Experimental research on compressive strength of UHPC spherical hinge

Exploring mechanical and durability properties of ultra-high performance concrete incorporating various steel fiber lengths and dosages

Experimental study on the interfacial shear performance between macro basalt fibers reinforced UHPC as repair material and normal concrete

In this paper, a new class of self-consolidating ultrahigh-performance concrete (UHPC) was investigated. The UHPC featured a compressive strength higher than 150 MPa with self-consolidating characteristics desirable for modular construction. This paper describes the development and characterization of UHPC, its large-scale processing techniques with conventional equipment, its verification with internal and surface microstructure analysis techniques, and the structural behavior of large-scale steel plate UHPC (S-UHPC) beams under out-of-plane loads. Based on a particle size distribution study, an optimum packing density was achieved in the mixture that uses an uncommonly used undensified silica fume. The physical parameters of the ingredients and the resulting microstructure after hydration are considered essential for the design of self-consolidating UHPC materials. Distinguishing the three phases of the material after hydration using three-dimensional X-ray microtomography allowed the quantitative analysis of the UHPC microstructure. The internal microstructure study showed a significant reduction of macropores in UHPC compared to mortar specimens, which confirmed the physical attributes behind the improved material characteristics. A microstructure study of the material was also performed using scanning electron microscopy. In addition, a comparison of the experimental results of four large-scale steel plate concrete (SC) beam specimens cast with either conventional concrete or UHPC materials under three-point shear loading indicated that the developed UHPC materials significantly enhanced the ductility and capacity of the S-UHPC beams.

In recent years the California Department of Transportation (Caltrans) has turned to ultra-high performance concrete (UHPC) to meet the goals of constructability, seismic performance and durability of precast bridge element connections in accelerated bridge construction projects (ABC). Design details for the Laurel Street Overcrossing (OC) ABC Pilot Project, located in the seismically active California Bay Area, provide a resilient fixed connection between precast column and precast cap with a circular pattern of #14 reinforcing bars threaded through 4” corrugated UHPC filled ducts. The recently awarded Echo Summit Sidehill Viaduct Replacement project calls for the use of UHPC in adjacent box beam keyways to provide a quick and durable connection solution to be rapidly constructed during a 14-day full closure of heavily traveled Hwy 50 near Lake Tahoe. Caltrans’ first time use of UHPC for the connection of precast bridge elementsincluded special attention given to material testing, constructability considerations, QA/QC practices, and project specification development. In addition, validation of UHPC performance prior to field construction has been an important aspect of UHPC implementation in California. The Laurel Street OC column-to-cap connection detail developed for this project is based on UNR’s research “Next Generation of Bridge Columns for ABC in High Seismic Zones” (ref 1). The research project investigated eight connection types with varying outcomes. Upon review by the Caltrans Earthquake Committee the UHPC filled duct connection was selected as the preferred alternative due to performance, simplicity and reliability. The full-scale implementation of this connection consisted of a circular pattern of 20 No. 14 reinforcing bars extending from each column threaded through a precast drop cap via multiple 4- inch internal diameter corrugated galvanized metal ducts. The Laurel Street OC pilot project represents the first use of UHPC to connect precast bridge elements in California. In order to reduce risk and assure quality the Department required 2 types of full-scale UHPC mockups: The Pullout Mockup and the Fit Up and UHPC Placement Mockup. The purpose of the Pullout Mockup was to verify the performance of the reinforcing bar when bonded to the UHPC under tensile loading conditions. A full-scale mockup of precast concrete blocks with a single 4- inch internal diameter galvanized corrugated metal duct was fabricated to represent the in-field condition. A single No. 14 reinforcing bar was placed in the center of the UHPC filled duct. Caltrans Materials Engineering and Testing Services (METS) tested the specimen in a two-million-pound reaction frame. Testing confirmed that the failure mode of the connection was tensile failure in the reinforcing bar. The reinforcing bar achieved ultimate strength, fractured at a peak load of 216 kips and remained bonded to the UHPC throughout the testing. The contract required a full-scale mockup of the cap to column connection to demonstrate that the UHPC placement method filled spaces with UHPC and the steel fibers were uniformly distributed. To inspect the UHPC, the mock up was saw cut in several locations and visual inspection confirmed that the acceptance criteria had been met. UHPC keyways were chosen for the adjacent box beam superstructure of the Echo Summit Sidehill Viaduct for constructability and long-term performance of the superstructure. UHPC filled keyways generate savings in construction time and precast element weight by eliminating the need for transverse post tensioning, intermediate diaphragms, and a cast in place (CIP) bridge deck. The use of rapid strength UHPC (12 ksi in 12 hours) presented two areas of investigation to be performed by the owner prior to advertisement of the contract. The first was validation of estimating the concrete strength by the maturity method and the second was to determine the UHPC curing requirements prior to placement of a polyester concrete overlay. In early 2018 Caltrans obtained samples of the Lafarge Ductal mix design number JS1212 to conduct strength-maturity testing and bond beam testing. California specifications typically require a 28 day wait between concrete placement and polyester concrete overlay. Caltrans wanted to determine if this cure time could be reduced for UHPC applications. Bond beam testing (California Test 551) was used by METS to determine the overlay placement wait time required to attain sufficient bond strength between the Ductal JS1212 and the polyester concrete. Findings of the tests suggest that the UHPC is of sufficient strength for placement of the polyester overlay at 12 hours of age (12,000 psi) if heat cured at a temperature of approximately 100 degrees Fahrenheit for the first 12 hours. The maturity method to estimate the strength of UHPC without dependence of concrete compressivestrength testing provided a method that aligned with an ABC schedule. Strength-maturity testing on JS1212 was performed in accordance with ASTM C1074 on both heat cured and room temperature specimens to develop strength maturity relationship and support the development of project specifications.

