Methods for Sampling of Aggregates for Concrete

IS 2430 - Scope Summary & Key Specifications

• Scope: This standard covers methods for sampling aggregates for concrete, focusing on sampling procedures, sample weights, and testing requirements.

Key Specifications from IS 2430

1. Weight of Gross Sample (Table 2)

• Note: For all-in-aggregates, gross sample weight = coarse aggregate weight (minimum) + 10 kg.

2. Sampling Procedure

• Minimum 10 increments per sample.
• Each increment ≥ 1 kg.
• Use suitable scoops (Fig. 1) with dimensions as below:

3. Testing and Reporting

• Each sample tested

IS 2430 - Definitions Summary

Clause 2.0 of IS 2430 provides definitions essential for understanding the standard related to aggregates for concrete.

Key Points:

• Definitions clarify terms used in testing and classification of aggregates.
• Testing follows IS 2386 (Parts 1 to 8), which detail methods for:
  • Particle size and shape
  • Deleterious materials and organic impurities
  • Specific gravity, density, voids, absorption, bulking
  • Mechanical properties
  • Soundness
  • Mortar making properties
  • Alkali aggregate reactivity
  • Petrographic examination

Important References:

Usage:

• Each aggregate sample must be tested individually for all relevant properties.
• Test results are reported per IS 2386 guidelines.

This ensures uniformity and reliability in aggregate quality assessment for concrete.

flowchart TD
    A[Aggregate Sample] --> B[Test per IS 2386 Parts 1-8]
    B --> C{Properties Tested}
    C --> D[Particle Size & Shape]
    C --> E[Deleterious Materials]
    C --> F[Specific Gravity & Absorption]
    C --> G[Mechanical Properties]
    C --> H[Soundness]
    C --> I[Mortar Properties]
    C --> J[Alkali Reactivity]
    C --> K[Petrographic Examination]
    B --> L[Report Results]

Note: For exact definitions, refer to Clause 2.0 of IS 2430 and respective parts of IS 2386.

IS 2430: Sources and Types of Aggregates – Key Points

1. Types of Aggregates (Clause 2.1 & 2.4)

• Aggregates include:
  • Crushed stone, crushed boulders
  • Gravel, sand
  • Industrial by-products or other inert materials
• All-in Aggregates: Combination of fine and coarse aggregates.

2. Sampling of Aggregates (Clause 4.2.2 & Table 2)

• For all-in aggregates, gross sample weight = mass of coarse aggregates (minimum) + 10 kg.

3. Sampling Scoop Dimensions (Fig.1)

• Use at least 10 increments, each ≥ 1 kg, taken at regular intervals with the scoop.

Summary Diagram

IS 2430: Sampling Procedures for Aggregates

Key Points & Tables

1. Sampling Importance

• Sampling must reflect the true nature of materials.
• Use every precaution to avoid bias.

2. Sub-Lots Division (Clause 4.2.1)

• Divide the lot into sub-lots of approximately equal size.
• Refer to Table 1 (not detailed here) for the number of sub-lots.

3. Gross Sample Weight (Clause 4.2.2 & Table 2)

• For all-in aggregates:
  [ \text{Gross sample weight} = \text{mass of coarse aggregates (min)} + 10,kg ]

4. Sampling Increments

• Take at least 10 increments, each ≥ 1 kg.
• Use a scoop (Fig. 1) at regular intervals on the conveyor.

5. Scoop Dimensions & Capacity

IS 2430 - Sampling from Conveyors (Clause 4.2)

Key Specifications:

• Sampling Points:

  • If discharge point sampling is not feasible, take increments from center, left, and right of the moving belt width.
  • Use a scoop to sweep the conveyor to capture very small materials.

• Number of Increments:

  • Minimum 10 increments per gross sample.
  • Each increment ≥ 1 kg.

Weight of Gross Sample (Table 2):

• Note: For all-in-aggregates, gross sample weight = coarse aggregate weight + 10 kg.

Scoop Dimensions (Fig. 1):

IS 2430: Sampling from Loaded Carriers - Key Points

Sampling Procedure (Clause 4.3.2.1 & 4.3.3)

• Select minimum 25% of carriers randomly from the sub-lot (use IS 4905-1968, Clause 3.1 for random selection).
• From each selected carrier, take 10 increments evenly spaced.
• Each increment must weigh ≥ 1 kg.
• Total increments combined form the gross sample quantity as per Table 2 of IS 2430.
• Increments are collected using a suitable scoop (refer Fig. 1 of IS 2430).
• For loaded carriers, 10 increments are taken at random points on the aggregate surface using sectional sampling.

Sampling Tools

• Use a scoop designed for uniform increments.
• Sampling at loading/unloading to ensure representativeness.

Summary Table (Sampling from Loaded Carriers)

flowchart LR
  A[Sub-lot of carriers] --> B[Randomly select ≥25% carriers]
  B --> C[Take 10 increments per selected carrier]
  C --> D[Each increment ≥1kg using scoop]
  D --> E[Combine increments to form gross sample]
  E --> F[Sample tested as per Table 2 requirements]

This ensures a representative, statistically valid sample for quality assessment.

