10mm vs 20mm Aggregate: Why Size Matters?

When choosing aggregate for concrete or construction work, the size makes a massive difference to your project’s strength, workability, and cost. The main difference between 10mm and 20mm aggregate lies in their applications: 10mm aggregate works best for thin sections, detailed work, and smooth finishes, whilst 20mm aggregate suits structural concrete, foundations, and mass concrete where maximum strength matters.

This guide breaks down everything you need to know to make the right choice for your specific project.

What Is Aggregate and Why Size Matters

Aggregate forms the backbone of concrete, making up 60-80% of the mixture. These crushed stone or gravel pieces provide strength, reduce shrinkage, and keep costs manageable.

The nominal size directly affects:

• Concrete strength and durability
• Workability during mixing and pouring
• Surface finish quality
• Material costs
• Pumping requirements

Key Differences Between 10mm and 20mm Aggregate

Size and Grading

10mm Aggregate:

• Nominal maximum size: 10mm
• Passes through 10mm sieve
• Retained on 4.75mm sieve
• More uniform particle distribution

20mm Aggregate:

• Nominal maximum size: 20mm
• Passes through 20mm sieve
• Retained on 10mm sieve
• Wider range of particle sizes

Strength Characteristics

Property	10mm Aggregate	20mm Aggregate
Compressive Strength	Higher (better bonding)	Lower (larger voids)
Flexural Strength	Superior	Good
Surface Area	Higher	Lower
Cement Requirement	More	Less

Why 10mm Often Produces Stronger Concrete:

• Smaller particles create better particle packing
• Increased surface area improves cement-aggregate bonding
• Reduced bleeding and segregation
• More uniform stress distribution

When to Use 10mm Aggregate

Ideal Applications

Structural Elements:

• Beams and columns under 300mm thickness
• Reinforced concrete slabs
• Precast concrete components
• Bridge decks and structural repairs

Specialised Uses:

• High-strength concrete (above M40 grade)
• Architectural concrete with exposed finishes
• Concrete pumping applications
• Decorative concrete work

Thin Sections:

• Any concrete section under 150mm thick
• Wall panels and cladding
• Intricate architectural details
• Areas with dense reinforcement

Advantages of 10mm Aggregate

• Superior workability – easier to place and compact
• Smooth surface finish – ideal for exposed concrete
• Better pumpability – flows through pipes without blocking
• Reduced segregation – maintains uniform mix
• Higher strength potential – better particle interlocking

Disadvantages

• Higher cost – more expensive per cubic metre
• Increased cement demand – requires more paste to coat particles
• Processing costs – more energy needed to crush to smaller sizes

When to Use 20mm Aggregate

Ideal Applications

Mass Concrete Work:

• Foundations and footings
• Mass concrete structures
• Road construction and pavements
• Dam construction
• Large concrete pours

Structural Applications:

• Thick walls (above 300mm)
• Large beams and columns
• Industrial flooring
• Retaining walls

Economic Projects:

• Non-critical concrete work
• Backfill concrete
• Blinding concrete
• General construction where cost matters most

Advantages of 20mm Aggregate

• Cost-effective – lower price per cubic metre
• Reduced cement requirement – less paste needed
• Good for mass concrete – suitable for large pours
• Widely available – easier to source in most areas
• Lower processing costs – less energy to produce

Disadvantages

• Workability issues – harder to place in thin sections
• Segregation risk – larger particles can separate
• Pumping limitations – may block concrete pumps
• Surface finish – rougher texture on exposed surfaces
• Strength limitations – generally produces lower strength concrete

Concrete Mix Design Considerations

Water-Cement Ratio Impact

With 10mm Aggregate:

• Requires lower water-cement ratio for given workability
• Better control over concrete consistency
• Reduced bleeding and segregation

With 20mm Aggregate:

• May need higher water content for workability
• Risk of increased porosity if not carefully controlled
• More prone to segregation during transport

Workability Requirements

10mm Mixes:

• Achieve higher slump with less water
• Maintain consistency longer
• Better for intricate formwork

20mm Mixes:

• Need careful mix design for adequate workability
• May require plasticisers for thin sections
• Best suited for simple, thick sections

Cost Analysis and Economic Factors

Material Costs

Cost Factor	10mm Aggregate	20mm Aggregate
Aggregate Price	15-25% higher	Baseline
Cement Requirement	10-15% more	Standard
Total Mix Cost	8-12% higher	Baseline
Labour Costs	Lower (easier placement)	Higher (more effort)

Long-term Economics

10mm Aggregate Benefits:

• Reduced maintenance due to higher durability
• Better surface quality reduces finishing costs
• Improved pumpability saves labour time
• Higher strength allows thinner sections

20mm Aggregate Benefits:

• Lower initial material costs
• Suitable for large volume pours
• Readily available in most markets
• Standard equipment and practices

Mixing and Placement Guidelines

For 10mm Aggregate Concrete

Mixing:

1. Add aggregate first, then cement
2. Mix dry materials for 30 seconds
3. Add water gradually whilst mixing
4. Mix for 90-120 seconds total
5. Check consistency and adjust if needed

Placement:

• Can be pumped through 100mm diameter pipes
• Suitable for congested reinforcement areas
• Requires normal vibration techniques
• Self-levelling properties in fluid mixes

For 20mm Aggregate Concrete

Mixing:

1. Ensure adequate mixer capacity for particle size
2. Longer mixing times may be required
3. Add water carefully to prevent segregation
4. Check for uniform distribution

Placement:

