Cohesion of Fine Recycled Concrete Aggregate: Properties and Applications
The cohesion of fine recycled concrete aggregate (FRCA) is a critical factor influencing its performance in construction applications. As the demand for sustainable building materials grows, understanding the cohesive properties of FRCA becomes essential for optimizing its use in new concrete mixes, road bases, and other engineering applications.
Factors Affecting Cohesion in FRCA
1. Particle Shape and Texture: Unlike natural sand, FRCA often exhibits irregular shapes and rough surfaces due to the crushing process. These characteristics enhance mechanical interlocking, improving cohesion but may reduce workability in fresh concrete.
2. Residual Cement Paste: FRCA contains adhered mortar from its original concrete, which can increase water demand and influence bonding. While this paste may improve cohesion, excessive amounts can lead to higher porosity and reduced strength.
3. Moisture Content: The absorption capacity of FRCA is typically higher than natural aggregates due to its porous structure. Proper moisture conditioning is crucial to prevent premature water loss in mixtures, ensuring adequate cohesion during placement.
4. Gradation and Fines Content: Well-graded FRCA with a balanced proportion of fine particles improves packing density and cohesion. However, excessive fines (e.g., particles <75 μm) can hinder performance by increasing shrinkage and cracking risks.
Enhancing Cohesion for Practical Use
To maximize the benefits of FRCA, several strategies can be employed:
- Pre-Soaking: Saturating FRCA before mixing reduces water absorption during curing, enhancing cohesion and minimizing strength loss.
- Blending with Natural Aggregates: Combining FRCA with natural sand or coarse aggregates balances workability and mechanical properties while maintaining cohesion.
- Chemical Admixtures: Superplasticizers or pozzolanic additives (e.g., fly ash) can mitigate water demand issues and improve the interfacial transition zone (ITZ) between aggregates and new cement paste.
Applications of Cohesive FRCA
FRCA with optimized cohesion is suitable for:
- Structural Concrete: When properly treated, FRCA can replace up to 30% of natural fine aggregates in load-bearing elements without compromising durability.
- Road Sub-Bases: The cohesive nature of FRCA makes it ideal for stabilizing granular layers in pavement construction, reducing settlement risks.
- Masonry Mortars: Finely processed FRCA can enhance bond strength in mortars due to its angular particles and residual cementitious properties