Waste fly ash (WFA) and secondary aluminum dross (SAD) are common solid wastes inducing environmental pollution. These materials contain certain active substances that can be used in cement-based materials. Therefore, cement concrete can be used to solidify these solid wastes. In this study, the influence of the assembly unit of secondary aluminum dross (SAD) and waste fly ash (WFA) on the properties of ultra-high-performance concrete (UHPC) is investigated. The slump flow, the plastic viscosity, the yield shear stress, and the initial setting time of fresh UHPC are measured. Moreover, the flexural and compressive strengths and the dry shrinkage rate (DSR) are determined. The electrical resistance and reactance are tested. The electron microscopy spectroscopy (EDS), thermogravimetric analysis (TG), and X-ray diffraction spectrum (XRD) curves are obtained for revealing the mechanism of macroscopic performances. Results show that due to the optimal specific surface area and the volcanic ash effect, the UHPC with the assembly unit of 50% SAD and 50% WFA provides the highest slump flow, DSR, and mechanical strengths, while the corresponding plastic viscosity, yield shear stress, and electrical resistance are the lowest. The SAD can delay the setting time of UHPC. The relationship between the electrical resistance or the electrical reactance and the mass ratio of SAD accords with the quadratic function. The corresponding electrical resistance is the lowest. The relationship between the mechanical strengths and the electrical resistance fits with the cubic function. The leaching amounts of Zn and Cr increase in the form of cubic function with the immersing time. Meanwhile, the SAD can decrease the Zn and Cr by 0%–46.3% and 0%–45.2% respectively. As obtained from the EDS results, the element of Al is increased by adding SAD. The XRD curves show that the crystals of Al2O3 are increased and the SiO2 crystals are decreased by the added SAD. UHPC with 50% SAD exhibits the highest compact microstructures and the least Ca(OH)2 and 3CaO·SiO2 hydration products. The TG results show that UHPC with 50% SAD shows the lowest TG values of all the groups. This research will provide new UHPC materials and techniques applied in solidifying the WFA and SAD in the future.

This paper introduces an experimental research about the influences of the curing type on accelerated carbonation, capillary water absorption and permeability of a range of different self-compacting lightweight concrete (SCLC) mixtures in comparison with those of chosen conventional vibrated lightweight concrete (LC) and self-compacting concrete (SCC). Seven different concrete compositions are considered: four SCLC, two SCC and one LC mixtures. All of the SCLC mixtures and one of the SCC and one LC mixture with a constant powder dosage of $$550\,\hbox {kg}/\hbox {m}^{3}$$ was designed to be containing $$440\,\hbox {kg}/\hbox {m}^{3}$$ of cement and $$110\,\hbox {kg}/\hbox {m}^{3}$$ of fly ash. The other SCC mix was designed to have lower cement dosage for similar strength characteristic. Basaltic pumice aggregate of the SCLC was replaced with expanded perlite aggregate by 10, 20 and 30%. All mixtures were cured by two different curing types. Among the permeability properties of the samples, permeability, capillary water absorption and carbonation properties were measured. The results showed that the production of SCLC mixture as the result of the use of basaltic pumice and expanded perlite seems to be possible. The density of SCLC with basaltic pumice and expanded perlite was about $$1900\,\hbox {kg}/\hbox {m}^{3}$$ , while the density of SCC was $$2300\,\hbox {kg}/\hbox {m}^{3}$$ . Generally, permeation properties of SCLC such as carbonation and capillary water absorption got worse, since the porous aggregate was used. However, SCLC’s compressive strength per density was more efficient than SCC’s.

