• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.11a
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• pp.55-56
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• 2014

In this research, the effect of types of aggregate and SP on fundamental properties of ultra-high performance concrete of 80 MPa of compressive strength was evaluated to provide solution for high cost of ultra-high performance concrete. As the results of a series of tests, the mixture using limestone and silica aggregates showed improved workability rather than the mixture using granite aggregate. For compressive strength of UHPC, the UHPC mixtures using limestone and silica aggregates showed higher compressive strength than the UHPC mixture using granite aggregate while all mixtures satisfied target compressive range.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.3
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• pp.149-160
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• 2015

This study reports the interfacial bond strength between Ultra High Performance Concrete (UHPC) and Normal Strength Concrete (NSC). While previous studies have focused on the interfacial strength between NSC substrate and UHPC overlay, this study use precast UHPC for enhanced constructability and replacement of formwork. The factors affecting the interface strength are comprehensively reviewed. It can be classified into: interface shape, degree of hardening and moisture condition of UHPC before combining with NSC, and curing condition of composite materials. Conducted experiments verify the effects of each factor on the interface strength and, accordingly show different failure modes. In particular, a new failure mode of the failure of a part of UHPC was firstly found in the case of sample with rough interface between UHPC and NSC. The other factors of the degree of hardening and the moisture and curing conditions of UHPC were discussed. This research will provide a valuable foundation to utilize the UHPC as a composite material.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.5
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• pp.125-132
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• 2019

Ultra-high performance concrete (UHPC) has high compressive and tensile strengths due to the particle packing, and its ductile behavior can be ensured by utilizing steel fibers. However, since the UHPC members exhibit different characteristics of crack behavior and tensile behavior from normal concrete, the tension stiffening and cracking characteristics of the UHPC should be accurately modeled for the design and analysis of the UHPC members. In this study, uniaxial tension tests was conducted on the UHPC members with strands, where the test variables were diameter and reinforcing ratio of strands. Detailed analyses were also conducted to identify the tensile characteristics and crack behavior of the UHPC members. By comparing the test results with current code provisions and other models proposed by existing researchers, their applicability for estimation of crack behavior of the UHPC members was examined.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.11a
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• pp.13-14
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• 2014

Ultra high performance concrete (UHPC) consists of cement, silica fume (SF), sand, fibers, water and superplasticizer. Typical water/binder-ratios are 0.15-0.20 with 20-30% of silica fume. The development off properties of hardening UHPC relates with both hydration of cement and pozzolanic reaction of silicafume. In this paper, by considering the production of calcium hydroxide in cement hydration and its consumption in the pozzolanic reaction, a numerical model is proposed to simulate the hydration of UHPC. The degree of hydration of cement and degree of reaction of silica fume are obtained as accompanied results from the proposed hydration model. The properties of hardening UHPC, such as degree of hydration of cement, calcium hydroxide contents, and compressive strength, are predicted from the contribution of cement hydration and pozzolanic reaction. The proposed model is verified through experimental data on concrete with different water-to-binder ratios and silica fume substitution ratios.

• Structural Engineering and Mechanics
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• v.81 no.5
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• pp.539-550
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• 2022

A detailed experimental program was conducted to investigate the flexural behavior of ultra high performance concrete (UHPC) beams reinforced with high strength steel (HSS) rebars with a specified yield strength of 600 MPa via direct tensile test and monotonic four-point bending test. First, two sets of direct tensile test specimens, with the same reinforcement ratio but different yield strength of reinforcement, were fabricated and tested. Subsequently, six simply supported beams, including two plain UHPC beams and four reinforced UHPC beams, were prepared and tested under four-point bending load. The results showed that the balanced-reinforced UHPC beams reinforced with HSS rebars could improve the ultimate load-bearing capacity, deformation capacity, ductility properties, etc. more effectively owing to interaction between high strength of HSS rebar and strain-hardening characteristic of UHPC. In addition, the UHPC with steel rebars kept strain compatibility prior to the yielding of the steel rebar, further satisfied the plane-section assumption. Most importantly, the crack pattern of the UHPC beam reinforced with HSS rebars was prone to transform from single main crack failure corresponding to the normal-strength steel, to multiple main cracks failure under the condition of balanced-reinforced failure, which validated by the conclusion of direct tensile tests cooperated with acoustic emission (AE) source locating technique as well.

