Ultra-high Performance Cementitious Composites Research Articles

Effect of Fiber Type and Fiber Hybrids on Strain-Hardening and Multiple Cracking Properties of the Ultra-High Performance Cementitious Composites under Uniaxial Loads

Five series of strain hardening ultra-high performance cementitious composites (SHUHPCC) incorporated with different types of fibers and hybrid fibers were produced. Three types of fibers (steel fiber, polyvinyl alcohol fiber and polyethylene fiber) were used as mono or hybrid reinforcement in SHUHPCC with the same volume fraction of 2%. The primary strengths, strain hardening and multiple cracking behaviors of hybrid fiber reinforced SHUHPCC under the uniaxial tensile are investigated. Test results show that the SHUHPCC containing PE fibers exhibited higher strain hardening capacity and lower first cracking strength than composites reinforced with mono PVA fiber or mono steel fiber. The composites containing PVA fibers or steel fibers have higher tensile strength and first cracking strength than the composite reinforced by mono PE fiber. Hybridization reinforcement with different fibers is able to make up defects of mono fiber reinforcement for SHUHPCC. The change laws of tensile strength and uniaxial compression strength of SHUHPCC with mono PE fiber and mono PVA fiber are opposite to each other.

Strain hardening ultra-high performance fiber reinforced cementitious composites: Effect of fiber type and concentration

Abstract An experimental work was carried out to investigate the effects of micro-steel, hooked-steel, and micro-glass fibers on the mechanical properties and ductility of Ultra-high Performance Cementitious Composites (UHPC). The aspect ratios of the of micro-steel, hooked-steel, and micro-glass fibers were 7.17, 55 and 722, respectively. At a water-binder ratio of 0.195, three groups of UHPCs containing 0.25, 0.5, 0.75, 1, 1.5, and 2% fiber volume fractions were produced and tested for compressive strength, splitting tensile strength, modulus of elasticity, flexural strength, load-displacement behavior, fracture energy, and characteristic length. Test results revealed that the mixes with 2% of micro steel fiber exhibited the best compressive strength of 180 MPa as well as the highest splitting tensile strength and modulus of elasticity. However, the mixes with 2% of hooked steel fiber displayed a strain hardening load-displacement behavior with a substantially enhanced ductility. The results also showed that the beneficial influence of using micro glass fiber began to decrease after 1.5% of the fiber volume.

Properties of low binder ultra-high performance cementitious composites: Comparison of nanosilica and microsilica

This paper presents the effect of using binary and ternary blends of nanosilica (NS) and microsilica on the mechanical properties of low binder ultra-high performance cementitious composites (UHPCs). For this, two concrete groups were designed with and without silica fume by weight of cement with a constant water/binder ratio and total binder content. Commercially available NS was used in partial substitution of cement at 0%, 0.5%, 1%, 2% and 3% by weight. The results show that among different NS contents, UHPC containing 2% NS exhibited the best results of compressive strength, splitting tensile strength, modulus of elasticity, flexural strengths, load–displacement behavior and fracture energy at 90days. The samples of UHPC containing binary cementitious materials (NS and SF) gave better results than concretes containing only NS. Additionally, the effect of 1% NS is almost equal to that 10% of SF.

Theoretical study of UHPCC composite column behaviors under axial compression

To improve the durability and service life of reinforced concrete column such as bridge piers, an advanced composite column made of Ultra High Performance Cementitious Composites (UHPCC) permanent form is proposed. Based on elasticity plasticity theory, axial compression behavior of the composite column was studied theoretically. The first circumferential cracking load and ultimate limit loading capacity are derived for the composite column. Short composite column compression tests and numerical simulations using FEM method were carried out to justify the theoretical formula. The effects of UHPCC tube thickness on the axial compression behavior were studied. Using the established theoretical model and numerical simulation, the large dimension composite columns are calculated and analyzed with different UHPCC tube thickness. These studies may provide a reference for advanced composite column design and application.

