• Journal of Korean Association for Spatial Structures
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• v.20 no.4
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• pp.111-121
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• 2020

There has been increasing interest in UHPC (Ultra-High Performance Concrete) materials in recent years. Owing to the superior mechanical properties and durability, the UHPC has been widely used for the design of various types of structures. In this paper, machine learning based compressive strength prediction methods of the UHPC are proposed. Various regression-based machine learning models were built to train dataset. For train and validation, 110 data samples collected from the literatures were used. Because the proportion between the compressive strength and its composition is a highly nonlinear, more advanced regression models are demanded to obtain better results. The complex relationship between mixture proportion and concrete compressive strength can be predicted by using the selected regression method.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.05a
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• pp.193-194
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• 2021

Ti-salt agglomerated titanium dioxide photocatalyst from sludge, which has various and excellent functions such as nitrogen oxide removal performance, antifouling performance, and bacteria removal performance, is intended to be applied to UHPC. The UHPC used in this study is supposed to have a high compressive strength of 100~200MPa and a high flowability of 600mm or more with a slump flow. Titanium dioxide is fixed to the UHPC surface by sieving through a test sieve and compaction and painting using a vibration compactor, and this is tested according to ISO 22197-1. The NO removal amount is evaluated by classification the result range.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.345-348
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• 2008

A Cement account for the most amount than other materials in the material composition of ultra-high-performance concrete. If we especially consider the effect of high temperature curing on the cement hydration and the problems of autogenous shrinkage, heat of hydration we need selection of proper cement type by grasping influence of cement in the properties of UHPC. Therefore, in this paper we examined properties of fluidity, compressive strength and elastic modulus of UHPC due to domestic portland cement types. In results, we could get a result that the low heat cement increase fluidity, compressive strength in UHPC compare with high early strength cement and ordinary portland cement. we are systematically going to examination on the influence of UHPC by domestic portland cement types.

• Advances in concrete construction
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• v.15 no.3
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• pp.161-170
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• 2023

Ultra-high-performance concrete (UHPC) is produced using high amount of cementitious materials, very low water/cementitious materials ratio, fine-sized fillers, and steel fibers. Due to the dense microstructure of UHPC, it possesses very high strength, elasticity, and durability. Besides that, the UHPC exhibits high ductility and fracture toughness due to presence of fibers in its matrix. While the high ductility of UHPC allows it to undergo high strain/deflection before failure, the high fracture toughness of UHPC greatly enhances its capacity to absorb impact energy without allowing the formation of severe cracking or penetration by the impactor. These advantages with UHPC make it a suitable material for construction of the structural members subjected to special loading conditions. In this research work, the UHPC mixtures having three different dosages of steel fibers (2%, 4% and 6% by weight corresponding to 0.67%, 1.33% and 2% by volume) were characterized in terms of their mechanical properties including facture toughness, before using these concrete mixtures for casting the slab specimens, which were tested under high-energy impact loading with the help of a drop-weight impact test setup. The effect of fiber content on the impact energy absorption capacity and central deflection of the slab specimens were investigated and the equations correlating fiber content with the energy absorption capacity and central deflection were obtained with high degrees of fit. Finite element modeling (FEM) was performed to simulate the behavior of the slabs under impact loading. The FEM results were found to be in good agreement with their corresponding experimentally generated results.

• Structural Engineering and Mechanics
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• v.50 no.6
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• pp.709-722
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• 2014

Ultra-High Performance Concrete (UHPC) is an innovative new material that, in comparison to conventional concretes, has high compressive strength and excellent ductility properties achieved through the addition of randomly dispersed short fibers to the concrete mix. This study presents the results of an experimental investigation on the behavior of axially loaded UHPC short circular columns wrapped with Carbon-FRP (CFRP), Glass-FRP (GFRP), and Aramid-FRP (AFRP) sheets. Six plain and 36 different types of FRP-wrapped UHPC columns with a diameter of 100 mm and a length of 200 mm were tested under monotonic axial compression. To predict the ultimate strength of the FRP-wrapped UHPC columns, a simple confinement model is presented and compared with four selected confinement models from the literature that have been developed for low and normal strength concrete columns. The results show that the FRP sheets can significantly enhance the ultimate strength and strain capacity of the UHPC columns. The average greatest increase in the ultimate strength and strain for the CFRP- and GFRP-wrapped UHPC columns was 48% and 128%, respectively, compared to that of their unconfined counterparts. All the selected confinement models overestimated the ultimate strength of the FRP-wrapped UHPC columns.

