MixDesignCalc 2026 — Lean Concrete Mix Design: IS 456 Nominal Mixes (1:3:6 & 1:2:4), Applications (Blinding PCC, DLC, Levelling, Cyclopean), When Designed Mix Is Better, Economy Analysis, Plum Stone Option, Batch Quantities Calculator & M10 vs M15 vs M20 Comparison
M10 and M15 are lean concretes — mixes with low cement content designed to fill volume economically rather than carry significant structural load. Their purpose is:
They are not appropriate for: any reinforced concrete element, any element carrying significant structural load, any exposure class above Mild (IS 456 Table 3), or any element where durability is a design criterion.
IS 456:2000 Table 5 shows no minimum grade requirements for Mild exposure plainly because for plain concrete the code does not impose a minimum. However, IS 456 Table 5 footnote and IS 456 Cl.6.1.2 are clear: for reinforced concrete, even in Mild exposure, M20 is the practical minimum (IS 456 Table 5 lists M20 for Mild RCC). Using M15 for reinforced columns, slabs, or beams — even in Mild exposure — does not meet IS 456 requirements for reinforced concrete elements. M15 is for plain concrete only.
IS 456 Table 9 specifies two nominal mixes for lean concrete:
M10: 1 : 3 : 6 (cement : FA : CA) by volume
M15: 1 : 2 : 4 (cement : FA : CA) by volume
M20: 1 : 1.5 : 3 (last nominal mix — Mild exposure plain concrete only)
These ratios are by volume, not mass. The volume of cement is taken as one unit; FA and CA are proportioned by gauge box accordingly.
The nominal mix ratios in IS 456 Table 9 are proportions by dry volume. Because fine aggregate (sand) bulks up when damp, practical batching requires gauge boxes or the commonly used gauge box method to account for bulking. The table below gives the typical ingredient masses per m³ based on volumetric proportioning.
| Grade | Nominal Mix Ratio | Cement (kg/m³) | FA — Sand (kg/m³) | CA — Stone (kg/m³) | Water (L/m³ approx.) | Fresh Density (kg/m³) | Notes |
|---|---|---|---|---|---|---|---|
| M10 | 1 : 3 : 6 | 210–230 | 630–690 | 1260–1380 | 180–220 | 2280–2500 | High slump OK (100–150mm); blinding, DLC |
| M15 | 1 : 2 : 4 | 280–310 | 560–620 | 1120–1240 | 185–210 | 2145–2380 | Moderate slump (75–100mm); plain structural |
| M20 | 1 : 1.5 : 3 | 360–400 | 540–600 | 1080–1200 | 185–200 | 2165–2400 | Last nominal mix — designed mix preferred for RCC |
For nominal mix concrete batched by gauge box (farma) on site:
Damp sand (5–8% moisture) occupies 20–30% more volume than dry sand of the same mass. When gauge boxes are filled with damp sand, the actual sand mass is 20–30% less than intended — the mix becomes leaner than the nominal ratio specifies. This is the biggest source of inconsistency in nominal mix concrete batching. Either:
(1) Reduce gauge box volume by the bulking factor (test monthly with IS 2386 Pt.3 bulking test), or
(2) Switch to weigh batching (eliminates bulking error entirely) — mandatory for M25+ and recommended for all consistent quality concrete.
M10 blinding PCC below a raft slab, M10 DLC sub-base in a rural road project, M15 filling concrete for a non-structural wall — these are correct and code-compliant applications of nominal mix. The nominal mix system exists precisely for these low-risk, low-consequence applications.
For a 200 m³ M10 blinding pour:
Nominal 1:3:6: cement ≈ 225 kg/m³ × 200 = 45,000 kg = 900 bags
Designed M10 (IS 10262, 40mm MSA, w/c 0.70): cement ≈ 195 kg/m³ × 200 = 39,000 kg = 780 bags
Saving: 120 bags × ₹380/bag = ₹45,600 — enough to cover the cost of a mix design and trial mix several times over. For large lean concrete pours, designed mix is more economical even without SP.
Cyclopean concrete is made by incorporating clean, sound rubble or plum stones (large rounded boulders or broken rock pieces) into M10 base concrete. IS 456:2000 Clause 8.2.6 permits plum stone up to a maximum of 20% to 40% by volume of the total concrete volume, depending on the section size.
