Complete Guide to Fine & Coarse Aggregate Properties for Concrete Mix Design 2026 — IS 383:2016, IS 2386 Test Methods, Grading Zones, Specific Gravity, Abrasion, M-Sand, Recycled Aggregate & ASR
Explore Aggregate GuideAggregates are the inert granular materials — sand, gravel, crushed stone, or recycled concrete — that form 60–80% of the total volume of concrete. Far from being passive fillers, aggregates profoundly influence concrete's compressive strength, workability, durability, density, shrinkage, and economy. Selecting the right aggregate type, size, and grading is therefore one of the most important decisions in concrete mix design per IS 383:2016 "Coarse and Fine Aggregate for Concrete — Specification" and IS 10262:2019.
In 2026, the Indian concrete industry faces three major aggregate-related challenges: rapid depletion of natural river sand driving adoption of manufactured sand (M-sand); growing use of recycled concrete aggregate (RCA) under IS 17452:2022; and increasing awareness of alkali-silica reactivity (ASR) as infrastructure projects extend their design life to 100+ years. This guide covers all aggregate types, their key properties, test methods, selection criteria, and their specific role in IS 10262:2019 mix design calculations.
Manufactured Sand (M-Sand): IS 383:2016 for the first time fully recognised and specified M-sand as a fine aggregate for structural concrete, including grading limits, particle shape requirements, and methylene blue value test
Recycled Aggregate: IS 383:2016 laid groundwork; IS 17452:2022 now provides full specification for recycled concrete aggregate (up to 30% coarse replacement)
Grading Zones: Zone classification retained (I–IV) but limits revised; combined grading permitted for mixed-size blends
Deleterious Substances: Updated limits for clay lumps, silt, organic matter, and coal/lignite; stricter controls for HPC grades M40+
Full standard: IS 383:2016 available at bis.gov.in. Test methods: IS 2386 Parts 1–8
Fine aggregate (FA) is all material passing the 4.75mm IS sieve. It fills the voids between coarse aggregate particles, provides workability, and contributes to the paste volume. The grading (particle size distribution) of fine aggregate has a more significant impact on concrete workability and water demand than coarse aggregate grading, making FA quality control critically important.
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| IS Sieve Size | Zone I – Coarse (% Passing) | Zone II – Standard (% Passing) Preferred | Zone III – Medium Fine (% Passing) | Zone IV – Very Fine (% Passing) | Combined Grading (% Passing) |
|---|---|---|---|---|---|
| 10 mm | 100 | 100 | 100 | 100 | 100 |
| 4.75 mm | 90 – 100 | 90 – 100 | 90 – 100 | 95 – 100 | 95 – 100 |
| 2.36 mm | 60 – 95 | 75 – 100 | 85 – 100 | 95 – 100 | 80 – 100 |
| 1.18 mm | 30 – 70 | 55 – 90 | 75 – 100 | 90 – 100 | 70 – 100 |
| 600 µm | 15 – 34 | 35 – 59 | 60 – 79 | 80 – 100 | 55 – 100 |
| 300 µm | 5 – 20 | 8 – 30 | 12 – 40 | 15 – 50 | 10 – 50 |
| 150 µm | 0 – 10 | 0 – 10 | 0 – 10 | 0 – 15 | 0 – 15 |
| Fineness Modulus (FM) | 3.5 – 4.0 | 2.9 – 3.5 | 2.3 – 2.9 | 1.6 – 2.3 | 2.6 – 3.5 |
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| Property | Test Method | River Sand (Typical) | M-Sand (Typical) | IS 383:2016 Limit | Effect on Concrete |
|---|---|---|---|---|---|
| Specific Gravity (SSD) | IS 2386 Part 3 | 2.60 – 2.67 | 2.60 – 2.68 | Report actual value | Controls FA mass from volume; critical IS 10262 input |
| Water Absorption (%) | IS 2386 Part 3 | 0.5 – 1.5% | 1.0 – 2.5% | Report; use for batch water correction | Affects free water calculation; monsoon batch water correction |
| Silt Content (Field Test) | IS 2386 Part 2 (Sedimentation) | 1 – 4% | 0.5 – 3% | ≤ 3% (by volume, field test) | High silt increases water demand; weakens paste-aggregate bond |