• Computers and Concrete
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• v.12 no.4
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• pp.413-429
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• 2013

The primary aim of this study is to develop a three dimensional finite element (FE) model to predict the axial stress-strain relationship and ultimate strength of the FRP-wrapped UHPC columns by comparing experimental results. The reliability of four selected confinement models and three design codes such as ACI-440, CSA-S806-02, and ISIS CANADA is also evaluated in terms of agreement with the experimental results. Totally 6 unconfined and 36 different types of the FRP-wrapped UHPC columns are tested under monotonic axial compression. The values of ultimate strengths of FRP-wrapped UHPC columns obtained from the experimental results are compared and verified with finite element (FE) analysis results and the design codes mentioned above. The concrete damage plasticity model (CDPM) in Abaqus is utilized to represent the confined behavior of the UHPC. The results indicate that agreement between the test results and the non-linear FE analysis results is highly satisfactory. The CSA-S806-02 design code is considered more reliable than the ACI-440 and the ISIS CANADA design codes to calculate the ultimate strength of the FRP-wrapped UHPC columns. None of the selected confinement models that are developed for FRP-wrapped low and normal strength concrete columns can safely predict the ultimate strength of FRP-wrapped UHPC columns.

• 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.

• 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.

• Steel and Composite Structures
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• v.48 no.6
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• pp.649-666
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• 2023

In the current scenario, conventional concrete faces a substantial challenge in the modern era of the construction industry. Today's structures are massive, featuring innovative designs and strict time constraints. Conventional concrete does not provide the required compressive strength, tensile strength, flexural strength, toughness, and cracking resistance. As a result, most of engineers and professionals prefer to use ultra-high-performance concrete (UHPC), based on its wide advantages. Several advantages like mechanical and durability properties of UHPC provides dominant properties than the traditional concrete. Mix proportions of UHPC consists of higher powder content which provides maximum hydration and pozzolanic reaction, thereby contributing to the enhancement of the UHPC properties. Apart from that the nanomaterials provides the filler behavior, which will further improve the density. Enhanced density and mechanical properties lead to improved durability properties against water absorption and other typical chemicals. Nanomaterials are the most adopted materials for various applications, ranging in size from 0.1 nanometers to 100 nanometers. This article explores the effects of nanomaterial application in UHPC as a replacement for cementitious material or as an additive in the UHPC mix. The physical and durability properties modifications and improvements of UHPC, as well as negative effects, limitations, and shortcomings, are also analyzed.

• Journal of the Korea Concrete Institute
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• v.28 no.2
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• pp.177-185
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• 2016

This paper concerns the flexural behavior of steel fiber-reinforced ultra-high-performance concrete (UHPC) beams with compressive strength of 150 MPa. It presents experimental research results of hybrid steel fiber-reinforced UHPC beams with steel fiber content of 1.5% by volume and steel reinforcement ratio of less than 0.02. This study aims at investigating of compressive and tensile behavior of UHPC to perform a reasonable prediction for flexural capacity of UHPC beams. Tensile behavior modeling was performed using load-crack mouth opening displacement relationship obtained from bending test. The experimental results show that steel fiber-reinforced UHPC is in favor of cracking resistance and ductility of beams. The ductility indices range from 1.6 to 3.0, which means high ductility of hybrid steel fiber-reinforced UHPC. Test results and numerical analysis results for the moment-curvature relationship are compared. Though the numerical analysis results for the bending capacity of the UHPC beam without rebar is larger than test result, the overall comparative results show that the bending capacity of steel fiber-reinforced UHPC beams with compressive strength of 150 MPa can be predicted by using the established method in this paper.