presentation

This study analyzes the eco-design of concrete using a hybrid binder (HB) combined with recycled aggregates (RA) to mitigate CO2 emissions.
Focus on the impact of different RA percentages and binder types on technical performance metrics such as compressive strength (CS), carbonation (DC), and chloride migration (DCl).
Results show that the percentage of RA is more significant than the binder type in influencing concrete performance.

Incorporation of concrete design parameters in functional units shows carbon footprint reductions between 10-60% for HB when considering strength and transport properties.
Optimizing RA percentages is crucial for achieving environmental benefits.

Historical work indicates sodium sulfate activation can enhance CS in high GGBFS mixtures, influencing early-age properties without altering binder quantities.
Activators, particularly sodium sulfate, play a vital role in enhancing strength through their interaction with binders and facilitating the formation of beneficial phases at early ages, leading to a denser microstructure.

Use of RAs in Europe is becoming standard due to the aim of a circular economy.
However, RAs are often limited to low percentages in structural concrete due to concerns about quality.
Durability studies on RA concrete yield variable results based on RA quality and mix design.

Emphasizing the need for studies at the concrete level, the paper aims to evaluate microstructure and transport properties across mixes with varying RA contents compared to commercial CEM III/B.
The use of sophisticated packing techniques can optimize the performance of concrete while minimizing carbon footprint.

Binders used include CEM III/B, CEM I N, and GGBFS, with sodium sulfate serving as the activator.
Natural aggregates alongside RA made from C&DW have been employed, influencing water absorption rates and mix density.
Adjustments in mix designs took into account the morphology and absorption characteristics of RAs.

Ultrasonic Pulse Velocity (UPV): Measuring setting and hardening phases to assess early strength development and microstructural changes.
Compressive Strength (CS): Evaluated against standard cubic samples at various hydration durations.
Water Absorption and Density Tests: Used to determine permeability and overall mix density over time.
Rapid Chloride Migration and Resistivity Tests: Assessing durability and electrical resistance indicative of corrosion risks.
Water Penetration Tests: Conducted to evaluate the effectiveness of barrier properties.
Natural Carbonation Measurements: Analyzed to measure penetration depth of CO2.
Life-Cycle Assessment (LCA): Used to evaluate the environmental impacts of concrete mixes throughout their life cycle, particularly focusing on CO2 emissions.

Enhanced workability and better slump ratings were noted in the hybrid binder mixes compared to CEM III/B due to the activator's effect.
Densities decreased with RA; however, concrete produced with the hybrid binder maintained superior densities relative to mixed CEM III/B outcomes.

Hybrid systems yielded significantly greater CS, especially at early hydration stages.
RA inclusion adversely affected strength metrics noted from 7 days onwards, highlighting binders' maxima in mitigating this reduction.

Analyses of pore structures revealed that while porosity increased with RA content, hybrid binds performed slightly better than CEM III/B in water absorption and permeability indicators, revealing resilient bond capacities.

Tested concretes meet high standards for chloride diffusion and exhibit low corrosion risk.
Carbons showed increased rates with RA; however, the hybrid mix corruption remained lower than CEM III/B mixes, suggesting structural integrity remains firmer.

Approximately 75% of total CO2 emissions stems from binder production, revealing the importance of selecting eco-efficient binding materials.
The study concluded that while replacing natural aggregates with RA has limited direct benefits, it plays a role in resource efficiency and landfill reduction.
Effective strategies combining RA usage with hybrid binders can lead to significant sustainability advancements, making them viable alternatives in low-carbon concrete production.

The incorporation of higher RA percentages lowers the concrete density but enhances life-cycle sustainability when paired with the hybrid binder.
The HB yields higher early-age performance while maintaining quality comparable to CEM III/B under durability assessments.
Combined strategies towards lower carbon output alongside circular economy principles show promising results in creating refined concrete qualities.