Self-Compacting Concrete Mix Design: SCC Tests, Proportioning and Trial Procedure

Self-compacting concrete (SCC) is designed to flow under its own weight, fill formwork and pass through reinforcement without mechanical vibration. Unlike conventional concrete, SCC must achieve a suitable balance between filling ability, passing ability, viscosity and segregation resistance. This article explains SCC mix proportioning with an illustrative M30 calculation, aggregate moisture correction, laboratory trial batching and fresh-concrete tests.

Self-compacting concrete, or SCC, flows under its own weight, fills formwork and passes through reinforcement without mechanical vibration. It must also remain uniform, with the coarse aggregate distributed throughout the concrete.

SCC is useful for congested reinforcement, complicated formwork, walls, columns and precast elements where conventional compaction is difficult.

However, SCC requires more than a high slump-flow value. Its materials and proportions must provide suitable flow, passing ability, viscosity and resistance to segregation.

This article explains SCC mix design in simple language, including an illustrative M30 calculation, moisture correction, laboratory batch quantities and fresh-concrete test procedures.

What Makes Concrete Self-Compacting?

SCC must provide four related fresh-concrete properties.

A mix may spread widely but still block between reinforcing bars. Another mix may pass through reinforcement but allow aggregate to settle.

The selected mix must satisfy the combination of properties required for its intended placement.

Standards and References

For Indian projects, relevant references include:

Use the applicable editions, amendments and project requirements. When different references use different apparatus or classification systems, do not combine their procedures or limits without an approved basis.

Materials Used in SCC

Cement and supplementary cementitious materials

Cement provides binding action. Fly ash, GGBS, silica fume or other approved supplementary cementitious materials may contribute to strength development, durability and fresh-concrete behaviour.

Their suitability depends on the material properties, replacement level and project requirements.

Powder and filler

Powder and cementitious material are not necessarily the same.

In SCC terminology, powder includes particles smaller than 0.125 mm. Depending on the materials, this can include cement, supplementary cementitious materials, filler and part of the aggregate fines.

An inert filler contributes to the powder volume but should not automatically be counted as cementitious material when calculating the water–cementitious material ratio.

Fine aggregate

Fine aggregate contributes to the mortar that carries coarse aggregate through the formwork.

Check its grading, particle shape, fines, absorption and moisture content. Variations in sand moisture can significantly change SCC behaviour.

Coarse aggregate

Select the aggregate size and quantity to suit reinforcement spacing, cover, member geometry and the flow path.

Excessive coarse aggregate can cause blocking. Reducing it too much can increase paste demand and cost.

Superplasticizer

A suitable high-range water-reducing admixture helps achieve flow while controlling water content.

Select the dosage through compatibility checks and trials using the actual cement, supplementary cementitious materials and aggregates.

Viscosity-modifying admixture

A viscosity-modifying admixture, or VMA, may help improve stability.

It is not compulsory in every SCC mix. A suitable powder system and aggregate grading may provide adequate stability without it.

Information Required Before Mix Design

Establish the following before calculating quantities:

• Concrete grade and target mean strength.
• Exposure conditions and durability limits.
• Cement and supplementary cementitious material types.
• Aggregate size, grading, specific gravity and absorption.
• Aggregate moisture content.
• Required slump-flow, viscosity, passing ability and segregation resistance.
• Transport, waiting and placing time.
• Pumping requirements.
• Admixture properties and recommended dosage range.
• Strength-testing ages and acceptance requirements.

The approved requirements should reflect the actual member and construction method.

SCC Mix-Design Procedure

A practical sequence is:

1. Define strength, durability and fresh-concrete requirements.
2. Select the materials and aggregate size.
3. Select a preliminary water–cementitious material ratio.
4. Estimate water, binder and admixture quantities.
5. Select a preliminary coarse aggregate volume.
6. Calculate fine aggregate using the absolute-volume method.
7. Correct aggregate and added-water quantities for moisture.
8. Prepare laboratory trials.
9. Check fresh properties, retention, density and strength.
10. Adjust the mix and verify it under production conditions.

The calculations produce a starting mix. Trials establish whether that mix actually behaves as SCC.

Worked Example: Preliminary M30 SCC Mix Design

The following calculation illustrates the method. It is not a construction-approved mix.

1 Assumed design information

The air content and coarse aggregate volume are preliminary assumptions. They must be checked through testing and trial performance.

The exposure condition is not specified in this example. Therefore, durability compliance must be checked separately before adopting any proportions.

2 Material properties

SSD means saturated surface-dry: the aggregate pores are filled with water, but there is no free surface water.

Use measured properties for the actual materials.

3 Calculate target mean strength

For this example, compare:

Target mean strength = fck + 1.65S

= 30 + (1.65 × 5)

= 38.25 MPa

Also:

Target mean strength = fck + X

= 30 + 6.5

= 36.50 MPa

Adopt the higher value:

Target mean strength = 38.25 MPa

This target allows for strength variation. It is different from the specified characteristic strength of 30 MPa.

