۱- Introduction

۲- Microstructure of RAC

۳- Defects in RAC microstructure

۴-  Enhancement treatments

۵- Conclusions

References

Abstract

Recycled concrete aggregate (RCA) differ from natural aggregate as the former contains attached mortar. Given the recycling process of RCA, that is, by crushing, the microstructure presents several disadvantages, such as porosity, micro-cracks, as well as weak interface transition zones (ITZs), which will also damage the mechanical properties and durability of recycled aggregate concrete (RAC). According to current literature, the microstructure of RAC is mainly affected by ITZs and the porosity of RCA. This paper summarises the principles, advantages and disadvantages of the methods for improving the microstructure of RCA from four aspects, such as removal of attached mortar in the RCA, surface coating on RCA, different mixing methods and CaCO3 precipitation. Methods are also discussed from the aspects of environment, RCA particle size and application, which provide readers with a reference for improving the microstructure of RCA.

Introduction

Since the beginning of the 21st century, with the rapid development of urbanisation and industrialisation, the construction industry has consumed large amounts of natural resources and produced large amounts of construction and demolition waste [1]. The impact on the environment according to Oikonomou [2] is ‘‘Take 50% of raw materials from nature, consume 40% of total energy, and create 50% of total waste”; and construction became the industry with the largest impact on the environment [3]. Concrete is widely used in the construction industry because of its low price, wide application and the ability to take any shape [3,4]. It is a composite material prepared from a certain proportion of cementitious materials, water, aggregates and admixtures [5]. The construction industry produces about 25 billion tons of concrete annually worldwide [6]. Developing countries, such as China and India, which are among the top 10, are the biggest consumers of concrete [3,5].