Study on fracture behavior of polypropylene fiber reinforced concrete with bending beam test and digital speckle method

Peng Cao,Decheng Feng,Changjun Zhou,Wenxin Zuo 사단법인 한국계산역학회 2014 Computers and Concrete, An International Journal Vol.14 No.5

Portland cement concrete, which has higher strength and stiffness than asphalt concrete, has been widely applied on pavements. However, the brittle fracture characteristic of cement concrete restricts its application in highway pavement construction. Since the polypropylene fiber can improve the fracture toughness of cement concrete, Polypropylene Fiber-Reinforced Concrete (PFRC) is attracting more and more attention in civil engineering. In order to study the effect of polypropylene fiber on the generation and evolution process of the local deformation band in concrete, a series of three-point bending tests were performed using the new technology of the digital speckle correlation method for FRC notched beams with different volumetric contents of polypropylene fiber. The modified Double-K model was utilized for the first time to calculate the stress intensity factors of instability and crack initiation of fiber-reinforced concrete beams. The results indicate that the polypropylene fiber can enhance the fracture toughness. Based on the modified Double-K fracture theory, the maximum fracture energy of concrete with 3.2% fiber (in volume) is 47 times higher than the plain concrete. No effort of fiber content on the strength of the concrete was found. Meanwhile to balance the strength and resistant fracture toughness, concrete with 1.6% fiber is recommended to be applied in pavement construction.

Experimental Determination of Concrete Fracture Properties with Modified S-FPZ Model

Yon, Jung-Heum,Kim, Tai-Hoon Korea Concrete Institute 2006 International Journal of Concrete Structures and M Vol.18 No.e3

Modified singular fracture process zone(S-FPZ) model is proposed in this paper to determine a fracture criterion for continuous crack propagation in concrete. The investigated fracture properties of the proposed fracture model are strain energy release rate at a micro-crack tip and the relationship between crack closure stress(CCS) and crack opening displacement(COD) in the FPZ. The proposed model can simulate the actual fracture energy of experimental results fairly well. The results of the experimental data analysis show that specimen geometry and loading condition did not affect the CCS-COD relation. However, the strain energy release rate is a function of not only specimen geometry but also crack extension. The strain energy release rate remained constantly at the minimum value up to the crack extension of 25 mm, and then it increased linearly to the maximum value. The maximum fracture criterion occurred at the peak load for specimens of large size. The fracture criterion remained at the maximum value after the peak load. The variation of the fracture criterion is caused by micro-cracking and micro-crack localization. The fracture criterion of strain energy release rate can simply be the size effect of concrete fracture, and it can be used to quantify the micro-cracking and micro-crack localizing behavior of concrete.

Signal-based AE characterization of concrete with cement-based piezoelectric composite sensors

Youyuan Lu,Zongjin Li,Lei Qin 사단법인 한국계산역학회 2011 Computers and Concrete, An International Journal Vol.8 No.5

The signal-based acoustic emission (AE) characterization of concrete fracture process utilizing home-programmed AE monitoring system was performed for three kinds of static loading tests (Cubic-splitting, Direct-shear and Pull-out). Each test was carried out to induce a distinct fracture mode of concrete. Apart from monitoring and recording the corresponding fracture process of concrete, various methods were utilized to distinguish the characteristics of detected AE waveform to interpret the information of fracture behavior of AE sources (i.e. micro-cracks of concrete). Further, more signal-based characters of AE in different stages were analyzed and compared in this study. This research focused on the relationship between AE signal characteristics and fracture processes of concrete. Thereafter, the mode of concrete fracture could be represented in terms of AE signal characteristics. By using cement-based piezoelectric composite sensors, the AE signals could be detected and collected with better sensitivity and minimized waveform distortion, which made the characterization of AE during concrete fracture process feasible. The continuous wavelet analysis technique was employed to analyze the wave-front of AE and figure out the frequency region of the P-wave & S-wave. Defined RA (rising amplitude), AF (average frequency) and P-wave & S-wave importance index were also introduced to study the characters of AE from concrete fracture. It was found that the characters of AE signals detected during monitoring could be used as an indication of the cracking behavior of concrete.