School of Architecture Engineering, Harbin Engineering University, Harbin 150001, ChinaABSTRACT The flexural behavior test of UHPC segmental box girder which has 160 MPa co mpressive strength and 15.4 m length was carried out. The effect of steel fibers in combination with reinforcing bars on improving the ductile performance of UHPC box girder was evaluated by comparing the flexural behavior of the UHPC segmental box girders made by the two kinds of mixing portion. The test variables are volume fraction of steel fibers and the arrangement of reinforcing bars. The behavior of UHPC box girder BF2 composed of 1% volume fraction of steel fibers and longitudinal reinforcing bars in web and upper flange with stirrup showed the similar ductile behavior with the girder BF1 composed of 2% volume fraction without stirrup in elastic stress region . But BF1 had the better stiffness an d showed the more ductile behavior in inelasti c stress region. Segmen tal interfaces of UHPC box girder have not any crack and slide until the final flexural collapse load. Keywords : ultra high performance concrete (UHPC), segment box girder, flexural behavior, reinforced bars, steel fiber

Factors affecting bond development between Ultra High Performance Concrete (UHPC) and steel bar reinforcement

This research focused on improving ultra high-performance concrete (UHPC) toughness through the addition of annealed plain carbon steel fibers and stainless steel fibers that both exhibit increased ductility and strain hardening compared with conventional steel fibers used for concrete reinforcement. Implementing optimized heat treatments and selecting proper alternative alloys can improve the postyield carrying capacity of UHPCs through plastic deformations, phase transformations, and fiber pullout. This research focused on the flexural response and dynamic penetration resistance of a UHPC known as Cor-Tuf with three different steel fiber types: plain carbon steel, stainless steel that can exhibit phase transformation-induced plasticity, and annealed carbon steel with reduced tensile strength but increased ductility and strain hardening. Annealed carbon steel fibers were able to reduce mass loss by 0.8 % for 5-cm-thick dynamic impact panels. By using a phase-transformable stainless steel, the ultimate flexural strength increased from 32.0 to 42.5 MPa (33 % increase) and the postimpact velocity decreased an average of 31.5 m/s for 2.5 and 5-cm-thick dynamic impact panels. Phase transformations (austenitic to martensitic) were quantified in the stainless steel fibers of postyielded UHPC specimens using a vibrating sample magnetometer. Stainless steel fibers sampled from the postyielded tensile face of a flexural beam increased from 75 to 107 emu/g. The results of the study evidence improvements in tensile properties and toughness that can be accomplished by modifying the stress versus strain response of steel fiber reinforcement and including new energy dissipation mechanisms such as phase transformation.

Considering its superior engineering properties, ultrahigh performance concrete (UHPC) has emerged as a strong contender to replace normal strength concrete (NSC) in diverse construction applications. While the mechanical properties of UHPC have been thoroughly explored, there is still dearth of studies that quantify the durability of UHPC, especially for sustainable mixtures made with local materials. Therefore, this research aims at investigating the alkali-silica reactivity (ASR) potential in sustainable UHPC in comparison with that of NSC. Sustainable UHPC mixtures were prepared using waste untreated coal ash (CA), raw slag (RS), and locally produced steel fibers. UHPC and benchmark NSC specimens were cast for assessing the compressive strength, flexural strength, and ASR expansion. Specimens were exposed to two curing regimes: accelerated ASR conditions (as per ASTM C1260) and normal water curing. UHPC specimens incorporating RS achieved higher compressive and flexural strengths in comparison with that of identical UHPC specimens made with CA. ASR expansion of control NSC specimens exceeded the ASTM C1260 limits (>0.20% at 28 days). Conversely, experimental results demonstrate that UHPC specimens incurred much less ASR expansion, well below the ASTM C1260 limits. Moreover, UHPC specimens incorporating steel fibers exhibited lower expansion compared to that of companion UHPC specimens without fibers. It was also observed that the mechanical properties of NSC specimens suffered more drastic degradation under accelerated ASR exposure compared to UHPC specimens. Interestingly, UHPC specimens exposed to accelerated ASR conditions attained higher mechanical properties compared to that of reference identical specimens cured in normal water. Therefore, it can be concluded that ASR exposure had insignificant effect on sustainable UHPC incorporating CA and RS, especially for specimens incorporating fibers. Results indicate that UHPC is a robust competitor to NSC for the construction of mega-scale projects where exposure to ASR conducive conditions prevails.