The plum stones must be: clean and free of soil or organic matter; non-reactive to cement; placed carefully by hand (not dropped) into the freshly poured base concrete; and surrounded on all sides by a minimum 150mm of M10 concrete mortar. The base M10 mix must be workable enough to fully surround and interlock with the plum stones.
Maximum plum stone content: Not exceeding 20% by volume of the plain concrete for mass concrete sections, or up to 40% for very large mass fills where specified by the engineer.
Minimum plum stone size: No dimension less than 150mm (ensures stone is properly bedded).
Maximum plum stone size: No dimension more than 1/3 of the minimum section dimension.
Placement: Plum stones shall be placed gently into the plastic concrete — not dropped. After placing, sufficient concrete shall be vibrated around each stone to ensure full contact.
Location restriction: No plum stone within 300mm of any exposed surface, and none within 300mm of any reinforcement or construction joint.
OPC 43 (IS 8112) is adequate for M10 and M15 — these grades are far below the minimum strength an OPC 43 cement can achieve. The lower clinker cost vs OPC 53 makes it marginally cheaper. Suitable for all Mild exposure applications. Avoid for sulfate-bearing soils.
PPC (IS 1489, 15–35% fly ash) is the preferred cement for M10/M15 mass concrete: lower heat of hydration (reduces thermal cracking risk in large sections), fly ash contribution improves long-term strength and density, marginally cheaper than OPC 53. Sg ≈ 2.89 — use correct Sg if doing designed mix calculation.
For M10/M15 in sulfate-bearing soils (IS 456 Table 4 Sulfate Classes 3–5 — SO₄ >1.2 g/L in soil or >0.5 g/L in groundwater): specify SRC cement (IS 12330, low C₃A ≤ 3.5%) per IS 456 Table 4 requirements. Even for lean blinding concrete, sulfate attack on the PCC layer is a real mechanism that undermines the structural concrete above it.
The MSA constraints of IS 456 Cl.5.3.1 (section/4, bar spacing, cover) typically don't apply to plain concrete — but practical and technical constraints still limit MSA:
Blinding PCC (50–75mm thick): MSA ≤ 20mm — larger aggregate cannot be properly compacted in a thin layer and creates voids at the layer edges.
Standard PCC, mass concrete: MSA 40mm — standard choice, good economy (lower water demand vs 20mm).
DLC sub-base: MSA 40mm per IRC:SP:49 — must not exceed 40mm for compactability under roller.
Cyclopean base concrete: MSA 40–63mm for the base mix (not the plum stones). The mix must be fluid enough to flow around large plum stones — use 40mm to maintain workability.
| Parameter | M10 | M15 | M20 (Nominal) | M25 (Designed) |
|---|---|---|---|---|
| fck (MPa) | 10 | 15 | 20 | 25 |
| fcm (MPa) — IS 10262 | 15.8 | 20.8 | 26.6 | 33.25 |
| IS 456 Nominal Mix | 1:3:6 ✅ | 1:2:4 ✅ | 1:1.5:3 ✅ (plain only) | ❌ Designed mix only |
| Permitted for RCC? | ❌ No | ❌ No | ✅ Yes (Mild exposure) | ✅ Yes (Moderate+) |
| IS 456 Exposure min grade | Not applicable | Not applicable | Mild exposure plain | Moderate (RCC min) |
| IS 456 Max w/c (if exposed) | No limit (plain) | No limit (plain) | 0.60 (Mild RCC) | 0.50 (Moderate) |
| IS 456 Min Cement | None specified | None specified | 300 kg/m³ (if RCC) | 300 kg/m³ |
| Typical cement (kg/m³) | 210–250 | 280–320 | 330–380 | 370–440 |
| Trial mix required? | No (nominal) | No (nominal) | No (nominal) / Yes (designed) | Yes — mandatory |
| Designed mix recommended? | For >50 m³ pours | For >50 m³ pours | Always for RCC | Always — code requirement |
| Plum stone permitted? | ✅ Up to 40% | ✅ Up to 20% | Limited | Not applicable |
| DLC use (IRC:SP:49)? | ✅ Primary grade | ❌ Overqualified | ❌ Too rich | ❌ Not applicable |
| Est. cost (₹/m³ at ₹380/bag) | ₹1,596–1,748 | ₹2,128–2,432 | ₹2,508–2,888 | ₹2,812–3,344 |