Methods of Test for Aggregates for Concrete, Part VIII: Petrographic Examination

IS 2386 Part 8 — Scope & Key Specifications

Scope (Clause 0.5)

• Final test values must be rounded off per IS 2-1960 rules.
• Maintain significant figures consistent with the standard's specified values.

Apparatus for Specimen Preparation (Clause 3.2.1)

• Rock-cutting saw: 350 mm diamond blade.
• Grinding wheel: Horizontal, 400 mm diameter.
• Polishing wheel: 200–300 mm diameter.
• Abrasives: Silicon carbide grit (No. 150, 180, 220).
• Other essentials: Microscope slides (25x45 mm), Canada balsam, mounting medium, laboratory oven, Jones riffle sampler, micro cover glasses.

Particle Count Calculation (Clause 3.6.1.4, Table III)

• Similar data applies for 12.5 mm, 10 mm, and 4.75 mm sieves.

Summary

• Use specified apparatus for sample prep.
• Calculate particle counts using Table III.
• Round results per IS 2-1960.

flowchart LR
    A[Sample Collection] --> B[Specimen Preparation]
    B --> C[Cutting with Rock Saw]
    C --> D[Grinding & Polishing]
    D --> E[Particle Counting on Sieves]
    E --> F[Calculate Percent Composition (Table III)]
    F --> G[Report Results (Rounded per IS 2-1960)]

This ensures standardized, reproducible aggregate testing per IS 2386 Part 8.

IS 2386 Part 8: Terminology and Definitions — Key Formulas & Tables

Particle Count Calculation (Clause 3.6.1.4, Table III)

IS 2386 Part 8: Apparatus and Supplies for Petrographic Examination

Key Apparatus & Supplies (Clauses 3.2.1 & 3.2.2)

| Specimen Examination | Polarizing microscope | Mechanical stage, multiple objectives, compensators (full/quarter-wave, quartz wedge) | | | Microscope lamps | Preferably including sodium arc lamp | | | Stereoscopic microscope | Magnification 6X to 60X | | | Magnet or electromagnet | For magnetic mineral identification | | | Needle holder and points | For handling specimens | | | Dropping bottle | 60 ml capacity | | | Forceps | Smooth, straight-pointed | | | Petri culture dishes | For sample handling | | | Lens paper | For cleaning lenses |

Additional Important Supplies (Clause 1.785 & Notes)

• Immersion Media: Refractive index range from 1.410 to 1.785 in steps of 0.005.

  • Requires frequent calibration using an Abbe Refractometer with compensating prisms or sodium arc lamp illumination due to temperature sensitivity.

IS 2386 Part 8: Selection and Preparation of Samples

1. Apparatus for Specimen Preparation (Clause 3.2.1)

• Rock-cutting saw: 350 mm diamond blade (preferred)
• Grinding wheel: Horizontal, 400 mm diameter
• Polishing wheel: 200–300 mm diameter
• Abrasives: Silicon carbide grit (No. 150, 180, 220), emery
• Microscope slides: 25 x 45 mm, clear and non-corrosive
• Mounting medium: Canada balsam in xylene or suitable alternatives
• Laboratory oven
• Jones riffle sampler

2. Sample Quantities for Undeveloped Sand and Gravel (Clause 3.3.4)

Note: "" means unselected or as per field conditions.

3. Particle Count for Precision (Clause 3.4.1.1)

• Minimum 300 particles per sieve fraction should be identified and counted for reliable results.
• Larger counts needed for precise estimation of minor constituents.

4. Calculation of Particle Counts (Clause 3.6.1.4)

IS 2386 Part 8: Examination Procedures - Key Apparatus & Specifications

1. Apparatus for Preparation of Specimens (Clause 3.2.1)

• Rock-cutting saw: Diamond blade, 350 mm diameter.
• Grinding wheel: Horizontal, 400 mm diameter.
• Polishing wheel: 200-300 mm diameter.
• Abrasives: Silicon carbide grit (No. 150, 180, 220), emery.
• Microscope slides: Clear, non-corrosive, 25 x 45 mm.
• Canada balsam: Neutral, in xylene (mounting medium).
• Laboratory oven for drying.
• Plate glass squares: ~300 mm edges for thin-section grinding.
• Jones riffle sampler with pans.

2. Apparatus for Examination of Specimens (Clause 3.2.2)

• Polarizing microscope: Mechanical stage, multiple objectives (low to high power), full & quarter-wave compensators, quartz wedge.
• Microscope lamps: Preferably sodium arc lamp.
• Stereoscopic microscope: Magnifications 6X to 60X.
• Magnet or electromagnet.
• Needle holder and points, forceps (smooth, straight-pointed).
• Dropping bottle: 60 ml capacity.
• Petri culture dishes, lens paper.

