Use Of Ultra-high Performance Concrete Research Articles

Considerations on the use of ultra-high performance concrete for water tanks

The development of ultra-high strength and high performance concrete is a relatively new field in the profile industry. The last 150 years have shown that, despite getting more and more resistance, the practical applications have been too many times due to innovations in materials science. This phenomenon seems to be caused by the increased costs per unit of volume, as resistance increases, as well as a cautious retention of using new materials in practical applications. The present study aims to be an encouragement of practical structural applications by presenting an Ultra High Performance Concrete (UHPC), developed with locally available materials. As it is known, concrete is the main building material worldwide. In the last decades, his leadership position has been strengthened by the constant concern of the researchers and by obtaining the various types of concrete with increasing performances from the point of view of the fresh and hardened state, obtaining special structural applications.

Service Life Design of Deck Closure Joints in ABC Bridges: Guidelines and Practical Implementation

Closure joints are commonly used in bridge deck to connect two adjacent prefabricated elements in accelerated bridge construction. The current practice of closure joints utilizes the use of different materials such as normal strength concrete and ultra-high performance concrete with the use of different reinforcement details such as straight bars, hooked bars, and headed bars. The design of closure joint to meet strength limit state is quite simple, however, the design for service life for these joints is quite challenging. Framework for service life design of closure joints in bridges, built using accelerated bridge construction techniques, is developed in this paper. This framework includes several steps: 1) identification of project requirements especially those influences the service life of closure joints; 2) identification and selection of feasible closure joint types suitable for the project requirements; 3) identification of factors which influence the service life of closure joints along with mode of failures and consequences; 4) identification of suitable approaches or strategies for mitigating failure modes or assessing the risk of damage; 5) modification of closure joint detail using mitigation strategies which may result in the development of several alternatives and options for each closure joint type; 6) estimation and comparison of service life for each modified alternative using finite or target service life approach; and 7) conducting life-cycle cost analysis for each modified alternative along with the selection of the optimum closure joint details to meet both strength and service life demand. This framework is used in practical design implementation example for 1400-ft long bridge in Boston, Massachusetts, US. Several closure joints details were studied under this research such as the use of normal strength concrete with straight bars, 180-degree hooked bars, 90-degree hooked bars, and headed bars along with the use of ultra-high performance concrete with straight bars. This paper summarizes the outcome of the design for service life of those closure joints comparatively.

Use of UHPC slab for continuous composite steel-concrete girders

The loss of composite action at the hogging moment zone for a continuous composite girder reduces the girder stiffness and strength. This paper presents an experimental investigation of the use of an ultra-high performance concrete (UHPC) slab at the hogging moment zone and a normal concrete (NC) slab at the sagging moment zone. The testing was conducted to verify the level of loading at which composite action is maintained at the hogging moment zone. Four two-span continuous composite girders were tested. The thickness of the UHPC varied between a half and a full depth of slab. The degree of shear connection at the hogging moment zone varied between full and partial. The experimental results confirmed the effectiveness of the UHPC slab to enhance the girder stiffness and maintain the composite action at the hogging moment zone at a load level much higher than the upper service load limit. To a lesser degree enhanced performance was also noted for the smaller thickness of the UHPC slab and partial shear connection at the hogging moment zone. Plastic analysis was conducted to evaluate the ultimate capacity of the girder which yielded a conservative estimation. Finite element (FE) modeling evaluated the girder performance numerically and yielded satisfactory results. The results indicated that composite action at the hogging moment zone is maintained for the degree of shear connection taken as 50% of the full composite action and use of UHPC as half depth of slab thickness.

Investigating the Impacts of Ultra-Fine Calcium Carbonate in High-Volume Fly Ash Concrete for Structural Rehabilitation for Sustainable Development

An estimate shows that approximately 50% of global annual construction activities account for the repair and retrofitting of structures and constructed facilities. Therefore, structural rehabilitation and repair are becoming hot topics among researchers, in order to find innovative and comprehensive solutions. Ultra-high-performance concrete (UHPC) is designed to achieve high strength and long-term durability. Such types of concrete offer a solution for complicated repair and retrofitting jobs. Although many benefits of using UHPC have been derived, many concerns have also been identified with the use of UHPC—sustainability is considered a critical concern due to the requirement of large proportions of cement, which results in an increase in cost and environmental impacts. This paper presents a recipe for UHPC that contains a small ratio of cement and a large proportion of fly ash, i.e., up to 50%, as a cement replacement material (CRM). In order to achieve long-term durability and increase bonding with old concrete or brickwork for repair and retrofitting purposes, ultra-fine calcium carbonate (UFCC) is also added. In selecting an appropriate material for structural repair, it is essential to acquire an understanding of the material behavior. Therefore, this research was focused on providing a comprehensive guide to the behavior and strength performance of UHPC. The experimental results have shown that the highest strength of UHPC with low cement content can be achieved using a binary combination of high-volume fly ash (HVFA) and ultra-fine CaCO3 (UFCC) as a substitution for cement by up to a ratio of 50% in the recipe. The UHPC with low cement content displayed excellent repair and retrofitting potential for structural strengthening in regions of high stress by developing a strong bond with the existing concrete substrate.