4 Check the water–cementitious material ratio

Total cementitious material:

350 + 150 = 500 kg/m³

Therefore:

w/cm = 190 ÷ 500

w/cm = 0.38

This is a trial selection. Strength results must establish whether it is suitable for the actual materials.

The use and proportion of fly ash must also satisfy the applicable project and durability requirements.

5 Account for water in the liquid admixture

Assumed admixture water:

5 × 0.60 = 3 kg/m³

Therefore, for aggregates in SSD condition:

Separate mixing water = 190 − 3

Separate mixing water = 187 kg/m³

The assumed 60% water content must be replaced with reliable product information.

In the volume calculation below, the full liquid admixture volume is included. Its water is therefore excluded from the separate-water volume to avoid double counting.

6 Calculate absolute volumes

For a solid material:

Absolute volume = Mass ÷ (Specific gravity × 1,000)

For the liquid admixture:

Volume = Mass ÷ Density

Fine aggregate volume:

1.000000 − 0.690923 = 0.309077 m³

7 Calculate aggregate masses

Fine aggregate, SSD:

0.309077 × 2.65 × 1,000

= 819.06 kg/m³

Coarse aggregate, SSD:

0.300000 × 2.70 × 1,000

= 810.00 kg/m³

8 Preliminary quantities on an SSD basis

The effective free water is 190 kg/m³, including 3 kg/m³ assumed to come from the admixture.

The calculated total batch mass is approximately 2,321 kg/m³. This is a theoretical value; actual fresh density and yield must be measured.

Aggregate Moisture Correction

The laboratory calculation uses SSD aggregate quantities. Actual aggregates may contain more or less water.

For this example, assume:

Both absorption and total moisture percentages are expressed relative to oven-dry aggregate mass.

Use:

Oven-dry mass = SSD mass ÷ (1 + absorption fraction)

Wet batch mass = Oven-dry mass × (1 + total moisture fraction)

Free surface water = Oven-dry mass × (moisture fraction − absorption fraction)

1 Fine aggregate correction

Oven-dry mass:

819.06 ÷ 1.01 ≈ 810.95 kg

Wet batch mass:

810.95 × 1.04 ≈ 843.38 kg

Free surface water:

810.95 × (0.04 − 0.01) ≈ 24.33 kg

2 Coarse aggregate correction

Oven-dry mass:

810.00 ÷ 1.005 ≈ 805.97 kg

Wet batch mass:

805.97 × 1.01 ≈ 814.03 kg

Free surface water:

805.97 × (0.01 − 0.005) ≈ 4.03 kg

3 Correct the separately added water

Water to add:

190 − 3 − 24.33 − 4.03

= 158.64 kg/m³

4 Moisture-corrected batch quantities

Check the effective water:

158.64 + 24.33 + 4.03 + 3.00 = 190.00 kg/m³

The water–cementitious material ratio remains:

190 ÷ 500 = 0.38

Repeat the correction whenever aggregate moisture changes. These wet batch quantities apply only to the assumed moisture conditions.

Laboratory Trial-Batch Quantities: Example for 0.05 m³

Concrete proportions are normally expressed per cubic metre. Laboratory quantities are obtained by multiplying them by the chosen batch volume.

For an illustrative 0.05 m³ batch, equivalent to 50 litres:

Batch quantity = Quantity per m³ × 0.05

Use suitable weighing equipment and round quantities only within the approved batching accuracy.

A 50-litre batch is an example, not a mandatory Indian standard batch size.

Choose the batch volume according to mixer capacity, fresh-concrete tests, specimens, repeat testing and handling losses.

For example, one 150 mm cube has a volume of:

0.15 × 0.15 × 0.15 = 0.003375 m³

Six cubes require:

6 × 0.003375 = 0.02025 m³, or 20.25 litres

Fresh-property tests require additional concrete. A 50-litre batch may therefore be insufficient for the full testing programme and six cubes. Plan a larger batch where necessary, and do not return tested concrete to the specimen-making sample.

SCC Test Procedures

The following are short procedure summaries. Use the complete specified standard for apparatus dimensions, sampling and reporting.

1 Slump-flow and T500

Slump-flow measures horizontal spread. T500 indicates the time required to reach a 500 mm spread.

Procedure

1. Level, clean and dampen the plate and cone; remove excess water.
2. Centre the cone, fill without compaction and strike level.
3. Clear spilled concrete within 30 seconds.
4. Lift vertically in 1–3 seconds.
5. Time from cone separation until concrete first touches the 500 mm circle.
6. Measure the final largest diameter and its perpendicular; repeat with a new sample if their difference exceeds 50 mm.

Calculation

Slump-flow = (D₁ + D₂) ÷ 2

For D₁ = 690 mm and D₂ = 710 mm:

Slump-flow = 700 mm

Record T500 separately.

2 V-funnel

The V-funnel indicates flow behaviour through a restricted opening.

