Self-Compacting Concrete Utilizing Recycled Aggregates

Self-compacting concrete (SCC) represents a key innovation in modern construction, combining high fluidity with stability to fill formwork under its own weight without mechanical vibration. The incorporation of recycled concrete aggregate (RCA) into SCC addresses critical sustainability challenges by reusing construction and demolition waste, reducing demand for virgin materials and lowering carbon footprint. RCA differs from natural aggregate in water absorption, surface texture and adhered mortar content, factors that influence fresh-state rheology, setting time and hardened-state properties. Optimising mix designs often requires adjustments in water-to-binder ratio, dosages of superplasticiser and incorporation of supplementary cementitious materials such as fly ash or silica fume. Research has demonstrated that partial replacement of natural coarse and fine aggregates with RCA can achieve comparable workability and adequate compressive strength for structural and non-structural applications, provided that mix proportions and quality control protocols are rigorously applied. The global relevance of this approach spans emerging economies managing large volumes of demolition waste and advanced markets aiming for circularity in high-performance concrete elements, from densely reinforced frames to precast panels. Current advances emphasise predictive modelling, standardisation of RCA processing and synergistic use of mineral admixtures to mitigate strength reductions and durability concerns such as permeability and shrinkage.

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Research from all publishers

A recent experimental investigation assessed self-compacting concrete incorporating high volumes of fly ash alongside varied levels of coarse RCA (0–100%). The study confirmed that mixes containing 50% fly ash and up to 100% RCA met recognised flowability criteria, though compressive strength and flexural strength decreased by around 4–5% and 3% respectively. Chloride permeability rose but remained within low-permeability thresholds, illustrating a viable pathway for high-fly-ash SCC with full RCA substitution.

A predictive framework based on effective porosity indices has been introduced to estimate key mechanical properties of RCA-SCC. By correlating capillary-water-absorption-derived porosity with compressive strength, modulus of elasticity and tensile and flexural strengths, regression models achieved accuracy margins of ±10–20% across mixes containing 0–100% coarse and fine RCA. This approach enables practitioners to forecast performance without exhaustive testing and to tailor RCA fractions to target structural requirements.

In a feasibility study of European recycling protocols, SCC production with 20%, 50% and 100% coarse RCA was evaluated against a natural aggregate control. Results highlighted only minor reductions in fresh-state self-compactability and mechanical strengths up to 50% substitution. Even at full replacement, compressive and tensile strengths remained within acceptable ranges for conventional and densely reinforced elements. This work underlines the importance of standardised RCA processing to harmonise quality and to facilitate widespread adoption of circular concrete solutions.

Self-Compacting Concrete Utilizing Recycled Aggregates publication trend

The graph below shows the total number of articles in self-compacting concrete utilizing recycled aggregates across all publications each year (not limited to Nature Index journals).

Technical terms

Self-Compacting Concrete (SCC): A highly flowable concrete that spreads into place and encapsulates reinforcement without vibration.

Recycled Concrete Aggregate (RCA): Crushed material derived from demolition concrete used to replace natural aggregate.

Workability: The ease with which fresh concrete can be mixed, placed and finished without segregation.

Porosity Index: A metric reflecting the volume fraction of voids in hardened concrete, influencing mechanical and transport properties.

Supplementary Cementitious Material: Industrial by-product (e.g. fly ash, silica fume) used to partially replace Portland cement and enhance durability.

References

1. The Influence of Recycled Coarse Aggregate Content on the Properties of High-Fly-Ash Self-Compacting Concrete. Civil Engineering Journal (2024).
2. Porosity-based models for estimating the mechanical properties of self-compacting concrete with coarse and fine recycled concrete aggregate. Journal of Building Engineering (2021).
3. Recycling Aggregates for Self-Compacting Concrete Production: A Feasible Option. Materials (2020).