Research on the Influences of Crack-Depth Ratio on Fracture Energy of Ultra-High Performance Cementitious Composites

For the study of fracture characteristics of ultra-high performance cementitious composites(ECC),16 different sizes of three-point bending beams were made and ultimate load, ultimate deflection and crack mouth opening displacement ,the curve andcurve of ECC were contructed,with the method of fracture work recommendedby RILEM , the external work was respectively calculated by the curve ofand, which determined the fracture energy of ECC.Results show that two kinds of calculation result are roughly equal;The influence of size effect on fracture character was: fracture energy increased with the increasing of the crack-depth ratio, the fracture energy of concrete specimen is the maximum when the crack-depth ratio is 0.4 ; is proportional to the initial crack-depth of the specimen, but there is no relationship betweenand crack-depth ratio. This paper would have great significance for the study of fracture characteristics of ECC.

Structural behaviors of sustainable hybrid columns under compression and flexure

Structural behaviors of a sustainable hybrid column with the ultra high performance cementitious composites (UHPCC) permanent form under compression and flexure were studied. Critical state and failure stage characters are analyzed for large and small eccentricity cases. A simplified theoretical model is proposed for engineering designs and unified formulas for loading capacity of the hybrid column under compression and flexure loads are derived, including axial force and moment. Non-linear numerical analysis is carried out to verify the theoretical predictions. The theoretical predictions agree well with the numerical results which are verified by the short hybrid column tests recursively. Compared with the traditional reinforced concrete (RC) column, the loading capacity of the sustainable hybrid column is improved significantly due to UHPCC confinements.

Effects of nano-SiO2 particles on the mechanical and microstructural properties of ultra-high performance cementitious composites

In this research the effects of nano-SiO2 particles on the mechanical performance, hydration process and microstructure evolution of ultra-high performance cementitious composites were investigated by different methods. The results showed that the compressive and flexural strength increased with the increase of the nano-SiO2 content up to 3% and due to agglomeration of nano-SiO2 particles, the mechanical properties decreased slightly when the nano-SiO2 content was more than 3%. The hydration process was accelerated by the addition of nano-SiO2. The porosity and the average pore diameter decreased with the increase of the nano-SiO2 content and aging. The microstructure was more homogenous and dense for nano-SiO2 specimens as compared to the control specimen. All of these improvements could be mainly attributed to the pozzolanic and filler effects of nano-SiO2.

Comparison of Flexural Tensile Behaviors with Different Filling Directions in Producing UHPCC Flexural Member

본 연구는 UHPCC (Ultra High Performance Cementitious Composites)에서 섬유배열 유도의 효율성을 평가하기 위한 연구의 일환으로, 흐름특성을 달리한 다양한 방법으로 UHPCC 부재를 제작하여 휨거동의 변화를 비교하고, 섬유 배열특성과의 상관관계를 정성적으로 분석하였다. 실험을 통해 섬유배열 유도방법에 따라 휨거동의 차이가 크게 나타남을 확인하였다. 일반적인 휨실험체 제작방법으로, 섬유가 주인장방향으로 배열되도록 유도한 경우가 다른 방법으로 제작된 휨실험체에 비해 더 높은 휨인장강도와 낮은 변동성을 보였다. 따라서 실제 UHPCC 부재에서의 재료의 휨인장강도는 실험실 수준에서 측정한 휨인장강도와 비교하여 크게 다를 수 있고, 변동성도 더 크게 나타날 수 있음을 반드시 고려해야 할 것이다. 한편, UHPCC의 유동흐름에 따른 섬유의 배열특성의 변화를 흐름의 종류 및 경계면 효과를 고려하여 정성적으로 예측하였으며, 이러한 예측결과는 실험에서 여러 가지 형태로 유도된 유동흐름에 따른 휨인장거동의 변화를 잘 설명하였다. This study was intended to estimate the efficiency of inducing fiber arrangement in UHPCC (Ultra High Performance Cementitious Composites). For the purpose, UHPCC members produced by several different placing methods according to flow characteristics were prepared; flexural behaviors were compared and correlation between the flexural behavior and the characteristics of fiber arrangement was investigated. Test results showed that placing method for inducing specific fiber arrangement had a considerable influence on the flexural performance. The standard specimen in which fibers are induced to be directed parallel to the principle tensile direction presented higher flexural tensile strength but lower variation. Therefore it should be considered that the flexural tensile strength actually developed in UHPCC member may be highly different and in lager variation. The qualitative variation of fiber arrangement according to the flow of UHPCC was also predicted considering the flow pattern and the boundary effect; the prediction provided good explanation to the difference in the flexural behavior according to the induced flow.