Procedure

1. Clean and dampen the funnel; close its gate.
2. Fill without compaction, strike level and position a receiving container.
3. Wait 10 ± 2 seconds, then open the gate.
4. Record the time until the opening first becomes visible from above, to 0.1 second.

For example, report a measured time as 9.4 seconds. Compare it with the specified requirement.

3 L-box

The L-box assesses passing ability through bars.

Procedure

1. Level the box and close the gate.
2. Fill the vertical compartment and wait 60 ± 10 seconds.
3. Open the gate smoothly.
4. After flow stops, determine mean depths behind the gate, H₁, and at the far end, H₂, from three readings across each location.
5. Calculate H₂ ÷ H₁.

For H₁ = 100 mm and H₂ = 88 mm:

Passing ratio = 0.88

IS 1199 (Part 6):2018 covers the three-bar arrangement. Identify the arrangement in the report.

4 Sieve segregation

Procedure

1. Cover 10 ± 0.5 litres of concrete; rest 15 ± 0.5 minutes.
2. Note bleeding.
3. Pour 4.8 ± 0.2 kg, including bleed water, onto a 4.75 mm sieve, with the container top 500 ± 50 mm above it.
4. After 120 ± 5 seconds, lift without agitation and weigh the passed material.

Segregation (%) = passed-material mass ÷ poured-concrete mass × 100.

For 480 g passing from 4,800 g:

Segregation = 10%

Subtract the receiver mass when calculating the passed-material mass.

5 Additional tests

Use J-ring or U-box testing when required by the specification. Their apparatus, measurements and acceptance criteria must follow the selected method.

Visual observations are also useful, but they do not replace a specified quantitative segregation test.

Interpreting Trial Results

Define acceptance requirements before comparing trials.

For illustration only, suppose a project specifies:

These are example project requirements, not universal SCC limits.

Suppose three trials produce:

Under these assumed requirements:

• Trial A fails the flow, T500 and passing requirements.
• Trial B satisfies the four listed requirements.
• Trial C exceeds the flow and segregation limits.

Trial B can proceed to further verification. These fresh results alone do not establish strength, durability, workability retention or production suitability.

Troubleshooting SCC Trials

Change one variable at a time where practical and record the effect. Adding water without checking the resulting water ratio can invalidate the trial.

Workability Retention and Strength Verification

Test the mix at times that represent transport, waiting, pumping and placement.

For example, laboratory observations may be planned at initial mixing, 30 minutes and 60 minutes. The actual intervals should match the project.

Record any approved admixture adjustment and repeat the relevant checks afterward.

Prepare and cure strength specimens using the applicable procedure for SCC. Check the specified ages, including later ages where required for the binder system.

A satisfactory initial flow does not establish that the concrete will remain suitable until placement.

Production Trials and Site Control

A laboratory mix must be verified using the actual production equipment and delivery process.

Production trials should check:

• Batching and admixture-dosing accuracy.
• Mixer performance and mixing time.
• Aggregate moisture correction.
• Concrete temperature and workability retention.
• Fresh density and yield.
• Pumping and placement behaviour.
• Specified fresh and hardened properties.

Maintain a traceable record linking the approved mix, batch quantities, delivery, test samples and results.

Reassess the mix when significant changes occur in material source, aggregate grading, admixture product or production conditions.

Formwork, Placement and Curing

Formwork

Provide tight joints and adequate support.

SCC can impose substantial fresh-concrete pressure. Formwork design should normally allow for full hydrostatic pressure unless a justified alternative is established. Bottom-up pumping can create additional local pressure.

Placement

Use a controlled discharge rate and an approved placing sequence. Limit free fall and horizontal travel according to the verified method.

SCC should fill the formwork without routine mechanical vibration. Investigate poor filling rather than assuming vibration will correct an unsuitable mix.

Curing

Begin curing promptly using the specified method.

Self-compaction does not remove the need for curing. Protect exposed surfaces from moisture loss and maintain the required curing conditions.

Recommended SCC Trial Record

Frequently Asked Questions

Is M30 SCC a fixed mix ratio?

No. M30 identifies the strength grade. SCC proportions depend on the materials, durability requirements and fresh-concrete performance.

Is VMA compulsory?

No. Use it when trials show that additional viscosity control is needed and the selected product is suitable.

Can SCC be pumped?

Yes, but pumpability should be verified for the actual equipment, pipeline and placement conditions.

Is 50 litres the standard laboratory batch size?

No. It is a convenient example for scaling quantities. Select enough concrete for the mixer, tests, specimens and expected losses.

Does passing the slump-flow test mean the mix is approved?

No. The mix must satisfy all specified fresh and hardened requirements, including retention and production verification where required.

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The information on this website is provided for educational purposes only.

It does not replace project-specific engineering design, professional advice, approved drawings or construction specifications. Examples, calculations and suggested procedures should not be adopted directly for construction without appropriate verification. Always check the latest applicable standards and amendments, local requirements, project specifications, material-test results and site conditions. Final design, testing, acceptance and construction decisions should be made by qualified professionals and the responsible project authorities.