Seismic fracture analysis of concrete arch dams incorporating the loading rate dependent size effect of concrete

Amir Pirooznia,Amir Javad Moradloo 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.79 No.2

The purpose of this study is to investigate the size effect, loading rate, and smeared crack models in the nonlinear seismic behavior of concrete arch dams. One of the important parameters in the design of arch concrete dams is the tensile strength of unreinforced mass concrete. Various fracture parameters obtained from experimental results reported for concrete in order to study the size-effect is used in this paper. In the present analysis, the smeared crack method is used in finite element analysis of the Morrow Point arch dam subjected to three components of the TAFT earthquake as a case study. The dependence of fracture, and especially of the size effect, on the loading rate is described. Models incorporating nonlinear analysis in three cases with and without the size effect of dam concrete and fluid-structure interaction are employed to evaluate and compare them. The water is taken as an inviscid, compressible fluid, and the foundation is rigid. From the study, it is concluded that the participation of the size effect leads to higher values of maximum displacements and stresses in benchmark points compared to the model that ignores the size effect. The crack initiation criterion based on the maximum tensile stress according to the size effect of concrete, and also the dynamic loading range should be defined. Results show considering fixed smeared crack models used in the concrete specimen as well as the size effect of concrete materials, will lead to the crack profile is more realistic and will represent near to real behavior of concrete fracture. The results are of significant interest for the concrete fracture of dams; hence the loading rate should be adopted for fracture properties obtained in dams.

Influence of coarse aggregate properties on specific fracture energy of steel fiber reinforced self compacting concrete

Raja Rajeshwari, B.,Sivakumar, M.V.N. Techno-Press 2020 Advances in concrete construction Vol.9 No.2

Fracture properties of concrete depend on the mix proportions of the ingredients, specimen shape and size, type of testing method used for the evaluation of fracture properties. Aggregates play a key role for changes in the fracture behaviour of concrete as they constitute about 60-75 % of the total volume of the concrete. The present study deals with the effect of size and quantity of coarse aggregate on the fracture behaviour of steel fibre reinforced self compacting concrete (SFRSCC). Lower coarse aggregate and higher fine aggregate content in SCC results in the stronger interfacial transition zone and a weaker stiffness of concrete compared to vibrated concrete. As the fracture properties depend on the aggregates quantity and size particularly in SCC, three nominal sizes (20 mm, 16 mm and 12.5 mm) and three coarse to fine aggregate proportions (50-50, 45-55, 40-60) were chosen as parameters. Wedge Split Test (WST), a stable test method was adopted to arrive the requisite properties. Specimens without and with guide notch were investigated. The results are indicative of increase in fracture energy with increase in coarse aggregate size and quantity. The splitting force was maximum for specimens with 12.5 mm size which is associated with a brittle failure in the pre-ultimate stage followed by a ductile failure due to the presence of steel fibres in the post-peak stage.

Evaluation of Fracture Process Zone in the Flexural Response of Different Concrete Materials Using DIC Method

Shengtao Li,Xudong Chen,Shengshan Guo 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.8

In the present paper, a digital image correlation (DIC) method is used to study the development of fracture process zones (FPZ) of different concrete materials in three-point bending test. Different concrete materials including original concrete, rubber concrete, self-compacting rubber concrete and pervious concrete are investigated. Firstly, the image of the FPZ and the crack opening displacement (COD) in FPZ is obtained by acquiring strain field and displacement field information. The relationship between the development of FPZ and the mechanical properties is further studied. It is found that there is a strong correlation between the FPZ and the post-peak strength reduction of concrete. The development characteristics of FPZ of different concrete materials are analyzed. The addition of rubber will result in stronger strain concentration in pre-peak stage compared to original concrete, and the FPZ will emerges at the earlier loading stage, but it can enhance the crack resistance of concrete in the post-peak stage. Self-compacting rubber concrete was observed to have higher bearing capacity and cracking resistance during fracture than that of the others. Pervious concrete has weak resistance to fracture, and there is almost no decline of the FPZ development rate in fracture process.