Preliminary design and structural responses of typical hybrid wind tower made of ultra high performance cementitious composites

Ultra High Performance Cementitious Composites with compressive strength 200MPa (UHPCC-200) is proposed for the structural design of super high hybrid wind turbine tower to gain durability, ductility and high strength design objectives. The minimal wall thickness is analyzed using basic bending and compression theory and is modified by a toque influence coefficient. Two cases of wall thickness combination of middle and bottom segment including varied ratio and constant ratio are considered within typical wall thickness dimension. Using nonlinear finite element analysis, the effects of wall thickness combinations with varied and constant ratio and prestress on the structural stress and lateral displacement are calculated and analyzed. The design limitation of the segmental wall thickness combinations is recommended.

Effect of silica fume and fly ash on hydration and microstructure evolution of cement based composites at low water–binder ratios

The hydration process of ultra-high performance cementitious composite (UHPCC) is distinctly different from common concrete owing to its low water–binder ratio (w/b). The effects of silica fume and fly ash on the hydration process and microstructure were investigated via different characterization methods in this work. The results indicated that the hydration process could be accelerated at the beginning by addition of silica fume, and fly ash, on the other hand, retarded hydration mainly in the dormant and acceleration periods. When they were incorporated together in cement, the result differed significantly from cement hydration at higher w/b (>0.35). As a result of Ca(OH)2 consumption by pozzolanic reaction, the porosity reduced (<4%) and the interface strengthened as the curing time increased. Nanoindentation results revealed that most hydration products of UHPCC were UHD C–S–H and unhydrated cement. The unhydrated cement particles were surrounded by UHD C–S–H, implying that the UHPCC had excellent mechanical performance and durability.

접촉 폭발 하중을 받는 RC 슬래브의 국부 손상 및 내폭 성능 평가

본 연구에서는 다양한 RC 슬래브의 접촉 발파 실험을 수행하여 내폭 성능을 평가하였다. RC 슬래브의 내폭 성능 향상을 위해 섬유 보강과 외부 CFRP 시트 보강을 도입하였다. 폭발하중 실험은 <TEX>$2,000{\times}1,000{\times}100mm$</TEX> RC 슬래브를 제작하였고, 일반 콘크리트와 강섬유 보강 콘크리트, 하이브리드 PVA 섬유 보강 시멘트 복합체, 초고성능 콘크리트를 적용하였다. 접촉 발파로 생긴 RC 슬래브의 손상 정도를 크레틀, 스폴과 브리치의 직경과 깊이로 평가하였다. 실험 결과를 LS-DYNA 유한요소해석 프로그램과 Morishita 등의 예측식으로 검증하고 비교분석하였다. 분석 결과, LS-DYNA 프로그램을 이용하여 크레틀, 스폴, 브리치의 직경 및 깊이에 대한 개략적인 예측이 가능하며, 폭발하중 하에서 손상부의 거시적 거동을 모사함으로써 부재의 파괴 이력을 나타낼 수 있었다. 국부 손상에 대한 세가지 예측식이 소개되어 있으나 경험식으로써의 한계가 존재하며, 이에 대한 추가 연구가 필요하다고 판단된다. In this study, the resistance of various reinforced concrete (RC) slabs subjected to contact detonation was assessed. In order to enhance the blast resistance, fibers and external FRP sheets were reinforced to RC slabs. In the experiment, the <TEX>$2,000{\times}1,000{\times}100mm$</TEX> sized RC slabs were fabricated using normal concrete (NC), steel fiber reinforced concrete (SFRC), polyvinyl alcohol fiber reinforced cementitious composite (PVA FRCC), and ultra-high performance cementitious composites (UHPCC). The damage levels of RC slabs subjected to contact detonation were evaluated by measuring the diameter and depth of crater, spall and breach. The experimental results were compared to the analyzed data using LS-DYNA program and three different prediction equations. The diameter and depth of crater, spall and breach were able to be predicted using LS-DYNA program approximately. The damage process of RC slabs under blast load was also well expressed. Three prediction equations suggested by other researchers had limitations to apply in terms of empirical approaches, therefore it needs further research to set more analytical considerations.