Finite element analysis of headed studs embedded in thin UHPC

With an increasing use of ultra-high performance concrete (UHPC) in civil engineering, steel-concrete composite structures continue to progress. However, studies focusing on headed studs embedded in UHPC are limited, which hinders the design of steel-UHPC composite structures. This paper investigates the shear-resisting behavior of headed studs embedded in thin UHPC by using the finite-element (FE) analysis technique. A FE model was established for a push-out test, aiming to reflect the plastic behavior of the specimens and to evaluate the damage process in the headed studs and UHPC. The analysis results were compared to test results. It was revealed that the load-slip curve, shear strength, and failure mode all agreed well with the experimental observations. A parametric analysis was performed based on the validated FE model. The influence of stud diameter, stud height, and compressive strength of UHPC on the shear behavior of the headed studs was revealed. Further, the shear strengths obtained in the FE analysis were compared to the results predicted through theoretical equations. The comparison indicates that for headed studs embedded in UHPC, the contribution of the weld collar should be considered to evaluate the shear strength.

Enhancing Resiliency and Delivery of Bridge Elements using Ultra-High Performance Concrete as Formwork

A feasibility study of the use of ultra-high performance concrete (UHPC) shell as a formwork is presented. The core concept of the research, developed by the first author, is prefabrication of UHPC shell which acts as a stay-in-place formwork. In the proposed approach, after transporting the UHPC shell to site, the construction of structural elements is completed by placing reinforcing cage inside the UHPC shell and post-pouring with normal concrete. The superior properties of UHPC provide excellent means to enhance the service life of bridge elements, while eliminating the need for assembling or stripping of formwork. As a proof of concept, a combination of experimental and numerical studies was conducted, results of which are reported here. Before conducting experimental work, numerical study in the form of finite element analysis was carried out to investigate performance of shell during placement of the normal concrete. To provide a baseline comparison between UHPC shell formwork and conventional methods, two test specimens were constructed and tested under three-point load setup. The shell test specimen demonstrated flexural strength, 14% greater than an equivalent normal strength concrete specimen. The UHPC shell test specimen failure occurred by debonding of shell at the interface and development of a large crack in the shell. The shell test specimen exhibited improved levels of ductility before failure. The preliminary analysis demonstrated that the idea is feasible and useful for accelerated bridge construction applications.

Numerical Investigation of the Nonlinear Composite Action of FRP-Concrete Hybrid Beams/Decks

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.

Development of Ultra High Performance Concrete and Reactive Powder Concrete with Nanosilica

The article is dedicated to the design and production of Ultra High Performance Concrete (UHPC) and Reactive Powder Concrete (RPC) using silica fume and nanosilica. Nanosilica and fine steel fibres were used for the production of RPC. Compressive strengths of UHPC and RPC above 150 MPa have been achieved. It has been demonstrated that UHPC and RPC can be produced using standard concrete mixing system without the use of activating mixing and without a special treatment regime during maturing of the concrete. Aging of the concrete took place in a normal environment, without elevated pressure or temperature. The aging process at 20 °C allows the use of UHPC and RPC for the ready-mixed concrete when working on high volume construction projects. Even without thermal treatment, without the application of solidification pressure and without autoclaving, RPC reached a compressive strength of more than 180 MPa and a flexural tensile strength after 60 days greater than 22 MPa. The high tensile bending strength may be considered as the main advantage of RPC, as the RPC parameters allow, for instance, the use for pre-stressed structural elements where a high initial strength is also required.

First Application of UHPC Bridge Deck Overlay in North America

Deterioration of existing bridge decks, which usually originates with the deck cracking on the top surface, is a common problem in North America. It causes frequent repair of the decks to limit further damage resulting from water/chloride ingress. Superior engineering and durability properties facilitate the use of ultra-high performance concrete (UHPC) as an attractive alternative for a deck overlay, minimizing both deck deterioration and maintenance costs. Recently developed UHPC thixotropic mix designs, which are different from commonly used self-leveling UHPC, enable UHPC overlay to be used on decks with slopes and meet specific crowning requirements. The use of a UHPC thixotropic mix design with 3.25% of steel fibers was successfully evaluated under laboratory conditions by applying it on sloping deck surfaces with appropriate roughness between the normal concrete (NC) and UHPC. The feasibility of applying this technology in the field was then investigated on a small bridge for the first time in North America in May 2016. This paper presents the details about the laboratory evaluation, field implementation of UHPC overlay, and lessons learned from this first UHPC overlay project in North America.

