Effect of aggregate content and size on the basic creep of concrete – An image-based meso-scale analysis Sen Zhang 1 , Ehab Hamed 2 and Chongmin Song 3 1 PhD candidate, UNSW Sydney, Sydney, Australia 2 Associate Professor, UNSW Sydney, Sydney, Australia 3 Professor, UNSW Sydney, Sydney, Australia Abstract: This paper investigates the sensitivity of the basic creep response of concrete to the aggregate content and size using a 2D meso-scale analysis. An image-based analysis is conducted based on a continuum approach, where concrete is treated as a three-phase material that consists of viscoelastic mortar, elastic coarse aggregate and air. Digital images representing the meso-structure of concrete are converted to meshes through a quadtree algorithm. The scaled boundary finite element method is used for the solution due to its ability of modelling arbitrarily sided polygons. The potential damage in the interfacial transition zone is modelled using cohesive zone model with traction separation laws. The basic creep model is based on a rate-type rheological model corresponding to a Kelvin chain that is converted to an incremental form and integrated into the meso-scale analysis. In the numerically generated concrete meso- structures with circular aggregates, the results show that higher aggregate content reduces the creep response whereas aggregate size has no significant impact on the creep response. Keyword: basic creep, meso-scale, scaled boundary finite element method 1. Introduction Serviceability of concrete is often hindered by the time-dependent behaviour of concrete, especially creep. The presence of creep may lead to excessive deformation, cracking or even failure of the structure. Empirical models that are used by engineers for predicting the creep response like B3 model [1] and fib model [2] for example, treat concrete as a homogeneous material. Such models have been found to exhibit significant uncertainties [3] and they fail to explain critical mechanisms like creep rupture, creep recovery, creep under multiaxial loading, relaxation, size effects and others. The reason for this is mainly attributed to the concrete composition, which is generally ignored in code models, but it determines the creep characteristics of concrete that originates from hardened cement paste that is restrained by to the presence of aggregates. The restraint depends on the random aggregate distribution, size, and shapes, which makes it difficult to predict creep using homogeneous material models. To better understand the creep response and to optimise the mix design for potential control of the long-term deformations, analysis and models at the meso-scale of concrete are needed. Application of meso-scale models for concrete are becoming more popular due to their capability of capturing internal structural effects. On the meso-scale, concrete is generally treated as a composite consisting of mortar and aggregates, with potential air voids in between. The presence of interfacial transition zone (ITZ) around aggregates has often been considered as well, which is known as the weakest region in concrete. So far, only limited attempts have been made to study the creep behaviour of concrete in the meso-scale [4,5], in which FEM is adopted for the analysis. Due to the complex geometry of concrete in the meso-scale, the generation of FEM mesh can be a difficult task. Such a problem can be overcome with the scaled boundary finite element method (SBFEM) [6] coupled with a quadtree mesh generation algorithm. Creep of concrete is generally divided into basic creep and drying creep, where basic creep is the strain developed in sealed specimen, while drying creep is the additional strain developed due to drying. Only basic creep behaviour using a meso-scale analysis is presented here. Concrete is treated as a three-phase composite consisting of viscoelastic mortar, elastic coarse aggregates, and air voids. The numerical analysis is conducted using (SBFEM) [6] based on a continuum approach. An automatic and robust quadtree decomposition algorithm is employed to convert images of concrete meso-structures into meshes. SBFEM allows the use of polygonal elements of arbitrary number of sides which makes it highly complementary with quadtree meshes and the presence of hanging nodes does not pose a problem. The decohesion of ITZ is captured using zero-thickness interface elements with traction separation laws. Details of the numerical model are presented in a previous study conducted by the authors [7]. Here, the model is used to analyse numerically generated concrete images using a take-and-place algorithm. Parametric studies are then carried out on concrete specimens subjected to uniaxial compression to investigate the effect of aggregate content and size on the basic creep.
Effect of aggregate content and size on the basic creep of concrete – An image-based meso-scale analysis
Jun 18, 2023
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Related Documents