Static, dynamic mechanical properties and microstructure characteristics of ultra-high performance cementitious composites

AbstractA new type of construction material named ultra-high performance cementitious composite (UHPCC) was developed in order to reduce the production cost and energy consumption of reactive powder concrete (RPC). Six different mixture proportions of UHPCC were designed, and their properties, including workability (slump test), static mechanical properties (compressive strength and flexure strength), and dynamic mechanical properties (dynamic compressive strength, toughness and fracture pattern), were investigated. Finally, the microstructure of the UHPCC was studied. The experiment result indicate that the compressive and flexural strength of UHPCC can reach 150–200 MPa and 15–50 MPa under standard curing conditions, respectively, which is close to RPC200. Besides, the steel fiber has significant improvement on mechanical properties of UHPCC. The dynamic impact test results show that UHPCC has obvious strain rate effects. Besides, UHPCC exhibits excellent properties to resist dynamic impact. The microstructure investigation showed that UHPCC has dense microstructures and very strong bonds of the interfacial transition zone between cementitious paste and fine aggregate steel fiber.

Structural analysis of circular UHPCC form for hybrid pier under construction loads

Ultra high performance cementitious composite material is applied to the design of multifunctional permanent form for bridge pier in this paper. The basic properties and calculating constitutive model of ultra high performance cementitious composite are introduced briefly. According to momental theory of thin-walled shell, the analytical solutions of structural behavior parameters including circumferential stress, longitudinal stress and shear stress are derived for UHPCC thin-walled circular tube. Based on relevant code of construction loads (MHURD of PPC 2008), the calculating parameter expression of construction loads for UHPCC thin-walled circular tube is presented. With geometrical dimensions of typical pier, the structural behavior parameters of UHPCC tube under construction loads are calculated. The effects of geometrical parameters of UHPCC tube on structural behavior are analyzed and the design advices for UHPCC tube are proposed. This paper shall provide a scientific reference for UHPCC permanent form design and UHPCC hybrid structure application.

Single and multiple dynamic impacts behaviour of ultra-high performance cementitious composite

Single and multiple dynamic impacts tests were conducted on ultra-high performance cementitious composite (UHPCC) with various volume fractions of steel fibers (0, 1%, 2%, 3%, 4%) by using the split hopkinson pressure bar (SHPB). Besides, the ultrasonic velocity method was used to test the damage on specimens caused by dynamic impacts. For single dynamic impact, the data suggest that UHPCC obviously presents dynamic strength enhancement. With increasing of strain rate, the peak stress and peak strain increase rapidly. For multiple dynamic impacts, the results show that addition of steel fibers can obviously enhance the properties of UHPCC to resist the repeated dynamic impacts. Firstly, the number of impacts sharply increases with the increasing of volume fraction of steel fibers. Secondly, the energy absorption ability linearly increases with addition of steel fibers. Thirdly, the steel fibers can prevent the disruption phenomenon and maintain the integrity of specimen.

초고성능 시멘트 복합체의 초기 재령 구속 수축 및 인장 크리프 특성

초고성능 시멘트 복합체(ultra-high-performance cementitious conposites, UHPCC)는 우수한 압축강도와 연성을 나타내기 때문에 구조 부재 적용 시 단면을 상당히 감소시키고, 낮은 물-결합재비와 고분말 혼화 재료의 사용으로 높은 수축 변형률이 발생하게 되어 거푸집 및 보강근 등의 구속에 의한 수축 균열의 발생 가능성이 크다. 그러므로 이 연구에서는 UHPCC의 수축을 저감시키기 위한 방법으로 팽창재와 수축 저감제를 조합하여 혼입하고 자유수축과 구속 수축 거동을 평가하여 적합성 여부를 산정하였다. 실험 결과 팽창재와 수축 저감제를 조합하여 혼입한 경우에 약 40~44%의 자유수축 저감 효과를 보였으며, 잔류 인장응력은 약 35%와 47% 감소하였다. 지속적인 구속 하중에 의한 인장 크리프의 발생으로 탄성 수축 응력의 약 61%, 64%가 이완되는 것으로 나타났으며, 따라서 구속 수축 거동을 평가할 때에는 반드시 크리프 효과를 고려해야 한다고 판단되었다. 구속도는 0.78~0.85로 나타났으며 팽창재와 수축 저감제의 혼입에의한 영향은 미미하였고 콘크리트 링의 두께가 클수록 감소하는 경향을 보였다. 또한, UHPCC의 인장 크리프 변형률을 측정하고 재령에 따라 변하는 구속 하중을 적용한 4-매개 변수 크리프 예측 모델과 비교하였다.