• Advances in concrete construction
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• v.8 no.1
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• pp.21-31
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• 2019

The rich recipe of ultra high performance concrete (UHPC) offers the higher mechanical, durability and dense microstructure property. The variable like cement/sand ratio, amount of supplementary cementitious material, water/binder ratio, amount of fiber etc. alters the UHPC hardened properties to any extent. Therefore, to understand the effects of these variables on the performance of UHPC, inevitably a stage-wise development is required. In the present experimental study, the effect of sand/cement ratio, the addition of finer material (fly ash and quartz powder) and, hybrid fiber on the fresh, compressive and microstructural property of UHPC is evaluated. The experiment is conducted in three phases; the first phase evaluates the flow value and strength attainment of ingredients, the second phase evaluates the efficiency of finer materials (fly ash and quartz powder) to develop the UHPC and the third phase evaluate the effect of hybrid fiber on the flow value and strength of ultra high performance hybrid fiber reinforced concrete (UHP-HFRC). It has been seen that the addition of fly ash improves the flow value and compressive strength of UHPC as compared to quartz powder. Further, the usage of hybrid fiber in fly ash contained matrix decreases the flow value and improves the strength of the UHP-HFRC matrix. The dense interface between matrix and fiber and, a higher amount of calcium silicate hydrate (CSH) in fly ash contained UHP-HFRC is revealed by SEM and XRD respectively. The dense interface (bond between the fiber and the UHPC matrix) and the higher CSH formation are the reason for the improvement in the compressive strength of fly ash based UHP-HFRC. The differential thermal analysis (DTA/TGA) shows the similar type of mass loss pattern, however, the amount of mass loss differs in fly ash and quartz powder contained UHP-HFRC.

• Resources Recycling
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• v.25 no.3
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• pp.20-28
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• 2016

Assessment on adequate dosage of superplasticizer in eco-friendly ultra-high performance concrete (UHPC) containing industrial by-products was carried out from the standpoint of workability. Various types of industrial by-products, including blast-furnace slag, coal bottom ash and rapid-cooled electric arc furnace oxidizing slag, were utilized, and the effects of dosage of superplasticizer on the workability and strength of UHPC containing the by-products were evaluated. By utilizing the by-products, the workability of UHPC was improved and required dosage of superplasticizer was reduced. In addition, the material cost for UHPC with by-products was decreased due to reduced dosage of superplasticizer.

• Computers and Concrete
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• v.29 no.6
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• pp.407-418
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• 2022

This paper numerically investigates the effect of changes in the mechanical properties (displacement, strain, and stress) of the ultra-high-performance concrete (UHPC) without rebar and the reinforced concrete (RC) using steel re-bars. This reinforced concrete is mostly used in the concrete bridge decks. A mixture of sand, gravel, cement, water, steel fiber, superplasticizer, and micro silica was used to fabricate UHPC specimens. The extended finite element method as used in the ABAQUS software is applied for considering the mechanical properties of UHPC, RC, and ordinary concrete specimens. To calibrate the ABAQUS, some experimental tests have been carried out in the laboratory to measure the direct tensile strength of UHPC by the compressive-to-tensile load converting (CTLC) device. This device contains a concrete specimen and is mounted on a universal tensile testing apparatus. In the experiments, three types of mixed concrete were used for UHPC specimens. The tensile strength of these specimens ranges from 9.24 to 11.4 MPa, which is relatively high compared with ordinary concrete specimens, which have a tensile strength ranging from 2 to 5 MPa. In the experimental tests, the UHPC specimen of size 150×60×190 mm with a central hole of 75 mm (in diameter)×60 mm (in thickness) was specially made in the laboratory, and its direct tensile strength was measured by the CTLC device. However, the numerical simulation results for the tensile strength and failure mechanism of the UHPC were very close to those measured experimentally. From comparing the numerical and experimental results obtained in this study, it has been concluded that UHPC can be effectively used for bridge decks.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.05a
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• pp.204-205
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• 2017

In this study, flowability and strength on ultra high performance concrete(UHPC) pre-mixed binders with fiber was investigated. The flow of UHPC with pre-mixed binders was higher than that of seperate mixing conditions. The UHPC using PVA fiber with high specific surface area showed a low flow compared to steel fiber. An pre-mixing method led to improved strength of UHPC and low deviation of specimens due to dispersion effect of each materials.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4A
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• pp.573-580
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• 2008

In this paper, we estimated the effect of the siliceous filler's particle size on the performance of Ultra High Performance Concrete (UHPC). Filler's particle diameters considered in this paper were about 2, 4, 8, 14, $26{\mu}m$ and the performance was evaluated by testing fluidity in fresh concrete, compressive strength, ultimate strain, elastic modulus and flexural strength in hardened concrete. We also carried out XRD and MIP tests to analyze the relationship between the mechanical properties and microstructure. Test results showed that the smaller filler's particle size improves flowability and strength properties. MIP results revealed that the smaller size of filler decreased the porosity and thus increased the strength of UHPC. From XRD analysis, we could find out there were little influence of filler's particle size on chemical reactivity in UHPC.