Jian Zhuang Xiao

Effects of Recycled Coarse Aggregates on the Carbonation Evolution of Concrete

Concrete exposing to atmosphere suffers from changes in its internal structure, for instance loss of alkalinity of the cover concrete and corrosion of steel rebar due to carbonation, which in extreme cases affect the safety, the reliability and the durability or the service life of the structure. Carbonation is one of the key environmental actions that may cause structural failure. This study aims to gain some new information on the carbonation resistance when recycled coarse aggregates are used to mix new concrete. The concrete’s resistance to carbonation is determined by measuring the carbonation depth of 100mm×100mm×300mm concrete prisms in according to GBJ 82-85. Two series of tests including 9 groups of recycled aggregate concrete specimens are carried out, in which the effects of the quality and replacement of recycled coarse aggregates on the carbonation behavior of recycled concrete are evaluated. The essential test results are presented and discussed in this paper. Based on the findings of the present study, in order to reduce the unfavorable effects of recycled coarse aggregates on the recycled concrete, limiting the compressive strength grade of original concrete and the replacement of recycled coarse aggregate is a good option under the condition of using recycled concrete in considered projects.

Micro-Damage Mechanisms and Property Fluctuation of Recycled Aggregate Concrete

In this paper, the basic damage mechanisms and the primary reasons for the property fluctuation of recycled aggregate concrete are investigated experimentally. By a comprehensive literature study and systematic laboratory tests, the interactions between the old and the new interfaces in recycled aggregate concrete are analyzed. In particular, the damage initiation and evolution mechanisms on the old and the new interfaces are studied in details. The essential factors affecting the fluctuation and its extent are investigated from the point of view of material sciences. The present results imply that the qualitative and quantitative changes of the old and the new interfaces during the loading process induce a notable fluctuation of the mechanical and the physical properties of recycled aggregate concrete. To reduce the fluctuation and improve the mechanical properties of the recycled aggregate concrete, effective controlling and processing measures are suggested and discussed.

Study on Recycled Aggregate Concrete Frame Joints with Method of Nonlinear Finite Element

With the achievements made in the research of mechanical properties for recycled aggregate concrete, this paper adopts the method of nonlinear finite element to analyze the seismic behavior of frame joints. The frame joints are made of recycled aggregate concrete. It also takes into account the bond behavior between steel bars and recycled aggregate concrete in the core area of the joints, and the force-displacement curve of the joints is calculated. Nonlinear finite element analysis shows that the results of the calculations are in accordance with the test results. It is concluded in this paper that, built models with nonlinear finite element method can be applied in simulating exactly the same seismic behavior of frame joints under low frequency reversed lateral loading.

Numerical Simulation on Damage and Failure of Recycled Aggregate Concrete with a Lattice Model

A random aggregate model of recycled aggregate concrete is developed in this paper on the base of a mixture ratio. Combining a lattice model with random aggregate of recycled aggregate concrete, lattice elements in the lattice model of recycled aggregate concrete can be classified into five types: (1) nature aggregate, (2) old hardened mortar, (3) new hardened mortar, (4) old interface transition zone (ITZ), and (5) new ITZ. The fundamental mechanical parameters of the lattice elements are chosen from the authors’ test as well as other references. A FORTRAN program of the lattice model is then written with basic theories of finite element method (FEM) for simulating the meso-structural damage of recycled aggregate concrete under uniaxial compression.

The State-of-the-Art Study on Long-Term Property of Recycled Aggregate Concrete

This paper presents a review of the literature on long-term property of recycled aggregate concrete (RAC), which includes the long-term strength, shrinkage, creep, durability and fatigue behavior. Based on many investigations carried out at home and abroad, it can be apparently observed that there are many differences in long-term property between the normal concrete and the RAC. However the long-term property of RAC can be improved and guaranteed by selecting the recycled aggregates replacement percentage, optimizing the mix proportion design, appending fiber or to restrict the environmental conditions. This paper can be helpful to the comprehensive understanding and further research of recycled aggregate concrete.

On Sensitivity of Thermal Parameters for Concrete Box Girder in the Sunshine

In this paper, the temperature field and the thermal effects on a concrete box girder in the sunshine are investigated. For this purpose, the finite element method (FEM) package ANSYS is applied. By varying the values of different thermal parameters, the sensitivity of the thermal parameters is explored. Numerical results are presented and discussed to show the influences of the thermal parameters and the temperature field on the deflection and the tensile stress of a single-span concrete bridge with a box cross section.

Bond Strength and Damage of Long Rebar Anchored in HPC under Static and Fatigue Loading

This paper presents an experimental study on the anchorage behaviour of long high-strength steel rebars embedded in high-performance concrete (HPC) under both static loading and fatigue loading. The HPC was designed as C60 with its cube compressive strength larger than 60 MPa, and the high-strength steel bar was adopted as HRB500 with its characteristic yield strength equals 500 MPa. Under 3×106 fatigue loading cycles and then followed by a monotonous static loading, the strain and the stress state of the reinforcement bar, and the bond stress between the concrete and the 700 mm-long bar were investigated. Based on the test results and the ANSYS finite element analysis, the bond behaviour between HPC and long high-strength steel bars is discussed.

Study on High Performance Concrete at High Temperatures in the past 10 Years

High performance concrete (hereafter, HPC) is well known by its high compressive strength, strong resistance to deformation and excellent durability. Whereas, HPC is prone to spall when exposed to high temperatures and it probably results in sharp reduction of the fire resistance and loading capacity of HPC elements and structures. This paper presents a summary of research achievements on fire-resistance behavior of HPC in the past 10 years including the mechanical behavior degradation, analysis of spalling mechanism, effect of various types of fiber and other factors influencing the post-fire properties of HPC material as well as structural behavior of HPC elements. Studies on micro-structure of HPC have been carried out, which will help build a more sophisticated recognition of its performance under high temperatures. In spite of the large number of research results, more improvement on HPC material and HPC structures are still needed because of the devastating consequences caused by strength degradation or spalling-to-collapse. Thus in this paper a new idea of HPC-composite structures is proposed, expected to decrease the probability of spalling.

Reliability Analysis of High-Strength Concrete Columns during a Fire

A reliability analysis was conducted on high-strength concrete (HSC) columns during a fire. The influences of fire’s randomness and explosive spalling of concrete were investigated. The fire resistance for axial loading capacity of HSC columns was in terms of steel yield strength and concrete compressive strength with considering the effect of elevated temperatures. The load random variables included dead load and sustained live load. The JC method was applied to calculate the reliability index of the fire resistance of axially loaded HSC columns. It was found that the randomness of fire and explosive spalling of concrete had a significant influence on reliability of HSC columns.

Seismic Test on a Damaged Structure with Recycled Concrete Blocks

A man-made damaged model of a one-storey block masonry structure with recycled aggregate concrete (RAC) was tested on a shaking table The Wenchuan earthquake wave, El Centro earthquake wave and Shanghai artificial wave were selected and input to the model with different earthquake levels in the shaking table tests. The recycled aggregate concrete (RAC) block masonry structure was damaged firstly by cutting the tie columns and its seismic behavior was experimentally investigated. The dynamic characteristics, the displacement response, the acceleration response were record. In comparison with the intact model, there is an obvious decrease in the seismic performance of the RAC block masonry man-made damage model.