Radiation shielding of ultra-high-performance concrete with silica sand, amang and lead glass

Barite in Malaysia is limited; therefore, a locally available alternative source must be identified to meet the requirements of high-density concrete for radiation shielding. We selected steel fibre-reinforced ultra-high-performance concrete (UHPC) samples with different inert materials, namely, silica sand, amang and lead glass, as the study object and tested them experimentally for their mechanical properties and radiation absorption capabilities. The UHPC samples showed compressive strength values exceeding 155 MPa at 28 days. Meanwhile, UHPC with lead glass underwent decreased of compression strength in a long period, and UHPC with amang caused an issue related to radiological safety despite that it was effective as a γ-ray shield. Thus, the use of UHPC with silica sand is practical for constructing nuclear facilities because of the abundance and cost-effectiveness of the involved materials.

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

Ultra-high performance concrete (UHPC) as a novel concrete material is associated with very high strength and low permeability to aggressive environment. There have been many studies focusing on the development of UHPC materials. More studies are needed to implement the knowledge obtained from material level into the structural design and construction level. This paper emphasizes on the structural modeling and performance assessment of bridge girders made of UHPC considering the major improvements in terms of structural performance, durability, environmental impacts, and cost-effectiveness in a long-time interval. Additionally, the effect of the concrete strength increase on the life-cycle environmental impact and cost is assessed on a structural scale. An illustrative example is established to demonstrate the use of UHPC within precast-prestressed girder bridge. It is found that the use of UHPC can result in a significant reduction of concrete volume and CO2 emissions compared with conventional bridge with the same span length. Additionally, the life-cycle cost and equivalent annual cost associated with these two bridges are compared. This study aims to aid the development and adaptation of novel materials within civil engineering to make optimal use of the favorable material properties.

A Stress Analysis of the Post-Tensioned Anchorage Zones Using UHPC

Researches on Ultra High Performance Concrete (UHPC) have been conducted worldwide owing to its outstanding durability and strength performances compared to those of normal concrete. The application of UHPC to prestressed concrete structures, which may seem to be the most appropriate and beneficial, may result significant improvement in the design of anchorage zones due to its high compressive and tensile strength. The size of anchorage blocks and amounts of reinforcements may be reduced drastically. This paper examines the stress magnitudes and distributions of post-tensioned anchorage zones using UHPC which have nominal compressive strength levels of 120, 150 and 180 MPa respectively, by FE analysis. The analytic results are verified with the existing experimental work of 180MPa UHPC. It can be concluded that the use of UHPC to post-tensioned members gives significant reduction of anchorage zone size and no reinforcements are required.

Roof Structural System Study with Use of UHPC

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.

Partial substitution of silica fume with fine glass powder in UHPC: Filling the micro gap

The design of ultra-high-performance concrete (UHPC) depends basically on the packing density and particle-size distribution (PSD) of its ingredients. The PSD of cement exhibits a gap at the micro scale that needs to be filled with finer materials such as silica fume (SF). Filling this gap solely with SF requires a high amount of SF (25% to 30% by wt. of cement) due to its extreme fineness. The use of high SF volume negatively effects concrete rheology. In addition, the limited resources and high cost of SF impede the wide use of UHPC in concrete market. This paper reports on a study to determine the possibility of producing and using fine glass powder (FGP) as a SF partial replacement in UHPC. The results show that FGP with a mean particle size (d50) of 3.8µm could be recommended as an optimal PSD to fill the gap between cement and SF particles. The results demonstrate that compressive strength values of 235 and 220MPa under 2days of steam curing can be achieved, respectively, when replacing 30% and 50% of SF with FGP, compared to 204MPa for the reference UHPC containing 100% SF. The rheology of fresh UHPC is improved by replacing SF particles with nonabsorptive glass particles.