| Clay Lumps (%) | IS 2386 Part 2 | 0.5 – 1.5% | Nil | ≤ 1.0% (M40+: ≤ 0.5%) | Clay lumps swell; cause popouts and surface cracking |
| Organic Impurities | IS 2386 Part 2 (Colorimetric) | Nil to Light | Nil | ≤ Light Yellow (reference colour) | Organic matter retards cement hydration; reduces strength |
| Chloride Content (%) | IS 2386 Part 1 | <0.03% typical | <0.01% typical | ≤ 0.05% (RCC); ≤ 0.025% (PSC) | Chloride causes steel corrosion; critical for durability |
| Sulphate Content (as SO₃) | IS 2386 Part 1 | <0.2% | <0.1% | ≤ 0.4% in aggregate; ≤ 4% in concrete total | Sulphate reacts with C₃A to form ettringite — cracking |
| Soundness (Na₂SO₄ 5 cycles) | IS 2386 Part 5 | <10% | <10% | ≤ 10% loss (sodium sulphate); ≤ 15% (magnesium) | Unsound particles disintegrate; cause concrete spalling |
| Methylene Blue Value (MBV) | EN 933-9 (M-sand) | N/A | ≤ 1.0 g/kg | ≤ 1.0 g/kg for M-sand (IS 383:2016) | MBV measures clay activity in fines — high MBV → poor durability |
| Bulk Density (loose) | IS 2386 Part 3 | 1450 – 1550 kg/m³ | 1500 – 1620 kg/m³ | Report | Used for volumetric batching conversion; not used in IS 10262 weight-based design |
River sand availability has declined sharply in India due to environmental restrictions on river bed mining. Manufactured sand (M-sand), produced by crushing granite or basalt, is now the primary fine aggregate in many Indian cities. Understanding the differences is essential for correct mix design and quality control.
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| Parameter | River Sand (Natural) | M-Sand (Manufactured) | MixDesignCalc Adjustment |
|---|---|---|---|
| Particle Shape | Rounded / sub-rounded (water erosion) | Angular / cubical (crusher product) | +7 kg/m³ water demand for M-sand vs river sand |
| Specific Gravity (SSD) | 2.60 – 2.67 | 2.60 – 2.68 (from granite/basalt parent) | Use actual SG; default 2.62 for M-sand in MixDesignCalc |
| Water Absorption | 0.5 – 1.5% | 1.0 – 2.5% (more porous surface) | Higher absorption correction needed for batch water |
| Fines Content (<75µm) | < 3% (natural) | 5 – 15% (crusher dust) | Fines up to 15% permitted (IS 383); wash if >15%; MBV test required |
| Grading Consistency | Variable (river source-dependent) | More consistent (controlled crusher settings) | Weekly sieve analysis recommended; less frequent variation |
| Workability | Better natural workability | Harsher; requires more paste for same workability | Use PCE SP to compensate without increasing water |
| Fineness Modulus | 2.4 – 3.5 (Zone I–III typical) | 2.3 – 3.2 (Zone II–III) | Adjust FA:CA ratio per zone same as river sand |
| Silt / Clay Content | 1 – 4% (field test) | 0.5 – 3% (rock dust, not clay); MBV test needed | Always MBV test M-sand before use; reject if >1.0 g/kg |
| Organic Impurities | Possible (riverbed organics) | Nil (crushed rock — no organic content) | No colorimetric test needed for M-sand; skip IS 2386 Part 2 organic test |
| Chloride Content | < 0.03% (inland rivers) | Nil (crushed granite/basalt) | No Cl⁻ concern with M-sand from non-coastal rock |
| Bulking Behaviour | Bulks up to 30–35% at 5% moisture | Bulks less; more predictable | Critical for volumetric batching; use weight batching for M-sand |
| Cost (2026) | Higher (scarcity + transport) | Lower in quarry-rich areas; comparable in cities | Economic driver for M-sand adoption in 2026 |
| IS Standard | IS 383:2016 (natural sand) | IS 383:2016 (M-sand provisions) + IS 16723 (2018) | Same grading zone classification applies |
Coarse aggregate (all material retained on 4.75mm IS sieve) forms the structural skeleton of concrete. Its strength, shape, surface texture, grading, and mineralogy directly affect concrete compressive strength, elastic modulus, shrinkage, and durability. IS 383:2016 specifies requirements for all coarse aggregate types used in structural concrete in India.