3. Notes

• Items marked with * indicate essential equipment or suitable alternatives.
• Proper specimen preparation and examination ensure accurate petrographic analysis.

flowchart LR
  A[Specimen Preparation] --> B[Cutting (Diamond Saw)]
  B --> C[Grinding (Silicon Carbide Grit)]
  C --> D[Polishing (Polishing Wheel)]
  D --> E[Mounting (Slides + Canada Balsam)]
  E --> F[Examination]
  F --> G[Polarizing Microscope]
  F --> H[Stereoscopic Microscope]
  F --> I[Magnet & Accessories]

For detailed calculations and reporting, refer to Clause 3.6 of IS 2386 Part 8.

IS 2386 Part 8: Petrographic Analysis of Coarse Aggregates - Key Points

1. Petrographic Identity & Quality (Clause 2.4.2, Table I & II)

• Aggregates classified by rock types (e.g., Chalcedonic cherts, Quartzites).
• Quality assessed chemically and physically:
  • Chemical Quality: Innocuous vs. Deleterious (e.g., high alkalies).
  • Physical Quality: Good, Satisfactory, Fair, Poor.
• Typical % by weight for 40-20 mm, 20-10 mm, and 10-4.75 mm sizes:

2. Petrographic Reporting (Clause 3.6, Table IV)

• Quantify constituents by particle count in sieve fractions.
• Report % particles by condition (weathering degree).
• Avoid subjective opinions; report only objective findings.

3. Typical Petrographic Characteristics (Clause 4.75)

• Weathering states: Moderately weathered (firm to hard), deeply weathered (absorptive).
• Specific rock behavior (e.g., chalcedonic cherts have poor bonding).

4. Workflow Summary (Petrographic Analysis)

flowchart TD
    A[Sample Collection] --> B[Sieve Analysis]
    B --> C[Microscopic Examination]
    C --> D[Identify Rock Types & Constituents]
    D --> E[Quantify by Weight & Particle Count]
    E --> F[Assess Chemical & Physical Quality]
    F --> G[Prepare Petrographic Report]

References:

• Use rock/mineral names as per IS 383:1963.
• Report includes gradation and petrographic composition.
• Petrographic analysis aids in evaluating aggregate suitability for

IS 2386 Part 8: Petrographic Analysis of Natural Sand – Key Points

Sample Preparation (Clause 3.4.1)

• Sieving: Natural sand samples are sieved per IS 2386 Part 1.
• Additional fraction: Material passing 75-micron IS sieve is tested without washing.
• Examination: Each sieve fraction is examined separately, starting from the largest size.
• Use stereoscopic and petrographic microscopes for identification.

Petrographic Composition & Quality (Table II, Clause 2.4.2)

*Deleterious materials may be high in alkalis.

Petrographic Characteristics (Clause 4.75)

• Chalcedonic cherts: Hard, massive, poor bonding.
• Weathering states:
  • Moderately weathered: fractured, firm to hard.
  • Deeply weathered: fractured, absorptive, firm to hard.

Summary of Procedure

flowchart TD
    A[Collect Sand Sample] --> B[Sieving as per IS 2386 Pt 1]
    B --> C[Separate Fractions by Size]
    C --> D[Examine Larger Fractions First]
    D --> E[Stereoscopic Microscope]
    E --> F[Petrographic Microscope for Small Fractions]
    F --> G[Estimate Proportions & Quality]
    G --> H[Prepare

IS 2386 Part 8: Examination of Ledge Rock and Core Samples

Key Specifications & Procedures

• Sampling:

  • Core diameters:
    • Massive rock: 55 mm diameter cores
    • Thinly bedded/complex rock: ≥ 100 mm diameter cores (Clause 3.3.1)
  • Cores drilled normal to dominant rock structure.
  • Entire core footage included; record elevations, depths, and core loss.

• Examination Procedure (Clause 3.5.2):

  • Examine ledge rock similarly to core samples.
  • For blasted broken stone, inspect whole sample, estimate rock type abundance.
  • Sample each rock type before further processing.
  • Follow core sample examination procedure (Clause 3.5.3).

• Recording (Clause 3.4.2.4):

  • Describe each rock type with:
    • Particle shape & surface
    • Texture, structure, pore space, grain packing, cementation
    • Mineral composition
    • Heterogeneities & physical condition
    • Presence of deleterious constituents for concrete
  • Record particle counts for sieve fraction tables.
  • Prepare weighted average compositions based on gradation.

