Recycled Aggregate Concrete Structures

This chapter introduces the basic strategy and possible procedure for recycled aggregate concrete (RAC) from a viewpoint of sustainable development of building industry. It then follows the advancement of the concrete recycling idea which is based on literature review. The outline of this book is also described at the end of this chapter.

In this chapter, the sources, quantity and classification of waste concrete are described and analyzed. The methods for reducing waste concrete are introduced. Furthermore, the reclaim of waste concrete, including reusing recycling philosophy and technology is described and discussed.

This chapter will mainly introduce the crushing and sieving techniques used around the world, the properties of recycled fine aggregate (RFA) and recycled coarse aggregate (RCA), the adhered old mortar and its influence on the properties of recycled aggregate concrete (RAC) and methods of pre-treating and enhancing techniques. This is fundamental to understand the differences between natural aggregate concrete (NAC) and RAC, and it is the basic premise for further studying the  behavior of the RAC materials and structures.

Worldwide research has shown that there exist clear differences between properties of recycled coarse aggregates (RCA) and those of natural coarse aggregates (NCA), such as porosity, water absorption, low surface density, higher crush value. According to the specific performance requirements of concrete, choosing appropriate raw materials, then designing the most economic, high-quality concrete based on the proper mix proportion methods, is the best way to overcome the shortcomings of the traditional design methods, and this puts forward new thoughts and design method.

Based on the microstructure analysis, recycled aggregate concrete (RAC) can be described as a five-phase composite that consists of natural aggregates (NA), old interfacial transition zone (old ITZ), old mortar, new interfacial transition zone (new ITZ) and new mortar. Due to the relatively low quality of the ITZs and old mortar compared to other phases, new micro cracks normally occurred in these regions first when RAC was under loading. Modeled recycled aggregate concrete (MRAC) which was composed of the new mortar matrix and some circular recycled coarse aggregate (RCA) discs embedded in a rectangular array. It is demonstrated that MRAC can be used to investigate the relation between the mesostructure of each phase and the mechanical behavior including static and dynamic as well as chloride diffusion properties of RAC. The obtained results indicated that the fracture process and crack pattern of MRAC were greatly affected by the relative strength of new mortar and old mortar. It was also found that the failure pattern of RAC was related to the water to cement ratio of the mixture.

This chapter intensively studied the strength indexes of recycled aggregate concrete (RAC), which includes the RAC compressive strength, tensile strength, flexural strength, the relationship of the conversion coefficients of RAC mechanical index, and the effects of elevated temperatures on the RAC strengths. The research results in this chapter are very important and useful for comprehensively understanding RAC material’s mechanical properties and their differences with natural aggregate concrete (NAC).

This chapter investigates the constitutive relationships of recycled aggregate concrete (RAC), including the static compressive stress–strain curve without/with confinements (confined by steel tubes and by glassfiber-reinforced plastic tubes) under axial compressive loading, the tensile stress–strain curve of RAC under axial tension loading, the shear transfer behavior across cracks of RAC as well as the compressive behavior of RAC under high strain rate loading. The influences of recycled coarse aggregate (RCA) influences strength, elastic modulus, peak and ultimate strength of RAC were evaluated. For the case of dynamic constitutive relationship of RAC, the effects of strain rate on failure pattern, compressive strength, initial elastic modulus, and peak strain were studied. Based on the constitutive relationships of RAC in this chapter, the related simulation studies can be executed.

This chapter analyzes the long-term properties of recycled aggregate concrete (RAC), including shrinkage, creep, carbonation resistance, chloride diffusion resistance, and fatigue behavior. Most studies have shown that the long-term properties of RAC are inferior to those of natural aggregate concrete (NAC), and some indicated that the long-term properties are better than those of NAC. RAC’s long-term properties are influenced by many factors such as recycled coarse aggregate (RCA) replacement percentage, water–cement (w/c) ratio, and mineral admixtures. The long-term properties of RAC can be improved through better control of these factors. This chapter will be helpful for a comprehensive understanding of and further research on RAC and provides an important basis and references for the engineering applications of RAC.

To popularize the recycled aggregate concrete (RAC) in civil engineering, sometimes it should be reinforced with steel bars. One of the most important requirements of reinforced concrete constructions is the bond between concrete and reinforcement. This chapter will consider the RAC replacement percentage and the steel rebar type including normal rebars and eroded rebars as the main experimental parameters. The aim of this work is to investigate the bond behavior between RAC and steel rebars and to establish a bond stress versus slip relationship between RAC and steel rebars.