SG: 2.63–2.72 | LA: 20–35%
SG: 2.68–2.85 | LA: 15–25%
SG: 2.55–2.65 | LA: 25–40%
SG: 2.60–2.70 | LA: 20–30%
SG: 2.40–2.55 | Absorption: 4–8%
SG: 0.80–1.80 | Density: 1400–2000 kg/m³
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| Property | Test Standard | Granite (Typical) | Basalt (Typical) | Limestone (Typical) | RCA (Typical) | IS 383 Limit (M20–M35) | IS 383 Limit (M40+) | Impact on Mix Design |
|---|---|---|---|---|---|---|---|---|
| Specific Gravity (SSD) | IS 2386 Pt3 | 2.63–2.72 | 2.68–2.85 | 2.55–2.65 | 2.40–2.55 | Report actual | Report actual | Primary IS 10262 input — V_CA = M_CA/(SG×1000) |
| Water Absorption (%) | IS 2386 Pt3 | 0.3–1.0% | 0.5–1.5% | 1.0–3.0% | 4.0–8.0% | Report; ≤2% preferred | ≤1% recommended | Batch water correction = M_CA × (SSD absorption − surface moisture)/100 |
| Los Angeles Abrasion (%) | IS 2386 Pt4 | 20–35% | 15–25% | 25–40% | 30–50% | ≤ 30% | ≤ 30% (same limit) | Weak aggregate limits max concrete strength regardless of w/c |
| Aggregate Impact Value (%) | IS 2386 Pt4 | 20–30% | 15–25% | 25–35% | 30–45% | ≤ 30% | ≤ 30% (for pavement: ≤ 24%) | Low AIV ensures aggregate does not crush under compaction |
| Aggregate Crushing Value (%) | IS 2386 Pt4 | 20–30% | 15–22% | 20–30% | 30–45% | ≤ 30% | ≤ 25% (for HPC) | Resistance to slow crushing load; complement to AIV |
| Flakiness Index (%) | IS 2386 Pt1 | 10–25% | 10–20% | 15–30% | Variable | ≤ 25% | ≤ 20% (HPC) | Flat/elongated particles reduce workability; increase water demand |
| Elongation Index (%) | IS 2386 Pt1 | 10–25% | 10–20% | 15–30% | Variable | ≤ 25% | ≤ 20% (HPC) | Elongated particles reduce concrete strength and workability |
| Soundness (5 cycles Na₂SO₄) | IS 2386 Pt5 | <8% | <6% | <10% | Variable | ≤ 10% | ≤ 10% | Unsound aggregate disintegrates in freeze-thaw or sulphate conditions |
| Chloride Content (%) | IS 2386 Pt1 | <0.03% | <0.02% | <0.05% | Variable | ≤ 0.05% (RCC) | ≤ 0.025% (PSC) | Aggregates are primary source of concrete chloride content |
| Deleterious Substances (%) | IS 2386 Pt2 | <1% | <0.5% | <1% | High (mortar content) | ≤ 1% clay lumps; ≤ 5% total | ≤ 0.5% clay lumps (M40+) | Clay, silt, organic matter reduce strength and durability |
| Alkali-Silica Reactivity | IS 2386 Pt7; ASTM C1260 | Low–Moderate | Low | Very Low | Depends on source | Expansion <0.10% (ASTM C1260) | Expansion <0.10% (mandatory IRC:112 bridges) | ASR causes gel expansion, cracking, structural failure over time |
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| CA Type | Nominal Size | IS Sieve Passing 100% | Percentage Passing Range | Water Demand vs 20mm (kg/m³) | Suitable Applications | Member Size Constraint |
|---|---|---|---|---|---|---|
| Single Size | 10 mm | 12.5 mm (100%) | 10mm: 85–100%; 4.75mm: 0–20% | +15–25 more than 20mm | Congested RCC, thin slabs (<100mm), precast | Min clear spacing ≥13mm; min section ≥40mm |
| Single Size | 20 mm Standard | 25 mm (100%) | 20mm: 85–100%; 4.75mm: 0–5% | Baseline | All general structural RCC; most common | Min clear spacing ≥27mm; min section ≥80mm |