Typical Data Table Format for Reporting

Summary Flowchart of Examination Process

flowchart TD
    A[Collect Core/Ledge Rock Samples] --> B[Inspect Sample Size & Type]
    B --> C{Is Sample Blasted Broken Stone?}
    C -- Yes --> D[Estimate Rock Type Abundance]
    D --> E[Sample Each Rock Type]
    C -- No --> E
    E --> F[Describe Rock Types (Shape, Texture, Composition, etc.)]
    F --> G[Particle Counts & Sieve Analysis]
    G --> H[Prepare Weighted Average Composition Tables]
    H --> I[Report Preparation]
``

IS 2386 Part 8 — Calculations and Reporting (Clause 3.6)

Key Points:

• Particle count per sieve fraction: Count total particles retained on each sieve size (e.g., 20 mm, 12.5 mm, 10 mm, 4.75 mm).

• Percentage calculation: For each constituent in a sieve fraction,

  [ \text{Percentage} = \frac{\text{Number of particles of constituent}}{\text{Total particles in sieve fraction}} \times 100 ]

• Reporting: Percentages are rounded to whole numbers; constituents ≤ 0.5% reported as traces.

• Weighted composition: Construct a table showing composition per sieve fraction and weighted composition for the whole sample (see Table IV in the code).

Example Table Format (from Table III):

Reporting Guidelines:

• Group minor constituents to avoid rounding errors.
• Highlight constituents harmful to concrete even if in small amounts.
• Ensure totals per sieve fraction and whole sample equal 100% (excluding traces).

flowchart TD
    A[Count particles per sieve fraction] --> B[Calculate % per constituent]
    B --> C[Construct composition table]
    C --> D[Calculate weighted composition for whole sample]

IS 2386 Part 8: Interpretation of Petrographic Data - Key Points

1. Petrographic Analysis Tables (Clause 2.4.2 & Table II)

• Aggregate Size Ranges:
  • 40 mm to 20 mm
  • 20 mm to 10 mm
  • 10 mm to 4.75 mm

*Deleterious materials may be high in alkalies affecting durability.

2. Petrographic Characteristics (Clause 4.75)

• Weathering: Moderately to deeply weathered aggregates show increased fracturing and absorptivity.
• Cherts: Chalcedonic cherts are hard, massive but have poor bonding characteristics.
• Physical Quality: Firm to hard aggregates preferred.

3. Reporting Guidelines (Clause 2.4)

• Use rock and mineral names as per IS 383-1963.
• Report should include:
  • Petrographic identity
  • Proportion of constituents
  • Physical and chemical quality estimates

Summary:

• Petrographic data helps assess aggregate quality by chemical innocuousness and physical integrity.
• Use provided tables to classify aggregate quality by size.
• Identify deleterious constituents and weathering effects.
• Follow IS 383 nomenclature for consistency.

flowchart LR
    A[Aggregate Sample] --> B[Petrographic Examination]
    B --> C{Constituent Identification}
   

IS 2386 Part 8: Quality Assessment Criteria for Aggregates

Key Points & Tables

1. Petrographic Analysis (Clause 2.4.2, Table I)

• Rock Types are classified by particle size and quality:

• Interpretation: Deleterious materials reduce aggregate quality; quartzites are preferred.

2. Particle Count Calculation (Clause 3.6.1.4, Table III)

IS 2386 Part 8: References to Related Standards

• Rounding Off (Clause 0.5):
  Final test values shall be rounded as per IS 2:1960 (Rules for Rounding Off Numerical Values).

  • Retain the same number of significant digits as specified in the standard.

• Scope (Clause 0.6):
  This standard covers testing of concrete aggregates only, excluding contractual provisions.

• Reference to Latest Versions (Clause 0.4):
  All Indian Standards cited should be taken as their latest editions.

• Particle Count Calculation (Clause 3.6.1.4, Table III):
  Provides the number and percentage of particles retained on sieves (20mm, 12.5mm, 10mm, 4.75mm) for various constituents (A1, A2, Ag, B1, B2, B3, C1, C2, C3).
  Example snippet:

Key IS Codes Often Referenced:

• IS 2:1960 – Rounding off rules
• IS 2386 (Parts 1-7) – Aggregate testing methods
• IS 383 – Specification for coarse and fine aggregates

flowchart LR
  A[IS 2386 Part 8] --> B[Testing of Aggregates]
  A --> C[Rounding off per IS 2:1960]
  A --> D[Use latest IS versions]
  B --> E[Particle Count Table III]
  E --> F[Sieve Sizes: 20, 12.5, 10, 4.75 mm]

Summary: Use latest IS standards, round results per IS 2, and refer to Table III for particle count calculations.