Caltrans Implementation of UHPC Connections for ABC Projects

Despite a recent high-profile application at Hammersmith Flyover, adoption of Ultra High Performance Concrete (UHPC) in the UK remains limited. This contrasts with use globally which continues to grow. A state of the art study was undertaken on behalf of Highways England, the government-owned company responsible for operating and maintaining the UK’s Strategic Road Network, with objectives to identify possible applications and benefits of UHPC, barriers to use,and recommendations to promote increased use on Highways England’s infrastructure. Applications for new-build (full components, in-situ connections) and structural enhancement(link slabs, deck overlays, column jacketing) were identified. Highways England owns a wide range of transport infrastructure, including 6800+ concrete bridges, the majority of which are over40 years old. This makes structural rehabilitation an important topic, and provides justification for promoting implementation of UHPC. The absence of UK standards and guidance for design and execution of UHPC is a key barrier to widespread adoption; some other European countries making use of UHPC have some form of published literature. Further issues include lack of experience amongst designers and contractors, limited numbers of UHPC suppliers, and the absence of knowledge and precedent regarding technical approval. Recommendations are made for stimulating use of UHPC in the short term and include preparation of an action plan identifying additional sources of funding (e.g. innovation funds), conducting a whole life cost benefits analysis, and developing a clear approvals process for UHPC. To pave the way for widespread implementation in the longer term, recommendations include sponsorship of pilot projects,engagement with the academic community, and promotion amongst designers and sub-contractors.

Over the course of the last few years, the NYSDOT has strived to institutionalize the use of Ultra High Performance Concrete (UHPC). To ensure that the NYSDOT was receiving a consistent product, a non-proprietary UHPC mix design was developed. Additionally, UHPC is an effective material for constructing durable and efficient closure pours between precast elements. Over the course of many years, NYSDOT has developed several innovative details for precast elements that exploit the enhanced properties of UHPC to connect these prefabricated elements. These elements include precast deck panels, NEXT beams, deck bulb-tees, and adjacent boxes. These details have been standardized in the official NYSDOT Bridge Detail (BD) sheets. NYSDOT has also looked to develop, apply, and evaluate innovative uses for UHPC. Details for UHPC link slabs and joint headers have been included on several projects as a trial installation. Additionally, NYSDOT has been developing a testing program with FHWA to determine if UHPC can be used to rehabilitate steel girders with deficient top flange compressive capacity for installation on another project. Finally, NYSDOT is considering the use of UHPC as a full width overlay to rehabilitate a deteriorated concrete slab on an adjacent prestressed concrete box-beam bridge. If these installations prove effective, then their details can be included in future standard details.

Performance assessment and design of ultra-high performance concrete (UHPC) structures incorporating life-cycle cost and environmental impacts

Pull-out behavior of cluster stud-post pouring UHPC connectors in prefabricated steel-concrete composite beam

<p>Ultra-high performance concrete (UHPC) provides superior properties compared to conventional concretes. However, due to the high cost of materials and lack of familiarity and design codes, the use of UHPC is still limited in structural applications. Research at New Mexico State University (NMSU) has developed nonproprietary UHPC using materials local to New Mexico, USA. The mixture proportions reduce costs while improving sustainability and maintaining the advanced mechanical and durability properties characteristic of UHPC. The superstructure of Bridge 9706, a two-span bridge near Anthony, New Mexico, was recently constructed to incorporate one span using nonproprietary UHPC and one span using high-performance concrete (HPC). To investigate the behavior of the bridge, load tests were conducted. External sensors were attached to the girders of both spans to measure strains during testing. Additionally, digital image correlation (DIC) was used on the sides of the exterior girders to measure deflections and strains. Loaded trucks were used to apply a load to the bridge through different load paths and configurations. Results of the load tests are presented and the behavior of the UHPC and HPC span under similar load conditions are compared.</p>