| Single Size | 40 mm | 50 mm (100%) | 40mm: 85–100%; 20mm: 0–20%; 4.75mm: 0–5% | −15–25 less than 20mm | Mass concrete, large rafts, dams, large pile caps | Min clear spacing ≥53mm; min section ≥160mm |
| Single Size | 63 mm | 80 mm (100%) | 63mm: 85–100%; 4.75mm: 0–5% | −25–35 less than 20mm | Dam construction, very large mass pours only | Min clear spacing ≥84mm; min section ≥252mm |
| Graded | 20mm + 10mm Blend | 25 mm (100%) | Designed for optimum packing; 60:40 or 70:30 mix | −5–10 less than 20mm single | HPC M50+; better aggregate packing; reduces voids | Same as 20mm single size constraints |
| IS 383 Combined | All-in Aggregate | As specified | Combined grading within IS 383 limits | Variable | Not recommended for structural concrete — variable grading | Not suitable for HPC |
Specific gravity and water absorption are the two aggregate properties most directly used in IS 10262:2019 mix design calculations. Getting these values wrong — particularly using a default SG when the actual material is significantly different — is one of the most common causes of volume balance errors in concrete mix design.
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| Aggregate Type | SSD SG (Typical Range) | MixDesignCalc Default SG | Water Absorption (Typical %) | Error if Wrong SG Used | When to Test |
|---|---|---|---|---|---|
| River Sand (FA) | 2.60 – 2.67 | 2.65 | 0.5 – 1.5% | ±0.05 SG → ±15 kg/m³ FA mass | Each new source; monthly minimum |
| M-Sand (FA) | 2.60 – 2.68 | 2.62 | 1.0 – 2.5% | ±0.05 SG → ±15 kg/m³ FA mass | Each new quarry source; fortnightly minimum |
| Granite (CA 20mm) | 2.63 – 2.72 | 2.68 | 0.3 – 1.0% | ±0.05 SG → ±20 kg/m³ CA mass | Each new quarry source; monthly |
| Basalt (CA 20mm) | 2.68 – 2.85 | 2.75 | 0.5 – 1.5% | ±0.05 SG → ±20 kg/m³ CA mass | Each new quarry source; monthly |
| Limestone (CA) | 2.55 – 2.65 | 2.60 | 1.0 – 3.0% | Using granite SG 2.68 → −23 kg/m³ CA error | Each new source; monthly |
| Recycled CA (RCA) | 2.40 – 2.55 | Must test — no default | 4.0 – 8.0% | Using granite SG → underestimates CA by 50+ kg/m³ | Every delivery lot; absorption particularly variable |
| Lightweight CA (LECA) | 0.80 – 1.80 | Must test — no default | 10 – 25% | Using normal SG → catastrophic volume error | Each batch grade; pre-soak required |
Alkali-Silica Reaction (ASR) is a chemical reaction between reactive silica minerals in certain aggregates and alkali hydroxides (from cement, mix water, or external sources) in concrete pore solution. The reaction produces a hygroscopic silica gel that absorbs water and expands, causing internal cracking, surface spalling, and structural failure — often appearing 5–25 years after construction. In 2026, with India's infrastructure projects targeting 100+ year design lives, ASR prevention has become a critical specification requirement for all bridges (IRC:112:2020) and major infrastructure.