Punching strength of flat plates reinforced with UHPC and double-headed studs

To verify the beneficial use of UHPC in the highly stressed region of column-slab connections, a total of ten punching tests on reinforced concrete slabs were performed. All interior column-slab connections included double-headed studs as shear reinforcement. Nine test specimens were in addition strengthened by fibre-reinforced Ultra High Performance Concrete (UHPC) units. These elements were built in around the columns in the slab compression zone, replacing there the normal strength concrete (NSC). UHPC units with three different diameters were applied. To allow for a flexible combination of UHPC unit and double-headed studs, most of the UHPC units were separated into four parts with joints in between and were provided with channels for the double-headed studs. The slabs including a UHPC element reached significantly higher failure loads than the test specimens without such an element. In the slabs including the UHPC units with smaller diameter, a clear punching shear failure outside the elements was observed. In the case of the larger UHPC units, significant cracks occurred inside the elements, indicating the initiation of a failure of the UHPC.

An Evaluation of Shaped Charge Experiments Using Concrete Components

The current contribution presents and evaluates a series of experimental results of shaped charge jets impinging concrete targets. The purpose of this study is threefold. Firstly, the dimensions of the damaged areas, namely the crater, spalling and perforation/penetration regions were measured. Crater dimensions are found to be independent of target thickness whilst spalling dimensions are not. Secondly, the depths of penetration of Normal Strength Concrete (NSC) and Ultra High Performance Concrete (UHPC) were compared. In these experiments the use of UHPC does not provide, on average, a significant reduction in the total depth of penetration, whilst being three times more expensive than NSC. Thirdly, the following three jet properties inside and behind the target were examined: jet velocity, jet mass and jet kinetic energy. The amount by which these properties are reduced in concrete and in air is quantified and compared. As a long term goal, these experiments aim to contribute to the assessment of existing protective structures and, likewise, to the design of future ones.

Early-Age Strength of Ultra-High Performance Concrete in Various Curing Conditions.

The strength of Ultra-High Performance Concrete (UHPC) can be sensitively affected by the curing method used. However, in contrast to the precast plant production of UHPC where a standard high-temperature steam curing is available, an optimum curing condition is rarely realized with cast-in-place UHPC. Therefore, the trend of the compressive strength development of UHPC was experimentally investigated in this study, with a focus on early-age strength by assuming the various curing conditions anticipated on site. Concrete specimens were cured under different conditions with variables including curing temperature, delay time before the initiation of curing, duration of curing, and moisture condition. Several conditions for curing are proposed that are required when the cast-in-place UHPC should gain a specified strength at an early age. It is expected that the practical use of UHPC on construction sites can be expedited through this study.

The Challenges Related to Interface Bond Characterization of Ultra-High-Performance Concrete With Implications for Bridge Rehabilitation Practices

Abstract 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.

Punching Shear Enhancement of Flat Slabs with Partial Use of Ultrahigh-Performance Concrete

Previous studies have clearly shown that flat slabs made of ultrahigh-performance concrete (UHPC) have considerably higher punching shear strength than their counterparts made of conventional concrete. However, it may not be economically feasible to construct an entire slab out of UHPC. As such, the objective of the research reported in this paper was to determine the optimal use of UHPC within the critical punching shear area, while the remainder of the slab is made of normal concrete. Ten flat slab specimens with two different steel reinforcement ratios and three different areas (or depths) of UHPC were tested under a concentric load to study the effect of UHPC on punching shear capacity of flat slabs. Test results showed that full-depth application of UHPC within the area enclosed by a perimeter located at a distance equal to the slab thickness from the column face could enhance punching shear capacity of the slab by 70%. This configuration was deemed to be the optimal application of UHPC in flat slabs. On the other hand, half-depth application of UHPC does not significantly improve shear capacity of flat slabs. The research reported in this paper also questioned the applicability of two available punching shear models for flat slabs made fully or partially out of reinforced UHPC.

초고성능 콘크리트의 양생 조건에 따른 강도 발현 특성

Ultra-High Performance Concrete (UHPC) has recently been one of the most active research fields in Korea as well as in foreign countries, because it can contribute to a longer life and economic efficiency of structures. Although precast-type UHPC fabricated in a factory is preferable in terms of quality control and reduction of construction period, there exist, even in the precast structure, some parts that need to be cast in-place such as the joints between precast segments. In the cast-in-place UHPC, however, it is probable that an optimum curing condition can hardly be realized in contrast to the factory production. In this study, therefore, the trend of compressive strength development of UHPC was experimentally investigated by assuming various inferior curing conditions that may be anticipated at a construction site. Concrete specimens were fabricated and cured under different conditions with the variables such as curing temperature, delay time before the initiation of curing, duration of curing time and moisture condition. The strengths were compared with those of the specimens cured by standard high temperature steam. Through the analysis of the test results, some minimum requirements for curing have been proposed that are required when the UHPC is cast in-place. It is expected, through this study, that practical use of UHPC in construction sites can be increased.