• Requires 150mm minimum pipe diameter for pumping
• Needs careful handling to prevent segregation
• May require more intensive vibration
• Best placed in lifts to prevent separation

Quality Control and Testing

Key Tests for Both Sizes

Fresh Concrete Tests:

• Slump test for workability
• Density checks
• Air content measurement
• Setting time determination

Hardened Concrete Tests:

• 28-day compressive strength
• Flexural strength testing
• Durability assessments
• Permeability testing

Specific Considerations

10mm Aggregate:

• Monitor for over-mixing
• Check cement content doesn’t exceed requirements
• Ensure adequate curing for high-strength mixes

20mm Aggregate:

• Watch for segregation during transport
• Verify adequate compaction achieved
• Check aggregate gradation regularly

Environmental and Sustainability Factors

Carbon Footprint

10mm Production:

• Higher energy consumption during crushing
• Increased cement requirements raise CO2 emissions
• Transport costs may be higher due to processing locations

20mm Production:

• Lower processing energy requirements
• Reduced cement content lowers carbon footprint
• Often sourced locally, reducing transport emissions

Recycling and Waste

Both sizes can incorporate recycled concrete aggregate, though 10mm recycled material is less common and more expensive to produce.

Common Problems and Solutions

Issues with 10mm Aggregate

Problem: High material costs Solution: Use only where benefits justify extra expense

Problem: Over-vibration leading to segregation Solution: Use shorter vibration periods with high-frequency equipment

Problem: Excessive cement content Solution: Optimise mix design with admixtures

Issues with 20mm Aggregate

Problem: Concrete won’t pump properly Solution: Switch to 10mm or modify pump configuration

Problem: Poor surface finish Solution: Use smaller aggregate near formed surfaces

Problem: Segregation during placement Solution: Reduce drop height and use proper placement techniques

Regional Availability and Standards

UK Standards and Specifications

Both aggregate sizes must comply with:

• BS EN 12620 (Aggregates for concrete)
• BS 8500 (Concrete mix specifications)
• Local authority specifications

Availability Factors

10mm Aggregate:

• May require ordering in advance
• Limited suppliers in rural areas
• Higher transport costs possible

20mm Aggregate:

• Readily available nationwide
• Standard stock item for suppliers
• Competitive pricing due to demand

Making the Right Choice: Decision Framework

Choose 10mm Aggregate When:

• Section thickness under 300mm
• High strength concrete required (M40+)
• Concrete pumping essential
• Exposed surfaces need smooth finish
• Dense reinforcement present
• Architectural quality important

Choose 20mm Aggregate When:

• Mass concrete applications
• Cost is primary concern
• Section thickness over 300mm
• Simple formwork and placement
• Standard strength grades sufficient
• Large volume pours planned

Mixed Aggregate Approach

Sometimes using both sizes together optimises performance:

• 70% 20mm + 30% 10mm for structural concrete
• Improves packing density
• Balances cost and performance
• Reduces cement requirement vs 10mm alone

Frequently Asked Questions

Can I mix 10mm and 20mm aggregate together?

Yes, combining aggregates often improves concrete performance. A typical ratio is 70% coarse (20mm) and 30% fine coarse (10mm) aggregate. This improves particle packing whilst controlling costs.

Which aggregate size is stronger?

10mm aggregate typically produces higher strength concrete due to better particle packing and increased surface area for cement bonding. However, proper mix design matters more than aggregate size alone.

Why is 10mm aggregate more expensive?

10mm aggregate costs more because it requires additional crushing and screening processes. The extra processing energy and reduced yield from quarry operations increase production costs.

Can I pump concrete with 20mm aggregate?

Yes, but you’ll need larger diameter pumping equipment (minimum 150mm) and may face blockage issues. 10mm aggregate pumps more reliably through standard 100mm systems.

Which size is better for foundations?

For most residential foundations, 20mm aggregate provides adequate strength at lower cost. However, for heavily loaded foundations or complex reinforcement layouts, 10mm aggregate offers better placement and strength.

How does aggregate size affect concrete curing?

Larger aggregates like 20mm create more heat during curing in mass concrete, requiring careful temperature control. 10mm aggregate generates less heat and allows more even curing in thicker sections.

What’s the minimum section thickness for each size?

As a rule of thumb, minimum thickness should be 3-4 times the maximum aggregate size. So 30-40mm minimum for 10mm aggregate, and 60-80mm minimum for 20mm aggregate.

Do I need different equipment for each aggregate size?

Most standard concrete equipment handles both sizes, but 20mm aggregate may require larger mixer openings and discharge chutes. Pumping equipment definitely needs different specifications.

Summary and Key Takeaways

Choosing between 10mm and 20mm aggregate depends on balancing performance requirements with project economics. Here’s what you need to remember:

Use 10mm aggregate for:

• Thin concrete sections and detailed work
• High-strength applications
• Concrete pumping projects
• Smooth surface finishes
• Complex reinforcement layouts

Use 20mm aggregate for:

• Mass concrete and foundations
• Cost-sensitive projects
• Thick structural elements
• Standard strength requirements
• Large volume pours

Key considerations:

• 10mm typically produces 10-15% higher strength
• 20mm aggregate reduces material costs by 8-12%
• Workability and placement requirements often determine the choice
• Local availability affects practical decision-making

The right choice comes down to understanding your specific project requirements, budget constraints, and performance expectations. When in doubt, consult with your concrete supplier or structural engineer to optimise your mix design for the best results.

For more detailed technical specifications, refer to the Concrete Society’s technical reports or consult BS EN 206 standards for comprehensive concrete specifications.