What Is a Concrete Mix Ratio?

 🔍 What Is a Concrete Mix Ratio?

A concrete mix ratio refers to the proportions of the three key ingredients that make up concrete:

1. Cement – the binding material that hardens and gives strength.

2. Sand (fine aggregate) – fills the gaps and helps improve workability.

3. Coarse Aggregate – gives bulk and strength (usually crushed stones or gravel).

4. Water – activates the cement to form a paste that binds the aggregates.

Example:

A mix ratio of 1:2:4 means:

1 part cement

2 parts sand

4 parts aggregate

This is a volume-based ratio.

📘 Why Different Ratios Are Used

Different concrete grades are used for different applications based on the required compressive strength (measured in MPa or N/mm² after 28 days of curing).

✅ Common Concrete Grades and Their Ratios

Grade Mix Ratio (C:S:A) Compressive Strength (28 days) Use Case

M5 1:5:10 5 MPa Pathways, levelling concrete

M7.5 1:4:8 7.5 MPa Sub-base in roads

M10 1:3:6 10 MPa Plain concrete, footings

M15 1:2:4 15 MPa Flooring, driveways

M20 1:1.5:3 20 MPa Beams, slabs, columns

M25 1:1:2 25 MPa High-load structures, commercial buildings

> Note: Higher grades like M30, M35, M40 require design mix (done by engineers based on structural requirements, not just nominal ratios).

🧮 How to Use the Ratio for 1m³ of Concrete

Let’s say you want to prepare 1 cubic meter (m³) of concrete using the M20 mix (1:1.5:3):

Step 1: Add the parts of the mix

1 + 1.5 + 3 = 5.5 parts

Step 2: Determine material quantity

Let’s use 1m³ of dry materials (which actually gives you about 0.9m³ of wet concrete).

🧱 Cement:

\text{Cement part} = \frac{1}{5.5} \times 1 = 0.1818 \, m³

1 bag of cement = 0.035 m³

So:

\text{No. of bags} = \frac{0.1818}{0.035} \approx 5.2 \text{ bags}

🏖️ Sand:

\text{Sand} = \frac{1.5}{5.5} = 0.2727 \, m³

🪨 Aggregate:

\text{Aggregate} = \frac{3}{5.5} = 0.5455 \, m³

💧 Water:

Water-cement ratio (W/C) for M20 is usually 0.5

Water = 0.5 \times 50 kg = 25 liters per 50kg bag

So, for 5.2 bags = 25 × 5.2 = 130 liters

📌 Important Tips

1. Mixing Concrete

Always mix dry materials first (cement, sand, and aggregate).

Add water gradually to achieve the desired consistency.

Overwatering weakens concrete.

2. Curing

Concrete should be cured (kept moist) for at least 7–14 days, ideally 28 days.

Curing ensures proper hydration and strength development.

3. Strength and Workability

More cement = stronger concrete but more cost and heat.

More sand = more workable but weaker.

More aggregate = stronger but harder to place.

🧱 Choosing the Right Mix

If you’re doing this… Use this mix

Foundation footing M15 or M20

Slabs and beams M20 or M25

Pavement or walkway M10 or M15

Structural columns M25 and above