This paper deals with the roof structural system using prestressed girders made of ultra-high performance concrete (UHPC). One of the aims of this study is to verify whether the option of the UHPC girders could be under certain boundary conditions competitive with the commonly used construction materials. Due to its high strength, UHPC enables the design of the structural elements with the high load bearing capacity and with smaller slenderness compared to normal strength concrete elements. The price of UHPC is currently still very high compared to the normal strength concretes or steel. Therefore, its use for the usual designed structures does not recently seem too economically attractive. The effect of material savings is nonnegligible in the case, that a self-weight of the structure forms dominant component of the total load. In addition to the high strength, UHPC has very high resistance to environmental influences. It is therefore likely, that UHPC could be advantageously applied e.g. for the roofing of industrial buildings of chemical plants with high aggressive environments, because there are high demands on the life cycle of the structure.

Mechanical and durability performance of ultra-high-performance concrete incorporating SCMs

Development length of sand-coated GFRP bars embedded in Ultra-High performance concrete with very small cover

One of the major barriers to the use of UHPC (ultra-high performance concrete) in the precast industry is the high cost relative to conventional concrete. Often, the properties of UHPC are not fully utilized throughout a member. One solution is to create a hybrid member with UHPC in zones of high or unpredictable stresses while filling the rest of the section with a conventional concrete. Constructing such a member will require innovative techniques to achieve a successful bond between the two different materials. This paper is unique in that it investigates the bond behavior when both materials are in the fresh state. Several specimens of 2 × 2 × 17 inches (50x50x431 mm) were fabricated for direct tension tests. These specimens were fabricated with half UHPC and half SCC (self-consolidating concrete). The interface between the two types of concrete was perpendicular to the tensile force so that the bond was in direct tension. All materials were placed immediately after mixing and were separated by a removable barrier. Time dependency of the bond strength was controlled by removing the barrier at different times after placing. The quality of the bond strength between fresh UHPC and fresh SCC was compared to the tensile strength of the SCC. The results were used to determine a maximum allowable time by which both concretes can be combined while maintaining an acceptable bond strength.

Electromagnetic method field test for characterizing steel fibers in ultra-high performance concrete (UHPC)

Interfacial slip can cause rigidity degradation and stress concentration in fiber-reinforced polymer-concrete hybrid beam (FCHB). Therefore, precisely evaluating the composite action between fiber-reinforced polymer (FRP) and concrete of FCHB plays a pivotal role in structural analysis and design. Previous push-out tests showed that most connections for FCHB behave nonlinearly in load-slip relationships even at a low load level. However, existing analytical equations have their limitations due to the assumption of linear load-slip interfacial relationship which is not suitable for FCHB. The originality of this paper is to propose a finite difference method (FDM) to elaborate the interfacial slip and shear stress. FDM agreed well with the analytical solutions of the linear load-slip relationships for connections. Results indicate that higher accurateness can be obtained by using more elements. And 40 elements for half span of FCHB can reduce the error of numerical results to 1%. Then, the proposed FDM was expanded to predict the interfacial behavior of FCHB considering nonlinear interfacial load-slip relationships. It was found that perforated FRP rib connections can ensure nearly full composite action and the bolted connection can lead to a very high slip level. The use of ultra-high performance concrete (UHPC) results in a higher degree of composite action than normal concrete. The deflection considering slip was computed by adding deformation under full composition action and that caused by the slip effect. It was suggested that high strength steel bolts are effective both in normal concrete and UHPC. When the slip modulus is suggested to be larger than 20 kN/mm, the capacity per bolt should be larger than 20 kN.

