A crane lifts the arch into place during the night, and subsequently the Pearl-Chain arch is stabilized by casting a fill material between the spandrel walls of the arch. Finally, the road surface is cast on top of the fill material.
New bridges are designed for a service lifetime of at least 100 years. Hence, the specifications of the materials used in Pearl-Chain Bridges are high. This PhD study documents that the materials used in Pearl-Chain Bridges have the necessary strength and durability to ensure their longevity. The scope of the PhD study is limited to assessing the fill material placed on the Pearl-Chain arch, and the mortar joints and lightweight aggregate concrete used in the Pearl-Chain arch itself. This is because these materials, and the application of them, differ from the materials in typical bridge superstructures.
Typically, arch bridges are filled with sub-base gravel; however, in order to examine the possibilities of using alternative fill materials, cement-stabilized gravel and pervious concrete were also investigated. The most suitable fill material for Pearl-Chain Bridges depends on the particular bridge design; the results obtained and presented in the present PhD study provide guidance on how to decide which fill material is most suitable regarding strength, permeability and freeze-thaw durability. In particular, the PhD study explored in depth the use of pervious concrete, because pervious concrete is a relatively unknown material in Denmark. The applicability was demonstrated by using pervious concrete fill in the very first 26 meter-long Pearl-Chain Bridge constructed. Compared with sub-base gravel and cement-stabilized gravel, pervious concrete considerably improves the drainage properties of the superstructure, which has a positive influence on the longevity of Pearl-Chain Bridges.
The mortar joints in the Pearl-Chain arch were found to be prone to crack formation during hardening, which is undesirable since it provides easy access for water and chloride ions to reach the post-tensioning wires, and initiate corrosion. This crack formation was eliminated by using an expansive mortar product with a constant expansion, and by applying a primer to the concrete surfaces adjacent to the joint, whereby the porosity along the construction joint was decreased. It was documented that the mortar joints did not decrease the durability of the Pearl-Chain arches with regard to chloride ingress, water absorption, or freeze-thaw durability. The work carried out on lightweight aggregate concrete was, from many perspectives, pioneering. This was mainly because most prior knowledge concerning lightweight aggregate concrete mix design was based on experience and had not been documented in scientific papers, but also because the lightweight aggregate concrete in Pearl-Chain Bridges can be exposed to freeze-thaw, which is not the case with lightweight aggregate concrete in typical fields of application. The freeze-thaw durability of lightweight aggregate concrete was improved by the introduction of air entrainment, which was demonstrated by measuring and correlating the air content of fresh lightweight concrete with the freeze-thaw behavior of hardened lightweight concrete. Recommendations are given to a freeze-thaw resistant lightweight aggregate concrete mix design for Pearl-Chain Bridges, which has greater strength properties than the current lightweight aggregate concrete used in Super-Light Decks for indoor purposes.
Original languageEnglish
PublisherTechnical University of Denmark, Department of Civil Engineering
Number of pages178
ISBN (Electronic)9788778774323
Publication statusPublished - 2016
SeriesB Y G D T U. Rapport


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