IS 2430 - Sampling from Stacks or Stock Piles (Clause 4.4)

Key Specifications:

• Avoid biased samples due to segregation (coarser particles tend to roll outside).
• For coarse/all-in aggregates, use power equipment to create a small sampling pile by mixing materials from various levels and locations.
• If power equipment is unavailable, take increments equally from top third, middle, and bottom third of the pile volume.
• Use a vertical board above the sampling point to prevent segregation.
• Remove the outer segregated layer before sampling.
• Sampling should be done during stacking or breaking of the pile for best representativeness.

Sampling Procedure Summary:

flowchart LR
    A[Main Stock Pile] --> B[Remove Outer Layer]
    B --> C[Take increments from Top, Middle, Bottom]
    C --> D[Combine increments into Small Sampling Pile]
    D --> E[Sample for Testing]

This method ensures representative and unbiased samples from segregated stock piles.

IS 2430: Reduction of Gross Sample – Key Points

1. Gross Sample Weight (Table 2)

• Note: For all-in-aggregates, gross sample = coarse aggregate mass + 10 kg.

2. Sampling Procedure

• Take at least 10 increments, each ≥1 kg, using a suitable scoop (Fig. 1).
• Increments taken at regular intervals along a trench or exposed pile sides.
• Mix and reduce gross sample repeatedly until lab sample quantity (per IS 2386) is obtained.

3. Scoop Dimensions (for increments)

Summary Formula for Sample Reduction:

• Gross Sample Weight ≥ Minimum from Table 2.
• Number of increments ≥ 10, each ≥ 1 kg.
• Laboratory Sample Weight as per

IS 2430: Reduction by Riffle Divider - Key Points

1. Process (Clause 5.2)

• Mix aggregates thoroughly.
• Pour into riffle divider.
• Repeat with different riffle sizes matching aggregate size.
• Ensures representative sample reduction.

2. Sampling & Sub-lots (Clause 4.2.1 & Table 1)

• Lot divided into sub-lots of approximately equal size during conveyor discharge.
• Number of sub-lots per Table 1 (not fully provided here).

3. Gross Sample Weight (Clause 4.2.2 & Table 2)

• Minimum gross sample weight depends on max nominal size.
• At least 10 increments ≥ 1 kg each, taken at regular intervals using a scoop.

4. Sampling Scoop Dimensions (Fig.1)

Coning and Quartering Method (IS 2430 - Clause 5.3)

• Procedure:

  1. Mix aggregate sample thoroughly.
  2. Scoop the sample to form a cone-shaped pile, dropping each scoop at the same spot to maintain the central axis.
  3. Flatten the cone by pressing the top with a smooth scoop surface.
  4. Cut the flattened pile into four equal quarters by two perpendicular lines intersecting at the center.
  5. Reject two diagonally opposite quarters and keep the other two.
  6. Repeat the process until the desired sample size is achieved.

• Accuracy Tips:

  • Use damp material for fine and all-in aggregates to minimize segregation.
  • Ensure precise quartering to maintain representative particle size distribution.

Key Tables from IS 2430:

Scoop Dimensions for Sampling:

IS 2430: Packing and Marking of Samples - Key Points

• Separate Packing:
  Each sample must be packed individually to avoid contamination or loss of fines (Clause 6.1).

• Care in Packing:
  Use airtight, moisture-proof containers or bags. Ensure no loss of fine material during transport.

• Marking:
  Clearly mark each package with:

  • Sample identification number
  • Source details (lot, sub-lot, date)
  • Type of material
  • Any special handling instructions

• Sample Reduction (Coning and Quartering - Clause 5.3):

  1. Form a cone-shaped pile by pouring material at the same spot.
  2. Flatten the cone top evenly.
  3. Cut into four equal quarters with two perpendicular lines.
  4. Reject two diagonally opposite quarters and mix the remaining halves for the reduced sample.

• Sub-lots Division (Clause 4.3.1):
  Divide lots into sub-lots approximately equal in size as per Table 1 (not shown here, typically based on total lot size).

Summary Table: Packing & Marking Checklist

flowchart TD
    A[Aggregate Sample] --> B[Mix thoroughly]
    B --> C[Form cone-shaped pile]
    C --> D[Flatten top]
    D --> E[Cut into 4 quarters]
    E --> F[Reject 2 opposite quarters]
    F --> G[Mix remaining halves]
    G --> H[Pack separately in airtight container]
    H --> I[Mark with identification details]
    I --> J[Dispatch to laboratory]

Note: Always refer to the full IS 2430 for detailed packing materials and marking formats.

IS 2430: Number of Tests and Reporting of Test Results

Key Points:

• Sample Information (Clause 6.2.1): Each sample should be accompanied by:

  • Name & address of origin (quarry, river-bed, etc.)
  • Proposed use of material
  • Geographic location and shipping details

• Testing Requirements (Clause 7.1):

  • Each sample must be tested individually for all requirements.
  • Test results reported as per IS 2386 (Parts 1 to 8) - 1963.

• Reporting (Clause 0.6): Round off test results per IS 2-1960.

Summary Table for Number of Tests & Reporting

flowchart TD
    A[Sample Collection] --> B[Include Origin & Use Info]
    B --> C[Sample Testing]
    C --> D{Test as per IS 2386 Parts 1-8}
    D --> E[Particle Size & Shape]
    D --> F[Deleterious Materials]
    D --> G[Specific Gravity & Absorption]
    D --> H[Mechanical Properties]
    D --> I[Soundness]
    D --> J[Mortar Properties]
    D --> K[Alkali Reactivity]
    D --> L[Petrographic Exam]
    E & F & G & H & I & J & K & L -->