3D mesoscale modeling and fracture property study of rubberized self-compacting concrete based on uniaxial tension test

Highlights

• The first numerical simulation of 3D mesoscale model contained all the six phases of rubberized self-compacting concrete (RSCC) under uniaxial tension was conducted based on the full-curve uniaxial tension test.

• The mechanical property and crack formation process of RSCC was studied through the established 3D mesoscale model.

• The fracture mechanism of RSCC was studied by comparing the generation, growth, and development of internal cracks in the specimen through 3D mesoscale simulation result.

• The crack morphology of RSCC and ordinary concrete were compared and studied, the incorporation of rubber optimized the aggregate gradation, increased interfacial transition zone (ITZ) area and the porosity of the whole specimen.

Abstract

Rubberized concrete is a new type of building material intended to ultilise waste rubber with a potential for significant economic and environmental benefits. However, its strength is lower than the strength of ordinary concrete due to the introduction of rubber material, which might affect its application in practical engineering. To improve the mechanical performance of rubberized self-compacting concrete (RSCC), it is a necessary to study the internal mechanisms of strength formation, degradation and failure. Based on the uniaxial tensile test of RSCC, this work reports on the development and validation of a mesoscale model of RSCC, which accounts for its heterogeneity. RSCC is considered to be composed of mortar, coarse aggregate, rubber particles, aggregate-mortar interface transition zone (A-M ITZ), rubber particle-mortar interface transition zone (R-M ITZ), and initial defects. The mesoscopic model is validated by comparing the simulation results with test results. The model is then used to analyse the mechanical properties, crack generation and propagation, and expansion of self-compacting concrete (SCC) and RSCC are compared and analysed. Further, the effects of different volume fractions of rubber on the mechanical properties of RSCC are studied. It is found that the mechanical properties and final fracture surface morphology of RSCC with different rubber content are significantly different, and the causes of these differences are discussed.

Introduction

Nowadays, waste rubber, predominantly from used tires, has become the second-largest polymer pollutant and its disposal has attracted increasing attention across countries and governments. The treatment of waste rubber generally included physical processing, chemical decomposition, stacking, landfill, and combustion. Among these, landfill, burning, and chemical decomposition are very harmful to the environment, and natural placement cannot clear up the waste rubber for a short period. An effective method to deal with the waste rubber is by crushing used tires and adding them into rubberized concrete after physical processing. Rubberized concrete can effectively solve the problem of disposal of rubber products such as used tires and has unique advantages in environmental protection.

In the production process of rubberized concrete, rubber powder or rubber particles are used to replace the coarse and fine aggregates inside the concrete by equal volume or equal mass. The incorporation of rubber particles changes concrete properties from the known properties of plain concrete. Eldin [1], Toutanji [2], Topcu [3], Guoqiang li [4], F. Hernandez [5], [6] demonstrated experimentally that with the increase of rubber content, the compressive strength, flexural strength and tensile strength of concrete specimens decreased, while plastic properties improved significantly. L. Zheng [7], Feng Liu [8] studied the seismic performance of rubberized concrete by vibration test. The test results showed that the damping ratio of rubber concrete was much higher than the ordinary concrete, and the dynamic elastic modulus was lower than the ordinary concrete. Wang her Yung [9] studied the durability of RSCC through experiments. The results showed that the toughness and durability of RSCC could be significantly improved when the rubber content was 5%. These scholars have made many contributions to explore the property of rubberized concrete and expand the engineering utilization of rubberized concrete. A common conclusion from their research is that the incorporation of rubber can significantly improve the apparent density, durability, shock absorption, impact resistance, heat insulation, sound insulation, and other properties of concrete but at the same time its strength will decline substantially. To improve the strength of rubberized concrete, the crack pattern and failure mechanism need to be studied and understood in sufficient detail, e.g. via explicit representation of its constituents using meso-scale models. However, little attention has been given to this type of modelling of rubberized concrete [10]. One of the very few contributions is the work by Feng Liu [11] who considered the rubberized concrete as a composite of aggregate, rubber and mortar, which however is quite different from the actual rubberized concrete where interfacial transition zones (ITZs) are known to control damage initiation and propagation. Another notable work is by ZH Xie [12], who analysed the mechanical properties of rubberized concrete by a 2D model, where the material contained four phases: aggregate, rubber, mortar, and aggregate-mortar interface. This work, however, omitted explicit representation of the phase with weakest mechanical properties, namely R-M ITZ. Furthermore, 2D analysis is not a reliable approach to studying the complex crack patterns forming in real materials. To the best of our knowledge, a study regarding rubberized concrete as a six-phases material composed of aggregate, rubber, mortar, voids, A-M ITZ, R-M ITZ, in a 3D mesoscale heterogeneous model has not been proposed to date. Such a study would allow for substantially more realistic representation of the rubberized concrete mesostructure and correspondingly more reliable analysis and discussion of its mechanical properties. In this paper, appropriate 3D meso-scale model is proposed and validated using uniaxial tensile tests. The model is used to investigate the crack formation mechanism and mechanical properties of rubberized concrete.

The paper is organised as follows. Uniaxial tension tests of rubberized self-compacting concrete with different rubber particle content are presented in Section 2. Based on the test results, a 3D mesoscale model of rubberized self-compacting concrete is established and presented in Section 3. The parameters and constitutive law of the 3D model are determined by the test results and trial calculations. Model validation is performed in Section 4, where comparison between simulations and experiments is shown. Section 5 presents parametric studies investigating the effects of rubber content on the strength, crack initiation, crack propagation and fracture morphology. Both test results and simulation results show that the toughness of RSCC is improved compared with that of SCC without rubber particle. The incorporation of rubber particles reduces the failure rate of the whole prism and controls the final fracture morphology of the uniaxial tensile cracks of RSCC.