This chapter focus on the basic structural behavior of recycled aggregate concrete (RAC) components, which includes the bending and shear behavior of RAC beam, the flexural and shear behavior of RAC semi-precast beam, the flexural behavior of RAC gradient slab, the punching shear behavior of steel fiber reinforced RAC slab, the behavior of RAC column under eccentric compression. The suitability of the code formulae to calculate RAC’s bending and shear capacity was verified, and based on this, a reliability analysis for RAC elements was carried out, investigating RAC beam bending moment and shear capacity reliability, analyzing the cracking patterns, deflections, bearing capacities of U, and C-typed semi-precast beams, studing the gradient slabs through experiment and the FEM analysis, analyzing the effectiveness of both recycled aggregate replacement percentage and steel fiber volume ratio when it refers to the punching shear of the slab, and carring out the reliability analysis of RAC column under axial compression and eccentric compression loading.

In this chapter, the studies on the seismic performance of recycled aggregate concrete (RAC) columns and confined RAC columns are performed. The main parameters in these studies are recycled coarse aggregate (RCA) replacement percentage, construction sequence, bond–slip effect, and confinement. Based on these investigations, failure pattern, hysteresis curves, skeleton curves, energy dissipation, and stiffness deterioration laws of RAC columns and confined RAC columns are analyzed. The RCA effect on seismic performance of columns is significant. The construction sequence can also affect the seismic behavior of columns. It was discovered that the confinement obviously improved the seismic performance of RAC columns.

In this chapter, the seismic performance of recycled aggregate concrete (RAC) frame joints, plane frame, cast-in-situ space frame, and precast space frame was discussed. The detailed conclusion can be found in the following sections. Generally speaking, the failure modes of RAC structures are similar to those of natural aggregate concrete (NAC) structures, but the seismic performance is slightly lower.

The experimental study was focused on the seismic performance of recycled aggregate concrete (RAC) hollow block walls confined by ring beam and tie column under low cyclic horizontal loading. Investigations on the damage process, failure mode, load-bearing, and deformation capacity show that the hollow block wall with RAC has favorable displacement ductility and energy dissipation capacity. Furthermore, the contribution of ring beam-tie column system to the seismic performance of RAC hollow block walls was also examined. The results show that the vertical compression stress of RAC hollow blocks is the main factor influencing the seismic performance, whereas the reinforcement ratio for ring beams and tie columns only has limited effects. Compared with the hollow block wall with NAC, the hollow block wall with RAC has similar seismic performance. Furthermore, a full-scale model of a RAC block masonry building with the tie column + ring beam + cast-in-situ slab system, was tested on the MTS shake table. The natural frequency, equivalent stiffness, structural damping ratio, acceleration response, seismic force response, displacement response, base shear response, structural fragility, etc. were analyzed and discussed. The test results demonstrate that RAC block masonry structure confined by the “tie column + ring beam” system is a good solution to withstanding earthquakes. The storey drift ratio and the overall behavior satisfy requirements of the Chinese design code. Generally, RAC block masonry structure bounded by the tie column-ring beam system with proper design exhibits good seismic behavior and can resist earthquake attacks under different seismic levels.

In this chapter, the premix recycled concrete and recycled aggregate mortar are introduced from the viewpoint of strength, slump, pumping performance and other technical points firstly. Then the precast products of recycled aggregate concrete (RAC), such as the brick, block, hollow block masonry and panel are introduced, and all of these products are investigated for application in real engineering project. The performance of mentioned RAC products and construction method has been evaluated through some case studies including pavements—Fudan Road, cast-in-situ frame, precast RAC frame, RAC masonry structure, steel frame filled with recycled aggregate bricks and RAC frame-shear wall in high-rise building. The results indicated that the RAC is feasible to be used in engineering. Finally, the construction of RAC is analyzed from the aspects of economic benefits, environmental benefits, and management strategies. The quality control of RAC products and scientific management of construction of RAC will ensure the application of RAC on a wider scale.

At present, many countries and regions worldwide have already formulated recycled concrete technology standards and guidelines. This chapter is based on the research results from the aforementioned chapters and the recycled concrete practical work. In brief, the recycled concrete applied technology guidelines will help in the application of recycled aggregate concrete material and structures.