Possibility to Improve Strength and Structural Stability of Bridge Deck Slabs by Using Ultra High Performance Fiber Reinforced Concrete

Abstract

Parts of the bridges in Sweden and other countries have shown to have a too low resistance with respect to deterioration. This leads to costly repair interventions that disturbs the traffic and results in high Life Cycle Costs (LCC) for the bridges. This investigation primarily focuses on the mechanical behavior, durability and rheological properties and application of UHPFRC to develop more robust bridge deck slabs. UHPFRC shows better performance at post-cracking due to the strain hardening behavior with distributed micro-cracks, enhancing the service life of bridge deck slabs. The main idea is to use Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) to harden those zones of the structure that are exposed to severe environment and high mechanical loading. This conceptual idea combines efficiently protection and resistance properties of UHPFRC and significantly improves the structural performance of the rehabilitated concrete structure in terms of durability and life-cycle costs. The concept is validated by means of four applications demonstrating that the technology of UHPFRC is mature for cast in-situ and prefabrication using standard equipment for concrete manufacturing. Moreover an inventory of two bridges in Sweden has been used as case study to investigate the possibility of use of UHPFRC for rehabilitation. I. INTRODUCTION Reinforced concrete is the most widely used construction material for bridges. The bridge decks are constantly subjected to concentrated traffic loads and are exposed to environment actions. Consequently, they deteriorate faster than other parts of the bridge. Also during winter, de-icing salts are used to keep the roads and bridges free from ice. De-icing salts, which are generally a mixture of sodium chloride and calcium chloride penetrate into the concrete and cause deterioration of the concrete structure and in particular, the steel reinforcement. These structures show excellent performance in terms of structural behavior and durability except for those zones that are exposed to severe environmental and mechanical loading (1). Rehabilitation of deteriorated concrete structures is a heavy burden also from the socio-economic viewpoint since it also leads to significant user costs. As a consequence, novel concepts for the rehabilitation of concrete structures must be developed. Sustainable concrete structures of the future will be those requiring just minimum interventions of only preventative maintenance with no or only little service disruptions. Over the last 10 years, considerable efforts to improve the behavior of cementicious materials by incorporating fibers have led to the emergence of Ultra-High Performance Fiber Reinforced Concretes (UHPFRC). These novel building materials provide the structural engineer with an unique combination of (a) extremely low permeability which largely prevents the ingress of detrimental substances such as water and chlorides and (b) very high strength, i.e., compressive strength higher than 150 MPa, tensile strength higher than 10 MPa and with considerable tensile strain hardening (up to more than 2‰ of strain) and softening behavior (with fracture energy of more than 15'000 J/m2). In addition, UHPFRC have excellent rheological properties in the fresh state allowing for easy casting of the self-compacting fresh material with conventional concreting equipment (2). Consequently, UHPFRC has an improved resistance against severe environmental and mechanical loading thus providing significantly improved structural resistance and durability to concrete structures. This paper presents an original concept for the rehabilitation of concrete structures. The concept is described and validated by means of four applications. Finally, two case studies were performed. In the first case study, the use of UHPFRC for rehabilitation of existing bridges was theoretically applied on a bridge deck slab. An existing bridge with insufficient durability for the deck slab and deteriorated edge beams was chosen as a reference bridge. In second case study, a comparison was made between an industrially produced bridge alternative and a reference composite bridge, conventionally produced with a cast in-situ normal strength concrete bridge deck slab. The new alternative bridge solution considered of main steel girders and prefabricated normal strength bridge deck elements joined and covered with UHPFRC.