Over the past decade there has been a significant increase in the number of concrete transportation structures reaching the end of their service lives, typically as a result of age and severe degradation. This deterioration is often the result of exposure to aggressive environments and substantial increases in vehicle loading. Rehabilitation is typically the most appropriate solution for these structures because of the high cost of full replacement, resulting in the need for cost-effective and suitable solutions for rehabilitation. Ultra-high-performance concrete (UHPC), one of the more recent advances in construction materials, appears to be a promising material for the repair of concrete structures. The potential benefit of UHPC is primarily derived from its negligible permeability, which prevents water or chemical penetration, and its high mechanical properties, which serve to increase the bearing capacity of the structure. Some of the primary challenges associated with the use of UHPC as a repair material are uncertainty in the bond performance and interaction with the existing substrate material. This paper focuses on the characterization of the interface bond and compatibility between UHPC and normal concrete. The testing program was conducted in the spirit of ASTM because no standard test methods currently exist for UHPC. In addition, a series of numerical models were developed to support the results obtained in the experimental investigations. The results highlight the exceptional performance of the bond, but they also demonstrate a number of challenges with respect to characterizing the bond. Specific challenges included characterization of surface roughness, premature specimen failure, material strength mismatch, and the quality and consistency of the testing methods used.

Shear behavior of FRP-UHPC composite beams enhanced by FRP shear key: Experimental study and theoretical analysis

Natural plant fibers represent a sustainable alternative to conventional fiber reinforcement materials in cementitious materials due to their suitable mechanical properties, cost-effective availability and principle carbon neutrality. Due to its high tensile strength and stiffness as well as its worldwide distribution along with rapid growth, bamboo offers itself in particular as a plant fiber source. In experimental studies on concrete beams reinforced with plant fibers, a positive influence of the fibers on the flexural behavior was observed. However, the load-bearing effect of the fibers was limited by the poor bond, which can be attributed, among other things, to the swelling behavior of the fibers. In addition, the plant fibers degrade in the alkaline environment of many cementitious building materials. In order to improve the bond and to limit the alkalinity and to increase the durability, the use of ultra-high performance concrete (UHPC) offers itself. Since no tests have been carried out, investigations on the flexural behavior of UHPC with bamboo fibers were carried out at the Institute of Concrete Construction of Leibniz University Hannover. The test results show a significantly improved load-bearing behavior of the fibers and the enormous potential of the combination of UHPC and bamboo fibers.

Ultra-high-performance concrete (UHPC) is a new type of high-performance cement-based composite. It is widely used in important buildings, bridges, national defense construction, etc. because of its excellent mechanical properties and durability. Freeze thaw and salt erosion damage are one of the main causes of concrete structure failure. The use of UHPC prepared with multi-walled carbon nanotubes (MWCNTs) is an effective method to enhance the durability of concrete structures in complex environments. In this work, the optimal mix proportion based on mechanical properties was obtained by changing the content of MWCNTs and water binder ratio to prepare MWCNTs UHPC. Then, based on the changes in the compressive strength, mass loss rate, and relative dynamic modulus of elasticity (RDME), the damage degree of concrete under different salt erosion during 1500 freeze-thaw (FT) cycles was analyzed. The changes in the micro pore structure were characterized by scanning electron microscope (SEM) and nuclear magnetic resonance (NMR). The test results showed that the optimum mix proportion at the water binder ratio was 0.19 and 0.1% MWCNTs. At this time, the compressive strength was 34.1% higher and the flexural strength was 13.6% higher than when the MWCNTs content was 0. After 1500 salt freezing cycles, the appearance and mass loss of MWCNTs-UHPC prepared according to the best ratio changed little, and the maximum mass loss was 3.18%. The higher the mass fraction of the erosion solution is, the lower the compressive strength and RDME of concrete after FT cycles. The SEM test showed that cracks appeared in the internal structure and gradually increased due to salt freezing damage. However, the microstructure of the concrete was still relatively dense after 1500 salt freezing cycles. The NMR test showed that the salt freezing cycle has a significant influence on the change in the small pores, and the larger the mass fraction of the erosion solution, the smaller the change in the proportion of pores. After 1500 salt freezing cycles, the samples did not fail, which shows that MWCNTs UHPC with a design service life of 150 years has good salt freezing resistance under the coupling effect of salt corrosion and the FT cycle.