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 modelling of steel-tube confined concrete columns considering confining and bonding effects

The engineering properties of concrete with recycled aggregates (RAC) can vary more widely than normal aggregate concretes (NAC). Because concrete-filled steel tubes do not rely solely on t...

Response and Modeling of Steel Tubes Filled with Recycled Fine and Coarse Aggregate Concretes under Long-Term Loading

The models for the stress-strain relationship under elevated temperatures and thermal properties of recycled aggregate concrete (RAC) are essential in the fire resistance design of RAC structures, while no such models are available for RAC made with fine recycled aggregate (FRA). To establish the above models, 33 RAC prisms with three FRA replacement levels (0%, 50%, and 100%) under five temperatures (20 °C, 200 °C, 400 °C, 600 °C, and 800 °C) were tested for the uniaxial compressive stress-strain relationship; Meanwhile, thermal properties (including the specific heat, thermal conductivity, and thermal expansion) of these concrete mixes under a temperature range of 20–800 °C were also tested. A prediction model for the RAC stress-strain relationship under elevated temperatures was proposed by extending the model for RAC under normal temperature. Based on the test data, models for the thermal properties of RAC with FRA were also established. Results showed that the FRA does not change the shear failure mode of concrete, while decreased the peak stress by up to 33% and elastic modulus by up to 31%; The influence of FRA keeps similar when temperature varies from 20 °C to 800 °C; the specific heat increases by 16% on average while the thermal conductivity decreases by 8%–15% with the FRA replacement ratio increased to 100%; the thermal expansion of concrete under temperature higher than 500 °C decreased by up to 22% when using 100% FRA; the proposed models have good accuracy for the stress-strain relationship and thermal properties of RAC. 

Yue Geng

Papers

Time-dependent modelling of steel-tube confined concrete columns considering confining and bonding effects

Response and Modeling of Steel Tubes Filled with Recycled Fine and Coarse Aggregate Concretes under Long-Term Loading

Models for uniaxial stress-strain relationship and thermal properties of fine recycled aggregate concrete exposed to elevated temperatures

Design formulae for Long-Term responses of continuous Steel-Recycled aggregate concrete composite slabs

Tests and prediction model for time-dependent internal relative humidity of recycled aggregate concrete due to self-desiccation