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| Aggregate Type / Mineralogy | ASR Risk Level | Reactive Mineral | Common Regions in India | Recommended Test | Mitigation Strategy |
|---|---|---|---|---|---|
| Quartzite (high-stress quartz) | HIGH | Strained/deformed quartz | Rajasthan, Bundelkhand, Chhattisgarh, Delhi NCR | ASTM C1260 + Petrography | GGBS 40%+; Fly Ash 25%+; or LiNO₃; low-alkali cement |
| Siliceous (chert-bearing) Limestone | HIGH | Chert nodules, microcrystalline quartz | Rajasthan, MP, Gujarat, Bihar | ASTM C1260 + Petrography | Avoid chert-bearing limestone; test and reject if reactive |
| Greywacke / Meta-sandstone | HIGH | Strained quartz + clay minerals | Eastern Ghats, Jharkhand, Odisha | ASTM C1260 + ASTM C1293 | Low-alkali cement + GGBS 35%+; petrographic screening mandatory |
| Granite (fresh, unweathered) | LOW–MODERATE | Minor strained quartz; generally low reactivity | Deccan Plateau, Tamil Nadu, Karnataka | Petrography; ASTM C1260 if weathered | Generally safe; test if weathered or from new quarry |
| Basalt / Trap Rock | LOW | Very low reactive silica | Maharashtra, Telangana, Karnataka (Deccan Trap) | Petrography screening | Generally safe — preferred aggregate for long-life structures |
| Limestone (pure, non-chert) | VERY LOW | CaCO₃ — non-reactive | Rajasthan, MP, AP (pure formations) | Petrography to confirm chert-free | No ASR mitigation needed if confirmed chert-free |
| River Gravels (mixed mineralogy) | MODERATE (variable) | Mixed — depends on catchment geology | All river systems — mineralogy varies by basin | ASTM C1260 always | Test each river gravel source — reactivity cannot be assumed |
| Recycled Concrete Aggregate | VARIABLE | Depends on original aggregate used | All urban areas | ASTM C1260 + check demolition records | If original aggregate was reactive, RCA carries risk — test always |
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| Test Method | Standard | Duration | Acceptance Criterion | Reliability | Recommended For |
|---|---|---|---|---|---|
| Petrographic Examination | IS 2386 Pt7; ASTM C295 | 1–2 weeks | No reactive minerals identified by petrographer | Qualitative — expert-dependent | First-screen before mortar bar tests; all new quarries |
| Mortar Bar Test (ASTM C1260) | ASTM C1260; IS 2386 Pt7 | 16 days (14 + 2) | <0.10% at 16 days = non-reactive; 0.10–0.20% = inconclusive; >0.20% = reactive | High — accelerated, widely used | All IRC:112 bridges; any long-life structure; quartzite and greywacke |
| Concrete Prism Test (ASTM C1293) | ASTM C1293 | 12 months | <0.04% at 12 months = acceptable | Best correlation to field performance | Definitive confirmation; World Bank / ADB funded projects |
| Chemical Test (IS 2386 Pt7 Method) | IS 2386 Part 7:1963 | 24 hours | Plot on Sc vs Rc chart — potentially deleterious zone | Lower — many false positives | Screening only; confirm with C1260 if deleterious zone |
Recycled concrete aggregate — crushed concrete from demolished structures — is now formally permitted in structural concrete in India under IS 17452:2022 "Recycled Aggregate Concrete — Specification". This standard permits up to 30% coarse recycled aggregate replacement in concrete up to M40 grade, opening significant opportunities for sustainable construction while requiring careful attention to RCA's distinct properties.
