Using recycled aggregate s from construction and demolition waste can preserve natural aggregate resources, reduce demand of landfill, and contribute to sustainable built environment. This study provides a comprehensive review on recycled aggregate (RA) and recycled aggregate concrete (RAC) regarding their history, recycling, reuse and manufacture process, inherent defects (e.g. existing of additional interfacial transition zones in RAC), and materials properties. Specifically, these properties of RAC include fresh concrete workability, physical and chemical properties (i.e. density, carbonation depth, and chloride ion penetration), mechanical properties (i.e. compressive, flexural, and splitting tensile strength as well as elastic modulus), and long-term performance (i.e. freezing-thawing resistance, alkali-silica reaction resistance, creep, and dry shrinkage). On top of that, methods for improving RAC mechanical properties and long-term performance are summarized and categorized into three groups, i.e. (1) reduction of recycled aggregate porosity, (2) reduction of old mortar layer on recycled aggregate surface, and (3) property improvement without recycled aggregate modification (i.e. different concrete mixing design and addition of fibre reinforcement). Next, current regression-based models and artificial intelligence models on the prediction of compressive strength, modulus, and compressive stress-strain curves of RAC are reviewed and the ir limitations of those models are discussed. Furthermore, the state-of-the-art RAC applications are presented. Additionally, challenges of RAC application are reviewed taking China as an example. The link between material from CDW and EU green policy are discussed by analysing the previous research projects funded by European Commission. Finally, future perspectives of RAC research focus are discussed, i.e. development of “green” treatment methods on recycled aggregate s , further direction on nanoparticle application in RAC, and the establishment of database for RAC strength prediction.

A Comprehensive Review on Recycled Aggregate and Recycled Aggregate Concrete

Influence of the incorporation of recycled coarse aggregate on water absorption and chloride penetration into concrete

Recycled aggregate concrete is used as an alternative material in construction engineering, aiming to environmental protection and sustainable development. However, the compressive strength of this concrete material is considered as a crucial parameter and an important concern for construction engineers regarding its application. In the present work, the 28-days compressive strength of recycled aggregate concrete is investigated through four artificial intelligence techniques based on a meta-heuristic search of sociopolitical algorithm (i.e. ICA) and XGBoost, called the ICA-XGBoost model. Based on performance indices, the optimum among these developed models proved to be ICA-XGBoost model. Namely, findings demonstrated that the proposed ICA-XGBoost model performed better than the other models (i.e. ICA-ANN, ICA-SVR, and ICA-ANFIS models) in estimating compressive strength of recycled aggregate concrete. The suggested model can be used in construction engineering in order to ensure adequate mechanical performance of the recycled aggregate concrete and allow its safe use for building purposes.

A novel artificial intelligence technique to predict compressive strength of recycled aggregate concrete using ICA-XGBoost model

Testing and analysis of axially loaded normal-strength recycled aggregate concrete filled steel tubular stub columns

This paper discusses the state-of-the-art of the fine recycled concrete aggregates (fRCA), focusing on their physical and chemical properties, engineering properties and durability of concretes with fRCA. Based on the systematic review of the published literature, it is impossible to deduce without any further research the guidelines and tools to introduce the widespread application of the fRCA in new concrete whilst keeping the cement contents at least the same or preferably lower. Namely, what is still missing is knowledge on key physico-chemical properties and their relation to the quality of the concrete mix and the concrete performance. This paper sets the foundations for better understanding the quality of fRCA obtained either from parent concrete specifically produced in the laboratory, with controlled crushing and sieving of the recycled aggregates or from field structures. By comparing properties of fRCA with properties of fine natural aggregates, the key limiting properties of fRCA are identified as the high water absorption of fRCA, moisture state of fRCA, agglomeration of particles and adhered mortar. As such, continuous quality of fRCA is hard to be obtained, even though they may be more continuous in terms of chemistry. Advanced characterization techniques and concrete technology tools are needed to account for limiting properties of fRCA in concrete mix design.

Use of fine recycled concrete aggregates in concrete: A critical review

Time-dependent behaviour of expansive concrete-filled steel tubular columns

Prediction of the elastic modulus and the splitting tensile strength of concrete incorporating both fine and coarse recycled aggregate

This study aims to develop a drying shrinkage model for recycled aggregate concrete (RAC) using both fine and coarse recycled aggregate (termed FRA and CRA, respectively). An experiment was conducted to measure the drying shrinkage of RAC with varying replacement ratios of CRA (0%, 50%, and 100%) and two types of FRAs (0%, 50%, and 100%). Test results show that: (1) both FRA and CRA have significant influence on the development of drying shrinkage, (2) the influence of FRA on the development of drying shrinkage decreases with increasing content of CRA, and (3) the influence of FRA on the final drying shrinkage is almost independent of the CRA. For example, the use of 100% FRA results in an increase of 23%–41% for concrete with 0% CRA. Similarly, 100% FRA results in 29%–38% increase for concrete with 100% CRA. Based on the results, a new model with two influence factors is proposed accounting for the influence of recycled aggregate on the development of drying shrinkage and on the final value of drying shrinkage of RAC; the expression was validated using a database of RAC shrinkage test data.

Yue Geng

Papers

Testing and analysis of axially loaded normal-strength recycled aggregate concrete filled steel tubular stub columns

Time-dependent behaviour of expansive concrete-filled steel tubular columns

Prediction of the elastic modulus and the splitting tensile strength of concrete incorporating both fine and coarse recycled aggregate

Time-dependent drying shrinkage model for concrete with coarse and fine recycled aggregate

Creep behaviour of concrete using recycled coarse aggregates obtained from source concrete with different strengths