Experimental and Numerical Analysis of Fracture Processes in Concrete

A combined experimental and numerical approach is adopted to investigate fracture processes in concrete. The experimental programme focuses on the failure of concrete subjected to mixed mode I and II loading. The influence of shear load on the nucleation and propagation of cracks in concrete is studied by means of four-point-shear tests on single and double edge notched beams. A numerical model for simulating fracture is developed in which the heterogeneous microstructure of concrete is implemented. The model is used to carry out simulations of different fracture experiments. In Chapter 1 of this report the subject of the investigation is clarified. Chapter 2 deals with a summary of research regarding tensile fracture and combined tensile and shear fracture of concrete. An overview of different types of experiments is given. Furthermore numerical models and simulations of fracture tests are discussed. The experiments conducted in the present investigation are described in Chapter 3. Beam specimens with one or two notches, made of different concrete mixes are loaded in fourpoint- shear. All experiments are carried out under displacement control using a closed loop hydraulic system. In the developed test set-up experiments can be carried out either with freely rotating or fixed supports. The results of the various experiments are presented in Chapter 4. The experimental outcome is presented by means of crack patterns, different load-deformation curves and details of cracks obtained with an optical microscope. In Chapter 5 the numerical model is explained. Different ways of implementing heterogeneity are presented. The determination of the various input parameters is discussed. Simulations of different types of experiments are presented in Chapter 6, i.e. uniaxial tensile tests, four-point-shear tests, pull-out of anchor bolts and mixed mode tests on plate specimens. The last chapter includes a discussion of the results and a summary of the conclusions. The main conclusion derived from the experimental part of this investigation is that fracture in concrete is a mode I mechanism, even if the external loading on a specimen is a combination of tensile and shear. The numerical model developed has proved able to predict fracture in concrete quite accurately. Simulations with the model increase insight into the fracture mechanism.Design & ConstructionCivil Engineering and Geoscience

Experimental and numerical analysis of fracture processes in concrete

Civil Engineering and Geoscience

Porous network concrete: A new approach to make concrete structures self-healing using prefabricated porous layer (abstract)

Structural EngineeringCivil Engineering and Geoscience

Modeling of expansion and cracking due to ASR with a 3D lattice model

It is generally possible to consider modeling of ASR damage in concrete in two main groups: modeling of gel formation and its expansion; modeling of ASR related damage. In this paper, authors take an attempt to combine both: simulating the correct crack formation and the connected concrete expansion. It is aimed to simulate ASR damage in a cementitious material bearing reactive aggregates. The model that is used is a 3D lattice type model. It models concrete on a meso-scale in which particles embedded in a cement matrix are taken into account. The particle structure is obtained by CT-scanning of samples. With the model the concrete expansion can be simulated. One of the inputs in the model is the local expansion of the gel. For that the mechanical properties of the gel should be known, which are obtained from an experimental procedure developed by the authors.Structural EngineeringCivil Engineering and Geoscience

Modelling chloride diffusion in cracked concrete: A lattice approach

In this paper, a 3D lattice model is proposed as a tool to simulate chloride diffusion in (cracked) cement based materials. The procedure consists of two (computationally independent) steps: simulating fracture with the fracture lattice model, previously developed, and simulating chloride diffusion process using the newly developed transport lattice model. Essentially, the output of the first step is used as an input for the second. In this manner, coupling between the mechanics and the transport simulation is achieved. In the paper, basic procedures for both steps are outlined, with the emphasis on the chloride transport simulation. Chloride penetration is assumed to be driven only by the diffusion process, while other mechanisms are neglected. Diffusion coefficient of chloride through the cracks is assumed to depend on the crack width, using relationships available in the literature. This study should provide more insight to the process of chloride penetration in cracked concrete, and allow quantification of the influ-ence of cracking on the process.Structural EngineeringCivil Engineering and Geoscience

Mimicking Bone Healing Process to Self Repair Concrete Structure Novel Approach Using Porous Network Concrete

To repair concrete cracks in difficult or dangerous conditions such as underground structures or hazardous liquid containers, self healing mechanism is a promising alternative method. This research aims to imitate the bone self healing process by putting porous concrete internally in the concrete structure to create a porous network similar to ‘spongious bone’. When crack is formed and detected by sensors, healing agent can be infused into the porous network so as to fill up voids and seal a crack or cracks in the concrete body. This idea was tested using cylindrical samples. A porous concrete core was placed in the center of the concrete cylinder. Uniaxial direct tensile load was applied to create cracks close to the notch of the sample. A healing action was performed by injecting healing agent manually. The results show that a macro-crack is sealed and strength of concrete is regained. Therefore, the concept is considered as to be feasible for self repair mechanism in concrete.Structural EngineeringCivil Engineering and Geoscience

Lattice modeling of fracture processes in numerical concrete with irregular shape aggregates

The fracture processes in concrete can be simulated by lattice fracture model [1]. A lattice network is usually constructed on top of the material structure of concrete, and then the mechanical properties of lattice elements are assigned, corresponding with the phases they represent. The material structure of concrete can be obtained experimentally by X-ray computed tomography. Alternatively it is also possible to simulate a virtual material structure of concrete. A simple way to represent the material structure of concrete is to put multiple spheres in a matrix, where the spheres are interpreted as aggregates. This assumption of the shape of aggregates might have influences on the fracture processes in concrete, such as the microcracks propagation path. Recently the Anm material model was proposed and implemented, which can produce a material structure of concrete with irregular shape aggregates [2]. The irregular shape is represented by a series of spherical harmonic coefficients. The method to determine these spherical harmonic coefficients from aggregate shapes was elaborated in [3]. The further mechanical performance evaluation would benefit from this more realistic material structure. In this paper a material structure of concrete is simulated by the Anm material model. A number of irregular shape particles are planted in a matrix. This material structure is then converted into a voxelized image. Afterwards a random lattice mesh is made, and three types of lattice elements are defined, which represent aggregates, matrix and interface respectively. A uniaxial tensile test is set up and simulated by fixing all the lattice nodes at the bottom of the specimen and imposing a prescribed unit displacement onto all the nodes at the top. The lattice fracture analysis gives the stress-strain response and microcracks propagation, from which some mechanical properties such as Young's modulus, tensile strength and fracture energy can be predicted.Structural EngineeringCivil Engineering and Geoscience

Self-healing in ECC stimulated by SAP under flexural cyclic load (abstract)

Structural EngineeringCivil Engineering and Geoscience

A healable concrete structure

Structural EngineeringCivil Engineering and Geoscience

Fibre-matrix interface properties in a wood fibre reinforced cement matrix

Wood fibres can be a low cost reinforcement for cementitious materials for structural applications. In order to design a ductile cementitious material reinforced with softwood fibres the fibrematrix interface properties are studied. Pullout tests have been carried out to determine the bond strength and the influence in the pullout behaviour of the physical, chemical and mechanical properties of both the fibres and the cement matrix. Other fibre-matrix interface characteristics have been evaluated using an Environmental Scanning Electron Microscope (ESEM), a CT-scanner and optical microscopes. Matrix and fibre must be suitably designed in order to allow the fibre to be pulled out without rupture. A controlled mode of telescopic bonding during the pullout will be beneficial to increase the dissipated energy and develop ductility in the composite. Understanding the pullout behaviour in detail will be useful in the development of wood fibre reinforced cementitious materials.Structural EngineeringCivil Engineering and Geoscience