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| Property | Natural CA (Granite) | Recycled CA (RCA) | IS 17452:2022 Limit | Mix Design Adjustment |
|---|---|---|---|---|
| Specific Gravity (SSD) | 2.63–2.72 | 2.40–2.55 | ≥ 2.20 | MUST enter actual tested SG — never use granite default for RCA |
| Water Absorption (%) | 0.3–1.0% | 4.0–8.0% | ≤ 8.0% | Large batch water correction; pre-soak RCA before mixing |
| Los Angeles Abrasion (%) | 20–35% | 30–50% | ≤ 45% (IS 17452) | Weaker — limit RCA to M40 maximum; check each lot |
| Mortar Content (%) | ~0% (no mortar) | 20–45% | Report; affects SG and absorption | High mortar content → lower SG, higher absorption — test each lot |
| Chloride Content (%) | <0.03% | 0.01–0.15% (variable) | ≤ 0.05% (IS 17452) | Test chloride — marine-sourced RCA may exceed limits; reject if >0.05% |
| Sulphate Content (SO₃ %) | <0.1% | 0.1–1.0% (variable) | ≤ 1.0% (IS 17452) | Sulphate from gypsum in old concrete — check total concrete SO₃ |
| ASR Risk | Source-dependent | Inherits risk from original aggregate | Test per IS 2386 Pt7 | Always test RCA for ASR — if original aggregate was reactive, so is RCA |
| Max Replacement Level | 100% (baseline) | Up to 30% of CA | 30% max coarse (IS 17452) | Set CA input in MixDesignCalc as 70% natural + 30% RCA blend |
| Maximum Concrete Grade | Any grade | M40 maximum | M40 (IS 17452:2022) | Do not use RCA for M45+ regardless of tested properties |
| CO₂ Saving | Baseline | ~30–50% vs virgin CA | — | GRIHA/IGBC green rating credits for RCA use |
Why Pre-Saturate: RCA with 5% absorption, used at 500 kg/m³, will absorb 25 litres of water from the mix if batched oven-dry. This dramatically increases effective w/c ratio above the design value, reducing strength by 10–20 MPa.
Pre-Saturation Method: Soak RCA in water for 30–60 minutes before batching until absorption is satisfied. Drain surface water. Batch at SSD condition — measure surface moisture and apply batch water correction as normal.
Alternatively — Absorption Correction Method: Batch RCA at air-dry condition, but add extra water equal to (absorption − surface moisture) × RCA mass / 100. This extra water compensates for aggregate absorption and maintains the design free water content in the mix.
Key Rule: Never batch RCA at oven-dry condition without correction — always use either pre-saturation or absorption correction. Enter RCA's actual tested absorption % in MixDesignCalc for automatic batch water correction.
Selecting the most appropriate aggregate combination for a given concrete application requires balancing strength requirements, durability needs, aggregate availability, and cost. The following guide consolidates IS 456:2000, IS 10262:2019, IS 383:2016, IRC:112:2020, and 2026 industry practice.
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| Application / Grade | Preferred FA Type & Zone | Preferred CA Type & Size | Max CA Size (mm) | Special Requirements | Aggregates to Avoid |
|---|---|---|---|---|---|
| PCC / Blinding (M5–M15) | River sand or M-sand, any zone | Granite or limestone, 20–40mm | 40 | No special requirements | — |
| General RCC (M20–M25, Mild) | River sand Zone II or M-sand Zone II | Granite 20mm; sieve LA <30% | 20 | Silt <3%; organic test if river sand | Zone IV sand; Limestone for M25+ |
| RCC Slabs & Beams (M25–M35) | River sand Zone II or M-sand (MBV <1.0) | Granite 20mm; LA <30% | 20 | Grading check weekly; FM within ±0.2 of design | Zone IV sand; high-silt river sand; limestone CA |
| High-Rise Columns M35–M50 | M-sand Zone II (consistent grading) | Granite or basalt 20mm; LA <25% | 20 | SPcE mandatory; column bar spacing check for max size | Zone III/IV sand; limestone; RCA |
| Bridges (IRC:112:2020) | M-sand Zone II or river sand Zone II; Cl⁻ test mandatory | Granite or basalt 20mm; LA <30%; ASR test mandatory | 20 | ASR test (ASTM C1260) <0.10%; petrography; MoRTH Sec.1700 | Quartzite without ASR clearance; limestone; RCA for bridges |