Investigation on the flexural behavior of UHPCC considering the effect of fiber orientation distribution

This study aims to investigate the effect of fiber orientation distribution on the flexural behavior of ultra high performance cementitious composites (UHPCC) and to propose an analytical approach which enables to predict the flexural behavior considering probabilistic fiber orientation distribution. A three-point bending test with the notched beams was carried out and the fiber orientation distribution was quantitatively estimated by the help of image analysis process. The measured fiber orientation distributions for two different flexural performances confirmed that the fiber orientation distribution has a strong impact on the deflection hardening behavior in bending. Finite element analyses were performed to predict flexural behavior of UHPCC considering the difference in fiber bridging behavior depending on the fiber orientation distribution. The analytical results were in good agreement with the experimental results.

Numerical simulation of the variation of fiber orientation distribution during flow molding of Ultra High Performance Cementitious Composites (UHPCC)

Abstract In this paper, the variation of the fiber orientation distribution along the flow of fresh UHPCC was studied. In order to describe the rotational motion of a single fiber, Jeffery’s equation was adopted, in which the interaction among fibers is neglected. Two cases of flow patterns were considered: shear flow and radial flow. Starting with a three-dimensional random distribution of fibers, the fiber orientation distribution along the flow distance was simulated. These results reveal that fibers gradually become more parallel (in the case of shear flow) and perpendicular (in the case of radial flow) to the flow direction as the flow distance increases. This approach will be useful to predict flow-dependent tensile behavior considering the change of fiber orientation distribution.

Combined Influence of Expansive and Shrinkage Reducing Admixtures on the Shrinkage Behavior of Ultra-High Performance Concrete

Since ultra-high performance cementitious composite (UHPCC) exhibits remarkable compressive strength and ductility, its application for structural member provides significant reduction of the section. The use of low water-to-binder ratio and admixtures with high fineness induce large shrinkage strain, leading to the possibility of large occurrence of shrinkage cracks due to the restraints of the form and reinforcing bars. Therefore, this study admixes a combination of expansive and shrinkage reducing agents as a solution to reduce the shrinkage of UHPCC. The eventual appropriateness is computed to evaluate the free shrinkage and restrained shrinkage behaviors. From the test results, the admixing of a combination of expansive and shrinkage reducing agents is seen to achieve a reduction of the free shrinkage by 30% to 50% at 28 days and a reduction of the strain of the external steel by about 19%.

CSA계 팽창재 및 수축 저감제의 혼입에 따른 UHPCC의 초기 수축 거동 평가

이 연구에서는 실리카퓸 및 수축 저감제, 팽창재, 고성능 감수제의 혼입을 변수로 한 초고성능 시멘트 복합체(UHPCC)의 초기 수축 거동을 평가하기 위하여 화학수축 및 자기수축 실험을 수행하고, 응결 측정 결과와 비교하여 UHPCC의 자기건조 시작 시점에 대하여 분석하였다. 실험 결과, 실리카퓸 및 수축 저감제는 초기 화학수축을 증가시키는 경향을 보였으며, 고성능 감수제는 시멘트와 배합수의 수화 반응을 지연시키고 화학수축을 저감시키는 것으로 나타났다. 수축 저감제와 팽창재를 조합하여 적용한 경우 약 49%의 자기수축 저감 효과를 보였으며, 팽창재는 경화를 촉진 시키는 것으로 나타났다. 또한 UHPCC는 다수의 섬유 혼입과 낮은 물-결합재비에 의해 초결 이전부터 자기건조 현상이 발생하는 것으로 나타났다.

UHPCC의 압축응력-변형률 관계에 대한 강섬유 혼입률의 영향

The effect of steel-fiber contents on the compressive behavior of ultra high performance cementitious composites (UHPCC) was studied to propose a compressive behavior model for UHPCC. The experiments considered fiber contents of 0~5 vol.% and the results indicated that compressive strength and corresponding strain as well as elastic modulus were improved as the fiber contents increased. Compared to the previous study results obtained from concrete with compressive strength of 100MPa or less, the reinforcement effect on strength showed similar tendency, while the effect on the strain and elastic modulus were much less. Strength, strain, and elastic modulus according to the fiber contents were presented as a linear function of fiber reinforcement index (RI). Fiber reinforcement in UHPCC had no influence on the shape of compressive behavioral curve. Considering its effect on compressive strength, strain, and elastic modulus, a compressive stress-strain relation for UHPCC was proposed.