유한요소법에 의한 콘크리트의 진행성 파괴해석

송하원 한국콘크리트학회 1996 콘크리트학회지 Vol.8 No.1

콘크리트의 파괴진행영역은 콘크리트의 균열선단의 브리징영역과 미세균열영역으로 구성되는 비선형영역으로서 콘크리트의 파기거동을 지배한다. 파괴진행영역을 고려한 파괴역학은 콘크리트에 유용하게 적용될 수 있으며 파괴진행영역 모델의 개발은 콘크리트의 파괴현상을 규명하는데 매우 중요하다. 본 논문에서는 콘크리트의 균열진행을 해석하기 위하여 선형 인장 연화곡선을 사용한 Dugdale-Barenblatt형 모델로 콘크리트의 브리징영역을 모델링하였고 이를 이산균열방법을 사용하여 단지 요소경계면에 파괴진행영역을 발생시켜 유한요소 해석하는 방법과 요소내의 불연속 균열면을 도입한 균열요소를 사용함으로써 이산균열방법의 결점을 보완한 해석방법을 제시하였다. 또한 해석 예를 통해 균열진행해석에 사용된 유한요소모델을 검증하였다. The fracture process zone in concrete is a region ahead of a traction-free crack, in which two major mechanisms, microcracking and bridging, play important roles. The toughness due to bridging is dominant compared to toughness induced by microcracking, so that the bridging is dominani: mechanism governing the fracture process of concrete. Fracture mechanics does work for concrete provided that the fracture process zone is being considered, so that the development of model for the fracture process zone is most important to describe fracture phenomena in concrete. In this paper the bridging zone, which is a part of extended rnacrocrack with stresses transmitted by aggregates in concrete, is modelled by a Dugdale-Barenblatt type model with linear tension-softening curve. Two finite element techniques are shown for the analysis of progressive cracking in concrete based on the discrete crack approach: one with crack element, the other without crack element. The advantage of the technique with crack element is that it dees not need to update the mesh topology to follow the progressive cracking. Numerical results by the techniques are demonstrated.

Fracture properties of concrete using damaged plasticity model -A parametric study

J.S. Kalyana Rama,D.R. Chauhan,M.V.N Sivakumar,A. Vasan,A. Ramachandra Murthy 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.64 No.1

The field of fracture mechanics has gained significance because of its ability to address the behaviour of cracks. Predicting the fracture properties of concrete based on experimental investigations is a challenge considering the quasi-brittle nature of concrete. So, there is a need for developing a standard numerical tool which predicts the fracture energy of concrete which is at par with experimental results. The present study is an attempt to evaluate the fracture energy and characteristic length for different grades of concrete using Concrete Damage Plasticity (CDP) model. Indian Standard and EUROCODE are used for the basic input parameters of concrete. Numerical evaluation is done using Finite Element Analysis Software ABAQUS/CAE. Hsu & Hsu and Saenz stress-strain models are adopted for the current study. Mesh sensitivity analysis is also carried to study the influence of type and size of elements on the overall accuracy of the solution. Different input parameters like dilatation angle, eccentricity are varied and their effect on fracture properties is addressed. The results indicated that the fracture properties of concrete for various grades can be accurately predicted without laboratory tests using CDP model.

Obtaining equivalent fracture toughness of concrete using uniaxial compression test

Zongjin Li,Yanhua Zhao 사단법인 한국계산역학회 2010 Computers and Concrete, An International Journal Vol.7 No.4

From typical stress-axial strain curve and stress-volume strain curve of a concrete under uniaxial compression, the initiation and localization of microcracks within the interior of the specimen can be identified. The occurrence of random microcrack indicates the end of the linear elasticity, and the localization of microcrack implies formation of major crack, which triggers the onset of unstable crack propagation. The interval between initiation and localization of microcracks is characterized by a stable microcrack growth. Based on fracture behavior observed from a uniaxial compressive test of a concrete cylinder, a model has been developed to extract fundamental fracture properties of a concrete, i.e. the equivalent fracture toughness and the size of fracture process zone. The introduction of cracking Poisson’s ratio accounts for tensile failure characteristics of concrete even under uniaxal compression. To justify the validity of the model proposed, tests on three-point bending have been performed to obtain the fracture toughness in accordance with two parameter fracture model and double-K fracture model. Surprisingly, it yields favorably comparable results and provides an encouraging alternative approach to determine fracture properties for concretes.

A cohesive model for concrete mesostructure considering friction effect between cracks

Yi-qun Huang,Shao-wei Hu 사단법인 한국계산역학회 2019 Computers and Concrete, An International Journal Vol.24 No.1

Compressive ability is one of the most important mechanical properties of concrete material .The compressive failure process of concrete is pretty complex with internal tension, shear damage and friction between cracks. To simulate the complex fracture process of concrete at meso level, methodology for meso-structural analysis of concrete specimens is developed; the zero thickness cohesive elements are pre-inserted to simulate the crack initiation and propagation; the constitutive applied in cohesive element is established to describe the mechanism of crack separation, closure and friction behavior between the fracture surfaces. Aseries of simulations were carried out based on the model proposed in this paper. The results reproduced the main fracture and mechanical feature of concrete under compression condition. The effect of key material parameters, structure size, and aggregate content on the concrete fracture pattern and loading carrying capacities was investigated. It is found that the inner friction coefficient has a significant influence on the compression character of concrete, the compression strength raises linearly with the increase of the inner friction coefficient, and the fracture pattern is sensitive to the mesostructure of concrete.