Effects of steel fibres on dynamic strength of UHPC

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

A spherical hinge structure is a key swivel bridge element that must be considered when evaluating friction characteristics and lubrication properties to meet the rotation requirement. Polytetrafluoroethylene (PTFE)-based spherical hinge sliders and lubrication coating have been employed for over 20 years, but with the growing tonnage of swivel bridge construction, their capacity to accommodate the required lubrication properties can be exceeded. In this manuscript, the optimal friction coefficient of the spherical hinge is obtained through the finite element analysis method. Four lubrication coatings and four spherical hinge sliders are prepared and tested through a self-developed rotation friction coefficient test, four-ball machine test, dynamic shear rheological test, and compression and shear performance test to evaluate the lubrication and friction properties of the spherical hinge structure. The results of the finite element analysis show that the optimum rotation friction coefficient of the spherical hinge structure is 0.031–1.131. The test results illustrate that the friction coefficient, wear scar diameter, maximum non-seize load, phase transition point, and thixotropic ring area of graphene lubrication coating are 0.065, 0.79 mm, 426 N, 14.6%, and 64,878 Pa/s. The graphene lubrication coating has different degrees of improvement compared with conventional polytetrafluoroethylene lubrication coating, showing more excellent lubrication properties, bearing capacity, thixotropy, and structural strength. Compressive and shear tests demonstrate that polyether ether ketone (PEEK) has good compressive and shear mechanical properties. The maximum compressive stress of PEEK is 87.7% higher than conventional PTFE, and the shear strength of PEEK is 6.07 times higher than that of PTFE. The research results can provide significantly greater wear resistance and a lower friction coefficient of the spherical hinge structure, leading to lower traction energy consumption and ensuring smooth and precise bridge rotation.

Reactive Powder Concrete (RPC) is a type of ultra-high performance concrete, this dense composite material generally characterized by high cement content, high durability, low porosity, low water/cement ratio and in most cases contains steel fibers as new types of concrete appears, further investigation for their mechanical properties are needed. This work aims to give a better understanding of RPC behavior by deriving formulas to calculate the modulus of elasticity and the splitting tensile strength in relation with compressive strength and steel fibers content. This study is based on data obtained from the experimental investigation done in this work and from others pervious works. The parametric study is based mainly on the silica fume content which is used in four different ratios (12 %, 15 %, 20 % and 25 %), the use of micro steel fibers 15 mm in length, 0.2 mm in diameter and aspect ratio of 75 added in ratios of (0 %, 1 %, 1.5 % and 2 %), and water/cement in ratios of (16 %, 18 %, 20 % and 22 %), respectively. The proposed equations show a better behavior in comparison to some available equations that were used in the estimation of modulus of elasticity and splitting tensile strength of reactive powder concrete, the coefficient of variation for the proposed equations (COV) decrease to 10.677% and 10.455% respectively.

In various infrastructure applications, ultra-high-performance concrete (UHPC) has been investigated widely for its exceptional structural and durability qualities. Although UHPC structures have proved structural stability at the structural level, fiber dispersion and fiber orientation due to casting procedure and construction processes remain concerns. Fiber orientation and structural performance of UHPC members are strongly influenced by the casting flow direction of freshly mixed UHPC, formwork geometry, rebar arrangement, casting device, and rheology of the mixtures. Different professional organizations across various countries have released UHPC design codes and guidelines, and each addressed fiber orientation in a distinctive way. An extensive review of the influence of various factors on fiber orientation in structural elements is presented in this article. A review of existing structural design guidelines for UHPC and steel fiber-reinforced concrete materials from France, Germany, Japan, South Korea, Canada, Switzerland, Australia, and the United States was conducted. The method used to account for fiber orientation and dispersion was discussed. The effect of undesirable fiber orientation was compensated by different design reduction factors introduced by several design codes. Additionally, this paper discusses the underlying rationale for these design factors. The paper concludes by making recommendations to design professionals and suggesting future research directions.