| Marine Structures (Extreme) | M-sand (low Cl⁻); Cl⁻ test mandatory | Basalt or granite 20mm; LA <25%; very low absorption | 20 | All aggregates: Cl⁻ test; SO₄ test; ASR test; GGBS cement | Any aggregate with Cl⁻ >0.025%; limestone; quartzite |
| Mass Concrete (Dams, Rafts) | River sand Zone I or II | Granite 40mm; low heat priority | 40 or 63 | Large aggregate reduces heat of hydration; low alkali cement | Zone IV sand; 10mm CA; high-absorption aggregates |
| Concrete Pavement (IRC:58, M40+) | M-sand Zone II | Granite or basalt 20mm; LA <30%; AIV <24% | 20 – 25 | Flexural strength >4.5 MPa; AEA if freeze-thaw zone; DLC sub-base | Limestone CA for M40+ pavement; RCA; quartzite (ASR) |
| HPC / M50–M70 | M-sand Zone II; consistent FM ±0.1; low MBV | Basalt 20mm preferred; LA <20%; absorption <0.8% | 20 (10mm blend preferred) | Aggregate strength must exceed concrete strength; thorough testing | Limestone; quartzite; Zone III/IV sand; RCA |
| Sustainable / Green Concrete (2026) | M-sand (rock quarry byproduct) Zone II | 30% RCA (IS 17452) + 70% granite; ASR test RCA | 20 | Max M40; test RCA absorption per lot; SCM + RCA combination | River sand (environmental restriction); >30% RCA |
Q: What is the maximum silt content allowed in sand for concrete?
IS 383:2016 and IS 2386 Part 2 specify maximum 3% silt by volume (field sedimentation test) for fine aggregate used in concrete. For M40+ HPC: reduce to 1–2%. Excess silt increases water demand, weakens paste-aggregate bond, and reduces durability. Test the field sedimentation test on every new sand delivery before use.
Q: Can M-sand be used for all grades of concrete?
Yes — IS 383:2016 fully permits M-sand for all structural grades. The key requirements: correct grading zone, MBV ≤ 1.0 g/kg, no organic impurities. In MixDesignCalc, select "M-Sand correction" which adds +7 kg/m³ to the base free water content. Always use weight batching for M-sand — volumetric batching is unreliable due to angular particle packing.
Q: What is fineness modulus and why does it matter?
Fineness modulus (FM) is the sum of cumulative percentages retained on standard sieves (4.75mm, 2.36mm, 1.18mm, 600µm, 300µm, 150µm) divided by 100. A higher FM means coarser sand. FM affects water demand, workability, and concrete surface finish. Target FM 2.9–3.5 (Zone II) for most concrete. A change of ±0.2 in FM from the design value requires adjustment of FA:CA ratio by ±3–5%.
Q: How often should I test aggregates at a construction site?
IS 383:2016 does not prescribe frequency explicitly but best practice: SG and absorption — each new source change, monthly minimum. Sieve analysis / FM — weekly for M-sand, fortnightly for river sand. Silt content — every delivery (2-minute field test). Organic test — every delivery of river sand. LA abrasion — each new quarry source. For NABL-certified mix design, tests at each new lot with test certificate dates within 3 months of submission.
Q: Can recycled aggregate (RCA) be used for M40 concrete?
Yes — IS 17452:2022 permits up to 30% coarse recycled aggregate in M40 concrete. However, every delivery lot must be tested for SG, absorption, chlorides, sulphates, and ASR. Batch water correction for high absorption is critical. The use of SCMs (fly ash 20%+ or GGBS 30%+) is strongly recommended alongside RCA to compensate for the slight reduction in strength and durability. Not permitted for M45 or above, or for bridges and PSC.
Q: Which aggregate is best for marine concrete?
Basalt is the preferred coarse aggregate for marine concrete — very low absorption (0.5–1.5%), excellent strength (LA 15–25%), and minimal ASR risk. For fine aggregate, use M-sand (no natural chloride) rather than river sand near coast. All aggregates must be tested for Cl⁻ <0.025% (for PSC and prestressed elements). Combine with PSC or OPC + 50–65% GGBS for maximum chloride resistance.